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  • richardmitnick 3:46 pm on May 15, 2015 Permalink | Reply
    Tags: , CERN ATLAS, ,   

    From Physics: “Viewpoint: A More Precise Higgs Boson Mass” 

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    May 14, 2015
    Chris Quigg, FNAL and ENS

    A new value for the Higgs boson mass will allow stronger tests of the standard model and of theories about the Universe’s stability.

    Figure 1: Values of the top quark and W boson masses measured in experiments (green) and inferred from calculations (blue). The inner and outer ellipses represent 68% and 95% confidence levels, respectively, for the measured and inferred values. Within current experimental and theoretical uncertainties, the two ways of determining the top quark and W boson masses agree. A more precise value of the Higgs mass would narrow the width of the blue ellipses, whereas improved measurements of the top quark and W boson masses would shrink the green ellipses, making for a more incisive test for new physics. (Note, the calculations assume the Higgs mass has a central value of 125.14GeV, which differs insignificantly from the new measurement by ATLAS and CMS, but does not affect the width of the blue ellipses.)

    A great insight of twentieth-century science is that symmetries expressed in the laws of nature need not be manifest in the outcomes of those laws. Consider the snowflake. Its structure is a consequence of electromagnetic interactions, which are identical from any direction, but a snowflake only looks the same when rotated by multiples of 60∘ about a single axis. The full symmetry is hidden by the particular conditions under which the water molecules crystallize. Similarly, a symmetry relates the electromagnetic and weak interactions in the standard model of particle physics, but we know it must be concealed because the weak interactions appear much weaker than electromagnetism.

    Standard Model of Particle Physics. The diagram shows the elementary particles of the Standard Model (the Higgs boson, the three generations of quarks and leptons, and the gauge bosons), including their names, masses, spins, charges, chiralities, and interactions with the strong, weak and electromagnetic forces. It also depicts the crucial role of the Higgs boson in electroweak symmetry breaking, and shows how the properties of the various particles differ in the (high-energy) symmetric phase (top) and the (low-energy) broken-symmetry phase (bottom).

    To learn what distinguishes electromagnetism from the weak interactions was an early goal of experiments at CERN’s Large Hadron Collider (LHC).

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

    A big part of the answer was given in mid-2012, when the ATLAS and CMS Collaborations at the LHC announced the discovery of the Higgs boson in the study of proton–proton collisions [1].


    CERN CMS Detector

    Now the discovery teams have pooled their data analyses to produce a measurement of the Higgs boson mass with 0.2% precision [2]. The new value enables physicists to make more stringent tests of the electroweak theory and of the Higgs boson’s properties.

    The electroweak theory [3] is a key element of the standard model of particle physics that weaves together ideas and observations from diverse areas of physics [4]. In the theory, interactions are prescribed by gauge symmetries. If nature displayed these symmetries explicitly, the force particles would all be massless, whereas we know experimentally that the weak interactions must—because they are short-ranged—be mediated by massive particles. The so-called Higgs field was introduced to the electroweak theory to hide the gauge symmetry, leading to weak force particles (W± and Z0) that have mass but a photon that is massless.

    The Higgs boson is a spin-zero excitation of the Higgs field and the “footprint” of the mechanism that hides the electroweak gauge symmetry in the standard model. The Higgs boson’s interactions are fully specified in terms of known couplings and masses of its decay products, but the theory does not predict its mass. Instead, experimentalists must measure the energies and momenta of the Higgs boson’s decay products and determine its mass using kinematical equations. Once that mass is known, the rates at which the Higgs boson decays into different particles can be predicted with high precision, and compared with experiment. For a mass in the neighborhood of 125 giga-electron-volts (GeV), the electroweak theory foresees a happy circumstance in which several decay paths occur at large enough rates to be detected.

    ATLAS and CMS are large, broad-acceptance detectors located in multistory caverns about 100 meters below ground [5]. In the discovery run of the LHC, the ATLAS and CMS Collaborations searched for decays of a Higgs boson into bottom-quark–antiquark pairs, tau-lepton pairs, and pairs of electroweak gauge bosons: two photons, W+W−, and Z0Z0. The actual discovery was based primarily on mass peaks associated with either the two-photon final states or Z0Z0 pairs decaying to four-lepton (electrons or muons) final states. These channels, for which the ATLAS and CMS detectors have the best mass resolution, form the basis of their new report.

    Both of the “high-resolution” final states are relatively rare: the standard model predicts that only about 1/4% of Higgs boson decays produce two-photon states; the four-lepton rate is predicted to be nearly 20 times smaller. The two-photon channel exhibits a narrow resonance peak that contains several hundred events per experiment; the Z0Z0 to four-lepton channel yields only a few tens of signal events per experiment. To see these events in the first run of the LHC, the ATLAS and CMS collaborations chose different detector technologies, and therefore different measurement and calibration methods [2]. These differences make pooling the data complicated, but also allow the experimentalists to cross-check systematic uncertainties in their separate measurements. Their combined analyses yield a Higgs boson mass of 125.09±0.24GeV, the precision of which is limited by statistics and by uncertainties in the energy or momentum scale of the ATLAS and CMS detectors.

    The first consequence of the new, precise mass value is sharper predictions, within the standard model, for the relative probabilities of different Higgs boson decay modes and production rates [6]. So far, the measured decay modes and production rates agree with standard-model predictions. The current uncertainties in the measured rates are large, but they will be narrowed in the coming runs at the LHC and at possible future colliders. Evidence of any deviation would suggest that the Higgs boson does not follow the standard model textbook, or that new particles or new forces are implicated in its decays.

    With a precisely known Higgs boson mass MH, theorists can also make more refined predictions of the quantum corrections to many observables, such as the Z0 decay rates. These predictions test the consistency of the electroweak theory as a quantum field theory. Figure 1 illustrates a telling example [7]. The diagonal blue ellipses show the values of the W boson and top quark masses required to reproduce a selection of electroweak observables once MH is fixed. (The narrow and wide ellipses represent 68% and 95% confidence levels, respectively.) The range of masses depends on MH, and the precision with which it is known controls the width of the blue ellipses. The preferred range overlaps the green ellipses, which show the directly measured values of the W boson and top quark masses. In the future, more precise values for the masses of the Higgs boson, W boson, and top quark could unveil a discrepancy that might lead to the discovery of new physics.

    The specific value of MH constrains speculations about physics beyond the standard model, including supersymmetric or composite models. Perhaps most provocative of all is the possibility that the measured value of the mass is special. Quantum corrections influence not just the predictions for observable quantities, but also the shape of the Higgs potential that lies behind electroweak symmetry breaking in the standard model. According to recent analyses, the newly reported value of the Higgs boson mass corresponds to a near-critical situation in which the Higgs vacuum does not lie at the state of lowest energy, but in a metastable state close to a phase transition [8]. This might imply that our Universe is living on borrowed time, or that the electroweak theory must be augmented in some way.

    With LHC Run 2 about to commence, now at higher energies, particle physicists can look forward to a new round of exploration, searches for new phenomena, and refined measurements. Combined analyses and critical evaluations, such as the measurement of the Higgs boson mass discussed here, will help make the most of the data. We still have much to learn about the Higgs boson, the electroweak theory, and beyond.


    Fermilab is operated by Fermi Research Alliance, LLC, under Contract No. DE-AC02-07CH11359 with the United States Department of Energy. I thank the Fondation Meyer pour le développement culturel et artistique for generous support.


    1. G. Aad et al. (ATLAS Collaboration), “Observation of a New Particle in the Search for the Standard Model Higgs Boson with the ATLAS Detector at the LHC,” Phys. Lett. B 716, 1 (2012); S. Chatrchyan et al. (CMS Collaboration), “Observation of a New Boson at a Mass of 125 GeV with the CMS Experiment at the LHC,” 716, 30 (2012)
    2. G. Aad et al. (ATLAS Collaboration†), “Combined Measurement of the Higgs Boson Mass in pp Collisions at s=7 and 8 TeV with the ATLAS and CMS Experiments,” Phys. Rev. Lett. 114, 191803 (2015)
    3. The electroweak theory was developed from a proposal by S. Weinberg, “A Model of Leptons,” Phys. Rev. Lett. 19, 1264 (1967); A. Salam “Weak Electromagnetic Interactions,” in Elementary Particle Theory: Relativistic Groups and Analyticity (Nobel Symposium No. 8), edited by N. Svartholm (Almqvist and Wiksell, Stockholm, 1968), p. 367; http://j.mp/r9dJOo ; The theory is built on the SU(2)L⊗U(1)Y gauge symmetry investigated by S. L. Glashow, “Partial Symmetries of Weak Interactions,” Nucl. Phys. 22, 579 (1961)
    4. C. Quigg, “Electroweak Symmetry Breaking in Historical Perspective,” Ann. Rev. Nucl. Part. Sci.; arXiv:1503.01756
    5. ATLAS Collaboration, “The ATLAS Experiment at the CERN Large Hadron Collider,” JINST 3, S08003 (2008); CMS Collaboration, “The CMS Experiment at the CERN Large Hadron Collider,” 3, S08004 (2008)
    6.S. Heinemeyer et al. (LHC Higgs Cross Section Working Group), Handbook of LHC Higgs Cross Sections: 3. Higgs Properties, Report No. CERN-2013-004; Tables of Higgs boson branching fractions are given at http://j.mp/1OrjQL0
    7. M. Baak et al. (Gfitter Group), “The global electroweak fit at NNLO and prospects for the LHC and ILC,” Eur. Phys. J. C 74, 3046 (2014); a more detailed version of Figure 1 may be found at http://j.mp/1cvuXGQ
    8. D. Buttazzo, G. Degrassi, P. P. Giardino, G. F. Giudice, F. Sala, A. Salvio, and A. Strumia, ”Investigating the Near-Criticality of the Higgs Boson,” J. High Energy Phys. 1312, 089 (2013)

    See the full article here.

    Please help promote STEM in your local schools.

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    Stem Education Coalition

    Physicists are drowning in a flood of research papers in their own fields and coping with an even larger deluge in other areas of physics. How can an active researcher stay informed about the most important developments in physics? Physics highlights a selection of papers from the Physical Review journals. In consultation with expert scientists, the editors choose these papers for their importance and/or intrinsic interest. To highlight these papers, Physics features three kinds of articles: Viewpoints are commentaries written by active researchers, who are asked to explain the results to physicists in other subfields. Focus stories are written by professional science writers in a journalistic style and are intended to be accessible to students and non-experts. Synopses are brief editor-written summaries. Physics provides a much-needed guide to the best in physics, and we welcome your comments (physics@aps.org).

  • 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.


    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.


    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.

    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

    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.

    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.

    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.

    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.

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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 5:23 pm on November 28, 2014 Permalink | Reply
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    From CERN: “ATLAS@Home looks for CERN volunteers” 



    Mon 01 Dec 2014
    Rosaria Marraffino

    ATLAS@Home is a CERN volunteer computing project that runs simulated ATLAS events. As the project ramps up, the project team is looking for CERN volunteers to test the system before planning a bigger promotion for the public.

    The ATLAS@home outreach website.

    ATLAS@Home is a large-scale research project that runs ATLAS experiment simulation software inside virtual machines hosted by volunteer computers. “People from all over the world offer up their computers’ idle time to run simulation programmes to help physicists extract information from the large amount of data collected by the detector,” explains Claire Adam Bourdarios of the ATLAS@Home project. “The ATLAS@Home project aims to extrapolate the Standard Model at a higher energy and explore what new physics may look like. Everything we’re currently running is preparation for next year’s run.”

    ATLAS@Home became an official BOINC (Berkeley Open Infrastructure for Network Computing) project in May 2014. After a beta test with SUSY events and Z decays, real production started in the summer with inelastic proton-proton interaction events. Since then, the community has grown remarkably and now includes over 10,000 volunteers spread across five continents. “We’re running the full ATLAS simulation and the resulting output files containing the simulated events are integrated with the experiment standard distributed production,” says Bourdarios.

    Compared to other LHC@Home projects, ATLAS@Home is heavier in terms of network traffic and memory requirements. “From the start, we have been successfully challenging the underlying infrastructure of LHC@Home,” says Bourdarios. “Now we’re looking for CERN volunteers to go one step further before doing a bigger public promotion.”

    This simulated event display is created using ATLAS data.

    If you want to join the community and help the ATLAS experiment, you just need to download and run the necessary free software, VirtualBox and BOINC, which are available on NICE. Find out more about the project and how to join on the ATLAS@Home outreach website.

    “This project has huge outreach potential,” adds Bourdarios. “We hope to demonstrate how big discoveries are often unexpected deviations from existing models. This is why we need simulations. We’re also working on an event display, so that people can learn more about the events they have been producing and capture an image of what they have done.”

    If you have any questions about the ATLAS@Home project, e-mail atlas-comp-contact-home@cern.ch

    See the full article here.

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    STEM Icon

    Stem Education Coalition

    ATLAS@Home is a research project that uses volunteer computing to run simulations of the ATLAS experiment at CERN. You can participate by downloading and running a free program on your computer.

    ATLAS is a particle physics experiment taking place at the Large Hadron Collider at CERN, that searches for new particles and processes using head-on collisions of protons of extraordinary high energy. Petabytes of data were recorded, processed and analyzed during the first three years of data taking, leading to up to 300 publications covering all the aspects of the Standard Model of particle physics, including the discovery of the Higgs boson in 2012.

    Large scale simulation campaigns are a key ingredient for physicists, who permanently compare their data with both “known” physics and “new” phenomena predicted by alternative models of the universe, particles and interactions. This simulation runs on the WLCG Computing Grid and at any one point there are around 150,000 tasks running. You can help us run even more simulation by using your computer’s idle time to run these same tasks.

    No knowledge of particle physics is required, but for those interested in more details, at the moment we simulate the creation and decay of supersymmetric bosons and fermions, new types of particles that we would love to discover next year, as they would help us to shed light on the dark matter mystery!

    This project runs on BOINC software from UC Berkeley.
    Visit BOINC, download and install the software and attach to the project.


  • richardmitnick 11:57 am on November 25, 2014 Permalink | Reply
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    From Times Beacon record via BNL: “BNL’s Pleier takes next steps after Higgs-boson” 


    Brookhaven Lab

    November 19, 2014
    Daniel Dunaief

    Marc-Andre Pleier photo from BNL

    While the United States was celebrating Independence Day two years ago, a group of people were cheering the discovery of something they had spent almost half a century seeking. Physicists around the world were convinced the so-called Higgs boson particle existed, but no one had found clear-cut evidence of it.

    At a well-attended press conference, scientists hailed the discovery, while recognizing the start of a new set of experiments and questions.

    As a part of the ATLAS team, Marc-Andre Pleier knew what the group was set to announce. He was very excited “to see the signal confirmed by an independent measurement.” Two years later, Pleier, a physicist at Brookhaven National Laboratory and a part of a group of more than 3,000 scientists from around the world, are tackling the next set of questions.


    The discovery “points to the Standard Model [of particle physics] being correct, but to know this we need to understand this new particle and its properties a lot better than we do now.”

    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.

    According to the Standard Model of particle physics, the Big Bang beginning to the universe should have created equal parts matter and antimatter. If it did, the two opposite energies would have annihilated each other into light. An imbalance, however, resulted in a small fraction of matter surviving, forming the visible universe. The origin of this imbalance, however, is unknown, Pleier said.

    “We know the Standard Models is incomplete,” he said, because there are observations of dark matter, dark energy and the antimatter/matter asymmetry in the universe that can’t be explained by this model. “We can test this” next chapter.

    Cosmic Microwave Background  Planck
    Cosmic Background Radiation per ESA/Planck

    The process Pleier studies allows him to test whether the particle is doing its job as expected. In addition to analyzing data, Pleier also has “major responsibility in upgrading the detector,” said Hong Ma, a group leader in the Physics Department at BNL who recruited Pleier to join BNL in 2009.

    Scientists at the [Large] Hadron Collider in Switzerland and at BNL and elsewhere are studying interactions that are incredibly rare among particles.

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

    Pleier is searching for interactions of vector bosons, which have spin values of one and are extremely large in the world of bosons. He is looking for cases where two W bosons interact with each other.

    “Only one event out of a hundred trillion events will be of interest to me,” said Pleier. Comparing those numbers to the world of biology, Pleier likened that to finding a single cell in an entire human body.

    In 2012, the Hadron Collider produced 34 such interactions. The collider produces about 40 million pictures per second. To find the ones that might hold promising information, scientists like Pleier need to use a computing grid. BNL is one of only 10 tier 1 centers for ATLAS and the only one in the United States. Thus far, scientists have been able to look at these collisions from energies at 8 trillion electron volts. They hope to measure similar data at 13 trillion electron volts next year.

    Ma said the increased energy of the collider will “put the Standard Model to an unprecedented level of tests,” allowing scientists to “measure the properties of Higgs boson to a higher precision.”

    Growing up in Germany, Pleier said he loved playing with Legos to see how things worked. He helped fix his own toys. When he was older, he worked to repair a motor bike his uncle had.

    What he’s doing now, he said, is exploring the fundamental building blocks of matter and their interactions. He likened it to examining the “construction kit” for the universe. While he’s a physicist, Pleier explained that he’s a Christian. “Some people think it has to be in conflict, but, for me, it clearly is not,” he said. “Each discovery adds to my admiration for God’s creation.”

    A resident of Middle Island, Pleier lives with his wife Heather, an English teacher who is staying home for now to take care of their three children.

    Pleier and Ma emphasized that the work at the collider is a collaborative effort involving scientists from institutions around the world.

    Michael Kobel, a professor at TU Dresden, head of the Institute for Particle Physics and Dean of Studies in the Department of Physics who has known Pleier for about nine years, likened the process of studying the high energy particles to exploring a cave, where scientists “get more light to look deeper” into areas that were in the dark before. Researchers, he said, are just entering this cave of knowledge, with “a lot of corners yet to be explored.”

    See the full article here.

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  • richardmitnick 6:36 pm on October 24, 2014 Permalink | Reply
    Tags: , , CERN ATLAS, , ,   

    From Nautilus: “Who Really Found the Higgs Boson” 



    October 23, 2014
    By Neal Hartman
    Illustration by Owen Freeman
    Also stock photos

    To those who say that there is no room for genius in modern science because everything has been discovered, Fabiola Gianotti has a sharp reply. “No, not at all,” says the former spokesperson of the ATLAS Experiment, the largest particle detector at the Large Hadron Collider at CERN. “Until the fourth of July, 2012 we had no proof that nature allows for elementary scalar fields. So there is a lot of space for genius.”


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

    She is referring to the discovery of the Higgs boson two years ago—potentially one of the most important advances in physics in the past half century. It is a manifestation of the eponymous field that permeates all of space, and completes the standard model of physics: a sort of baseline description for the existence and behavior of essentially everything there is.

    By any standards, it is an epochal, genius achievement.

    What is less clear is who, exactly, the genius is. An obvious candidate is Peter Higgs, who postulated the Higgs boson, as a consequence of the Brout-Englert-Higgs mechanism, in 1964. He was awarded the Nobel Prize in 2013 along with Francois Englert (Englert and his deceased colleague Robert Brout arrived at the same result independently). But does this mean that Higgs was a genius? Peter Jenni, one of the founders and the first “spokesperson” of the ATLAS Experiment Collaboration (one of the two experiments at CERN that discovered the Higgs particle), hesitates when I ask him the question.

    “They [Higgs, Brout and Englert] didn’t think they [were working] on something as grandiose as [Einstein’s relativity],” he states cautiously. The spontaneous symmetry breaking leading to the Higgs “was a challenging question, but [Albert Einstein] saw something new and solved a whole field. Peter Higgs would tell you, he worked a few weeks on this.”

    The ability of the precocious individual physicist to suggest a new data cut or filter is restricted.

    What, then, of the leaders of the experimental effort, those who directed billions of dollars in investment and thousands of physicists, engineers, and students from almost 40 countries for over three decades? Surely there must have been a genius mastermind directing this legion of workers, someone we can single out for his or her extraordinary contribution.

    “No,” says Gianotti unequivocally, which is rare for a physicist, “it’s completely different. The instruments we have built are so complex that inventiveness and creativity manifests itself in the day-by-day work. There are an enormous amount of problems that require genius and creativity to be spread over time and over many people, and all at the same level.”

    Scientific breakthroughs often seem to be driven by individual genius, but this perception belies the increasingly collaborative nature of modern science. Perhaps nothing captures this dichotomy better than the story of the Higgs discovery, which presents a stark contrast between the fame awarded to a few on the one hand, and the institutionalized anonymity of the experiments that made the discovery possible on the other.

    An aversion to the notion of exceptional individuals is deeply rooted within the ATLAS collaboration, a part of its DNA. Almost all decisions in the collaboration are approved by representative groups, such as the Institute Board, the Collaboration Board, and a plethora of committees and task forces. Consensus is the name of the game. Even the effective CEO, a role Gianotti occupied from 2009 to 2013, is named the “Spokesperson.” She spoke for the collaboration, but did not command it.

    Collectivity is crucial to ATLAS in part because it’s important to avoid paying attention to star personalities, so that the masses of physicists in the collaboration each feel they own the research in some way. Almost 3,000 people qualify as authors on the key physics papers ATLAS produces, and the author list can take almost as many pages as the paper itself.

    The genius of crowds: Particle physics collaborations can produce academic papers with hundreds of authors. One 2010 paper was 40 pages long—with 10 pages devoted to the authors list, pictured here.

    On a more functional level, this collectivity also makes it easier to guard against bias in interpreting the data. “Almost everything we do is meant to reduce potential bias in the analysis,” asserts Kerstin Tackmann, a member of the Higgs to Gamma Gamma analysis group during the time of the Higgs discovery, and recent recipient of the Young Scientist Prize in Particle Physics. Like many physicists, Tackmann verges on the shy, and speaks with many qualifications. But she becomes more forceful when conveying the importance of eliminating bias.

    “We don’t work with real data until the very last step,” she explains. After the analysis tools—algorithms and software, essentially—are defined, they are applied to real data, a process known as the unblinding. “Once we look at the real data,” says Tackmann, “we’re not allowed to change the analysis anymore.” To do so might inadvertently create bias, by tempting the physicists to tune their analysis tools toward what they hope to see, in the worst cases actually creating results that don’t exist. The ability of the precocious individual physicist to suggest a new data cut or filter is restricted by this procedure: He or she wouldn’t even see real data until late in the game, and every analysis is vetted independently by multiple other scientists.

    Most people in the collaboration work directly “for” someone who is in no way related to their home institute, which actually writes their paycheck.

    This collective discipline is one way that ATLAS tames the complexity of the data it produces, which in raw form is voluminous enough to fill a stack of DVDs that reaches from the earth to the moon and back again, 10 times every year. The data must be reconstructed into something that approximates an image of individual collisions in time and space, much like the processing required for raw output from a digital camera.

    But the identification of particles from collisions has become astoundingly more complex since the days of “scanning girls” and bubble chamber negatives, where actual humans sat over enlarged images of collisions and identified the lines and spirals as different particles. Experimentalists today need to have expert knowledge of the internal functioning of the different detector subsystems: pixel detector, silicon strip tracker, transition radiation tracker, muon system, and calorimeters, both hadronic and electromagnetic. Adjustments made to each subsystem’s electronics, such as gain or threshold settings, might cause the absence or inclusion of what looks like real data but isn’t. Understanding what might cause false or absent signals, and how they can be accounted for, is the most challenging and creative part of the process. “Some people are really clever and very good at this,” says Tackmann.

    The process isn’t static, either. As time goes on, the detector changes from age and radiation damage. In the end the process of perfecting the detector’s software is never-ending, and the human requirements are enormous: roughly 100 physicists were involved in the analysis of a single and relatively straightforward particle signature, the decay of the Higgs into two Gamma particles. The overall Higgs analysis was performed by a team of more than 600 physicists.

    The depth and breadth of this effort transform the act of discovery into something anonymous and distributed—and this anonymity has been institutionalized in ATLAS culture. Marumi Kado, a young physicist with tousled hair and a quiet zen-like speech that borders on a whisper, was one of the conveners of the “combined analysis” group that was responsible for finally reaching the level of statistical significance required to confirm the Higgs discovery. But, typically for ATLAS, he downplays the importance of the statistical analysis—the last step—in light of the complexity of what came before. “The final analysis was actually quite simple,” he says. “Most of the [success] lay in how you built the detector, how well you calibrated it, and how well it was designed from the very beginning. All of this took 25 years.”

    The deeply collaborative work model within ATLAS meant that it wasn’t enough for it to innovate in physics and engineering—it also needed to innovate its management style and corporate culture. Donald Marchand, a professor of strategy execution and information management at IMD Business School in Lausanne, describes ATLAS as following a collaborative mode of working that flies in the face of standard “waterfall”—or top down—management theory.

    Marchand conducted a case study on ATLAS during the mid-2000s, finding that the ATLAS management led with little or no formal authority. Most people in the collaboration work directly “for” someone who is in no way related to their home institute, which actually writes their paycheck. For example, during the construction phase, the project leader of the ATLAS pixel detector, one of its most data-intensive components, worked for a U.S. laboratory in California. His direct subordinate, the project engineer, worked for an institute in Italy. Even though he was managing a critical role in the production process, the project leader had no power to promote, discipline, or even formally review the project engineer’s performance. His only recourse was discussion, negotiation, and compromise. ATLAS members are more likely to feel that they work with someone, rather than for them.

    Similarly, funding came from institutes in different countries through “memorandums of understanding” rather than formal contracts. The collaboration’s spokesperson and other top managers were required to follow a politic of stewardship, looking after the collaboration rather than directing it. If collaboration members were alienated, that could mean the loss of the financial and human capital they were investing. Managers at all levels needed to find non-traditional ways to provide feedback, incentives, and discipline to their subordinates.

    One famous member of the collaboration is looked upon dubiously by many, who see him as drawing too much attention to himself.

    The coffee chat was one way to do this, and became the predominant way to conduct the little daily negotiations that kept the collaboration running. Today there are cafés stationed all around CERN, and they are full from morning to evening with people having informal meetings. Many physicists can be seen camped out in the cafeteria for hours at a time, working on their laptops between appointments. ATLAS management also created “a safe harbor, a culture within the organization that allows [employees] to express themselves and resolve conflicts and arguments without acrimony,” Marchand says.

    The result is a management structure that is remarkably effective and flexible. ATLAS managers consistently scored in the top 5 percent of a benchmark scale that measures how they control, disseminate, and capitalize on the information capital in their organization. Marchand also found that the ATLAS management structure was effective at adapting to changing circumstances, temporarily switching to a more top-down paradigm during the core production phase of the experiment, when thousands of identical objects needed to be produced on assembly lines all over the world.

    This collaborative culture didn’t arise by chance; it was built into ATLAS from the beginning, according to Marchand. The original founders infused a collaborative ethic into every person that joined by eschewing personal credit, talking through conflicts face to face, and discussing almost everything in open meetings. But that ethic is codified nowhere; there is no written code of conduct. And yet it is embraced, almost religiously, by everyone that I spoke with.

    Collaboration members are sceptical of attributing individual credit to anything. Every paper includes the entire author list, and all of ATLAS’s outreach material is signed “The ATLAS Collaboration.” People are suspicious of those that are perceived to take too much personal credit in the media. One famous member of the collaboration (as well as a former rock star and host of the highly successful BBC series, Horizon) is looked upon dubiously by many, who see him as drawing too much attention to himself through his association with the experiment.

    MIND THE GAP: Over 60 institutes collaborated to build and install a new detector layer inside a 9-millimeter gap between the beam pipe (the evacuated pipe inside of which protons circulate) and the original detector.ATLAS Experiment © 2014 CERN

    In searching for genius at ATLAS, and other experiments at CERN, it seems almost impossible to point at anything other than the collaborations themselves. More than any individual, including the theorists who suggest new physics and the founders of experimental programs, it is the collaborations that reflect the hallmarks of genius: imagination, persistence, open-mindedness, and accomplishment.

    The results speak for themselves: ATLAS has already reached its first key objective in just one-tenth of its projected lifetime, and continues to evolve in a highly collaborative way. This May, one of the first upgrades to the detector was installed. Called the Insertable B-Layer (IBL), it grew out of a task force formed near the end of ATLAS’s initial commissioning period, in 2008, with the express goal of documenting why inserting another layer of detector into a 9-millimeter clearance space just next to the beam pipe was considered impossible.

    Consummate opportunists, the task force members instead came up with a design that quickly turned into a new subproject. And though it’s barely larger than a shoebox, the IBL’s construction involved more than 60 institutes all over the world, because everyone wanted to be involved in this exciting new thing. When it came time to slide the Insertable B-layer sub-detector into its home in the heart of ATLAS earlier this year, with only a fraction of a millimeter of clearance over 7 meters in length, the task was accomplished in just two hours—without a hitch.

    Fresh opportunities for new genius abound. Gianotti singles out dark matter as an example, saying “96 percent of the universe is dark. We don’t know what it’s made of and it doesn’t interact with our instruments. We have no clue,” she says. “So there is a lot of space for genius.” But instead of coming from the wild-haired scientist holding a piece of chalk or tinkering in the laboratory, that genius may come from thousands of people working together.

    Neal Hartman is a mechanical engineer with Lawrence Berkeley National Laboratory that has been working with the ATLAS collaboration at CERN for almost 15 years. He spends much of his time on outreach and education in both physics and general science, including running CineGlobe, a science-inspired film festival at CERN.

    See the full article, with notes, 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” 


    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

    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 CMS New

    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.

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  • richardmitnick 12:01 pm on July 18, 2014 Permalink | Reply
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    From New Scientist: “Higgs boson glimpsed at work for first time” 


    New Scientist

    17 July 2014
    Lisa Grossman

    The world’s largest particle collider has given us our first glimpse of the Higgs boson doing its job.

    Fresh from the ATLAS detector at the Large Hadron Collider (Image: CERN)

    For 50 years, the Higgs boson was the final missing piece in the standard model of particle physics, which elegantly predicts how fundamental particles and forces interact. The ATLAS experiment at the Large Hadron Collider near Geneva, Switzerland, was one of the detectors that helped discover the Higgs in 2012.

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


    CERN LHC Map
    CERN/LHC map

    Now ATLAS physicists report seeing pairs of particles called W bosons scattering off each other inside the detector. This rare process can be used to test how the Higgs actually operates.

    “We know these particles very well, but we have never seen them interact in this way before,” says Marc-André Pleier at Brookhaven National Laboratory in New York. “With this measurement, we can check that the Higgs boson does its job.”

    W mystery

    The Higgs was dreamed up to explain why some force-carrying particles like the W and Z bosons have mass, while others such as the photon do not. In the process, theorists realised that the Higgs could solve another mystery involving the W boson. When they tried to calculate how often W bosons should interact with each other, the results were physically impossible without the Higgs and the theory started to break down. Allowing W bosons to toss a Higgs between them as they collided solved the problem.

    “This is one of the things that people put out there saying there must be a Higgs boson,” says Matthew Herndon at the University of Wisconsin Madison, who works on similar problems with another LHC experiment called CMS. It also makes W scattering one of the best places to look for physics beyond the standard model – which does not take gravity into account and cannot explain mysteries such as dark matter and dark energy.

    Since the Higgs’s discovery, physicists have been scrutinising its properties to see if it is the same particle predicted by the standard model or if it is a weird variant that will uncover chinks in the model’s armour.

    “We have a pretty good idea of what this boson should look like,” says Pleier. “Like a ‘wanted’ poster in the Wild West, where the eye colour or a scar or whatever correspond to certain quantum properties. This is what we do with direct measurements of the Higgs boson.”
    Higgs interrogated

    So far the Higgs has been frustratingly picture perfect. With the LHC shut down for an upgrade until 2015, it seemed that physicists would just have to wait to collect more information. But another way to interrogate the Higgs is to test how it operates. If W bosons can exchange more than one Higgs, for example, they should fly off each other much more often than the standard model predicts.

    “The rates of these scattering processes and the energies you see them at would be forced to change fairly dramatically,” says Herndon. “So this is a good bet for looking for new physics.”

    What has made this a challenge is that W bosons scatter off each other incredibly rarely at the LHC, even less often than a Higgs boson is produced. The LHC works by smashing protons together at close to the speed of light. Every so often, one of those protons will emit a W boson. We can only look for scattering if both protons happen to emit a W at the same time, and if those W bosons happen to be aimed at each other.

    ATLAS has seen evidence for 34 of these events among billions of collisions, says Pleier. So far, everything fits with the standard model’s predictions. But seeing the effect at all is a milestone, and Herndon says that the CMS experiment will be releasing its version of these results soon, adding to the data pool.

    “We’ve never looked in this corner of the standard model before,” says ATLAS team member Jake Searcy at the University of Michigan, Ann Arbor. “This is the start of something that’s going to be very interesting in the years to come.”

    See the full article here.

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  • richardmitnick 9:06 am on May 21, 2014 Permalink | Reply
    Tags: , CERN ATLAS, , ,   

    From CERN: “A new subdetector for ATLAS” 

    CERN New Masthead

    21 May 2014
    Abha Eli Phoboo

    Closest to the beam pipe where particle collisions will occur in the very heart of ATLAS, a new subdetector – the Insertable B-Layer – was recently put in place. The IBL team had been developing and practicing the insertion procedure and tooling for two years because of the operation’s delicate nature. Every possible test had been carried out. Unlike the dry runs above ground, the final procedure in the ATLAS cavern allowed only one chance.

    A team of physicists and engineers inspect the subdetector before its insertion into the ATLAS experiment (Image: Claudia Marcelloni De Oliveira/CERN)

    The insertion gap between the Inner Supporting Tube and the IBL detector is only 0.2 mm and the gap between the supporting tube and the Pixel is 1.9 mm. Despite this narrow space, the procedure went smoothly and the work was completed ahead of schedule.

    “The final insertion was the culmination of all the developments we’ve been doing,” says Heinz Pernegger, project leader of the Pixel Detector. “The mockups and demonstrations we’ve gone through, we had practiced so many times.”

    “It is so satisfying to see the IBL in place,” says Raphaël Vuillermet, who coordinated the engineering and installation. “The project started from a blank sheet of paper, with many problems to solve and few ideas about how to tackle them. Since then, we’ve gone through various phases. It is a very compact sub-detector because it had to contain all the services required for operation and still fit inside a tiny space that didn’t even exist previously, as only the reduction of the beam pipe diameter has allowed the insertion of this additional Pixel layer.”

    A tight fit! An engineer checks the subdetector as it is inserted into the ATLAS experiment (Image: Claudia Marcelloni de Oliveira/CERN)

    The problem given was that with higher luminosity in the LHC’s next run, significant radiation damage of the inner layers of the detector could occur, which meant ATLAS would lose tracking efficiency, especially in tagging the decay of the beauty quark – crucial for physics analyses. The idea was to minimize risks by creating an insertable layer instead of replacing the existing B-layer in the Pixel Detector. The IBL was born but the only way to integrate it was by shrinking the diameter of the beam pipe and inserting it into the gap between the Pixel Detector and the pipe.

    The IBL is now the new fourth layer in the inner detector region of ATLAS, an additional point for tracking particles. More points mean better precision which is always good for physics.

    The Insertable B-Layer (IBL) in the final stages of insertion. This subdetector is now the fourth layer in the inner detector region of the ATLAS experiment (Image: Claudia Marcelloni de Oliveira/CERN)

    Making space wasn’t the only challenge for the IBL project. Much of the technology did not exist. Increased luminosity in the LHC meant the IBL has to cope with high radiation and higher particle occupancy because of its proximity to the particle interaction point in the beam pipe. This also meant the number of hits on the detector and the amount of data collected will increase substantially. Faster read-out chips and two different silicon sensor technologies were developed. Pixel size was reduced to 50 by 250 micrometres, and a CO2-based cooling system was introduced as opposed to the C3F8. New carbon foam structures were invented to support the modules that make up the IBL. These staves had to be just firm enough to serve as mechanical support but flexible enough to be inserted.

    As remarkable as the developments were, even more remarkable is the collaborative nature of the project. Forty-seven institutes from 15 countries were involved in the IBL team. Its success, as does everything else in ATLAS, depended on the members.

    “The ambiance in the cavern during the insertion was pivotal,” says Sébastien Michal, who together with Raphaël Vuillermet, coordinated the engineering and installation. “There was a lot of confidence there because of the many practice sessions, but more importantly, there was a lot of trust.”

    See the full article here.

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  • richardmitnick 5:44 pm on May 7, 2014 Permalink | Reply
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    From Oak Ridge: “World’s Most Powerful Accelerator Comes to Titan with a High-Tech Scheduler” 


    Oak Ridge National Laboratory

    May 6, 2014
    Leo Williams

    The people who found the Higgs boson have serious data needs, and they’re meeting some of them on the Oak Ridge Leadership Computing Facility’s (OLCF’s) flagship Titan system.


    Researchers with the ATLAS experiment at Europe’s Large Hadron Collider (LHC) have been using Titan since December, according to Ken Read, a physicist at Oak Ridge National Laboratory and the University of Tennessee. Read, who works with another LHC experiment, known as ALICE, noted that much of the challenge has been in integrating ATLAS’s advanced scheduling and analysis tool, PanDA, with Titan.


    CERN LHC particles

    PanDA (for Production and Distributed Analysis) manages all of ATLAS’s data tasks from a server located at CERN, the European Organization for Nuclear Research. The job is daunting, with the workflow including 1.8 million computing jobs each day distributed among 100 or so computing centers spread across the globe.

    PanDA is able to match ATLAS’s computing needs seamlessly with disparate systems in its network, making efficient use of resources as they become available.

    In all, PanDA manages 150 petabytes of data (enough to hold about 75 million hours of high-definition video), and its needs are growing rapidly—so rapidly that it needs access to a supercomputer with the muscle of Titan, the United States’ most powerful system.

    “For ATLAS, access to the leadership computing facilities will help it manage a hundredfold increase in the amount of data to be processed,” said ATLAS developer Alexei Klimentov of Brookhaven National Laboratory. PanDA was developed in the United States under the guidance of Kaushik De of the University of Texas at Arlington and Torre Wenaus from Brookhaven National Laboratory.

    “Our grid resources are overutilized,” Klimentov said. “It’s a question of where we can find resources and use them opportunistically. We cannot scale the grid 100 times.”

    In order to integrate with Titan, PanDA team developers Sergey Panitkin from BNL and Danila Oleynik from UTA redesigned parts of the PanDA system on Titan responsible for job submission on remote sites (known as “Pilot”) and gave PanDA new capability to collect information about unused worker nodes on Titan. This allows PanDA to precisely define the size and duration of jobs submitted to Titan according to available free resources. This work was done in collaboration with OLCF technical staff.

    The collaboration holds potential benefits for OLCF as well as for ATLAS.

    In the first place, PanDA’s ability to efficiently match available computing time with high-priority tasks holds great promise for a leadership system such as Titan. While the OLCF focuses on projects that can use most, if not all, of Titan’s 18,000-plus computing nodes, there are occasionally a relatively small numbers of nodes sitting idle for one or several hours. They sit idle because there are not enough of them—or they don’t have enough time—to handle a leadership computing job. A scheduler that can occupy those nodes with high-priority tasks would be very valuable.

    “Today, if we use 90 or 92 percent of available hours, we think that is high utilization,” said Jack Wells, director of science at the OLCF. “That’s because of inefficiencies in scheduling big jobs. If we have a flexible workflow to schedule jobs for backfill, it would mean higher utilization of Titan for science.”

    PanDA is also highly skilled at finding needles in haystacks, as it showed during the search for the Higgs boson.

    According to the Standard Model of particle physics, the field associated with the Higgs is necessary for other particles to have mass. The boson is also very massive itself and decays almost instantly; this means it can be created and detected only by a very high-energy facility. In fact, it has, so far, been found definitively only at the LHC, which is the world’s most powerful particle accelerator.

    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.

    But while high energy was necessary for identifying the Higgs, it was not sufficient. The LHC creates 800 million collisions between protons each second, yet it creates a Higgs boson only once every one to two hours. In other words, it takes 4 trillion collisions, more or less, to create a Higgs. And it takes PanDA to manage ATLAS’s data processing workflow in sifting through the data and finding it.

    PanDA’s value to high-performance computing is widely recognized. The Department of Energy’s offices of Advanced Scientific Computing Research and High Energy Physics are, in fact, funding a project known as Big PanDA to expand the tool beyond high-energy physics to be used by other communities.

    See the full article here.

    ORNL is managed by UT-Battelle for the Department of Energy’s Office of Science. DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time.


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  • richardmitnick 5:01 am on March 29, 2014 Permalink | Reply
    Tags: , CERN ATLAS,   

    From ATLAS at CERN: “The Neutrino Puzzle” 



    March 21, 2014
    Sabine Crépé-Renaudin

    Having explored the latest results on what we call ‘heavy flavour’ or physics of particles containing a b-quark (see The Penguin Domination by Jessica Levêque), we embarked on a much lighter subject: neutrinos.

    It was as if a fresh breeze swept through the audience. Partly because we are surrounded by snow-capped mountains but mostly because of the topic — neutrino physics has been bubbling with activity these past few years. Many new measurements were shown, adding several pieces to the neutrino puzzle. But we are still far from having a clear idea of the picture we are trying to build, piece by piece.

    Neutrinos are special particles. They are at the heart of some of the most exciting fundamental problems that particle physicists are trying to solve. But neutrinos are elusive, a characteristic that makes it difficult to study them. Physicists must use their ingenuity to compete at developing new kinds of detectors capable of measuring neutrinos coming from different sources.

    Neutrinos sources studied by experiments

    There are a few things we know about neutrinos. In the Standard Model, neutrinos are neutral leptons that were thought to be massless. There are three neutrino species — electron, muon and tau neutrinos, each associated to the other three leptons in the Model — electron, muon and tau. They are the second most common particle in the universe after photon but are not well-known to the public. They interact with matter through weak interaction which makes them difficult to catch. But physicists like challenges and build experiments to detect and measure the flux of neutrinos coming from sources outside of our solar system or the sun, through the atmosphere, produced by terrestrial nuclear power plants or particle accelerators.

    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.

    Most of these experiments were only sensitive to one neutrino species and at first, all these measurements appeared to be inconsistent. The picture got clearer when the Super Kamiokande experiment in Japan established in 1998 that neutrinos can oscillate from one species to another. Which means that an electron-neutrino can transform itself into a muon-neutrino and vice-versa. This explains, for instance, why the solar electron-neutrino measured flux is well below the one predicted by the solar model — because a fraction of them oscillate into muon-neutrinos that were not detected. The important consequence of the oscillation is that it can only occur if neutrinos have mass!

    Neutrino masses with respect to the other Standard Model particles (fermions)

    Since then, new experiments have been built to measure the probability of oscillation between different neutrino species and infer a measurement of their mass. At the conference, several measurements of these parameters were shown and we now know with fair precision the different oscillation probabilities as well as the mass differences between neutrino species. However, we still don’t know the mass itself although cosmological experiments allow us to set an upper limit on the sum of the masses of the three neutrino species, which is below an eV (electronVolt). Moreover, new experimental inconsistencies appear: some experiments do not observe the expected number of neutrinos, even with the oscillations taken into account.

    So now, new questions have arisen: Where does the neutrino mass come from? Why is it so far from the other lepton masses? As it is massive and weakly interacting, could the neutrino be part of the dark matter of the universe? Is the neutrino its own anti-particle? Are there more than three neutrinos? Where are the high energetic neutrinos coming from?

    Some experiments like IceCube are now able to map neutrinos coming from the universe and this is like doing astronomy with neutrinos!

    Neutrino skymap as measured by the IceCube experiment

    During the session, several theoreticians proposed models that try to conciliate the different observations and answers to the above questions: Couldn’t there be a new species of neutrino in which the others could oscillate? Is the neutrino description in the standard model complete: couldn’t they have (as the other leptons) right-handed partners? This last option is interesting since it could explain why the standard neutrino mass is so small and perhaps also part of the universe dark matter as the right handed-neutrinos could be very massive.

    Theoretical talks alternated with experimental ones describing future experiments that are currently being developed to help solve the puzzle. These experiments are being built by smaller collaborations in comparison to the LHC teams. The experiments can be located in the South Pole to take advantage of the ice as an interacting medium for the detector or in the depth of a disused mine to fight efficiently against cosmic ray background. The proposed technologies are also very different depending on the aim of the measurement but all experiments need a very low and well-controlled background, as the number of observed neutrinos is always small.

    Stay tuned! There is no doubt that new results on neutrinos will come soon but in the meantime, my colleagues and I will catch some fresh air during a long lunch break up on the snowy mountains. After all, it is important to rest our brains in order to prepare for presentations of the top quark, the Higgs boson and other new results from the LHC in the next sessions.

    So, what does a particle physicist, with her brain at rest, see in the surrounding mountains?


    higgs decay
    Higgs decaying in two photons bump over background as seen by the ATLAS experiment

    the Higgs boson of course!!!

    See the full article here.

    [The writer’s failure to mention the work on neutrinos going on under the auspices of Fermilab is deplorable, to say the least.]

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