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

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

    FNAL Home


    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 2:41 pm on December 16, 2014 Permalink | Reply
    Tags: , , Boston University, , High Energy Physics, ,   

    From BU: “Trigger Happy” 

    Boston University Bloc

    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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    Boston University is no small operation. With over 33,000 undergraduate and graduate students from more than 130 countries, nearly 10,000 faculty and staff, 17 schools and colleges, and 250 fields of study, our two campuses are always humming, always in high gear.

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  • richardmitnick 9:20 pm on December 15, 2014 Permalink | Reply
    Tags: , High Energy Physics,   

    From SLAC: “Is the Higgs Boson a Piece of the Matter-Antimatter Puzzle?” 


    SLAC Lab

    December 15, 2014

    A SLAC Theorist and Colleagues Lay Out a Possible Way to Tell if the Higgs is Involved

    Several experiments, including the BaBar experiment at the Department of Energy’s SLAC National Accelerator Laboratory, have helped explain some – but not all – of the imbalance between matter and antimatter in the universe. Now a SLAC theorist and his colleagues have laid out a possible method for determining if the Higgs boson is involved.

    In a paper published in Physical Review D, they suggest that scientists at CERN’s Large Hadron Collider (LHC), where the Higgs was discovered, look for a specific kind of Higgs decay when the collider starts up again in 2015. The details of that decay could tell them whether or not the Higgs has a say in the matter-antimatter imbalance.

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

    “The time to plan a search strategy is now,” said Matt Dolan, a research associate in SLAC’s Particle Theory group and co-author of the paper. “That way, when the LHC begins to operate at full strength we’ll be ready.”

    Why there’s more matter than antimatter is one of the biggest questions confounding particle physicists and cosmologists, and it cuts to the heart of our own existence. In the time following the Big Bang, when the budding universe cooled enough for matter to form, most matter-antimatter particle pairs that popped into existence annihilated each other. Yet something tipped the balance in favor of matter, or we – and stars, planets, galaxies, life – would not be here.

    The recently discovered Higgs boson is directly connected to the issues of mass and matter. Asking whether the Higgs is involved in the preponderance of matter over antimatter seems a reasonable question.

    The paper is based on a phenomenon called CP – or charge-parity – violation, the same phenomenon investigated by BaBar. CP violation means that nature treats a particle and its oppositely charged mirror-image version differently.

    “Searching for CP violation at the LHC is tricky,” Dolan said. “We’ve just started to look into the properties of the Higgs, and the experiments must be very carefully designed if we are to improve our understanding of how the Higgs behaves under different conditions.”

    First, researchers need to confirm that the Higgs fits into the Standard Model, our current best explanation of matter, energy and the processes that turned them into us. A Higgs that fits the Standard Model where CP violation is concerned is called CP-even; one that does not is called CP-odd. A tell-tale sign that the Higgs is involved in CP violation is if it’s a mixture of even and odd.

    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.

    The theorists proposed that experimenters look for a process in which a Higgs decays into two tau particles, which are like supersized cousins of electrons, while the remainder of the energy from the original proton-proton collision sprays outward in two jets. Any mix of CP-even and CP-odd in the Higgs is revealed by the angle between the two jets.

    t
    In this illustration, two protons collide at high energy, producing a Higgs boson that instantly decays, producing two tau particles. The rest of the energy from the collision sprays outward in two jets (pink cones). Measuring the angle between these jets could reveal whether or not the Higgs is involved in charge-parity (CP) violation, which says that nature treats a particle and its oppositely charged antiparticle differently. A SLAC researcher and his colleagues propose such an experiment in a recent paper in Physical Review D. (SLAC National Accelerator Laboratory)

    “This is a very high-profile and involved analysis,” said Philip Harris, a staff physicist at CERN and co-author of the paper along with Martin Jankowiak of the University of Heidelberg and Michael Spannowsky of Durham University. A member of the CMS collaboration, Harris focuses on Higgs-to-tau-tau decays, evidence of which has only recently begun to mount.

    “I wanted to add a CP violation measurement to our analysis, and what Matt, Martin and Michael proposed is the most viable avenue,” Harris said, adding that he’s looking forward to all the data the LHC will generate when it starts up again early next year at its full design strength.

    “Even with just a few months of data we can start to make real statements about the Higgs and CP violation,” he said.

    Citation: Matthew Dolan et al., Physical Review D, 21 October 2014 (10.1103/PhysRevD.90.073008)

    See the full article here.

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    SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the DOE’s Office of Science.
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  • richardmitnick 5:21 am on December 15, 2014 Permalink | Reply
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    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

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  • richardmitnick 1:10 pm on December 9, 2014 Permalink | Reply
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    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)

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    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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    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
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    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
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    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.

    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 10:28 pm on December 3, 2014 Permalink | Reply
    Tags: , , , , , , High Energy 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 9:05 pm on December 3, 2014 Permalink | Reply
    Tags: , , High Energy Physics,   

    From Symmetry: “Searching for a dark light” 

    Symmetry

    December 03, 2014
    Manuel Gnida

    A new experiment at Jefferson Lab is on the hunt for dark photons, hypothetical messengers of an invisible universe.

    The matter we know accounts for less than 5 percent of the universe; the rest is filled with invisible dark matter and dark energy. Scientists working on a new experiment to be conducted at Thomas Jefferson National Accelerator Facility in Virginia hope to shed light on some of those cosmic unknowns.

    According to certain theories known as hidden-sector models, dark matter is thought to consist of particles that interact with regular matter through gravitation (which is why we know about it) but not through the electromagnetic, strong and weak fundamental forces (which is why it is hard to detect). Such dark matter would interact with regular matter and with itself through yet-to-be-discovered hidden-sector forces. Scientists believe that heavy photons—also called dark photons—might be mediators of such a dark force, just as regular photons are carriers of the electromagnetic force between normal charged particles.

    The Heavy Photon Search at Jefferson Lab will hunt for these dark, more massive cousins of light.

    “The heavy photon could be the key to a whole rich world with many new dark particles and forces,” says Rouven Essig, a Stony Brook University theoretical physicist who in recent years helped develop the theory for heavy-photon searches.

    Although the idea of heavy photons has been around for almost 30 years, it gained new interest just a few years ago when theorists suggested that it could explain why several experiments detected more high-energy positrons—the antimatter partners of electrons—than scientists had expected in the cosmic radiation of space. Data from the PAMELA satellite experiment; the AMS instrument aboard the International Space Station; the LAT experiment of the Fermi Gamma-ray Space Telescope and others have all reported finding an excess of positrons.

    INFN PAMELA
    INFN/PAMELA

    AMS 02
    AMS-02

    NASA Fermi LAT
    NASA/Fermi LAT

    NASA Fermi Telescope
    NASA/Fermi spacecraft

    “The positron excess could potentially stem from dark matter particles that annihilate each other,” Essig says. “However, the data suggest a new force between dark matter particles, with the heavy photon as its carrier.”

    Creating particles of dark light

    If heavy photons exist, researchers want to create them in the lab.

    Theoretically, a heavy photon can transform into what is known as a virtual photon—a short-lived fluctuation of electromagnetic energy with mass—and vice versa. This should happen only very rarely and for a very short time, but it still means that experiments that produce virtual photons could in principle also generate heavy photons. Producing enormous numbers of virtual photons may create detectable amounts of heavy ones.

    At Jefferson Lab’s Continuous Electron Beam Accelerator Facility, CEBAF, scientists will catapult electrons into a tungsten target, which will generate large numbers of virtual photons—and perhaps some heavy photons, too.

    Jlab CEBAF
    JLab/CEBAF

    “CEBAF provides a very stable, highly intense electron beam that is almost continuous,” says Jefferson Lab’s Stepan Stepanyan, one of three spokespersons for the international HPS collaboration, which includes more than 70 scientists. “It is a unique place for performing this experiment.”

    The virtual photons and potential heavy photons produced at CEBAF will go on to decay into pairs of electrons and positrons. A silicon detector placed right behind the target will then track the pairs’ flight paths, and an electromagnetic calorimeter will measure their energies. Researchers will use this information to reconstruct the exact location in which the electron-positron pair was produced and to determine the mass of the original photon that created the pair. Both are important data points for picking the heavy photons out of the bunch.

    The photon mass measured in the experiment matters because a heavy photon has a unique mass, whereas virtual photons appear with a broad range of masses. “The heavy photon would reveal itself as a sharp bump on top of a smooth background from the virtual photon decays,” says SLAC National Accelerator Laboratory’s John Jaros, another HPS spokesperson.

    The location in which the electron-positron pair was produced also matters because virtual photons decay almost instantaneously within the target, says Timothy Nelson, project lead for the silicon detector, which is being built at SLAC. Heavy photons could decay more slowly, after traveling beyond the target. So photons that decay outside the target can only be heavy ones. The HPS silicon detector’s unique ability to identify outside-of-target decays sets it apart from other experiments currently participating in a worldwide hunt for heavy photons.

    The HPS calorimeter, whose construction was led by researchers from the French Institut de Physique Nucléaire, the Italian Istituto Nazionale di Fisica Nucleare and Jefferson Lab, is currently being tested at Jefferson Lab, while scientists at SLAC plan to ship their detector early next year. The experiment is scheduled to begin in the spring of 2015.

    See the full article here.

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    Symmetry is a joint Fermilab/SLAC publication.


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