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  • richardmitnick 1:27 pm on December 18, 2014 Permalink | Reply
    Tags: , , , , , Particle Physics   

    From FNAL:- “Frontier Science Result: DZero Measuring the strange sea with silicon” 

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    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    Thursday, Dec. 18, 2014
    Leo Bellantoni

    Our last DZero result began like so:

    FNAL DZero
    DZero

    “The parts inside of a proton are called, in a not terribly imaginative terminology, partons. The partons that we tend to think of first and foremost are quarks — two up quarks and a down quark in each proton — but there are other kinds of partons as well.”

    This time, we start in the same place — with those unimaginatively named partons. There are three types.

    The first type comprises those alluded to above: quarks. The two up quarks and one down quark that make up protons are called valence quarks. They determine the electrical charge of the proton. There are six flavors of quark, and all the different combinations of three out of the six correspond to a particle of a specific type, called a baryon. (Well, almost. Top flavored quarks decay so quickly they never form a particle.)

    The second type of parton is the gluon. Gluons hold the quarks inside the proton together and are the mediators of the strong nuclear force. Just as electromagnetic energy comes in point-like units called photons, so energy of the strong nuclear force comes in units of the gluon.

    The third type of parton is the sea quark. A gluon can split into a quark-antiquark pair that exists for a fleetingly short time (10-24 seconds or less) before reforming back into a gluon.

    Sea quarks can be of any flavor. They very often are up or down quarks, just like the valence quarks. But they can also be strange quarks, and strange quarks do not exist as valence quarks in protons. A reaction with a strange quark in the initial state lets you measure these strange sea quarks in proton collisions.

    The reaction involves the collision of a strange sea quark from one proton (or antiproton) with a gluon from an antiproton (or proton) to produce a W boson and a charm quark. The charm quark, when produced with a large momentum transverse to the direction of the initial collision, will produce a narrow spray of particles all moving in roughly the same direction. Such a particle spray is called a jet. Because the charm quark will travel a few millimeters before decaying, the fact that there was a charm quark producing the jet can be inferred using the silicon based microstrip tracking detector at the very center of the DZero detector.

    q
    Top quark and anti top quark pair decaying into jets, visible as collimated collections of particle tracks, and other fermions in the CDF detector at Tevatron.

    FNAL CDF
    CDF

    FNALTevatron
    Tevatron map

    Silicon technology also helps identify jets produced from bottom flavored quarks. In fact, bottom quark jets are easier to find than charm quark jets. Measuring the production of bottom quark jets in events with a W boson provides important information about the nonvalence partons — specifically, gluons — of the proton.

    DZero has recently measured the production of both charm and bottom jets when a W boson is also produced. The new measurement uses more data than earlier analyses, and for the first time, we obtain information about the production (with a W) of charm and bottom jets that are produced with different momenta transverse to the collision axis. How the production varies with the transverse momentum is a valuable measurement tool to understand the various subprocesses at work. This is also the first measurement of charm-W production that relies upon the silicon microstrip tracking technology; previous measurements were based on less effective techniques.

    —Leo Bellantoni

    See the full article here.

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    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics.

     
  • richardmitnick 1:16 pm on December 17, 2014 Permalink | Reply
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    From FNAL: “Gaining support for new long-baseline neutrino experiment at Fermilab” 

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    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    Wednesday, Dec. 17, 2014
    Rob Roser

    i
    Jim Strait, project director for Fermilab’s proposed long-baseline neutrino experiment, answers a question at the Dec. 12 meeting to form a new collaboration at Fermilab. Photo: Reidar Hahn

    On Dec. 5 and 12, many of the world’s neutrino scientists gathered at CERN and Fermilab, respectively, to learn about the newly proposed next-generation long-baseline neutrino oscillation experiment. These meetings were established to discuss a new letter of intent (LOI) for the experiment.

    m
    More than 150 people attended the collaboration-forming meeting at Fermilab on Dec. 12. Photo: Reidar Hahn

    The LOI, which is currently signed by more than 350 scientists from more than 100 institutions around the world, leverages the Fermilab neutrino facility to undertake an experiment at Sanford Underground Research Facility in South Dakota.

    Sanford Underground Research Facility Interior
    Sanford

    The two meetings were designed to be identical in content. Fermilab Director Nigel Lockyer kicked off both meetings with a historical overview as well as a high-level plan forward. Jim Strait, project director for the proposed long-baseline neutrino experiment, discussed the Fermilab facility and what is being offered. ICFA Neutrino Panel Chair Ken Long and I presented the LOI in our role to bring the world’s long-baseline neutrino community together, and Fermilab Deputy Director Joe Lykken summarized the current discussions on the international governance process. Lively panel discussions followed, giving attendees a chance to interact with the LOI authors and learn more about the proposal. Copies of the talks are online.

    People can find the current draft of the LOI and sign it from the website. The deadline to sign it prior to its presentation to the PAC[?] is Jan. 11, 2015.

    The next step in the formation of this new international collaboration is its first meeting, to be held at Fermilab from Jan. 22-23. It is open to anyone who is interested in joining this new scientific endeavor. Sergio Bertolucci, CERN director of research and the interim Institutional Board chair for the collaboration, has called the meeting and will announce the agenda in the coming weeks.

    See the full article here.

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  • richardmitnick 2:41 pm on December 16, 2014 Permalink | Reply
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    From BU: “Trigger Happy” 

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    Boston University

    December 1, 2014
    Barbara Moran

    Physicist Tulika Bose talks about smashing protons to find new physics

    tb
    Tulika Bose, trigger coordinator for the Compact Muon Solenoid experiment at the Large Hadron Collider in Switzerland. “Trigger meetings are dramatic places,” she says. Photo by Jackie Ricciardi

    Tulika Bose is a science detective. A trigger-happy, atom-smashing, big question-asking physicist, who spends her days sifting though scraps of proton collisions for clues about the universe.

    Bose, an assistant professor of physics at Boston University’s College of Arts & Sciences, works at the Large Hadron Collider (LHC) in Switzerland, one of the most powerful particle accelerators ever built. The LHC smashes protons together 40 million times a second, and physicists like Bose sort through the wreckage. Bose is looking for particles (or their remains) that will substantiate (or dismiss) new theories that solve mysteries about the Big Bang and the nature of matter.

    In September 2014, Bose was appointed trigger coordinator for the Compact Muon Solenoid (or CMS) experiment at the LHC. She spoke with BU Research about what all those words mean, and why we should bother looking for “new physics” when the old physics seems to work just fine.

    c
    CMS

    BU Research: You were recently appointed the “trigger coordinator” for something called the CMS experiment. Can you explain what that is?

    Bose: Sure! At the LHC, we collide protons with protons to see what comes out of the collision, trying to find new particles and new physics. There are four major experiments and CMS is one of them. The name stands for Compact Muon Solenoid—a solenoid is a type of magnet, hence “solenoid” in the name. It’s a particle detector.

    How big is it?

    15 meters high (that’s about 50 feet) and 15 meters wide. A person next to it looks like a tiny little person.

    Then why is it called “compact”? It doesn’t seem very compact!

    Very good question. It’s a relative word, because it’s compact in comparison to another experiment, Atlas. Atlas is larger but less dense. CMS is more compact and dense.

    CERN ATLAS New
    ATLAS

    How does it all work?

    The LHC is like a huge racetrack. The protons go along in one direction, and then another beam of protons goes along in the other direction. Magnets bend them in a circular path. And most of the time these two beams are kept separated, except at four positions within this ring, where we have detectors with a different kind of magnet, which focuses the two beams together. And exactly at that point where this happens—where the two beams come together—is our CMS detector. The collision is happening right in the middle of the detector.

    How many protons collide?

    The beam has about 2,800 “bunches,” and a bunch has about 1,011 protons. So it’s a very intense bunch. But the collision point is very, very tiny, because the closer you can squeeze them, the more likely it is that an interesting collision will occur.

    How often do you collide them?

    The collisions are supposed to happen every 25 nanoseconds, which means—

    Continuously? All day?

    Yes, so 40 million times a second.

    That’s so much data!

    Yes, exactly. That’s the problem.

    I thought you did it, like, once a month or something.

    No. This is happening 40 million times a second and running over extended periods of time. Of course, I should clarify that for the past run, we ran at half that frequency. It was only 20 million times a second. But when we start taking data next year, it will be 40 million times a second. And this is the challenge. We just don’t have the kind of technology or the money to be writing out all of this data.

    What does it mean to “write out” data?

    Selecting and writing them to disk, so we can analyze it later. We need to cut down to a rate which is more manageable; I would say a few hundred events per second—at most, 1,000 events per second. So you want to go from 40 million times to 1,000. This has to be done in real time, and that’s where the trigger comes in. It’s literally a filter, or you’re “triggering” on interesting events. That’s where the name comes from.

    Now I get it—so you set up the filter beforehand?

    You set up the filter beforehand, and the filter fires every time an interesting event comes along. So that’s the trigger firing on something interesting.

    So it sees something interesting, it fires, and then that data is written.

    Right.

    And you’re the one who figures out the triggers!

    Yes! I lead the team that figures this out. It’s challenging, because whatever you say “no” to is literally going into the trash.

    That would be a terrible feeling.

    Yes. You want to make sure that all of the new physics, and the fun stuff, is not going into the trash. So we have a complicated trigger system. At the very first level, it makes some coarse decisions: Does this event have an electron? Does this event have a muon? Does the muon have a certain momentum? Does the electron have a certain momentum?

    And the reason it’s looking for those things is because those things would be boring? Or interesting?

    Muons and electrons are subatomic particles that are predicted to appear when certain other particles decay. We initially start with protons colliding with protons, so if energetic muons and electrons are produced, it indicates an interesting event. So the Level 1 part of the trigger has about three microseconds to make a decision. It doesn’t do detailed calculations. It doesn’t have that luxury. It just says, “This event seems interesting enough. I’m going to keep it.”

    Then comes the second level of the triggering system, which is called the High Level trigger. And this is essentially algorithms, which are trying to make more of an informed decision. They have a little bit more time, about 200 milliseconds per event, and can do some more detailed calculations. They can obtain the momentum with better resolution. They can try to figure out if two muons that they see come from a certain particle, which has a certain mass. Of course, all of this assumes that we understand what the new physics will be, which we don’t. This is the part that keeps people awake at night.

    You keep mentioning the “new” physics. What’s wrong with the old physics?

    It goes back to what’s called the Standard Model of particle physics. It’s essentially a set of very elegant equations that describe our current understanding of the universe. So we know, for example, that there are these light particles: the leptons, electrons, muons, taus; and associated with each one of these is a neutral particle called the neutrino. We also know that there are generations of quarks: there is up, down, strange, charm, bottom and top—or beauty and truth, as they’re sometimes called.

    s
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    We know all these very well. We also know that there are these forces, such as the magnetic force, the weak force, the strong force, and then the gravitational force. Now, each of these forces has an associated particle. One that is predicted, for example, is the graviton, which is a carrier of the gravitational force.

    Now, going back to your question: Why are we interested in other theories? The problem is that the Standard Model leaves us with some things that are not explained very well. Firstly, gravity. The Standard Model doesn’t quite include gravity in this full picture. And the carrier of gravity, which is this hypothetical particle called the graviton, we haven’t seen it. So the Standard Model does not include gravity, and that is something which people are not happy about, naturally.

    I can imagine.

    Then the other two big mysteries. At the very creation of the universe, right after the Big Bang, we had equal amounts of matter and antimatter. However, everything we see around us is primarily matter. So where has all the antimatter gone? Then the other big issue is that a large fraction of the universe is what’s called dark matter. Now, what is dark matter, really? Again, the Standard Model doesn’t quite explain that.

    So, to answer all of these big questions, you have to study these little tiny things.

    Yes, these big questions are driving the kind of physics we’re doing. These new theories, which try to answer these big questions, have various predictions about new particles, so we are actively searching for these new particles.

    Why do you like designing triggers?

    It’s a lot of responsibility, making sure that you’re not making a wrong decision. So I’ve always liked challenges. And these are very, very complicated detectors. And things can naturally go wrong in some part of the detector, and the first place this shows up is at the trigger. If you have bad electronics in a certain part of the detector, it will, for example, just start firing all the time. And so you will see it because the trigger rates will just go spiking up.

    And you’ll go, “Oh my God, we just found the new physics! Oh, never mind, we didn’t.”

    Exactly. This has happened a number of times. You get very excited because you start seeing spikes, and then you find out that no, this was faulty electronics.

    And then, for some reason, the people who work on the trigger are a certain kind of people. They are very passionate, they’re very dramatic, and the trigger meetings are dramatic places. People say, “I want certain kinds of triggers for my physics group, and you’ve got to give it to me or else I can’t do anything.”

    I had no idea that it was so operatic.

    [laugh] It’s always been like that. So it’s fun.

    See the full article here.

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  • richardmitnick 3:16 pm on December 15, 2014 Permalink | Reply
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    From SPACE.com: “Will We Ever Find Dark Matter?” Previously Covered Elsewhere, But K.T. is an Excellent Exponent of her Material 

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    SPACE.com

    December 11, 2014
    Kelen Tuttle, The Kavli Foundation

    Scientists have long known about dark matter, a mysterious substance that neither emits nor absorbs light. But despite decades of searching, they have not yet detected dark matter particles.

    With ten times the sensitivity of previous detectors, three recently funded dark matter experiments — the Axion Dark Matter eXperimen Gen 2, LUX-ZEPLIN and the Super Cryogenic Dark Matter Search at the underground laboratory SNOLAB — have scientists crossing their fingers that they may finally glimpse these long-sought particles.

    AXION DME
    University of Washington physicists Gray Rybka (right) and Leslie Rosenberg examine the primary components of the ADMX detector.
    Credit: Mary Levin, University of Washington

    LUX Dark matter
    LUX-ZEPLIN

    SUPER CDMS
    Super Cryogenic Dark Matter Search

    Late last month, The Kavli Foundation hosted a Google Hangout so that scientists on each of those experiments could discuss just how close we are to identifying dark matter. In the conversation below are three of the leading scientists in the dark matter hunt:

    Enectali Figueroa-Feliciano: Figueroa-Feliciano is a member of the SuperCDMS collaboration and an associate professor of physics at the MIT Kavli Institute for Astrophysics and Space Research.

    Harry Nelson: Nelson is the science lead for the LUX-ZEPLIN experiment and is a professor of physics at the University of California, Santa Barbara.

    Gray Rybka: Rybka leads the ADMX Gen 2 experiment as a co-spokesperson and is a research assistant professor of physics at the University of Washington.

    s
    The SuperCDMS experiment at the Soudan Underground Laboratory uses five towers like the one shown here to search for WIMP dark matter particles.
    Credit: Reidar Hahn, Fermilab

    Below is a modified transcript of the discussion. Edits and changes have been made by the participants to clarify spoken comments recorded during the live webcast. To view and listen to the discussion with unmodified remarks, you can watch the original video.

    The Kavli Foundation: Let’s start with a very basic, yet far from simple question. One of our viewers asks how do we know for sure that dark matter even exists. Enectali, I’m hoping you can start us off. How do you know that there’s something out there for you to find?

    E.F.F.: The primary evidence telling us dark matter is out there is from astronomical observations. In the 1930s, evidence first came in the observations of the velocities of galaxies inside galaxy clusters. Then, in the 1970s, it came in the velocities of stars inside galaxies. One way to explain this is if you imagine tying a string around a rock and twirling it around. The faster you twirl the rock on the string, the more force you have to use to hold onto that string. When people looked at the velocity rotations of galaxies, they noticed that stars were moving way too fast around the center of the galaxy to be explained from the force you could see due to gravity from the mass that we knew was there from our observations. The implication was that if the stars are moving faster than gravity could hold them together, there must be more matter than we can see holding everything in place.

    Today, many different types of observations have been done at the very largest scales, using clusters of galaxies and what’s called the cosmic microwave background. Even when we look at the small scale of particle physics, we know that there are things about the Standard Model that aren’t quite right. We’re trying to find out what’s missing. That’s part of what’s being done at the Large Hadron Collider
    at CERN and other collider experiments. Some of the theories predict particles that would be good candidates for dark matter. So from the largest cosmic scales to the smallest particle physics scales there are reasons to believe that dark matter is there and there are candidates for what that dark matter can be.

    Cosmic Microwave Background  Planck
    CMB erp ESA/Planck

    sm
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

    TKF: Harry, I’m hoping that you can follow up on that a little bit. Your experiment and the one Enectali works on both look for the most promising type of theoretical particle, one that interacts so weakly with the matter in our world that it’s called the WIMP. In fact there are more than thirty dark matter experiments that are currently planned or underway, and the great majority of them search for this same type of particle. Why do all these experiments focus on the WIMP?

    H.N.: First I want to emphasize that WIMP is an acronym, W-I-M-P, which stands for weakly interacting massive particle. “Massive” means a mass that’s anywhere from a little smaller than the mass of a proton up to many times the mass of a proton. The WIMP is so popular in part because it’s easy to fit into descriptions of the Big Bang — maybe the easiest to fit. The concept to understand here is called thermal equilibrium, and that’s just when you put something in the refrigerator it ends up at the same temperature as the refrigerator. I had a leftover sandwich last night from when I went out to dinner and I put in my refrigerator, and now it’s cold. In much the same way, with WIMPs we hypothesize that dark matter in the early universe was in thermal equilibrium with our matter. But after the Big Bang, the universe gradually cooled down and our matter fell out of equilibrium with the dark matter. Then the dark matter keeps finding itself and, through a process called annihilation, turning into our matter. But the reverse process can no longer go on because our matter doesn’t have enough thermal energy.

    To explain the current abundance of dark matter, the interaction between dark matter and us numerically must be about the same as the weak interaction. That’s W-I in WIMP: weakly interacting. It implies a numerical strength that is consistent with beta decay in radioactivity or, for example, the production of the Higgs particle at the Large Hadron Collider. That the weak interaction appears from this idea about the Big Bang appeals to people. Occam’s Razor, the idea that you don’t want to make things any more complicated than they need to be, makes it attractive. But it doesn’t prove it.

    There are at least two other ways to detect the WIMP. One is at the Large Hadron Collider, as Enectali mentioned, and another is in these WIMP annihilations, where the WIMPs find each other and turn into our matter in certain places in the universe such as the center of stars or the center of our galaxy. If we get lucky, we could hit a trifecta; we could see the same particle with experiments like mine — LUX/LZ — or Enectali’s SuperCDMS, we could see it in the Large Hadron Collider, and we could also see it astrophysically. That would be the trifecta.

    Of course there’s a second reason why so many people are building these WIMP experiments, and that’s that we’ve made a lot of progress in how to build them. There’s been a lot of creativity using many techniques to look for these things. I will say that’s partly true because they’re a little easier to look for than the axion, for which you need really talented and expert people like Gray and Leslie Rosenberg.

    TKF: That’s a nice segue into Gray’s experiment. Gray, you don’t look for the WIMP; instead, you look for something called the axion. It’s a very lightweight particle, with no electric charge and no spin that interacts with our world very rarely. Can you tell us a little bit more about your experiment and why you look for the axion?

    G.R.: I look for the axion because if I looked for WIMPs then I would have to compete with very smart people like Harry and Enectali! But there are other really good reasons as well. The axion is a very good dark matter candidate. We think it may exist because of how physics works inside nuclei. It’s different from the WIMP in that it’s extremely light and you look for it by coupling to photons or, say a radio frequency kind of energy. I got involved in this because I was looking at dark matter and saw that there are a lot of people looking for WIMPs and not many people looking for axions. It’s difficult to look for, but there have been some technical breakthroughs that help. For example, just about everyone has cell phones now and so a lot of work has been done at those frequencies — which just happen to be the right frequencies to use when looking for axions. Meanwhile, there’s a lot of work on quantum computers, which means that there’s also a lot of really nice low temperature radio frequency amplification. That too helps with these experiments. So the time is right be looking for axions.

    TKF: Besides the WIMP and the axion, there are a lot of other theorized particles out there. One of our viewers wrote in and would like to know how likely is it that dark matter is in fact neither of the particles that your experiments look for but rather is composed of super heavy particles called WIMPzillas.

    H.N.: The WIMPzilla has WIMP in its name, so that means it’s weakly interacting, and the zilla part is that it’s just as massive as Godzilla. The way it works is that all of our astrophysical measurements tell us how much mass there is per unit volume – essentially, the cumulative total mass per unit volume of dark matter. But these measurements don’t tell us how to apportion that mass. Are there a great many light particles or just a few really heavy particles? We can’t tell from astrophysical data. So it could be that the dark matter consists of just a few super duper heavy things, like WIMPzillas. But because there wouldn’t be many of them out there, to detect them you’d have to build it a gigantic detector. What we run into there is that nobody wants to give us billions of dollars to build that gigantic detector. It’s just too much money. I think that’s what keeps us from making progress on the idea of the WIMPzilla.

    LUX Dark matter
    The LUX detector before its large tank was filled with more than 70,000 gallons of ultra-pure water. The water shields the detector from background radiation.
    Credit: Matt Kapust, Sanford Underground Research Facility

    E.F.F.: There are many theoretical dark matter particles. We have to pick a combination of what we can look for with the experiments that we can build and what theory and our current understanding suggests are the best places to look. Now, not all of the theories have as good a foundation as others. Some would work but have different types of assumptions built into them and so we need to make a value judgment as experimentalists. We go to the “theory café” and choose which are the best courses on the menu, then we trim the list down to those that are the most feasible to detect, and then we look at which of those we can afford. That convolution of parameters is what prompts us to look for particular candidates. And if we don’t find dark matter in those places, we will look for them elsewhere. And of course there’s no reason why dark matter has to be one thing; it might be composed of several different particles. We might find WIMPs and axions and other things we don’t know of yet.

    TKF: One of our viewers points us to a press release issued last week by Case Western University that describes a theory in which dark matter is made up of macroscopic objects. This viewer would like to know whether there’s any reason why dark matter would be more likely to be made up of the individual exotic particles that you look for than it is to be made up of macroscopic particles.

    H.N.: Papers like that are one of the reasons this field is so exciting. There are just so many different ideas out there and there’s this big discussion going on all the time. New ideas come in, we discuss them and think about them, and sometimes the new idea is inconsistent but other times people say, “Wow we have no idea that could be great.”

    This concept that the dark matter might consist of particles that coalesce into solid or massive objects has been around for a long time. In fact, there was a search 20 or so years ago where they looked for large objects in our galaxy that were creating gravitational lensing. When you look at stars out in our galaxy, if they suddenly become brighter that’s evidence of a massive object moving in front of them. You might wonder how an object moving in front of something would give it more light, but that’s the beauty of gravitational lensing — the light focuses around the object. So this idea has been out there, and this paper looks to be a very careful reanalysis.

    Another example is an idea that’s been around for a long time that maybe there is a different kind of nuclear matter out there. Our nuclear matter is made of up and down quarks and maybe there’s another type of nuclear matter that involves the strange quark. People have been searching for that for 30 or 40 years, but we’ve never been able to find it. Maybe it exists and maybe it’s the dark matter we’re searching for. I would say that in some estimate of probabilities it’s less likely, but we could be wrong. What’s great is to have the scientific discussion always going because the probabilities get reassessed all the time.

    G.R.: These massive objects have a very amusing acronym. They’re massive compact halo objects, MACHOs. So for a while it was MACHOs versus WIMPs.

    E.F.F.: One thing that I would add is that this paper and this whole idea of the variety of models really highlights how diverse the possibilities for looking for dark matter are. In that paper, they looked into mica samples that had been buried for many, many years, looking for tracks. When you have a candidate, the theoretical community starts scanning every possibility of a signal that might have been left — not just in our detectors, but also in the atmosphere, in meteorites, in stars and in the structure that we see in the universe. There are other detectors out there that are more indirect than the ones we’ve specifically designed for dark matter. That’s one of the things that makes it exciting: maybe we find dark matter in our detectors and we might also find traces of it in other things that we haven’t even thought about yet.

    TKF: In the history of particle physics, there have been a number of particles that we knew existed long before we were able to detect them — and in a lot of cases, we knew a lot about these particles’ characteristics before we found them. This seems very different from where we are now with dark matter. Why is that? What is fundamentally different here?

    G.R.: We know about dark matter from gravitational interactions, and we have a hard time fitting gravity in with the fundamental particles to begin with. I think that’s a big part of it. Would you all agree?

    H.N.: There are some analogues, but you have to go back in time quite a bit. One of the famous analogues is the discovery of the neutron. The proton was discovered in a fantastic series of experiments during World War I by [Ernest] Rutherford, but he had good intuition and thought there should be another particle that’s like the proton that is neutral, which they called the neutron. Even though they had a pretty good idea what it should be like, it took 12 or 15 years for them to detect one because it was just difficult. Then there was an experiment done by Frederic and Irene Joliot-Curie and their group in France and they interpreted the results in a very strange way. But a guy named James Chadwick looked at their data and said, “My God that’s it!” He repeated the experiment and proved the existence of the neutron.

    That story is so important because the neutron is the key to most uses of nuclear energy. I suspect with dark matter we’ll have some sort of rerun of that. We’re all looking and somewhere, maybe even now, there’s a little bit of data that will cause someone to have an “Ah ha!” moment.

    E.F.F.: We also have this nice framework of the Standard Model, but right now we don’t really have one single theory of what should come after it. The most popular possibility is supersymmetry, which is one of the things that a large number of physicists at the Large Hadron Collider are trying to find. But it’s not at all clear that this is the solution of what lies beyond the Standard Model. That ambiguity leads to a plethora of dark matter models because dark matter lies outside of the framework of the Standard Model and we don’t know in which direction this model will grow or how it will change. Physicists are looking at all the possibilities, many of which have good dark matter candidates. There’s this chasm between where we are now and where the light of understanding is, and we don’t yet know which direction to go to find it. So people are looking in all possible directions generating a lot of great ideas.

    Supersymmetry standard model
    Standard Model of Supersymmetry

    TKF: It seems that the results of your experiments will direct the search in one way or another. One of our viewers would like to know a little bit more about how you go about detecting dark matter in your experiments. Since dark matter really doesn’t interact with us very much, how do you go about seeing it?

    G.R.: Our experiments use very different techniques. My experiment looks for axions that every once in a while couple to photons. They do so in a way that the photons produced are of microwave frequencies. This is quite literally the frequency used by your cell phone or in your microwave oven. So we look for a very occasional transmutation of an axion from the dark matter around us into a microwave photon. We also help this process along using a strong magnetic field. Because the frequency of the photon coming from the axion is very specific, this ends up being a scanning experiment. It’s almost like tuning an AM radio; you know there’s a signal out there at a certain frequency, but you don’t know what the frequency is so you tune around, listening to hear a station. Only we’re looking for a signal that’s coming from dark matter turning into photons.

    E.F.F.: Both Harry and I look for similar particles, these WIMPs. My experiment is particularly good at looking for WIMPs that are about the mass of a proton or a couple times heavier than that, while Harry’s experiment is better at looking for particles that are maybe a hundred to several hundred times heavier than the proton. But the idea is the same. As Harry mentioned before, we know the density of dark matter particles in our region of space in the galaxy, so we can calculate how many of these dark matter particles should be going through me, through you, through your room right now.

    If you stick out your hand and you assume that WIMPs are maybe sixty times the mass of the proton — I’m just picking a number here — you calculate that there should be about 20 million WIMPs going through your hand every second. Now these dark matter particles go straight through your hand and straight through the Earth, but perhaps very occasionally they interact with one of the atoms in the matter that the Earth is made of. So we build detectors that hope to catch some of those very, very rare interactions.

    My experiment uses a crystal made out of germanium or silicon that we cool down to milli-kelvin temperatures: almost at absolute zero. If you remember your high school physics, atoms stop vibrating when they get very, very cold. So the atoms in this crystal are not vibrating much at all. If a dark matter particle interacts with one of the atoms in the crystal, the whole crystal starts vibrating and those vibrations are sensed by little microphones that we call phonon sensors. They also release charge and we measure that charge as well. Both of those help us to determine not only the energy that was imparted to the target but what type of interaction it was: Was it an interaction like the one you would expect from a photon or an electron, or was it an interaction you would expect from a WIMP or perhaps a neutron? That helps us to distinguish a dark matter signal from backgrounds coming from radioactivity in our environment. That’s very important when you’re looking for a very elusive signal.

    TKF: In fact you even go to the extent of working far underground to reduce this background noise, is that right?

    E.F.F.: That’s right. And I’ll actually let Harry take it from here.

    H.N.: Our experiments are going to be in two different mines. Ours is about a mile underground in western South Dakota in the Black Hills — the same black hills mentioned in the Beatles song Rocky Raccoon. Meanwhile, Enectali is up in Sudbury, Ontario, where there’s a heavy metal mine.

    One analogy I wanted to bring up is that what Enectali and I do is a microscopic version of billiards. The targets — in my case are xenon and in his case germanium and silicon — are like the colored balls on a pool table, and what we’re trying to detect is the cue ball — the dark matter particle we can’t see. But if the cue ball collides with the colored balls, they suddenly move. That’s what we detect.

    As Enectali said, the reason we go deep in a mine and the reason we build elaborate shields around these things is so that we aren’t fooled by radioactivity or neutrons or neutrinos moving the billiard balls. And there are a lot fewer of these fakes when we go deep. Plus, it’s an awful lot of fun to go in these mines. I’ve been working in them for ten or fifteen years now and it’s great to go a mile underground.

    TKF: If one of your experiments is successful in seeing dark matter, Enectali you said in a previous conversation that the next steps would be to study the dark matter particle’s characteristics and use that knowledge to better understand the particle’s role in the universe. I’m hoping you can explain that last bit a little bit further. Just how far-reaching would such a discovery be?

    E.F.F.: We’re very lucky in that we get to ask these really big questions about what the universe is made of. We know that dark matter makes up about 25 or 26 percent of the universe, and through direct detection we’re trying to figure out what that is exactly.

    But even once we know the mass of the dark matter particle, we still need to understand a lot of other things: whether it has spin, whether it is its own anti-particle, all kinds of properties of the particle itself. But that’s not all that there is to it. This particle was produced some time ago. We want to know how it was produced, when it was produced, what did that do to the universe and to the formation of the universe. There’s a very complicated history of what happened in the universe between the Big Bang and today, and dark matter has a big role to play.

    Dark matter is the glue that holds all the galaxies, all the clusters of galaxies and all the super clusters together. So without dark matter, the universe would not look like it does today. The type of dark matter could change the way that structure formed. So that’s one very important thing that we would like to understand. Another thing is that we don’t really know how dark matter behaves here in our galaxy today. We know its density, but we don’t really know how it’s moving. We have some assumptions, but it will be very interesting to really understand the motion of dark matter – whether it’s clumpy, whether it has structures or streams, whether some of it is in a flat disk. The answers to these questions will have implications for the stars in our galaxy and beyond. All those things will be the next step in what we would love to be doing, which is dark matter astronomy.

    TKF: We have one last question from a viewer who identifies herself as “an interested artist.” Her question is: If you find dark matter, what are you going to call it? It won’t be dark anymore.

    G.R.: I can start with a bad idea. It was called dark matter originally because when you look up at the sky, there are things that produce light — like stars — and there are things that we know are out there because they interact gravitationally but they’re not producing light. They’re dark. But that name kind of implies that they absorb or block light, when in fact dark matter doesn’t. Light goes right through it. So you can call it clear matter, but dark matter at least sounds mysterious. Clear matter sounds rather boring.

    H.N.: I hope you get people better at language than physicists to answer this! If it’s physicists who name it, we’ll end up with a name like gluon. I’d prefer to have a better name than that. Since this viewer is an artist, I’ll point out a sculpture at the Tate in London by Cornelia Parker called Cold Dark Matter: An Exploded View. This idea that there’s something out there that we can’t sense yet is one of those things that sends chills down my spine. I think that scientists share that feeling of wonderment with artists.

    E.F.F.: I’d love to have a naming contest for this 20-some-odd percent of the universe. I think it would produce much better names than we would come up with on our own.

    See the full article here.

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  • richardmitnick 5:21 am on December 15, 2014 Permalink | Reply
    Tags: , , , , Particle Physics   

    From CERN: “CERN’s Large Hadron Collider gears up for run 2″ 

    CERN New Masthead

    12 Dec 2014
    Cian O’Luanaigh

    CERN today announced at the 174th session of the CERN Council that the Large Hadron Collider (LHC) is gearing up for its second three-year run. The LHC is the largest and most powerful particle accelerator in the world and the whole 27-kilometre superconducting machine is now almost cooled to its nominal operating temperature of 1.9 degrees above absolute zero. All teams are at work to get the LHC back online and the CERN Control Centre is in full swing to carry out all the requested tests before circulating proton beams again in March 2015. Run 2 of the LHC follows a 2-year technical stop that prepared the machine for running at almost double the energy of the LHC’s first run.

    lhc
    The Large Hadron Collider is preparing for running at higher energy in 2015 (Image: Maximilen Brice/CERN)

    “With this new energy level, the LHC will open new horizons for physics and for future discoveries,” says CERN Director-General Rolf Heuer. “I’m looking forward to seeing what nature has in store for us”.

    For the first time on 9 December 2014, the magnets of one sector of the LHC, one eighth of the ring, were successfully powered to the level needed for beams to reach 6.5 TeV, the operating energy for run 2. The goal for 2015 will be to run with two proton beams in order to produce 13 TeV collisions, an energy never achieved by any accelerator in the past.

    “After the huge amount of work done over the last two years, the LHC is almost like a new machine,” said CERN’s Director for Accelerators and Technology Frédérick Bordry. “Restarting this extraordinary accelerator is far from routine. Nevertheless, I’m confident that we will be on schedule to provide collisions to the LHC experiments by May 2015”.

    ALICE, ATLAS, CMS and LHCb, the four large experiments of the LHC, are also undergoing major preparatory work for run 2, after the long shutdown during which important programmes for maintenance and improvements were achieved. They will now enter their final commissioning phase.

    See the full article here.

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    Meet CERN in a variety of places:

    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New
    ALICE
    CERN ALICE New

    CMS
    CERN CMS New

    LHCb
    CERN LHCb New

    LHC

    CERN LHC New

    LHC particles

    Quantum Diaries

     
  • richardmitnick 1:10 pm on December 9, 2014 Permalink | Reply
    Tags: , , , , , Particle Physics   

    From FNAL: “Digging begins for Muon g-2 and Mu2e beamlines” 


    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    Tuesday, Dec. 9, 2014
    Rich Blaustein

    This month construction has commenced on beamline tunnel extensions for Fermilab’s two muon experiments, Mu2e and Muon g-2.

    2
    A team of physicists from all over the world, including postdocal researchers and graduate and undergraduate students, are working together to design, test, and build the Mu2e experiment. The Mu2e Collaboration is comprised of over one hundred physicists and continues to grow.

    w
    Mu2e will have the ability to indirectly probe energy scales well beyond the terascale being explored at the LHC. At these higher energies the effects of new particles or new forces may become evident and may provide evidence that the four known forces that govern particle interations – the gravitational, electromagnetic, weak and strong forces – unify at some ultra-high energy. (Credit: symmetry magazine/Sandbox Studio)

    t
    The Mu2e detector is a particle physics detector embedded in a series of superconducting magnets. The magnets are designed to create a low-energy muon beam that can be stopped in a thin aluminum stopping target. The magnets also provide a constant magnetic field in the detector region that allows the momentum of the conversion electrons to be accurately determined. These superconducting magnets are big. The first, to the left, is about 12 feet long at 4.5 Tesla; the middle, S-shaped section about 40 feet along the curve at about 2 Tesla, and the third about 30 ft long and almost six feet across at 1 Tesla. The Earth’s field, for comparison, is 0.0006 Tesla.
    (Credit: symmetry magazine)

    g2
    Muon g-2 (pronounced gee minus two) will use Fermilab’s powerful accelerators to explore the interactions of short-lived particles known as muons with a strong magnetic field in “empty” space. Scientists know that even in a vacuum, space is never empty. Instead, it is filled with an invisible sea of virtual particles that—in accordance with the laws of quantum physics—pop in and out of existence for incredibly short moments of time. Scientists can test the presence and nature of these virtual particles with particle beams traveling in a magnetic field.

    In the area of the current Delivery Ring (the former Antiproton Debuncher), southwest of the Booster, the existing beam tunnel will be extended approximately 200 feet, at which point it will branch in two separate directions. The Muon g-2 tunnel, about 75 feet long, will terminate in the MC-1 Building, which houses the experiment’s muon storage ring. The Mu2e tunnel, around 550 feet long, will head toward a new building to be constructed for the experiment. Construction is expected to take one year. The start of the construction of the Mu2e building is planned for 2015.

    g
    Fermilab has begun construction on new beamlines for its muon programs, Muon g-2 and Mu2e. Image: Fermilab

    Digging for the tunnels began this month. Part of Kautz Road will become permanently inaccessible, with a detour from South Booster Road and Indian Creek Road serving as the new road.

    Fermilab Accelerator Division physicist Mary Convery, who oversees the Muon Campus program, coordinated the tunnel designs with Tom Lackowski, project manager; Rod Jedziniak, project design coordinator; and Tim Trout, project construction coordinator, all of FESS.

    The primary challenge in constructing the beamlines will be in accommodating fixed features and structures, both man-made and natural.

    “The locations of the g-2 and Mu2e buildings were fairly fixed because there are already utility corridors underground,” Convery said. “There are also wetlands that we are trying not to disturb.”

    Convery said that these physical constraints were important considerations in designing the experiments’ beamlines, since the space available to accomplish the necessary beam manipulations was limited.

    “It is not only the geometry of the beamlines that we have to conform to,” Lackowski said. “We also have to make sure the many services — the cable trays and the water services for cooling — are all coordinated.”

    Because the two muon experiments use the same beamlines at different energies, they cannot be run simultaneously.

    For both experiments, protons will proceed through the Linac, course through the Booster and then travel through the Recycler. A set of beamlines connects the Recycler to the Muon Campus. For the Muon g-2 experiment, the proton beam hits a target, converting the beam to a mixture of pions, protons and muons. The particles circle the Muon Delivery Ring several times, where protons are then removed and the remaining pions decay into muons. When the Muon g-2 experiment is taking data, the muon beam will continue to the experiment in the MC-1 Building.

    In contrast, for the Mu2e experiment, the protons bypass the target station and are transported to the Delivery Ring. The Mu2e protons also circle the Delivery Ring, then continue as an all-proton beam to the target in the Mu2e building area.

    Convery says work is also being done on other technical upgrades, such as installing magnets, along the beamline route.

    She expects the Muon g-2 experiment to begin in 2017, with Mu2e starting later, as scheduled.

    “Fermilab people have worked together for many years on various beamline projects,” Lackowski said. “We have had a very tight relationship with Mary and other colleagues, so we believe the Muon Campus tunnel project will go well.”

    See the full article here.

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    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics.

     
  • richardmitnick 6:49 pm on December 7, 2014 Permalink | Reply
    Tags: , , , , , , Particle Physics   

    From htxt.africa via FNAL: “Meet Claire Lee, a South African ATLAS physicist at CERN” 


    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    htxtdotafrica

    Anyone with even a passing interest in the sciences must have wondered what it’s like to work at the European Organisation for Nuclear Research, better known as CERN. Based in Switzerland, it’s one of the world’s largest and most respected centres for scientific research, birthplace of the worldwide web and home of the gigantic underground particle accelerator, the Large Hadron Collider (LHC).

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

    What wonders await those who join its ranks? What marvels must there be in the midst of such concentrated brain power?

    Since our chances of landing a job at CERN are probably limited to exciting opportunities in catering or sanitation, we figured it’s better to ask someone who does know. Someone like South African phyicist Claire Lee, who works right on ATLAS – one of the two elements of the LHC project that confirmed the existence of the Higgs boson in 2012.

    CERN ATLAS New
    ATLAS

    Lee has been involved with CERN since 2008 and has lived at the Swiss institute with her family for the past three and a half years. htxt.africa’s Tiana Cline sat down with Lee for a chat about all-things CERN, astrophysics and the elusive Higgs.

    How did you get interested in physics?

    Haha, this is a funny story. I’ve always loved science as long as I can remember (when I was very little I wanted to be an astronaut or an archaeologist), and have been fascinated with space since I could walk. But it really started in high school when I read the book Sphere by Michael Crichton. There was a character in the book who was an astrophysicist and I remember thinking to myself “Astrophysicist has to be about the coolest job title in the world, I want to be that!” So I set off to university with astrophysics as my final goal; however the astro-related projects that I ended up doing just didn’t seem to ever grab my interest. It was only in 2004, when for my Honours project I followed a basic version of what a friend was doing for his PhD in high energy nuclear physics, that I really started feeling the excitement.

    ac
    ATLAS Collaboration

    So science and physics were always a passion?

    In physics, High Energy Physics (HEP) is definitely my favourite, with a focus on Higgs and Beyond the Standard Model (BSM) physics. Our current theoretical knowledge is culminated in what is known as the Standard Model of Particle Physics, though we know that the theory is not complete (it doesn’t explain dark matter or dark energy, for example, nor the neutrino masses, and we have no idea how to incorporate gravity into the mix). So clearly there is lots of work still to do that will keep us hopefully busy with discoveries (or at least progress) for a while.

    In other fields, I do enjoy following the latest results in cosmology (such as the Planck vs BICEP2 saga, and AMS) and in particular where the fields of cosmology/astrophysics and particle physics overlap.

    And on a more personal note, neuroscience and the way the brain learns is fascinating too.

    Before jetting off to CERN, you studied in South Africa at both Wits and the University of Johannesburg as well as in Taiwan…

    I started off doing a BSc degree at Wits, I took Physics, Math, Applied Math and Chemistry in first year (2001). I hated Chemistry, so I dropped that first, took a second year Astronomy course, and ended up with Physics & Applied Math in 3rd year. I then did an Honours in Physics which was possibly one of the most fun years I’ve had in my life (we were a great class – 2004). At the end of that year I travelled to Virginia, USA for three weeks to work on an experiment at Jefferson Lab which became the subject of my MSc. I finally finished the MSc in 2009, also through Wits, and then moved to UJ where my supervisor had moved.

    As of 2007 South Africa wasn’t yet involved in the ATLAS experiment (though we had been working on ALICE, as well as ISOLDE and some of the smaller NA experiments for quite some time). But the annual South African Institute of Physics (SAIP) Conference we met Ketevi Assamagan, a US citizen originally from Togo, who was working at Brookhaven National Laboratory (BNL) on ATLAS. He had been invited to South Africa to speak at the conference – I think by Zeblon Vilakazi, member of the ALICE collaboration and (I think) director of iThemba LABS at the time. A group of us, especially my supervisor Prof Simon Connell and myself, were particularly interested in the type of physics ATLAS was doing, and a year later (2008) we flew to CERN to attend one of the ATLAS collaboration internal conferences, and meet with some of the heads of the experiment to discuss our involvement.

    The end of 2008 also saw the launch of the South Africa – CERN Programme which brought all the groups working on the various experiments together under one consortium.

    “Our current theoretical knowledge is culminated in what is known as the Standard Model of Particle Physics, though we know that the theory is not complete…” — Claire Lee, South African particle physicist

    sm
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    ATLAS is an expensive experiment to keep running, and as such requires a financial commitment from its member institutions. There are yearly fees based on personnel (students are free), as well as a joining fee which equates to about R1M. The agreement was that we would have two years to account for the joining fee (from the DST), and BNL would cover our yearly fees in the meantime. In 2009 Prof Connell was at UJ, and Wits hired an ATLAS physicist Prof Trevor Vickey. Together they got their respective universities to commit to R250k each of the ATLAS joining fee, and the government to the other R500k, and in July 2010 the two universities were officially voted into the ATLAS collaboration as part of a single South African institute. (Since then UCT and then UKZN have joined the cluster.)

    I also lectured at UJ (first year calculus-based physics, extended programme) for two years from 2009-2011, and my son was born in May 2010.

    Thanks to popular TV shows like the Big Bang Theory, places like CERN and the idea of being a physicist has been somewhat romanticised. What is life at CERN really like?

    My best friend came to visit and described it as “Just like a huge university, with no undergrads” and that’s a pretty good explanation! There are so many facets to it, but for the most part you wouldn’t say you were at one of the world’s top scientific institutions just by walking around: most of the buildings were built to pretty utilitarian standards. We joke that all expense was spared above ground here, but it is part true as the most important part are the accelerators and detectors below ground. CERN itself employs less than 3 000 people – some scientists, but mostly staff in management, HR and engineering. There are about 10 000 people working on CERN projects in total, but most are attached to their own University or institute, and definitely not all at CERN at once!

    CERN has a large turnover of people, one of its missions is to train people in a worldwide environment and then let them take their experience back home, and so there is always a flux of especially young people moving in and out of the area (it gives you a whole new perspective on the concept of friends). A lot of people will move to CERN for a year or so of their PhD, especially at the start, to completely immerse themselves in the physics, and then move back to their home institute for the rest of their degree, just making occasional trips to CERN.

    It’s easy to just focus completely on the physics aspect, but of course there is a large social side too, and CERN has a number of clubs and societies for just about anything you can think of (sailing, dancing, karate, LGBT and so on). CERN also does a great deal of outreach – I have hosted a number of underground visits to ATLAS, and virtual visits to the control room, competed in, compared and judged the FameLab competition, as well as co-organised two standup comedy evenings!

    I think one of the things I really like about the CERN ethos in general is that it doesn’t matter who you are, what matters is what you are good at. And CERN has become pretty good at using the talents of their personnel to their best advantage (as long as you’re happy for them to be used, of course!).

    What has been the most interesting part about being at CERN since you moved to Switzerland at the end of June 2011?

    There have been so many interesting things – being on shift and looking after a part of the detector during the 2012 physics run was great, and the Higgs boson discovery and announcement was a huge highlight! But also the people – everyone I meet is pretty great in one way or another, and I have made some very close friends who are all amazing at what they do as well as in their extracurricular activities. It’s wonderful to be surrounded by so many exceptional people.

    Also, on a personal note, watching my son grow up in the French-speaking world has been amazing. He was just over a year old when we moved over, and at one and a half he started going to a French creche (my husband looked after him full-time for those first five months while I worked). He now speaks fluent French (WAY better than either of us) as well as English.

    l
    Lee hosting a “virtual visit” with Algeria from the ATLAS control room.

    A silly question – but what do you actually do on a day-to-day basis?

    My standard day is usually comprised of some mix of coding and attending meetings (either in person or remotely via Skype), interspersed with coffees and lunch. There are many different types of work one can do, since I am mostly on analysis this means coding, in C++ or Python, for example to select a particular subset of events that I am interested in from the full set of data. This usually takes a couple of iterations, where we slim down the dataset at each step and calculate extra quantities we may want to use for our selections.

    The amount of data we have is huge – petabytes of data per year stored around the world at various high performance computing centres and clusters. It’s impossible to have anything but the smallest subset available locally – hence the iterations – and so we use the LHC Computing Grid (a specialised worldwide computer network) to send our analysis code to where the data is, and the code runs at these different clusters worldwide (most often in a number of different places, for different datasets and depending on which clusters are the least busy at the time). At the ultimate or penultimate step our personalised datasets are usually small enough to put somewhere local (either on a laptop or university cluster) from which we can make nice-looking plots etc.

    Various meetings happen all day every day on ATLAS, though of course you only attend the ones relevant to the work you are doing as it would be impossible otherwise! Whether it’s an analysis- or performance-related meeting (analysis is, eg, a particular physics analysis, such as a Higgs measurement, while performance studies relate to the measurement and calibration of the physics objects – like electrons – that are used in the analyses) people will present their most recent work, and usually there will be some discussion on how to move forward.

    a
    View of the ATLAS cavern side A beginning of February 2008, before the lowering of the Muon Small Wheels.

    And on the ATLAS Experiment?

    The ATLAS experiment is one of the four large experiments at the LHC. It is also the biggest of the four detectors (in volume) and like CMS, is a general-purpose detector, designed to detect all particles from the high energy proton-proton collisions. This allows ATLAS to cover many different aspects of physics, from measurements of the Higgs boson to searches for new physics. The detector itself is built like a giant three-dimensional puzzle of different detector components, with each part measuring a different aspect of the final-state particles from the collisions as they move through the detector.

    To be able to do any analysis, after the data has been recorded the events have to be reconstructed, meaning that the signals from the different parts of the detector are combined and fitted into objects such as electrons, muons, jets etc. Analyses can then select events based on the objects they have in them – a Higgs boson decaying to four leptons, for example, would then select events containing electrons and/or muons.

    Other quantities based on these objects are also calculated, such as the missing transverse momentum, which is the vector sum of the energies of all the particles in the event, measured by the calorimeters (and comes about due to conservation of momentum). This is important for events where we have particles that we do not detect, such as neutrinos, and so the only way we know they are there is by noticing an imbalance in the total momentum (the neutrino would then be going in the other direction). A very large amount of missing momentum, by the way, could also be a signal for a supersymmetric particle, so this quantity is used in a number of analyses.

    I’ve done various things – I worked as an online expert for one of the ATLAS calorimeters, for example, making sure that it was running properly and able to take good data while the collisions were happening. This sometimes involved being called in the middle of the night to solve problems!

    But one of my main tasks, and what my thesis is on, has been developing a new and complimentary method of measuring the missing transverse momentum, only this time we use particle track momenta rather than calorimeter energy measurements. This method has proven to be very useful, especially when combining the result with the “traditional” measurement from the calorimeter, and is used in various Higgs analyses to help separate signal from background.

    We’ve heard that there are over 3 000 physicists working on ATLAS. Who are the other African scientists working at the institute? It must be interesting working with such a diverse group of people.

    Ketevi Assamagan (who is now a co-supervisor of mine), for example, was the first ATLAS physicist I ever met. My other supervisor (Rachid Mazini) works for Taiwan but he is originally from Morocco. And of course although the groups have grown in the past few years, the High Energy Physics community in South Africa is pretty small, and we all fall under the SA-CERN programme, so we know each other quite well.

    There are over 100 different nationalities represented on ATLAS, so you become quite culturally-aware, especially when it comes to being sensitive of others’ commitments around things like Thanksgiving, Ramadan, Christmas, etc, as well as personal issues like kids. I’ve found that people are in general pretty tolerant, and as long as your work is coming along well you are pretty free to work as you see fit.

    swh
    Several hundred of the 1 700 scientists contributing to the LHC accelerator and experiments gathered in CERN’s building 40.

    Back to South Africa – are you positive about the state of science/physics education here?

    Yes and no. I think universities are doing a good job, mostly, we do have some top quality researchers here in South Africa and are able to place well on the international scale. On the other hand, the quality of the schooling is going down terribly, and some of the students gaining university entrance nowadays and qualifying for these courses know extremely little. This only puts pressure on the universities, increasing lecturers’ loads, which is unfortunate.

    Science is tough generally, and the sort of high-pressure environment that ATLAS is even tougher, so you need to have some internal reason to continue doing what you do. Second, making sure you have really supportive people around you also is important, people who encourage you to succeed and are there for you when you need them. And finally, it’s about making contacts; attending meetings (in person if you can) and talking to people and presenting your work regularly, as well as more “fun” stuff like outreach, all helps to get people to know who you are and what you can do.

    See the full article here.

    Please help promote STEM in your local schools.

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    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics.

     
  • richardmitnick 12:04 pm on December 4, 2014 Permalink | Reply
    Tags: , , , , , Particle Physics,   

    From FNAL- “Frontier Science Result: CDF Wading through the swamp to measure top quark mass” 


    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    Thursday, Dec. 4, 2014
    edited by Andy Beretvas

    Even after the discovery of the Higgs boson, the top quark is still a focus of attention because of its peculiar position of being the heaviest quark in the Standard Model and for its possible role in physics beyond the Standard Model.

    sm
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    If the Standard Model is correct, the stability of the vacuum strongly depends on the mass of the Higgs boson and the top quark mass. In this context, scientists favor the scenario that the universe is in a metastable state. A precision measurement of the top quark mass helps to better determine the relative stability of that state in this scenario.

    At the Tevatron, top quarks were produced, mostly in pairs, only once in about 10 billion collisions. They decayed right away into a W boson and a b quark. In the most abundant and yet most challenging scenario, the final state contains six collimated sprays of particles, called jets, two of which likely originated from the b quarks, with peculiar, identifiable characteristics (allowing them to be “b-tagged”). This decay mode is usually called the all-hadronic channel, for which the signal is swamped by a background associated to the production of uninteresting multijet events, which were about a factor of 1,000 more abundant than the signal events.

    FNAL Tevatron
    Tevatron

    This new analysis uses the full CDF Run II data set.
The set contains nearly twice the number of top quark pairs as seen in our previous measurement. The analysis uses an improved simulation and relies on there being at least one b-tagged jet. An important part of the analysis is to minimize the uncertainty in our measurement of jet scale energies. Exploiting the expected behavior of top-antitop signal events, the huge background can be tamed through finely tuned requirements, yielding about 4,000 events, where about one event out of three is expected from the signal. The all-hadronic final state can then be fully reconstructed using the energies of the six jets, and the mass of the top quark can be derived comparing the data to simulations produced for different input values of the top quark mass (see the [below] figure).

    i
    The black dots plot the distribution of the reconstructed top mass for events containing one or more b-tags. The distribution is compared to the expected yield for background and signal events, normalized to the best fit.

    FNAL CDF
    CDF

    This procedure yields a value of 175.1 ± 1.2 (stat) ± 1.6 (sys) GeV/c2 for the top quark mass, with a 1 percent relative precision. This measurement complements the results obtained by CDF in other channels. Our measurement is consistent with the current world average (which includes our previous measurement in the all-hadronic channel), obtained from measurements by ATLAS, CDF, CMS and DZero. The top quark mass world average is 173.3 ± 0.8 GeV/c2.

    CERN ATLAS New
    ATLAS

    CERN CMS New
    CMS

    FNAL DZero
    DZero

    See the full article here.

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    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics.

     
  • richardmitnick 10:28 pm on December 3, 2014 Permalink | Reply
    Tags: , , , , , , , , , , Particle Physics   

    From isgtw: “Volunteer computing: 10 years of supporting CERN through LHC@home” 


    international science grid this week

    December 3, 2014
    Andrew Purcell

    LHC@home recently celebrated a decade since its launch in 2004. Through its SixTrack project, the LHC@home platform harnesses the power of volunteer computing to model the progress of sub-atomic particles traveling at nearly the speed of light around the Large Hadron Collider (LHC) at CERN, near Geneva, Switzerland. It typically simulates about 60 particles whizzing around the collider’s 27km-long ring for ten seconds, or up to one million loops. Results from SixTrack were used to help the engineers and physicists at CERN design stable beam conditions for the LHC, so today the beams stay on track and don’t cause damage by flying off course into the walls of the vacuum tube. It’s now also being used to carry out simulations relevant to the design of the next phase of the LHC, known as the High-Luminosity LHC.

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

    “The results of SixTrack played an essential role in the design of the LHC, and the high-luminosity upgrades will naturally require additional development work on SixTrack,” explains Frank Schmidt, who works in CERN’s Accelerators and Beam Physics Group of the Beams Department and is the main author of the SixTrack code. “In addition to its use in the design stage, SixTrack is also a key tool for the interpretation of data taken during the first run of the LHC,” adds Massimo Giovannozzi, who also works in CERN’s Accelerators and Beams Physics Group. “We use it to improve our understanding of particle dynamics, which will help us to push the LHC performance even further over the coming years of operation.” He continues: “Managing a project like SixTrack within LHC@home requires resources and competencies that are not easy to find: Igor Zacharov, a senior scientist at the Particle Accelerator Physics Laboratory (LPAP) of the Swiss Federal Institute of Technology in Lausanne (EPFL), provides valuable support for SixTrack by helping with BOINC integration.”

    c
    Volunteer computing is a type of distributed computing through which members of the public donate computing resources (usually processing power) to aid research projects. Image courtesy Eduardo Diez Viñuela, Flickr (CC BY-SA 2.0).

    Before LHC@home was created, SixTrack was run only on desktop computers at CERN, using a platform called the Compact Physics Screen Saver (CPSS). This proved to be a useful tool for a proof of concept, but it was first with the launch of the LHC@home platform in 2004 that things really took off. “I am surprised and delighted by the support from our volunteers,” says Eric McIntosh, who formerly worked in CERN’s IT Department and is now an honorary member of the Beams Department. “We now have over 100,000 users all over the world and many more hosts. Every contribution is welcome, however small, as our strength lies in numbers.”

    Virtualization to the rescue

    Building on the success of SixTrack, the Virtual LHC@home project (formerly known as Test4Theory) was launched in 2011. It enables users to run simulations of high-energy particle physics using their home computers, with the results submitted to a database used as a common resource by both experimental and theoretical scientists working on the LHC.

    Whereas the code for SixTrack was ported for running on Windows, OS X, and Linux, the high-energy-physics code used by each of the LHC experiments is far too large to port in a similar way. It is also being constantly updated. “The experiments at CERN have their own libraries and they all run on Linux, while the majority of people out there have common-or-garden variety Windows machines,” explains CERN honorary staff member of the IT department and chief technology officer of the Citizen Cyberscience Centre Ben Segal. “Virtualization is the way to solve this problem.”

    The birth of the LHC@home platform

    In 2004, Ben Segal and François Grey , who were both members of CERN’s IT department at the time, were asked to plan an outreach event for CERN’s 50th anniversary that would help people around the world to get an impression of the computational challenges facing the LHC. “I had been an early volunteer for SETI@home after it was launched in 1999,” explains Grey. “Volunteer computing was often used as an illustration of what distributed computing means when discussing grid technology. It seemed to me that it ought to be feasible to do something similar for LHC computing and perhaps even combine volunteer computing and grid computing this way.”

    “I contacted David Anderson, the person behind SETI@Home, and it turned out the timing was good, as he was working on an open-source platform called BOINC to enable many projects to use the SETI@home approach,” Grey continues. BOINC (Berkeley Open Infrastructures for Network Computing)is an open-source software platform for computing with volunteered resources. It was first developed at the University of California, Berkeley in the US to manage the SETI@Home project, and uses the unused CPU and GPU cycles on a computer to support scientific research.

    “I vividly remember the day we phoned up David Anderson in Berkeley to see if we could make a SETI-like computing challenge for CERN,” adds Segal. “We needed a CERN application that ran on Windows, as over 90% of BOINC volunteers used that. The SixTrack people had ported their code to Windows and had already built a small CERN-only desktop grid to run it on, as they needed lots of CPU power. So we went with that.”

    A runaway success

    “I was worried that no one would find the LHC as interesting as SETI. Bear in mind that this was well before the whole LHC craziness started with the Angels and Demons movie, and news about possible mini black holes destroying the planet making headlines,” says Grey. “We made a soft launch, without any official announcements, in 2004. To our astonishment, the SETI@home community immediately jumped in, having heard about LHC@home by word of mouth. We had over 1,000 participants in 24 hours, and over 7,000 by the end of the week — our server’s maximum capacity.” He adds: “We’d planned to run the volunteer computing challenge for just three months, at the time of the 50th anniversary. But the accelerator physicists were hooked and insisted the project should go on.”

    Predrag Buncic, who is now coordinator of the offline group within the ALICE experiment, led work to create the CERN Virtual Machine in 2008. He, Artem Harutyunyan (former architect and lead developer of CernVM Co-Pilot), and Segal subsequently adopted this virtualization technology for use within Virtual LHC@home. This has made it significantly easier for the experiments at CERN to create their own volunteer computing applications, since it is no longer necessary for them to port their code. The long-term vision for Virtual LHC@home is to support volunteer-computing applications for each of the large LHC experiments.
    Growth of the platform

    The ATLAS experiment recently launched a project that simulates the creation and decay of supersymmetric bosons and fermions. “ATLAS@Home offers the chance for the wider public to participate in the massive computation required by the ATLAS experiment and to contribute to the greater understanding of our universe,” says David Cameron, a researcher at the University of Oslo in Norway. “ATLAS also gains a significant computing resource at a time when even more resources will be required for the analysis of data from the second run of the LHC.”

    CERN ATLAS New
    ATLAS

    ATLAS@home

    Meanwhile, the LHCb experiment has been running a limited test prototype for over a year now, with an application running Beauty physics simulations set to be launched for the Virtual LHC@home project in the near future. The CMS and ALICE experiments also have plans to launch similar applications.

    CERN LHCb New
    LHCb

    CERN CMS New
    CMS

    CERN ALICE New
    ALICE

    An army of volunteers

    “LHC@home allows CERN to get additional computing resources for simulations that cannot easily be accommodated on regular batch or grid resources,” explains Nils Høimyr, the member of the CERN IT department responsible for running the platform. “Thanks to LHC@home, thousands of CPU years of accelerator beam dynamics simulations for LHC upgrade studies have been done with SixTrack, and billions of events have been simulated with Virtual LHC@home.” He continues: “Furthermore, the LHC@home platform has been an outreach channel, giving publicity to LHC and high-energy physics among the general public.”

    See the full article here.

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    iSGTW is an international weekly online publication that covers distributed computing and the research it enables.

    “We report on all aspects of distributed computing technology, such as grids and clouds. We also regularly feature articles on distributed computing-enabled research in a large variety of disciplines, including physics, biology, sociology, earth sciences, archaeology, medicine, disaster management, crime, and art. (Note that we do not cover stories that are purely about commercial technology.)

    In its current incarnation, iSGTW is also an online destination where you can host a profile and blog, and find and disseminate announcements and information about events, deadlines, and jobs. In the near future it will also be a place where you can network with colleagues.

    You can read iSGTW via our homepage, RSS, or email. For the complete iSGTW experience, sign up for an account or log in with OpenID and manage your email subscription from your account preferences. If you do not wish to access the website’s features, you can just subscribe to the weekly email.”

     
  • richardmitnick 8:10 pm on December 1, 2014 Permalink | Reply
    Tags: , , , , , , Particle Physics   

    From Scientific American- Don Lincoln of Fermilab “U.S. Particle Physics Program Aims for the Future” 

    Scientific American

    Scientific American

    November 25, 2014

    FNAL Don Lincoln
    Dr. Don Lincoln

    n the last few years, stories have abounded in the press of the successes of the Large Hadron Collider, most notably the discovery of the Higgs boson. This has led some to speculate that European research is ascendant while U.S. research is falling behind. While there is no argument that U.S. particle physics budgets have shrunk over the past decade, it is also inarguable that America is still huge player in this fascinating research sector, collaborating on projects in Europe and Asia while pursuing a strong domestic program as well.

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC at CERN

    To properly appreciate the breadth of the U.S.’s contribution to particle physics research, one must distinguish between the international program and the domestic one. The international program is currently (and appropriately) focused mostly on the LHC. The ring-shaped collider is, without a doubt, an amazing piece of equipment. It is 17 miles around, took a quarter century to plan and build, cost about $10 billion, and requires about 10,000 scientists to operate and study the data it generates. Four distinct experiments (ALICE, ATLAS, CMS and LHCb) were built to use the LHC to investigate some of mankind’s oldest scientific questions.

    CERN ALICE New
    ALICE

    CERN ATLAS New
    ATLAS

    CERN CMS New
    CMS

    CERN LHCb New
    LHCb

    Physicists employed by U.S. universities and national laboratories comprise about a third of the LHC experimental program, making the U.S. the single largest country involved in the project. Although the CERN laboratory itself employs more LHC scientists than any other single institution, America’s Fermilab and Brookhaven National Laboratory are uncontested seconds for CMS and ATLAS, respectively. American physicists lead many analysis efforts and the CMS collaboration even elected Professor Joe Incandela of the University of California, Santa Barbara to be the group leader.

    fnal
    Fermilab’s Main Ring and Main Injector as seen from the air. (Credit: Reidar Hahn/Fermilab)

    While there is no denying the attractiveness of the LHC as a scientific opportunity, U.S. scientists also pursue an active and vibrant U.S. domestic program. Fermilab serves as the hub for the American particle physics community and the laboratory’s accelerators, both present and future, are helping scientists blaze new trails into the fascinating subatomic world.

    Because the LHC is firmly ensconced as the highest energy facility in the world for the foreseeable future, Fermilab is focusing on a different technique to delve into the fundamental rules of the universe. By choosing to concentrate on making the highest intensity particle beams ever achieved, the U.S.’s domestic program is able to investigate some of the rarest phenomena ever imagined at energy scales that far exceed those accessible at the LHC. High energy means that individual beam particles are moving at unprecedented speeds, while high intensity means many particles focused on a tiny area, much like a magnifying lens can focus light. When many particles are brought into tight proximity, there is a small chance that a quantum mechanical fluctuation will allow an extremely unlikely and ultra-high energy interaction to occur.

    It’s easy to explain to people why building a higher energy facility is valuable, but understanding why higher intensity beams is a leading research strategy is a little more difficult and requires two insights. The first and simpler insight is to realize that in particle physics, we look for rare collisions between beams of particles. The reason we look for rare ones is that the common ones have been studied already.

    bnl
    The central campus of Brookhaven National Laboratory. The National Synchrotron Light Source II, under construction at the time of this photo, is at bottom, right. The 3.8-kilometer circumference ring of the Relativistic Heavy Ion Collider can be seen in the distance at the top of the frame. (Credit: Brookhaven National Laboratory)

    To observe the rarest collisions, one must simply make a lot of collisions and wait. It’s similar to trying to win the lottery. If you buy one ticket, you are unlikely to succeed, but if you buy many tickets there is a much higher chance that you have bought a winner.

    The more subtle insight hinges on the principles of physics, specifically quantum mechanics. While it is a firm rule of classical physics that energy is conserved, this rule is not so rigidly observed in the quantum realm. According to the tenets of the Heisenberg Uncertainty Principle, energy can simply appear, as long as it disappears quickly enough. Further, the larger the temporary energy imbalance, the shorter the duration. Thus, because they persist for so short a time, the large energy imbalances are very rare. And, as I have noted above, to study very rare processes, one must employ very intense beams.

    Using the current Fermilab accelerator complex, physicists are studying the interactions of neutrinos with matter. Neutrinos only experience the weak nuclear force and can pass through a lot of matter without interacting. To give a sense of scale, the sun constantly emits neutrinos. If we were determined to stop half of them, we’d need a wall composed of solid lead that is five light years thick! Given this reluctance to interact, the only way to ensure enough neutrino interactions to study is to generate incredibly intense beams and analyze them with massive particle detectors.

    The Fermilab MINOS and NOvA experiments shoot unprecedentedly bright beams of neutrinos from Chicago to northern Minnesota to study an interesting phenomenon called neutrino oscillations. Neutrinos are unique in that they can change their identity, vaguely as if an electron could change into a proton and back. It is hoped that understanding this oscillatory behavior might explain why the universe is made solely of matter when we believe that matter and antimatter existed in equal quantities when the universe began.

    FNAL NOvA
    FNAL NOvA

    mu
    The muon g-2 storage ring arrives at Fermilab, near Chicago, in July 2013 after a cross-country trip from Brookhavn National Laboratory on Long Island, New York. (Credit: Reidar Hahn/Fermilab)

    A second bright star in the constellation of U.S. particle physics research is the use of Fermilab’s accelerator complex to study muons, the heavy cousins of electrons. Scientists of the Muon g-2 experiment will measure the magnetic moment of muons. Earlier measurements at the Brookhaven National Laboratory were very precise – with eight digits of precision. However, there is a tantalizing tension between data and theoretical predictions. While both measurement and prediction are exquisitely precise, the two numbers disagree slightly. This disagreement is small, but is about three and a half times larger than the combined experimental and theoretical uncertainty. This discrepancy could signify the onset of new physics, which could involve supersymmetry, muon substructure or something entirely unexpected. Because Fermilab can generate more intense beams of muons than Brookhaven, the g-2 apparatus was moved from Long Island, New York to Chicago to investigate this question more thoroughly.

    Supersymmetry standard model
    Standard Model of Supersymmetry

    Yet another interesting question that has been investigated relates to unconventional muon decays. Most muons decay into electrons and two neutrinos, however there are reasons to suspect that perhaps muons might decay into electrons without neutrinos. The Mu2e experiment at Fermilab is scheduled to start recording data in a couple of years and this experiment will be sensitive to energy scales far higher than the LHC can achieve. Since neutrinos transform into other types of neutrinos and quarks can change into other quarks, physicists think that the transition of muons into electrons might be possible. Because this decay is expected to be very rare (if it exists at all), this is another reason to make high intensity muon beams.

    A multi-year study of the pressing physics questions by the entire U.S. particle physics community resulted in a firm recommendation to upgrade the Fermilab accelerator complex to further increase the amount of beam it can supply. Thus, the long term plan for the Fermilab laboratory is to increase the intensity of its neutrino beams by at least 50 percent and shoot these beams off to a detector to be located in South Dakota. Because neutrinos change their identity (i.e. oscillate) in flight, having detectors at different distances from Fermilab gives a complementary view of neutrino oscillations and it will shed more light on the phenomenon.

    FNAL LBNE

    But the U.S. community hasn’t forgotten the energy frontier. Eventually, there will be an accelerator that replaces the LHC as the energy leader. It will be a long time before any decisions are made on where that facility might be located (or even what kinds of beams will be needed: protons or electrons). But, to be prepared, several institutions across the U.S. are expanding their accelerator development programs. Whether the future facility is located in the U.S., Europe or Asia, U.S. accelerator scientists will be heavily engaged in developing the required technology.

    Even with tight budgets, the American particle physics community has continued to have a huge impact in humankind’s investigations of some of the oldest scientific questions, and continued support is key to maintaining this leading role.

    See the full article here.

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    Scientific American, the oldest continuously published magazine in the U.S., has been bringing its readers unique insights about developments in science and technology for more than 160 years.

     
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