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  • richardmitnick 11:18 am on February 13, 2015 Permalink | Reply
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    From FNAL- “Frontier Science Result: CMS “ 

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

    Friday, Feb. 13, 2015
    FNAL Don Lincoln
    Don Lincoln

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    Scientists in the CMS collaboration look for many different possible signatures that would reveal new physical phenomena. One interesting idea is massive and long-lived particles that stop inside the detector and then decay. [This is the whole picture. Not well done by FNAL.]

    CERN CMS New
    CMS

    “We are all agreed that your theory is crazy. The question that divides us is whether it is crazy enough to have a chance of being correct.”

    This quote is attributed to Niels Bohr speaking to Wolfgang Pauli when the latter was presenting a new theory in a seminar, but it works equally well when modern scientists make presentations about new theories to try to push forward our understanding of the cosmos. While there is no question that the Standard Model has been an enormous success, there remain unsolved mysteries.

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    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 early successes of the LHC have stringently constrained theoretical ideas that have been put forward as possible advances in our understanding of the rules of the universe. This leads scientists to think more creatively.

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC

    One such crazy idea (but is it crazy enough?) is that there exist very heavy and stable particles that can be created only in large accelerators like the LHC. Unlike most subatomic particles, which decay in less than the blink of an eye, these particles could persist for long times, ranging from microseconds to years.

    A number of theories make these predictions, and one originates in supersymmetry. All supersymmetric theories predict that there exists a set of particles that we’ve not yet discovered, although the different theories make quite different predictions as to the masses of these undiscovered particles.

    Supersymmetry standard model
    Standard Model of Supersymmetry

    An example of a supersymmetric theory that predicts long-lived particles is one in which the bosons have a very high mass, while the fermions have a very low mass. One of these fermions is the gluino, which is the supersymmetric analog of the gluon, a boson in the Standard Model.

    There are some requirements on the decay product of the gluino. Since the gluino carries color (the charge of the strong force) it must decay into a particle that also carries color. In the Standard Model, this would be a quark. And since the gluino is a supersymmetric particle, it must also have a supersymmetric decay particle. But since its supersymmetric partner would be massive, as all supersymmetric bosons are, the gluino cannot easily decay. The net result is that, under these conditions, the gluino could live for quite a long time.

    If such a particle exists and can be produced at the LHC, some of them will be produced with such a low velocity that they will interact with the CMS detector and stop moving, much as a ball rolling over a beach eventually stops. And, once stopped, the particle will eventually decay inside the detector. To be able to better identify these decays, scientists looked inside the detector in periods when no beam passed through it. Using the data, they were able to search for and set limits on long-lived particles with lifetimes ranging from a millionth of a second to more than fifteen minutes.

    So we’re left with the question: The theory is crazy, but is it crazy enough? Hopefully with the resumption of LHC operations later this year, we’ll finally find out.

    See the full article here.

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  • richardmitnick 1:40 pm on February 6, 2015 Permalink | Reply
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    From CERN: “Everything is illuminated” 

    CERN New Masthead

    Feb 2, 2015
    Katarina Anthony

    On Monday, 26 January, CMS installed one of the final pieces in its complex puzzle: the new Pixel Luminosity Telescope. This latest addition will augment the experiment’s luminosity measurements, recording the bunch-by-bunch luminosity at the CMS collision point and delivering high-precision measurements of the integrated luminosity.

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    Installing the PLT in the heart of the CMS experiment.

    No matter the analysis, there’s one factor that every experimentalist needs to know perfectly: the luminosity. Its error bars can make or break a result, so its high precision measurement is vital for success. With this in mind, the CMS collaboration tasked the BRIL (Beam Radiation Instrumentation and Luminosity) project with developing a new detector to record luminosity for Run 2. Working with experimentalists from across the CMS collaboration and CERN, BRIL designed, created and installed the small – but mighty – Pixel Luminosity Telescope (PLT).

    “During Run 1, our primary online luminosity measurements came from the forward hadron calorimeter, which we compared to the offline luminosity measurement using the pixel detector,” says Anne Dabrowski, BRIL deputy project leader and technical coordinator (CERN). “But as we move to higher and higher luminosities and pile-ups in Run 2, extracting the luminosity gets harder to do.” That’s where the PLT comes in. Designed with the new LHC Run 2 in mind, the PLT uses radiation-hard CMS pixel sensors to provide near-instantaneous readings of the per-bunch luminosity – thus helping LHC operators provide the maximum useful luminosity to CMS. The PLT is unconnected to the CMS trigger and reads out at 40 MHz (every 25 ns) with no dead-time.

    The BRIL team includes collaborators from CERN, Germany, New Zealand, the USA, Italy and Russia.

    Research and development on the PLT began ten years ago, with diamonds first considered for the pixel telescope planes. A PLT prototype was even installed along the LHC beam line during Run 1. “Diamond sensors would have been an excellent choice, as they do not need to be run at low temperatures to have an acceptable radiation damage signal loss,” says David Stickland, BRIL project leader (Princeton University). However – while the potential for a diamond PLT remains – the prototype results led the team to use a more tested and reliable material for Run 2: silicon.

    However, this practical decision would create new issues for the BRIL team to resolve: “Suddenly, heat was a real concern,” explains Anne. “If we wanted to get a good signal out of silicon sensors, we had to bring the telescopes down in temperature.” With only 18 months to go until installation, the BRIL team had to go back to the drawing board to try and fit a cooling structure into an already-constrained space.

    The PLT is comprised of two arrays of eight small-angle telescopes situated on either side of the CMS interaction point. Each telescope hovers only 1 cm away from the CMS beam pipe, where it uses three planes of pixel sensors to take separate, unique measurements of luminosity. (Image: A. Rao)

    “We were successful thanks to the ingenuity of the CMS engineering integration office and PH-DT engineers, in particular Robert Loos,” says David. “Rob designed an extraordinary 3D-printed cooling structure using a titanium alloy, using the ‘selective laser melting (SLM)’ technique in order to ‘grow’ the cooling structure we needed.” Despite the internal diameter of the cooling channels being less than 3 mm, the cooling structure can make right-angle turns at the drop of a dime and withstand pressure up to 15 bar. “It’s tremendously strong, light and compact. I don’t know how it could have been made without this technique,” David adds.

    This is only the first example of the innovative design used by the BRIL group. So while the telescope’s installation may be complete, our coverage of their work is not yet over. Look out for an article in the next edition of the Bulletin to find out more…

    See the full article here.

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    Meet CERN in a variety of places:

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    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New
    ALICE
    CERN ALICE New

    CMS
    CERN CMS New

    LHCb
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  • richardmitnick 11:53 am on January 27, 2015 Permalink | Reply
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    From CERN: “CMS pins down Higgs with first run data” 

    CERN New Masthead

    1
    New results from the CMS collaboration are pinning down the properties of the Higgs boson (Image: Maximilien Brice/CERN)

    27 Jan 2015
    André David

    With the Large Hadron Collider (LHC) preparing to restart in a few months, data from its first run has already been bearing fruit.

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    LHC

    A recent publication by the CMS collaboration brings together the broadest set of results to date about the properties of the Higgs boson. The paper, submitted to The European Physical Journal C (and available at arXiv:1412.8662) showcases what CMS physicists have learnt about the particle using data taken between 2011 and 2012 Together with another paper on the spin and parity of the boson, [arXiv:1411.3441] the results draw a picture of a particle that – for the moment – cannot be distinguished from the Standard Model predictions for the Higgs boson.

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    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 Standard Model of particle physics is a theoretical framework that explains how the basic building blocks of matter interact, governed by four fundamental forces. Developed in the early 1970s, it has successfully explained almost all experimental results and precisely predicted a wide variety of phenomena – including the mass of the Higgs boson.

    The CMS experiment recently combined measurements from different decays of the Higgs to extract the most precise measurement of its mass to date: 125.02±0.30 GeV, with a relative uncertainty of 0.2%. This uncertainty can be split into a systematic component (±0.15 GeV) and a statistical component (±0.26 GeV), which provides excellent prospects for Run 2 to yield an even more precise mass measurement, as more data will reduce the statistical component.

    The Higgs boson is the final piece of the Standard Model – when it was discovered by the CMS and ATLAS experiments in 2012, it was the last particle predicted by the Model to be verified experimentally.

    CERN ATLAS New
    ATLAS

    But with all parameters now experimentally constrained, physicists can use the Model to make even more specific predictions. For example, having measured the mass of the Higgs boson, the Standard Model makes unambiguous predictions as to what the Higgs boson’s other properties should be. Some, such as the boson’s spin (zero), parity (positive), and electric charge (neutral) stem directly from the symmetries of the Standard Model. But others, such as the strength with which the Higgs boson interacts (or couples) with other Standard Model particles are harder to check.

    The Higgs boson decays to many different particles, including photons, Z bosons, W bosons, tau leptons, b quarks and muons. Checking how the Higgs decays into these particles, and with what probabilities, will allow physicists to complete the picture and gain a better understanding of the Higgs.

    Finding no significant deviations with the Standard Model has set the bar high for the LHC’s Run 2. Theorists and experimentalists will continue working together to find a small wrinkle in the so far smooth Higgs boson picture. That small wrinkle that may point the way out of the Standard Model oasis, across the desert, and the as-yet unknown physics beyond. It’s going to be an exciting Run 2.

    See the full article here.

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    THE FOUR MAJOR PROJECT COLLABORATIONS

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    CERN ATLAS New
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    CMS
    CERN CMS New

    LHCb
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  • richardmitnick 10:20 am on November 14, 2014 Permalink | Reply
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    From FNAL- “Frontier Science Result: CMS Origin of the smallest masses” 


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

    Friday, Nov. 14, 2014
    Jim Pivarski

    Since the discovery of the Higgs boson two years ago, about 80 analyses have helped to pin down its properties. Today, we know that it does not spin, that it is mirror-symmetric, and that it decays into pairs of W bosons, pairs of Z bosons, pairs of tau leptons, and pairs of photons (through a pair of short-lived top quarks). There are even weak hints at a fifth decay mode: decays into pairs of b quarks. All of these results are in agreement with expectations for a Standard Model Higgs boson, but they are still coarse measurements with significant uncertainties.

    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.

    To say that this boson is a Standard Model Higgs is to say that it is exactly the particle that was predicted in 1964. That leaves a lot of room for surprises. Without interference from new phenomena, the rate that this boson decays into particle-antiparticle pairs would be proportional to the square of the mass of the particle-antiparticle pairs. The best way to check the proportionality of something is to look at it on an extreme range. Since the Higgs is believed to give mass to everything from 0.0005-GeV electrons to 173-GeV top quarks, there’s plenty of room to check.

    dots
    Muons (red) are 18 times lighter than tau leptons (blue), so we expect Higgs decays to muon pairs to be about 300 times less common than Higgs decays to tau pairs.

    The highest decay rates are easiest to detect, so only the heaviest particle-antiparticle pairs have been tested so far. The lightest particle-antiparticle decay that has been observed is Higgs to pairs of tau leptons, which are 1.8 GeV each. The next-lighter final state that could be observed is Higgs to pairs of muons, which are 0.1 GeV each. By the expected scaling, Higgs to muon pairs should be 300 times less common. However, muons are easy to detect and clearly identify, so they make a good target.

    Even if you combine all the LHC data collected so far, it would not be enough to see evidence of this decay mode. However, the LHC is scheduled to restart next spring at almost twice its former energy. Higher energy and more intense beams would produce more Higgs bosons, making a future detection of Higgs to muon pairs possible.

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

    To prepare for such a discovery and find potential problems early, CMS scientists searched for Higgs to muon pairs in the current data set. They didn’t find any, but they did establish that no more than 0.16 percent of Higgs bosons decay into muons, only a factor of 7 from the expected number, and then they used these results to project sensitivity in future LHC data. Incidentally, the Higgs boson is the first particle known to decay into tau lepton pairs much more (6.3 percent) than muon pairs (0.023 percent). All other particles decay into taus and muons almost equally.

    CERN CMS New
    CMS in the LHC at CERN

    They also searched for Higgs decays into electrons, the lighter cousin of muons and tau leptons. Since electrons are 200 times lighter than muons, Higgs to electron pairs is expected only 0.00000051 percent of the time. None were found, though an observation would been an exciting surprise!

    See the full article here.

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  • richardmitnick 10:31 am on October 31, 2014 Permalink | Reply
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    From FNAL- “Frontier Science Result: CMS Boosted W’s” 


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

    Friday, Oct. 31, 2014

    FNAL Don Lincoln
    Don Lincoln

    Today’s article covers an interesting topic. It’s interesting not because it explores new physics, but because of how it reveals some of the mundane aspects of research at the LHC. It also shows how the high energy of the LHC makes certain topics harder to study than they were during the good old days at lower-energy accelerators.

    At the LHC, quarks or gluons are scattered out of the collision. It’s the most common thing that happens at the LHC. Regular readers of this column know that it is impossible to see isolated quarks and gluons and that these particles convert into jets as they exit the collision. Jets are collimated streams of particles that have more or less the same energy as the parent quark or gluon. Interactions that produce jets are governed by the strong force.

    map
    In the green region, we show what a W boson looks like before it decays. Moving left to right, the boson is created with more and more momentum. In the yellow region, we repeat the exercise, this time looking at the same W boson after it decays into quarks, which have then turned into jets. Finally in the pink region, we look at a jet originating from a quark or gluon. This looks much like a high-momentum W boson decaying into quarks. Because ordinary jets are so much more common, this highlights the difficulty inherent in finding high-momentum W bosons that decay into jets.
    No image credit

    Things get more interesting when a W boson is produced. One reason for this is that making a W boson requires the involvement of the electroweak force, which is needed for the decay of heavy quarks. Thus studies of W bosons are important for subjects such as the production of the top quark, which is the heaviest quark. W bosons are also found in some decays of the Higgs boson.

    A W boson most often decays into two light quarks, and when it decays, it flings the light quarks into two different directions, which can be seen as two jets.

    But there’s a complication in this scenario at the LHC, where the W bosons are produced with so much momentum that it affects the spatial distribution of particles in those two jets. As the momentum of the W boson increases, the two jets get closer together and eventually merge into a single jet.

    As mentioned earlier, individual jets are much more commonly made using the strong force. So when one sees a jet, it is very hard to identify it as coming from a W boson, which involves the electroweak force. Since identifying the existence of W bosons is very important for certain discoveries, CMS scientists needed to figure out how to tell quark- or gluon-initiated jets from the W-boson-initiated jets. So they devised algorithms that could identify when a jet contained two lumps of energy rather than one. If there were two lumps, the jet was more likely to come from the decay of a W boson.

    CERN CMS New
    CMS

    In today’s paper, CMS scientists explored algorithms and studied variables one can extract from the data to identify single jets that originated from the decay of W bosons. The data agreed reasonably well with calculations, and the techniques they devised will be very helpful for future analyses involving W bosons. In addition, the same basic technique can be extended to other interesting signatures, such as the decay of Z and Higgs bosons.

    See the full article here.

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  • richardmitnick 2:05 pm on October 17, 2014 Permalink | Reply
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    From FNAL- “Frontier Science Result: CMS Off the beaten path” 


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

    Friday, Oct. 17, 2014
    Jim Pivarski

    The main concern for most searches for rare phenomena is to control the backgrounds. Backgrounds are observations that resemble the one of interest, yet aren’t. For instance, fool’s gold is a background for gold prospectors. The main reason that the Higgs boson was hard to find is that most Higgs decays resemble b quark pair production, which is a million times more common. You not only have to find the one-in-a-million event picture, you have to identify some feature of it to prove that it is not an ordinary event.

    This is particularly hard to do in proton collisions because protons break apart in messy ways — the quarks from the proton that missed each other generate a spray of particles that fly off just about everywhere. Look through a billion or a trillion of these splatter events and you can find one that resembles the pattern of new physics that you’re looking for. Physicists have many techniques for filtering out these backgrounds — requiring missing momentum from an invisible particle, high energy perpendicular to the beam, a resonance at a single energy, and the presence of electrons and muons are just a few.

    nu
    Most particles produced by proton collisions originate in the point where the beams cross. Those that do not are due to intermediate particles that travel some distance before they decay

    A less common yet powerful technique for eliminating backgrounds is to look for displaced particle trajectories, meaning trajectories that don’t intersect the collision point. Particles that are directly created by the proton collision or are created by short-lived intermediates always emerge from this point. Those that emerge from some other point in space must be due to a long-lived intermediate.

    A common example of this is the b quark, which can live as long as a trillionth of a second before decaying into visible particles. That might not sound like very long, but the quark is traveling so quickly that it covers several millimeters in that trillionth of a second, which is a measurable difference.

    In a recent analysis, CMS scientists searched for displaced electrons and muons. Displaced tracks are rare, and electrons and muons are also rare, so displaced electrons and muons should be extremely rare. The only problem with this logic is that b quarks sometimes produce electrons and muons, so one other feature is needed to disambiguate. A b quark almost always produces a jet of particles, so this search for new physics also required that the electrons and muons were not close to jets.

    CERN CMS New
    CERN CMS

    With these simple selection criteria, the experimenters found only as many events as would be expected from standard physics. Therefore, it constrains any theory that predicts displaced electrons and muons. One of these is “displaced supersymmetry,” which generalizes the usual supersymmetry scenario by allowing the longest-lived supersymmetric particle to decay on the millimeter scale that this analysis tests. Displaced supersymmetry was introduced as a way that supersymmetry might exist yet be missed by most other analyses. Experiments like this one illuminate the dark corners in which supersymmetry might be hiding.

    See the full article here.

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  • richardmitnick 7:04 pm on September 21, 2014 Permalink | Reply
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    From physicsworld: “A day in the life of CERN’s director-general” 

    physicsworld
    physicsworld.com

    Sep 16, 2014
    By Rolf-Dieter Heuer, Geneva

    There is no such thing as a typical day in the life of a CERN director-general (DG), certainly not this one in any case. In my experience, each incumbent has carved out a slightly different role for themself, shaped by the laboratory’s priorities and activities at the time of their mandate. For me, every day goes beyond science, management and administration, and I am particularly fortunate to have been DG through a remarkable period that has seen not only the successful launch of the Large Hadron Collider (LHC) and confirmation of the Brout–Englert–Higgs mechanism, but also an opening of CERN to the world – an area that I have pursued with particular vigour.

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

    dg
    All in a day’s work. (Courtesy: CERN)

    As I regularly joke, we have changed the “E” of CERN from “Europe” to “Everywhere”, and that has meant a lot of travel for the CERN DG, as we hold discussions with prospective new members of the CERN family. And when the CERN Council opened up membership to countries from beyond the European region in 2010, it seemed to me that we should also be extending our contacts in other directions as well.

    For that reason, I have taken up the CERN DG’s standing invitation to attend the World Economic Forum’s annual meeting in Davos, where I strive to get science further up the agenda, and I have actively pursued a policy of engagement with other international organizations. CERN’s host city is home to a concentration of international organizations like nowhere else on Earth, and our missions overlap in areas ranging from technology to standards to intellectual property. A typical day might see me paying a visit to the United Nations Office in Geneva, or receiving a visit from the ambassador of an existing or prospective CERN member state.

    But the role goes beyond one of diplomacy. The CERN DG has, first and foremost, a lab to run. Although I have a strong team of directors and department leaders to help me, issues ranging from liaison between experiments to delicate issues in human resources or dealings with officials from our two host states – France and Switzerland – find their way to my door. Each year is punctuated by fixed points for the meetings of advisory and governance bodies, for directorate meetings and presentations to personnel.

    With all this going on, there is no typical day, so I’ll describe the most untypical of all during my term of office: Wednesday 4 July 2012.

    I’d been told that people were so keen to have a seat in CERN’s main auditorium for that day’s Higgs-update seminar that some were prepared to camp out all night to secure their place, so I came in early to see if it were true. I expected to see a few hardy souls at 7 a.m., but not the long snaking queue, headed up by sleeping bags, that started outside the doors of the auditorium, carried on all the way along corridors and ended up down the stairs in main entrance lobby. The atmosphere was reserved, yet excited, with an air of expectation about it. I went up to my office to prepare my notes and gather my thoughts.

    We had not known until the last minute whether or not we would be announcing a discovery or just another step on the way. Yet the world was expectant. Peter Higgs and François Englert were at CERN, as were Gerry Guralnik and Carl Hagen – two of the three authors of the other pioneering paper from the 1960s that had anticipated what we now know as the Brout–Englert–Higgs mechanism. Robert Brout, unfortunately, did not live to see the confirmation of his ideas, while Tom Kibble – Guralnik and Hagen’s co-author – was at a parallel event in London. The press were also there in force, and the CERN Council’s meeting room was converted into a media centre for the day.

    Although just a few days earlier I didn’t know what message I’d be bringing to the expectant crowd, at 7 a.m. that day I had what I needed to announce a discovery. Over the preceding weeks and days, Fabiola Gianotti and Joe Incandela had each kept me up to date with the status of the analyses from the ATLAS and CMS experiments of which they were the spokespersons, and by the Friday before the seminar, I’d seen enough. Although by that time neither experiment was sure they’d be able to announce the required 5σ significance needed to claim discovery, I’d seen both experiment’s results, and that was enough for me to know that taken together the 5σ would be reached.

    CERN ATLAS New
    ATLAS

    CERN CMS New
    CMS

    rdh
    Wednesday 4 July 2012 was an extraordinary day. (Courtesy: CERN)

    By the time I went back down to the auditorium, the doors had been opened and people had taken their seats, yet the crowd outside seemed even bigger than before. Inside the room, the mood was an unusual mixture of party and scientific seminar. We were being watched around the world: nearly half a million people tuned in to the webcast, I’m told, and we had a room full of physicists in Melbourne assembled there on the eve of that year’s major particle-physics conference, beamed to a screen above my head. It culminated in joyous scenes as the experiments announced their results: as it turned out, they didn’t need me to announce the discovery. Peter Higgs, sitting next to François Englert whom he’d met for the first time that day, had a smile on his face that said it all.

    The seminar was over, but for me the day was just beginning. Fabiola, Joe and I were ushered into the media centre for a press conference, in which the theorists were given a front-row seat. Once the media scrum has subsided and Peter Higgs had graciously led the theorists in saying that this was a day for the experiments and there’d be time to talk to him later, the three of us recounted the story all over again before spending the day giving interview after interview.

    Eventually, the cameras stopped clicking, the microphones were put back in their bags, and it was time to head off for the airport to catch my flight to Melbourne for the conference. It was only when I got on the plane and ordered a glass of champagne that the enormity of the day sunk in. It had been an incredible day, full of emotion, leaving me happy not only with the result, but also with that fact that it had so strongly captured the world’s imagination.

    A day in the life of the CERN DG? Always challenging, sometimes exhausting, frequently frustrating but always rewarding. And although 4 July 2012 may not have been a typical day, it is for me one of the most memorable of all.

    See the full article here.

    PhysicsWorld is a publication of the Institute of Physics. The Institute of Physics is a leading scientific society. We are a charitable organisation with a worldwide membership of more than 50,000, working together to advance physics education, research and application.

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  • richardmitnick 12:34 pm on September 19, 2014 Permalink | Reply
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    From Fermilab- “Frontier Science Result: CMS Three ways to be invisible” 


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

    Friday, Sept. 19, 2014
    Jim Pivarski

    There is a common misconception that the LHC was built only to search for the Higgs boson. It is intended to answer many different questions about subatomic particles and the nature of our universe, so the collision data are reused by thousands of scientists, each studying their own favorite questions. Usually, a single analysis only answers one question, but recently, one CMS analysis addressed three different new physics: dark matter, extra dimensions and unparticles.

    CERN CMS New
    CMS

    CERN LHC Grand Tunnel
    CERN LHC Map
    CERN LHC particles
    LHC

    The study focused on proton collisions that resulted in a single jet of particles and nothing else. This can only happen if some of the collision products are invisible — for instance, one proton may emit a jet before collision and the collision itself produces only invisible particles. The jet is needed to be sure that a collision took place, but the real interest is in the invisible part.

    proton
    The quark structure of the proton. The color assignment of individual quarks is arbitrary, but all three colors must be present. Forces between quarks are mediated by gluons

    Sometimes, the reason that nothing else was seen in the detector is mundane. Particles may be lost because their trajectories missed the active area of the detector or a component of the detector was malfunctioning during the event. More often, the reason is due to known physics: 20 percent of Z bosons decay into invisible neutrinos. If there were an excess of invisible events, more than predicted by the Standard Model, these extra events would be evidence of new phenomena.

    The classic scenario involving invisible particles is dark matter. Dark matter has been observed through its gravitational effects on galaxies and the expansion of the universe, but it has never been detected in the laboratory. Speculations about the nature of dark matter abound, but it will remain mysterious until its properties can be studied experimentally.

    Another way to get invisible particles is through extra dimensions. If our universe has more than three spatial dimensions (with only femtometers of “breathing room” in the other dimensions), then the LHC could produce gravitons that spin around the extra dimensions. Gravitons interact very weakly with ordinary matter, so they would appear to be invisible.

    A third possibility is that there is a new form of matter that isn’t made of indivisible particles. These so-called unparticles can be produced in batches of 1½ , 2¾ , or any other amount. Unparticles, if they exist, would also interact weakly with matter.

    All three scenarios produce something invisible, so if the CMS data had revealed an excess of invisible events, any one of the scenarios could have been responsible. Follow-up studies would have been needed to determine which one it was. As it turned out, however, there was no excess of invisible events, so the measurement constrains all three models at once. Three down in one blow!

    LHC scientists are eager to see what the higher collision energy of Run 2 will deliver.

    See the full article here.

    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.

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  • richardmitnick 9:14 am on August 8, 2014 Permalink | Reply
    Tags: , CERN CMS, , ,   

    From Fermilab- “Frontier Science Result: CMS An ambidextrous W boson?” 


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

    Friday, Aug. 8, 2014

    Fermilab Don Lincoln
    Don Lincoln

    Of the four known subatomic forces, the weak force has what seems to be a particularly bizarre behavior. It’s a lefty. What exactly does that mean in the subatomic realm? To understand, you need to remember that fundamental particles spin and that they spin in a peculiar way.

    Suppose you’re playing catch with someone using a football. If you throw the football properly, the ball spins around the long axis of the ball. As you see the ball coming towards you, you see the ball spin in either a clockwise or counterclockwise direction. Scientists call the clockwise rotation left-handed, because if you take your left hand and aim your thumb in the direction the ball is moving (toward you), the fingers of your left hand naturally wrap in the clockwise direction.

    The strong and electromagnetic forces, with their gluons and photons, don’t care which way the particle is spinning. But the weak force, with its W boson, will interact with only a left-handed particle. W bosons just don’t interact with counterclockwise-spinning particles. And, while it seems weird, the theory of the weak force has long accommodated this fact.

    On the other hand, given the symmetry of the other forces, maybe the problem is that we just haven’t found the kind of W boson that interacts with right-handed particles. This isn’t an unreasonable conjecture — maybe the right-handed W bosons are just much heavier than the familiar left-handed versions. If that’s the case, then the LHC, with its high-energy beams, would be a perfect place for finding right-handed W bosons.

    While symmetry and aesthetic considerations might be enough reason to look for heavy right-handed W bosons, some related theoretical ideas have been proposed. One such thought involves the neutrino, which is the only particle that feels only the weak force. Neutrinos are incredibly light, much lighter than other particles that have mass. Given this discrepancy, maybe the neutrinos don’t get their mass from the Higgs boson as other particles do. It could be an entirely different mechanism. Neutrinos are also left-handed particles, and scientists have proposed that perhaps there exists a heavier and right-handed version. Under this theory, the masses of the left-handed and right-handed neutrinos are connected in that if one goes up, the other goes down. This connection is called the seesaw mechanism.

    Given the interesting possibilities, CMS searched for the two inextricably linked theoretical particles: heavy, right-handed W bosons and neutrinos. No evidence was found for either, although the new measurement is the most precise one thus far.

    See the full article here.

    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.

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  • richardmitnick 10:59 am on July 11, 2014 Permalink | Reply
    Tags: , CERN CMS, , , ,   

    From Fermilab- “Frontier Science Result: CMS Excited quarks” 


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

    Friday, July 11, 2014

    Fermilab Don Lincoln
    This article was written by Dr. Don Lincoln

    It is well known that the Standard Model of particle physics is incomplete and that it is an approximation of a deeper and more fundamental theory.

    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.

    One idea that might lead the way to a better understanding of the universe is that the quarks and leptons, particles now treated as point-like, are actually composite and made of even smaller particles. Given that the quarks and leptons have electrical charge, it follows that at least some of these hypothetical components also have electrical charge. And where electrical charge exists, the photon must follow. This is because photons are emitted by electrically charged particles.

    quark
    A proton, composed of two up quarks and one down quark. (The color assignment of individual quarks is not important, only that all three colors be present.)

    lepton
    Leptons are involved in several processes such as beta decay.

    If quarks and leptons contain smaller objects, these objects are bound together with some sort of force. Further, since we know that the quarks and leptons act very much like point-like particles, this force must be very strong. Still, it is possible that if you hit a quark or lepton hard enough, you might be able to add energy to the constituents. Physicists call these energy-added particles “excited” quarks and leptons. The hypothetical constituents would somehow radiate that added energy and return to the quiescent states that are the familiar quarks and leptons. This is kind of like hitting a hornet’s nest, which will cause a swarm of hornets to fly around before the insects return to a quiet state.

    If the constituent particles radiate energy, the quark might emit photons. The resulting signature of this excited quark would be a regular quark emitted with a lot of energy accompanied by the emitted photon. Since quarks turn into jets, the experimental signature is a jet and a photon. CMS scientists looked for this signature to try to find excited quarks. While no evidence was found, researchers were able to set limits on the energy scale at which excited quarks can be made. With the resumption of operations of the LHC in the spring of 2015, scientists will be able to look for even more massive excited quarks.

    CERN CMS Detector
    CERN/CMS

    See the full article here.

    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.


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