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  • richardmitnick 8:21 am on July 15, 2014 Permalink | Reply
    Tags: , , Brookhaven ATLAS, , , ,   

    From Brookhaven Lab: “Physicists Detect Process Even Rarer than the Long-Sought Higgs Particle” 

    Brookhaven Lab

    July 15, 2014
    Karen McNulty Walsh

    New stringent test of the Standard Model and the mechanism by which the Higgs imparts mass to other particles

    Scientists running the ATLAS experiment at the Large Hadron Collider (LHC), the world’s largest and most powerful “atom smasher,” report the first evidence of a process that can be used to test the mechanism by which the recently discovered Higgs particle imparts mass to other fundamental particles. More rare than the production of the Higgs itself, this process—a scattering of two same-charged particles called W bosons off one another—also provides a new stringent test of the Standard Model of particle physics. The findings, which so far are in agreement with predictions of the Standard Model, are reported in a paper just accepted by Physical Review Letters.

    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 Grand Tunnel
    LHC Tunnel

    CERN LHC Map
    LHC map

    “By measuring this process we can check whether the Higgs particle we discovered does its job the way we expect it to.”

    Brookhaven Lab/ATLAS physicist Marc-André Pleier

    “Only about one in 100 trillion proton-proton collisions would produce one of these events,” said Marc-André Pleier, a physicist at the U.S. Department of Energy’s Brookhaven National Laboratory who played a leadership role in the analysis of this result for the ATLAS collaboration. Complicating matters further, finding one such rare event is not enough. “You need to observe many to see if the production rate is above or on par with predictions,” Pleier said. “We looked through billions of proton-proton collisions produced at the LHC for a signature of these events—decay products that allow us to infer like Sherlock Holmes what happened in the event.”

    The analysis efforts started two years ago and were carried out in particular by groups from Brookhaven, Lawrence Berkeley National Laboratory, Michigan State University, and Technische Universität Dresden, Germany. Preliminary results were presented by Pleier at the “Rencontres de Moriond – QCD and High Energy Interactions” conference in March 2014. Now finalized based on a total of 34 observed events, the measured interaction rate is in good agreement with that predicted by the Standard Model, a theory describing all known fundamental particles and their interactions.

    “The Standard Model has so far survived all tests, but we know that it is incomplete because there are observations of dark matter, dark energy, and the antimatter/matter asymmetry in the universe that can’t be explained by the Standard Model,” Pleier said. So physicists are always looking for new ways to test the theory, to find where and how it might break down.

    “This process of W boson interactions is one we could never test,” Pleier said, “because we didn’t have enough energy or large enough data sets needed to see this very rare process—until we built the LHC.”

    Now with the LHC data in hand, the measured rate agrees with the prevailing theory’s predictions and establishes a signal at a significance level of 3.6 sigma—strong evidence, according to Pleier. “The probability for this measurement to be a mere background fluctuation is very small—about one in 6000,” he said. But the physicists would like to be more certain by collecting more data to reduce uncertainties and increase the level of significance.

    Candidate event for WW → WW scattering

    There’s another reason for continuing the quest: “By measuring this process we can check whether the Higgs particle we discovered does its job the way we expect it to,” Pleier said. “A wealth of models in addition to the Higgs mechanism exists to try to explain how fundamental particles get their mass. Measurements of such scattering processes can thus be both a fundamental test of the Standard Model and a window to new physics.”

    To test the Higgs mechanism, the scientists compare distributions of decay products of the W scattering process—how often they observe particular products at a particular energy and geometrical configuration.

    “It’s like a fingerprint,” Pleier said.“We have a predicted fingerprint and we have the fingerprint we measure. If the fingerprints match, we know that the Higgs does its job of mass generation the way it should. But if it deviates, we know that some other physics mechanism is helping out because the Higgs alone is not doing what we expect.”

    Again, so far, the data indicate that the Higgs is working as expected.

    “For the first time, we can rule out certain models or predictions that we could not before,” Pleier said. “To complete the job, we need more data, at higher energy, so we can see the fingerprint more clearly.”

    The LHC will resume data taking at increased collision energies—13 tera-electronvolts (TeV) instead of 8 TeV—in spring of 2015. The datasets collected will be up to 150 times the size of the currently available data and will allow for a detailed behind-the-scenes look at the Higgs at work.

    The ATLAS experiment at LHC is supported by DOE’s Office of Science and the National Science Foundation.

    Brookhaven National Laboratory serves as the U.S. host laboratory for the ATLAS experiment at the LHC, and plays multiple roles in this international collaboration, from construction and project management to data storage, distribution, and analysis, funded by the DOE Office of Science (HEP). For more information about Brookhaven’s role, see: http://www.bnl.gov/ATLAS/

    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. For more information, please visit science.energy.gov.

    See the full article here.

    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.

    DOE Office of Science

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  • richardmitnick 1:04 pm on October 2, 2013 Permalink | Reply
    Tags: , Brookhaven ATLAS, , , , , , ,   

    From Symmetry: “US participation in the Higgs discovery” 

    The search for the Higgs at experiments at the Large Hadron Collider was an international effort involving thousands of people, with physicists and engineers from US institutions playing a significant role throughout.

    October 01, 2013
    Don Lincoln

    Fermilab Don Lincoln
    Don Lincoln

    In 2012, the announcement of the Higgs particle rocked the world. A scientific discovery in which thousands of US scientists participated was blasted across the globe by over a thousand TV stations to more than a billion people. TIME magazine declared it to be the particle of the year and Fabiola Gianotti, leader of one of the teams who found it, a runner-up for person of the year. Science, the flagship journal of the American Association of the Advancement of Science, named it the breakthrough of the year.

    This discovery was a really big deal—so big that the media and information firm Thomson Reuters has predicted that this year’s Nobel prize in physics will go to two scientists who predicted the Higgs boson’s existence back in the 1960s.

    The data used to make this discovery was recorded at the Large Hadron Collider. Although the LHC is located at CERN in Europe, the discovery was an international one. Scientists from across the globe were involved in all stages of this discovery. More than 6000 researchers from institutions in more than 60 countries are currently participating in the LHC experiments.

    US participation

    Nearly 2000 physicists from the United States contributed to this effort; the United States provides more researchers than any other country. These scientists came from 96 US universities and research facilities in 33 states, plus Puerto Rico. Like all LHC collaborators, institutions in the United States built equipment at their home facilities and shipped them to CERN. American scientists also helped operate the experiments and played a major role in analyzing the data that led to the discovery of the Higgs boson.


    There are examples where US scientists have had a key impact. For instance, Joe Incandela, a professor of physics at the University of California, Santa Barbara, was in the international spotlight on July 4, 2012, when he announced the discovery of the new particle, as leader of a team of more than 3000 scientists on the CMS experiment.

    The two detectors that independently discovered the Higgs particle, ATLAS and CMS, can be thought of as huge digital cameras, each one larger than a five-story building and weighing many thousands of tons. And they are no ordinary cameras. They have 100 million pixels each and can take 40 million pictures every second. By sifting through these pictures, scientists are able to better understand how the universe works.

    us cost

    Fully a third of the cost of building and operating these detectors is borne by the United States. Together, the US Department of Energy and the National Science Foundation contributed about $165 million to the construction of each device. These two agencies have a long history of funding fundamental research, resulting in technical payoffs including such innovations as medical imaging and cancer treatment, materials science and high-performance computing.

    While the United States has supplied about 30 percent of the budget and manpower necessary to operate the LHC experiments, this number probably underestimates the impact of US scientists on the LHC research program. Brookhaven National Laboratory provides the second largest group of physicists working on the ATLAS experiment, eclipsed only by CERN itself. The situation is similar in CMS, where Fermi National Accelerator Laboratory is the second biggest research group.

    Hundreds of American graduate students have written their PhD theses on research tied to the LHC experiments and have moved on into the American technical workforce.

    America’s strong commitment to fundamental research ensures that US physicists will continue to play a central role in mankind’s millennia-long efforts to understand our universe.

    See the full article here.

    Symmetry is a joint Fermilab/SLAC publication.

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