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  • richardmitnick 7:32 am on July 24, 2015 Permalink | Reply
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    From ATLAS at CERN: “Early Run 2 results test event generator energy extrapolation” 

    CERN New Masthead

    23 July 2015

    ATLAS presented its first measurements of soft strong interaction processes using charged particles produced in proton–proton collisions at 13 TeV centre-of-mass energy delivered by the Large Hadron Collider at CERN. These measurements were performed with a dataset collected beginning of June under special low-luminosity conditions during which the frequency of multiple proton–proton scattering occurring in the same recorded collision event was strongly reduced.

    Measurements like this are important for understanding the collision energy dependence of such processes, as well as ensuring a successful description of the data by the Monte Carlo (MC) event generators. The accuracy of these simulations is critical for their subsequent use in ATLAS searches and measurements.

    Performing these measurements at an unprecedented collision energy with upgraded detector components in such a short scale was a challenge. During the Long Shutdown, many improvements were made to the detector, most relevant among them for these results was the addition of the innermost pixel layer, the insertable B-layer (IBL). Adding the IBL dramatically improved the accuracy of the track reconstruction and the identification of jets originating from bottom quarks, which is important for many searches. The commissioning of the IBL, alignment of different detector components and assessment of passive detector material is still ongoing. Figure 1 shows the number of hits in pixel layer per track. Generally, good agreement is observed, indicating a very good understanding of the ATLAS four-layer pixel system. The minor disagreements stem from the mismatch in simulation and data of the number of modules not working properly during that period of data-taking.

    The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity (which essentially represents the angular position from beam axis) and the dependence of the mean transverse momentum on the charged-particle multiplicity were presented, based on about 9 million events. The events contained at least one charged particle with transverse momentum greater than 500 MeV in the central part of the detector. The data were corrected with minimal model dependence to obtain inclusive distributions. Overall the Monte Carlo models, which were tuned to such similar measurements performed at lower centre-of-mass energies, seem to describe the data reasonably well. Figure 2 shows the mean number of charged particles in the central region compared to previous measurements at different collision energies, together with the MC predictions. The mean number of charged particles increases by a factor of 2.2 when collision energy increases from 0.9 TeV to 13 TeV.

    In the events where the leading track had a transverse momentum of at least 1 GeV, the accompanying activity was studied at the detector level. The azimuthal region perpendicular to the direction of the leading track is most sensitive to this accompanying activity, termed the underlying event (UE). The average number of tracks in each event and their transverse momentum sum are seen to show a gradual rise towards a “plateau” with rising leading track transverse momentum, a trend seen in previous measurements. Figure 3 shows the latter in the transverse region. Compared to 7 TeV results a 20% increase to the UE activity is observed and is predicted well by most of the models.

    These early measurements show a good understanding of the performance the upgraded ATLAS detector as well as the ability of the Monte Carlo event generators to describe the data at new collision energy.

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    Figure 1: Comparison of number of pixel hits distributions in data and simulation.

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    Figure 2: The average charged-particle multiplicity per unit of rapidity for eta= 0 as a function of the centre-of-mass energy.

    3
    Figure 3: Comparison of detector level data and MC predictions for average scalar pT sum density of tracks as a function of leading track pT.

    See the full article here.

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  • richardmitnick 8:19 pm on July 20, 2015 Permalink | Reply
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    From ATLAS at CERN: “First Run 2 Results to be Presented at EPS” 

    CERN New Masthead

    July 20, 2015

    For the past six weeks, the ATLAS experiment has been recording physics data from 13 TeV proton collisions. In this short time, they have recorded over 7,280 billion collisions – twice the amount recorded in 2010. Detector teams have been calibrating and aligning ATLAS’ various detectors at a remarkable speed. This effort allows ATLAS physicists to exploit the many upgrades made to the detector during Long Shutdown 1.

    ATLAS physicists are combing through this new wealth of data, performing detailed studies of Standard Model processes at unprecedented energies, the Higgs boson and the first searches for as-yet unobserved phenomena.

    The first results using the record-breaking Run 2 data will be presented at the European Physical Society conference on High Energy Physics (EPS-HEP) in Vienna, 22-29 July. It will be an exciting opportunity to see how these first few weeks of data-taking have progressed. Physics briefings will be released throughout the event, highlighting ATLAS’ results from the conference.

    EPS-HEP is the first of the major summer conferences for particle physics, where all of the LHC experiments will be presenting results. About seven hundred researchers from all over the world are expected to attend.

    Further results using Run 2 data will be presented at the Lepton Photon conference, 17-22 August, and the Large Hadron Collider Physics conference (LHCP2015), 31 August-5 September.

    See the full article here.

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  • richardmitnick 2:22 pm on July 16, 2015 Permalink | Reply
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    From Symmetry: “Something goes bump in the data” 

    Symmetry

    July 16, 2015
    Katie Elyce Jones and Sarah Charley

    The CMS and ATLAS experiments at the LHC see something mysterious, but it’s too soon to pop the Champagne.

    CERN CMS Detector
    CMS

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    ATLAS

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    An unexpected bump in data gathered during the first run of the Large Hadron Collider is stirring the curiosity of scientists on the two general-purpose LHC experiments, ATLAS and CMS.

    CMS first reported the bump in July 2014. But because it was small and insignificant, they dismissed it as a statistical fluke. Recently ATLAS confirmed that they also see a bump in roughly the same place, and this time it’s bigger and stronger.

    “Both ATLAS and CMS are developing new search techniques that are greatly improving our ability to search for new particles,” says Ayana Arce, an assistant professor of physics at Duke University. “We can look for new physics in ways we couldn’t before.”

    Unlike the pronounced peak that recently led to the discovery of pentaquarks, these two studies are in their nascent stages. And scientists aren’t quite sure what they’re seeing yet… or if they’re seeing anything at all.

    If this bump matures into a sharp peak during the second run of the LHC, it could indicate the existence of a new heavy particle with 2000 times the mass of a proton. The discovery of a new and unpredicted particle would revolutionize our understanding of the laws of nature. But first, scientists have to rule out false leads.

    “It’s like trying to pick up a radio station,” says theoretical physicist Bogdan Dobrescu of Fermi National Accelerator Laboratory who co-authored a paper on the bump in CMS and ATLAS data. “As you tune the dial, you think you’re beginning to hear voices through the static, but you can’t understand what they’re saying, so you keep tuning until you hear a clear voice.”

    On the heels of the Higgs boson discovery in the first run of the LHC, scientists must navigate a tricky environment where people are hungry for new results while relying on data that is slow to gather and laborious to interpret.

    The data physicists are analyzing are particle decay patterns around 2 TeV, or 2000 GeV.

    “We can’t see short-lived particles directly, but we can reconstruct their mass based on what they transform into during their decay,” says Jim Olsen, a professor of physics at Princeton University. “For instance, we found the Higgs boson because we saw more pairs of W bosons, Z bosons and photons at 125 GeV than our background models predicted.”

    Considering that the heaviest particle of the Standard Model, the top quark, has a mass of 173 GeV, if this bump is real and not a fluctuation, it indicates a significantly heavier particle than those covered in the Standard Model.

    2
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    While the theories being batted around at this early stage disagree on the particulars, most agree that, so far, this data bump best fits the properties of an extended Standard Model gauge boson.

    The gauge bosons are the force-carrying particles that enable matter particles to interact with each other. The heaviest bosons are the W and Z bosons, which carry the weak force. An extended Standard Model predicts comparable particles at higher energies, heavier versions known as W prime and Z prime (or W’ and Z’). Several theorists suggest the bump at 2 TeV could be a type of W prime.

    2
    ATLAS data shows an increased number of W and Z boson pairs at 2 TeV. Courtesy of: ATLAS collaboration

    But LHC physicists aren’t practicing their Swedish for the Nobel ceremony yet. Unexpected bumps are common and almost always fizzle out with more data. For instance, in 2003 an international collaboration working on the Belle experiment at the KEK accelerator laboratory in Japan saw an apparent contradiction to the Standard Model’s predictions in the decay patterns of particles containing bottom quarks.

    “It was really striking,” says Olsen. “The probability that the signal was due to sheer statistical fluctuation was only about one in 10,000.”

    Seven years later, after inundating their analysis with heaps of fresh data, the original contradiction from the Belle experiment withered and died, and from its ashes arose a stronger result that perfectly matched the predictions of the Standard Model.

    But scientists also haven’t written off this new bump as a statistical fluctuation. In fact, the closer they look, the more exciting it becomes.

    With most anomalies in the data, one experiment will see it while the other one won’t—a clear indication of a statistical fluctuation. But in this case, both CMS and ATLAS independently reported the same observation. And not only do both experiments see it, they see it at roughly the same energy across several different types of analyses.

    “This is kind of like what we saw with the Higgs,” says JoAnne Hewett, a theoretical physicist at SLAC National Accelerator Laboratory who co-authored a paper theorizing the bump could be a type of W prime particle. “The Higgs just started showing up as 2- to 3-sigma bumps in a few different channels in the two different experiments. But there were also false leads with the Higgs.”

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    CMS data summarizing the search for new heavy particles decaying into several decay channels. The search reveals hints of a structure near 2000 GeV (2 TeV). Courtesy of: CMS collaboration

    Scientists are seeing more Z boson and W boson pairs popping up at 2 TeV than the Standard Model predicts. But besides this curious excess of events, they haven’t identified any sort of clear pattern.

    “Theorists come up with the models that predict the patterns we should see if there is some type of new physics influencing our experimental data,” Olsen says. “So if this bump is new physics, then our models should predict what else we should see.”

    Even though this bump is far too small to signify a discovery and presents no predictable pattern, its presence across multiple different analyses from both CMS and ATLAS is intriguing and suspicious. Scientists will have to patiently wait for more data before they can flesh out what it actually is.

    “We will soon have a lot more data from the second run of the LHC, and both experiments will be able to look more closely at this anomaly,” Arce says. “But I think it would almost be too lucky if we discovered a new particle this soon into the second run of the LHC.”

    The latest results from these two studies will be presented at the European Physical Society conference in Vienna at the end of the month.

    See the full article here.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 6:41 am on June 6, 2015 Permalink | Reply
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    From ATLAS at CERN’s LHC: “Setting Off To New Energy Horizons” 

    CERN New Masthead

    June 4, 2015
    Andreas Hoecker & Marumi Kado, CERN

    1
    Display of a proton-proton collision event recorded by ATLAS on 3 June 2015, with the first LHC stable beams at a collision energy of 13 TeV. Tracks reconstructed by the tracking detector are shown as light blue lines, and hits in the layers of the silicon tracking detector are shown as colored filled circles. The four inner layers are part of the silicon pixel detector and the four outer layers are part of the silicon strip detector. The layer closest to the beam, called IBL, is new for Run 2. In the view in the bottom right it is seen that this event has multiple pp collisions. The total number of reconstructed collision vertices is 17 but they are not all resolvable on the scale of this picture..

    After a shutdown of more than two years, Run 2 of the Large Hadron Collider (LHC) is restarting at a centre-of-mass energy of 13 TeV for proton–proton collisions and increased luminosity. This new phase will allow the LHC experiments to explore nature and probe the physical laws governing it at scales never reached before.

    In this first long shutdown, during which the LHC was consolidated, the ATLAS experiment saw a flurry of activity ranging from upgrades and repairs of the detector, its electronics and the trigger system, to a reappraisal of the computing and software used for the data reconstruction and analysis. ATLAS physicists have also used the time without beam to finalise and improve their analyses of the Run-1 data. In spite of the small relative amount of data collected, only 1% of the total dataset expected for the entire LHC programme, the data recorded by ATLAS with collision energies up to 8 TeV have provided a wealth of physics results and led to more than four hundred scientific publications.

    The expectations were high for this unique experimental endeavour represented by the LHC and its ultra-sophisticated particle detectors of which ATLAS is the largest one. The tera (1012) electron-Volt energy scale to which the LHC collisions of high-energetic protons are sensitive was sought to reveal new particles or phenomenon related to the mechanism that gives mass to elementary particles. The most anticipated and acclaimed scenario, and key prediction of the Standard Model, was the Brout-Englert-Higgs mechanism that predicted a spin-zero Higgs boson with a mass in reach of the LHC. Such a boson was discovered in 2012 by the ATLAS and CMS experiments successfully culminating decades of experimental and theoretical effort. This discovery, and a plethora of other important results pushing the frontier of our knowledge, made the LHC Run-1 an astounding success.

    2
    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).

    What’s next? It doesn’t take long, when ambling the corridors along the ATLAS offices at CERN, to realise the suspense that reigns among the physicists running the experiment and preparing the analysis of the first Run-2 collisions. The new data, initially produced at 60% higher collision energy and promising to be several times more abundant than before, have the potential to dramatically extend the results from Run-1. The Higgs boson properties will be measured to much better precision, and new production and decay channels may be observed, further revealing the nature of this particle. Higgs physics will continue to be at the heart of Run-2, but the new data will also allow ATLAS to measure Standard Model processes at unprecedented energies and level of accuracy at hadron colliders, and detect yet unobserved rare processes. High-precision measurements of the masses and couplings of the heaviest known particles, are particularly important as they are indirectly sensitive to new phenomena entering the observed particle reactions through so-called virtual processes.

    These measurements, however, are challenging and will take time to complete. Yet the excitement felt in the ATLAS offices is due to another virtue of the higher collision energy in Run-2: the possibility of directly creating new, heavy particles in the most energetic proton–proton collisions owing to the proportionality relation between energy and mass. There are several reasons to conjecture the existence of such particles. Among these is dark matter, a phenomenon believed to involve physics beyond the Standard Model. Dark matter, if it couples to the known particles, could be produced at the LHC and detected by ATLAS in events with an apparent energy imbalance due to energy taken away by invisible (dark matter) particles. These particles could have any mass and couplings, and we neither know whether the LHC can produce them, nor whether the experiments can detect them, even if they existed. Another motivation for new phenomena beyond the Standard Model lies in an apparent shortcoming of the Higgs mechanism itself. Unlike matter particles, which by virtue of an underlying symmetry appear naturally light with respect to the extremely high energies that are thought to have existed during the earliest moments of the big bang, spin-zero particles such as the Higgs boson in the Standard Model do not have such a protective symmetry. It thus appears unnatural that the Higgs boson is so much lighter than these early energy scales where new phenomena are expected to govern physical laws. A new symmetry, such as the co-called “supersymmetry”, could solve that problem.

    Supersymmetry standard model
    Standard Model of Supersymmetry

    Other mechanisms exist; all have in common to introduce new particles of which some may be observable at the LHC, and these new particles could potentially play the role of dark matter as well. ATLAS physicists will therefore mine the new data to deeply and comprehensively search for new physics. The higher collision energy will help to rapidly surpass the sensitivity of the searches conducted during Run-1.

    Ample opportunities but also significant challenges are facing the experimentalists. Critical attention and patience are required for a precise understanding of the new data before drawing conclusions. ATLAS is ready for it.

    See the full article here.

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  • richardmitnick 5:03 am on June 2, 2015 Permalink | Reply
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    From ATLAS at CERN: Fast Forward tp Physics 

    CERN New Masthead

    As ATLAS gears up to record data from proton collisions delivered by the Large Hadron Collider (LHC) at an unprecedented energy level, here are glimpses from the last two years of preparations. For more information about the ATLAS Experiment please visit the official outreach page at http://www.atlas.ch

    Watch, enjoy, learn.

    See the full article here.

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  • richardmitnick 3:46 pm on May 15, 2015 Permalink | Reply
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    From Physics: “Viewpoint: A More Precise Higgs Boson Mass” 

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    Physics

    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.

    1
    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.

    2
    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 ATLAS New
    ATLAS

    CERN CMS Detector
    CMS

    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.

    Acknowledgments

    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.

    References

    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)

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    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.

    htxtdotafrica

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

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

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

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

    CERN ATLAS New
    ATLAS

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

    How did you get interested in physics?

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

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    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

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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.

    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.

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    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.

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    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.

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

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

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

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

    See the full article here.

    Please help promote STEM in your local schools.

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    Stem Education Coalition

    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
    Tags: , , , CERN ATLAS, ,   

    From CERN: “ATLAS@Home looks for CERN volunteers” 

    ATLAS@home

    ATLAS@home

    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.

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    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.”

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    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.

    Please help promote STEM in your local schools.

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    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.

    BOINCLarge

     
  • richardmitnick 11:57 am on November 25, 2014 Permalink | Reply
    Tags: , , CERN ATLAS, , ,   

    From Times Beacon record via BNL: “BNL’s Pleier takes next steps after Higgs-boson” 

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    Brookhaven Lab

    November 19, 2014
    Daniel Dunaief

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    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.

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    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.”

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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.

    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.

    BNL Campus

    Please help promote STEM in your local schools.

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    Stem Education Coalition

    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
    i1

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

    From Nautilus: “Who Really Found the Higgs Boson” 

    Nautilus

    Nautilus

    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 ATLAS New
    ATLAS

    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.

    team
    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.”
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    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.

    3
    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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