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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” 

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

    physicsworld
    physicsworld.com

    Sep 16, 2014
    By Rolf-Dieter Heuer, Geneva

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

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

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

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

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

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

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

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

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

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

    CERN ATLAS New
    ATLAS

    CERN CMS New
    CMS

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

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

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

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

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

    See the full article here.

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

    We engage with policymakers and the general public to develop awareness and understanding of the value of physics and, through IOP Publishing, we are world leaders in professional scientific communications.
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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” 

    NewScientist

    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.

    higgs
    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.

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

    CERN ATLAS New
    CERN/ATLAS

    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
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    From CERN: “A new subdetector for ATLAS” 

    CERN New Masthead
    CERN

    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.

    men
    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.”

    man
    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.

    tubes
    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.

    Meet CERN in a variety of places:

    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS

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    CERN ATLAS New
    ALICE
    CERN ALICE New

    CMS
    CERN CMS New

    LHCb
    CERN LHCb New

    LHC

    CERN LHC New

    LHC particles

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  • richardmitnick 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” 

    i1

    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.

    titan

    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 ATLAS New
    ATLAS

    CERN LHC particles
    LHC

    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.

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

    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.

    i2


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

    From ATLAS at CERN: “The Neutrino Puzzle” 


    ATLAS

    CERN ATLAS New

    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.

    souirces
    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.

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

    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!

    spec
    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!

    map
    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?

    mountain
    well…

    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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  • richardmitnick 4:35 am on March 29, 2014 Permalink | Reply
    Tags: , , CERN ATLAS, , ,   

    From ATLAS at CERN: “Is New Physics Running Out of Corners?” 

    CERN New Masthead

    March 23, 2014
    Eve Le Ménédeu

    Friday was the last occasion for Moriond participants to see new results on specific physics topics since Saturday is reserved for summary talks. The topic was ‘Beyond the Standard Model’ — a very large subject, which covers an incredible number of theoretical models, from Supersymmetry to Two-Higgs-Doublet Models, two of the most discussed topics of the day.

    schema
    Schema of top decays, ranging from unmerged to fully merged (boosted) (talk presented by Patricia Azzi at Moriond 2014).

    Each talk addressed more than one theoretical model, as the experiments prefer to focus on model-independent results. With each talk, however, the space left for new physics by latest measurements appeared smaller and smaller. In fact, Jean Iliopoulos highlighted in his summary talk that it is becoming harder to say “new physics must be around the corner,” as we are “running out of corners!” So, I’ll focus on a topic that appears less theoretical even if it is treated in close collaboration with theorists: searches for new physics with boosted topologies. This topic was presented by Patrizia Azzi on behalf of the ATLAS and CMS collaborations.

    What is a boosted topology? The term, which derives from “Lorentz boost”, is applied when a particle has energy equal to or above twice its mass. Due to their light masses, this is pretty much always the case for electrons and muons; they are considered “ultra-relativistic” and are not classified in this category. Rather, the term is reserved for much heavier particles, like W, Z or H bosons or top quarks – that is, particles that need much more energy to be boosted. These particles are unstable and are only observed by their decay products and, as a consequence of the boost, their decay products end up collimated in a single jet.

    As an example of a boosted topology, consider a top quark decaying into a W boson and a b quark. If the W boson decays hadronically, it produces two light jets. So, in the non-boosted case, we could expect to reconstruct the top quark from three jets: two light jets and one b-jet. In the boosted case, however, we only observe one collimated jet containing, in its substructure, the two light jets and the b jet. The challenge is to identify such a jet and recognize its components.

    Boosted topologies are also studied in searches for a Z’ boson (a heavy Z boson predicted in some new theories) decaying into a top – anti-top pair. The top quarks are boosted for a Z’ with mass above 1 TeV and, at the moment, Z’ are excluded below 1.65 TeV (at 99% Confidence Level) depending on the model. Such searches represent possible new “corners” for finding new physics, especially as the LHC centre of mass energy increases (from 8 TeV to 13-14 TeV) in Run 2.

    chart
    Reconstructed mass of tau leptons coming from Higgs decays (from talk presented by Riccardo Manzoni at Moriond 2014).

    At these energies, boosted topologies will also be important for Higgs boson decays to b quarks or τ leptons.

    Another very important topic — concerning the Standard Model and the Higgs boson — was brought up during the Young Scientist Forum. This session features PhD students, who are each given five minutes to present a topic and to answer one question, which is an excellent opportunity to present their work. And this topic, evidence of Higgs boson decays into τ leptons, was treated by two students: Nils Ruthmann for ATLAS and Riccardo Manzoni for CMS.

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

    This is a major result. Until the end of 2013, the Higgs had been only observed decaying into bosons (γγ, ZZ and WW), although the Standard Model predicts that it should also decay into fermions (ττ, bb,…), decays in these channels are difficult to identify due to high background rates and final states that are more difficult to extract (jets versus leptons or photons). Both analyses used multivariate techniques to achieve the goal.

    One of the more difficult challenges is to identify the tau leptons, which decay fully leptonically in 12% of the cases, leptonically and hadronically in 46% of the cases and fully hadronically in the rest (42%). The plot [above] illustrates the mass of tau leptons, as reconstructed in the hadronic decay mode. The final results present evidence of H → ττ at a significance of 4.1 σ for ATLAS and 3.2 σ for CMS. No new “corner” here, but more key support for the Standard Model, and a very important measurement.

    See the full article here.

    Meet CERN in a variety of places:

    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New
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    CERN ALICE New

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  • richardmitnick 12:46 pm on March 19, 2014 Permalink | Reply
    Tags: , , CERN ATLAS, , , , , , , ,   

    From Fermilab: “International team of LHC and Tevatron scientists announces first joint result” 


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

    Wednesday, March 19, 2014
    No Writer Credit

    Scientists working on the world’s leading particle collider experiments have joined forces, combined their data and produced the first joint result from Fermilab’s Tevatron and CERN’s Large Hadron Collider (LHC), past and current holders of the record for most powerful particle collider on Earth. Scientists from the four experiments involved—ATLAS, CDF, CMS and DZero—announced their joint findings on the mass of the top quark today at the Rencontres de Moriond international physics conference in Italy.

    Fermilab Tevatron
    Fermilab Tevatron

    CERN LHC
    Inside the LHC

    CERN ATLAS New
    CERN ATLAS

    Fermilab CDF
    Fermilab CDF

    CERN CMS New
    CERN CMS

    Fermilab DZero
    Fermilab DZero

    Together the four experiments pooled their data analysis power to arrive at a new world’s best value for the mass of the top quark of 173.34 plus/minus 0.76 GeV/c2.

    Experiments at the LHC at the CERN laboratory in Geneva, Switzerland and the Tevatron collider at Fermilab near Chicago in Illinois, USA are the only ones that have ever seen top quarks—the heaviest elementary particles ever observed. The top quark’s huge mass (more than 100 times that of the proton) makes it one of the most important tools in the physicists’ quest to understand the nature of the universe.

    The new precise value of the top-quark mass will allow scientists to test further the mathematical framework that describes the quantum connections between the top quark, the Higgs particle and the carrier of the electroweak force, the W boson. Theorists will explore how the new, more precise value will change predictions regarding the stability of the Higgs field and its effects on the evolution of the universe. It will also allow scientists to look for inconsistencies in the Standard Model of particle physics – searching for hints of new physics that will lead to a better understanding of the nature of the universe.

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

    “The combining together of data from CERN and Fermilab to make a precision top quark mass result is a strong indication of its importance to understanding nature,” said Fermilab director Nigel Lockyer. “It’s a great example of the international collaboration in our field.”

    A total of more than six thousand scientists from more than 50 countries participate in the four experimental collaborations. The CDF and DZero experiments discovered the top quark in 1995, and the Tevatron produced about 300,000 top quark events during its 25-year lifetime, completed in 2011. Since it started collider physics operations in 2009, the LHC has produced close to 18 million events with top quarks, making it the world’s leading top quark factory.

    “Collaborative competition is the name of the game,” said CERN’s Director General Rolf Heuer. “Competition between experimental collaborations and labs spurs us on, but collaboration such as this underpins the global particle physics endeavour and is essential in advancing our knowledge of the universe we live in.”

    Each of the four collaborations previously released their individual top-quark mass measurements. Combining them together required close collaboration between the four experiments, understanding in detail each other’s techniques and uncertainties. Each experiment measured the top-quark mass using several different methods by analysing different top quark decay channels, using sophisticated analysis techniques developed and improved over more than 20 years of top quark research beginning at the Tevatron and continuing at the LHC.

    The joint measurement has been submitted to the electronic arXiv and is available at: http://arxiv.org/abs/1403.4427

    See the full article here.

    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics.


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  • richardmitnick 11:16 am on December 4, 2013 Permalink | Reply
    Tags: , , CERN ATLAS, , , , ,   

    From Berkeley Lab: “Latest from ATLAS: Higgs Boson Behaves Just the Way it Should” 


    Berkeley Lab

    December 04, 2013
    Paul Preuss paul_preuss@lbl.gov

    At a CERN seminar November 26th, Aliaksandr (Sasha) Pranko of the Physics Division at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) presented key direct evidence that the “Higgs-like” particle discovered at CERN last year does what a Higgs is supposed to do: it couples not only to other bosons but to fermions as well. Pranko is a member of Berkeley Lab’s contingent of the ATLAS Collaboration at the Large Hadron Collider.

    higgs
    One of the ATLAS candidate events in which the collision of two protons yields a Higgs boson, which subsequently decays to two tau leptons. (Image ATLAS Collaboration, CERN)

    Pranko reported the results of the ATLAS search for pairs of fermions – including quarks, constituents of hadrons such as protons, and leptons, particles in their own right such as electrons and neutrinos. The ATLAS search concentrated on finding pairs of bottom (b) quarks; pairs of muons, which are heavier “cousins” of the electron; and pairs of tau leptons, cousins of the electron that are heavier still.

    The b-quark and muon searches yielded no events in excess of the cluttered experimental background, but the search for pairs of tau particles yielded striking results, showing marked evidence at a high level of confidence that a Higgs boson can indeed decay to a pair of taus. This was the first evidence that the Higgs couples with leptons.

    “Since Higgs coupling should be dependent on particle mass, tau coupling should be much bigger than muon coupling,” says Ian Hinchliffe, who leads Berkeley Lab’s ATLAS contingent. “The ATLAS experiment has very high resolution in muons, but the expected signal is very small.” And detecting decay to a pair of taus is very complicated, due to the large backgrounds and the missing energy carried off by neutrinos from the tau decays.

    Hinchliffe credits Pranko with co-inventing the “Missing Mass Calculator” method of reconstructing particle masses, in particular those of tau pairs, and serving as co-leader of the group responsible for the ATLAS Collaboration’s analysis of the data that revealed the Higgs’s coupling to the tau lepton.

    The ATLAS results were based on the full data set with the LHC’s colliding beams running at 8 TeV (eight trillion electron volts) center-of-mass proton collisions during the last year of its run, before it recessed for maintenance. The LHC is now preparing for even higher energy runs beginning in 2015.

    At a CERN seminar on December 3rd, the CMS experiment showed its updated results, which confirm the ATLAS observation in the tau-tau final state.

    See the full article here.

    A U.S. Department of Energy National Laboratory Operated by the University of California

    University of California Seal

    DOE Seal


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  • richardmitnick 9:23 am on November 27, 2013 Permalink | Reply
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    From CERN: “ATLAS sees Higgs boson decay to fermions” 

    CERN New Masthead

    27 Nov 2013
    Sylvie Brunet, Abha Eli Phoboo

    The ATLAS experiment at CERN has released preliminary results that show evidence that the Higgs boson decays to two tau particles. Taus belong to a group of subatomic particles called the fermions, which make up matter. This result – measured at 4.1 sigma on the 5-point scale particle physicists use to determine the certainty of a result – is the first evidence for a Higgs decay to fermions.

    For physicists, the discovery meant the beginning of a quest to find out what the new particle was, if it fit in the Standard Model, our current model of nature in particle physics, or if its properties could point to new physics beyond that model. An important property of the Higgs boson that ATLAS physicists are trying to measure is how it decays.

    sm
    Standard Model

    exp
    Graphical representation of a Higgs boson decaying to two tau particles in the ATLAS detector. The taus decay into an electron (blue line) and a muon (red line) (Image: ATLAS)

    The Higgs boson lives only for a short time and disintegrates into other particles. The various possibilities of the final states are called decay modes. So far, ATLAS physicists had found evidence that the Higgs boson decays into different types of gauge bosons – the kind of elementary particles that carry forces. The other family of fundamental particles, the fermions, make up matter. The tau is a fermion and behaves like a very massive electron.

    The Brout-Englert-Higgs mechanism was first proposed to describe how gauge bosons acquire mass. But the Standard Model predicts that fermions also acquire mass in this manner, so the Higgs boson could decay directly to either bosons or fermions. The new preliminary result from ATLAS shows clear evidence that the Higgs boson indeed does decay to fermions, consistent with the rate predicted by the Standard Model.

    This important finding was made possible through careful analysis of data produced by the LHC during its first run. Only with new data will physicists be able to determine if the compatibility remains or if other new models become viable. Fortunately, the next LHC run, which begins in 2015, is expected to produce several times the existing data sample. In addition, the proton collisions will be at higher energies, producing Higgs bosons at higher rates.

    ATLAS’ broad physics programme, which includes precision measurements of the Higgs boson, will continue to test the Standard Model. The years ahead will be exciting for particle physics as – the LHC experiments have found new territory that they have only just begun to explore.

    For a detailed account see “Higgs into Fermions” by the ATLAS collaboration.

    See the full article here.

    Meet CERN in a variety of places:

    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New
    ALICE
    CERN ALICE New

    CMS
    CERN CMS New

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    CERN LHCb New

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    CERN LHC New

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