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  • richardmitnick 12:51 pm on July 7, 2016 Permalink | Reply
    Tags: , , , Particle Accelerators, , Testing calorimeters at CERN   

    From ILC: “Practi-Cal” 

    Linear Collider Collaboration header
    Linear Collider Collaboration

    7 July 2016
    No writer credit found

    1
    Testing, testing… calorimeters in the test beam at CERN.

    Better together: two technological prototypes of the high-granularity calorimeters for a future ILC detector have been tested together with particle beams at CERN in a combined mode. The Semi-Digital Hadronic CALorimeter (SDHCAL) prototype with its 48 layers and the Silicon Electromagnetic CALorimeter (SiECAL) with its 10 units, both part of the CALICE collaboration, spent two weeks taking data on the “H2” beam line at CERN’s SPS. The principal goal of this beam test was to validate their combined data acquisition (DAQ) system developed by the teams working on the two calorimeters. After the fixing of a few problems that appeared during the data taking, the DAQ system ran smoothly and both prototypes took common data. This is what they will have to do in the future to register electron-positron collisions at the ILC.

    Physicists and engineers from six countries participated in this beam test: Belgium, China, France, Japan, Korea and Spain. Future tests will focus on studying the common response of these two calorimeters to the different kinds of particles. “The success of this combined test will certainly encourage other detectors proposed for the tracking system (Silicon and TPC detectors) to join the adventure…,” Imad Laktineh, professor at IN2P3’s Institut de Physique Nucléaire de Lyon,who supervised the combined beam test, hopes.

    More about calorimeter test beams here and here.

    See the full article here .

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    The Linear Collider Collaboration is an organisation that brings the two most likely candidates, the Compact Linear Collider Study (CLIC) and the International Liner Collider (ILC), together under one roof. Headed by former LHC Project Manager Lyn Evans, it strives to coordinate the research and development work that is being done for accelerators and detectors around the world and to take the project linear collider to the next step: a decision that it will be built, and where.

    Some 2000 scientists – particle physicists, accelerator physicists, engineers – are involved in the ILC or in CLIC, and often in both projects. They work on state-of-the-art detector technologies, new acceleration techniques, the civil engineering aspect of building a straight tunnel of at least 30 kilometres in length, a reliable cost estimate and many more aspects that projects of this scale require. The Linear Collider Collaboration ensures that synergies between the two friendly competitors are used to the maximum.

    Linear Collider Colaboration Banner

     
  • richardmitnick 12:23 pm on June 28, 2016 Permalink | Reply
    Tags: , , MAX IV synchrotron, Particle Accelerators,   

    From CERN: “Vacuum chambers full of ideas for the Swedish synchrotron” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    CERN

    27 Jun 2016
    Corinne Pralavorio

    CERN’s Vacuum, Surfaces and Coatings group has contributed to the development of vacuum chambers for the MAX IV synchrotron, which has just been officially opened in Sweden.

    1
    A section of the new 3 GeV MAXIV synchrotron at the time of installation. In the centre of the magnets you can see the vacuum chamber developed in collaboration with CERN. (Photo: Marek Grabski, MAX IV Vacuum group)

    On 21 June, the King and the Prime Minister of Sweden officially opened MAX IV, a brand-new synchrotron in Lund, Sweden. The summer solstice, the longest day of the year, was deliberately chosen for the ceremony: MAX IV, a cutting-edge synchrotron, will deliver the brightest X-rays ever produced to more than 2000 users.

    Some 1500 kilometres away, a team at CERN followed the opening ceremony with a touch of pride. The Vacuum, Surfaces and Coatings group in the Technology department (TE-VSC) participated in the construction of this new synchrotron. Its contribution lies at the very heart of the accelerator, in its vacuum chambers. The group developed the coating for most of the vacuum chambers in the larger of the two rings, which has a circumference of 528 metres and operates at an energy of 3 GeV.

    The CERN group was brought in to develop the coating for the vacuum chambers using NEG (Non-Evaporable Getter) material. A thin, micrometric layer of NEG ensures a high-grade vacuum: it traps residual gas molecules and limits the release of molecules generated by the bombardment of photons. The technology was developed at CERN in the late 1990s for the LHC: six kilometres of vacuum chambers in the LHC, i.e. those at ambient temperature, are coated with NEG material. CERN’s expertise in the field is therefore unique and recognised worldwide.

    2
    Prototype of the surface treatment process, developed at CERN, to coat the vacuum chambers of the MAX IV synchrotron. (Photo: Pedro Costa Pinto/CERN)

    “The MAX IV design was very demanding, as the cross-section of the vacuum chambers is very small, just 2.4 centimetres compared to 8 cm at the LHC,” explains Paolo Chiggiato, TE-VSC group leader. “In addition, some parts were geometrically complex.” Synchrotron light is extracted to experimental areas every 26 metres. At the extraction point, the chamber comprises two tubes that gradually diverge.

    The CERN group began its involvement in the project in 2014 and developed the chemical surface treatment method used for almost all the vacuum chambers in the large ring of MAX IV. Treatment of the cylindrically symmetrical vacuum chambers was carried out by a European firm and a European institute, to which CERN had already transferred the technology in the past. The most complex chambers, around 120 in total, were treated at CERN. Two benches for sputtering, the coating technique used, were developed at CERN. “These benches are equipped with a wire whose material is deposited onto the surface of the chamber. For the MAX IV chambers, the wire had a diameter of 0.5 millimetres and its alignment was critical,” explains Mauro Taborelli, leader of the Surfaces, Chemistry and Coatings section in the TE-VSC group. “The procedure was all the more complicated because the extraction chambers, in which the photons are extracted, have a tiny vertical aperture, of around 1 millimetre,” confirms Pedro Costa Pinto, leader of the team responsible for the vacuum deposition process.

    The vacuum chambers were delivered in 2014 and 2015. “It’s essential for us to participate in these types of project, which require lots of ingenuity, to be able to maintain and build on our know-how,” says Paolo Chiggiato. “By developing our expertise in this way, we will be ready for new projects at CERN.”

    See the full article here.

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    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

    LHCb
    CERN LHCb New II

    LHC

    CERN LHC Map
    CERN LHC Grand Tunnel

    CERN LHC particles

    Quantum Diaries

     
  • richardmitnick 11:51 am on June 15, 2016 Permalink | Reply
    Tags: , , , BNL sPHENIX, , Particle Accelerators, ,   

    From BNL: “Introducing…sPHENIX!” 

    Brookhaven Lab

    June 15, 2016
    Karen McNulty Walsh

    1
    Members of the new sPHENIX collaboration at a meeting held at Brookhaven Lab in May 2016, with co-spokespersons Dave Morrison (green T-shirt, jeans) and Gunther Roland (blue shirt, black jeans) front and center.

    From the very beginning, there were hints that particle collisions at the Relativistic Heavy Ion Collider (RHIC) were producing something unusual. This U.S. Department of Energy (DOE) Office of Science User Facility at Brookhaven National Laboratory was designed to recreate the incredibly hot and dense conditions of matter in the early universe by colliding atomic nuclei at high enough energies to “melt” their constituent protons and neutrons. The collisions would “free” those particles’ inner building blocks—quarks and gluons—so nuclear physicists could study their behavior unbound from ordinary matter.

    Results from RHIC show that these particle smashups have indeed created a superhot primordial soup called “quark-gluon plasma” (QGP)—but one in which the quarks and gluons, though liberated from their protons and neutrons, continue to interact strongly. These strong interactions make the plasma flow like a nearly “perfect” liquid.

    RHIC’s discovery of the perfect liquid set off a decade-long and very successful effort to characterize its remarkable properties—both at RHIC and at Europe’s Large Hadron Collider (LHC), where physicists conduct complementary studies of quark-gluon plasma for a few weeks of each year. But understanding exactly how the QGP’s perfect fluidity and other collective properties emerge from its point-like constituent particles remains a compelling mystery.

    To address that mystery, a group of nuclear physicists has formed a new scientific collaboration that will expand on discoveries made by RHIC’s existing STAR and PHENIX research groups. This new collaboration, made up of veterans of the field and researchers just beginning their careers, has precise ideas about the measurements its members would like to make—and hopes of upgrading the PHENIX detector to make those measurements at RHIC.

    “What remains to be done is to understand how the QGP’s properties arise or emerge from the underlying quark and gluon interactions,” said Massachusetts Institute of Technology physicist Gunther Roland, a longtime RHIC and LHC collaborator and now a co-spokesperson for the new collaboration..

    Brookhaven physicist Dave Morrison, the other co-spokesperson, agrees: “On the one hand we have a very successful theory that describes the quarks and gluons as free point-like particles. On the other hand, we have a whole set of measurements that describe the collective properties of the QGP. What we’d like to do is connect the two—the microscopic to the not-so-microscopic.”

    For now, the collaboration goes by the name sPHENIX: “s” for its focus on the strongly interacting particles and PHENIX for the anticipated use of key detector components and that experiment’s location in the RHIC ring once the existing PHENIX systems complete their data-taking lifetime at the end of this year’s run. But the collaboration leaders emphasize that there’s no need for members to be previously affiliated with PHENIX—or indeed with prior research at RHIC.

    “This is a new collaboration, and, if we get the go-ahead for this upgrade, this detector will have brand new capabilities,” Morrison said.

    2
    A schematic of the proposed sPHENIX detector, showing several key components: outer and inner hadronic calorimeters (HCal), electromagnetic (EM) calorimeter, tracking systems, and coils of the superconducting solenoid magnet

    BNL/RHIC Phenix

    BNL/ Phenix
    BNL/ Phenix another view

    Tracking probes from within the plasma

    Figuring out how the QGP’s properties emerge from its smallest particles requires a detector that can make more—and more precise—measurements of what’s going on in the plasma at different length scales.

    “Think about looking at a pond that behaves like a liquid,” Morrison explained. “You might see waves and flowing water. If you had a microscope that could dial down, at some point you would see water molecules—the particles that make up the water. If you know a lot about those particles and how they behave, you can try to understand how the properties of the pond arise from the properties of the molecules. That’s what we’d like to do with the QGP.”

    Particle detectors are the microscopes nuclear physicists use to dive down into the details of subatomic matter. But instead of shining visible light, electrons, or x-rays on the sample, particle detectors pick up signals from particles created within the collisions. Measuring how these particles move through and lose energy by interacting with the plasma will reveal information about the QGP at scales between the level of individual quarks and the long-scale collective behavior.

    “There has to be an evolution from the short-wavelength behavior to the long-wavelength behavior, and we want to probe that transition,” Roland said.

    Fast detector for precision measurements

    One set of particles sPHENIX physicists are interested in tracking are upsilons—each made of two heavy quarks bound together. Each different bound state has a different mass. The sPHENIX scientists want to understand how upsilons with different masses form and disassociate and otherwise interact with the plasma.

    They’re also interested in analyzing collimated streams of particles called jets—created as the energy of individual fast-moving quarks and gluons is transformed into a cascade of new particles. Measuring how much energy is lost by higher- and lower-energy jets will convey information about both the individual particle scale deep within the plasma and its long-range characteristics.

    “The higher the momentum, the more rarely it is produced. So you need a very fast detector that can capture a lot of collisions to increase the chances of spotting these important events,” Roland said.

    By removing outdated components from PHENIX and replacing them with new, custom-designed systems, the sPHENIX collaboration would transform that experiment into a “new” state-of-the-art detector that can capture as many as 15,000 events per second—a significant increase over STAR’s current capture rate of 2,000 events per second, or PHENIX’s 5,000—with all the components needed to differentiate among the three mass states of upsilons and tease apart the full energy scale of jets.

    “This transformed detector would be suited to record a huge fraction of what RHIC can produce,” Morrison said.

    Testing essential detector components

    Physicists and engineers at Brookhaven and elsewhere have already begun building prototypes and testing components that could be used to achieve the anticipated transformation. And this endeavor is attracting a new generation of physicists eager to get in on the ground floor of a new experiment.

    “I worked on PHENIX as grad student at Stony Brook University. Then, as a postdoc at Yale, I worked on the ALICE experiment at the LHC,” said Megan Connors, a RIKEN-BNL Research Center Fellow at Brookhaven Lab who will begin teaching and forming her own research group at Georgia State University next year. “When I came on the scene, both colliders were already up and running. So this is a chance to be involved from the start—to see how these experiments come to life, to be part of the formation of the collaboration and get involved in building the hardware in addition to analyzing the data.”

    3
    Megan Connors and Anne Sickles checking out calorimeter components at Brookhaven Lab.

    The piece of hardware that currently has her attention is a prototype “calorimeter” that would track and reconstruct the sprays of particles that make up jets, which recently underwent extensive testing at Fermi National Accelerator Laboratory.

    “A typical jet may contain 10 or 15 particles, but you need to tease those out from the hundreds of particles coming out of a heavy ion collision event,” Connors said. “And you need to capture all the particles to be able to reconstruct the jet and see how much energy it loses as it travels through the plasma.”

    You also need to know how much energy the jet had to start with. Most of the time jets are formed in back-to-back pairs. Both jets lose energy in the plasma. However sometimes, instead, a particle of light called a photon gets produced back-to-back with a jet. But unlike the jet particles, the photon shooting off in the opposite direction does not interact with the quarks and gluons in the plasma, so it doesn’t lose any energy.

    “If you have a photon going one way, and a jet going the other way, the jet and the photon had the same starting energy,” explained Anne Sickles, an sPHENIX collaborator from the University of Illinois at Urbana-Champaign who was also involved in the calorimeter design and testing. “So measuring the photon’s energy gives you the starting point. Measuring the particles that make up the jet and subtracting from the photon energy tells you how much energy the jet lost.”

    Using Fermilab’s Test Beam Facility, Sickles and some of her students shot a beam of electrons through portions of an “electromagnetic” calorimeter they designed to track photons and some of the other particles that make up jets. For the initial tests, the electrons—pure electromagnetic particles like photons—served as stand-ins for the photons. The aim of the tests was to be sure all areas of the detector respond in a similar way, and that there’s no variation between pieces built by Sickles and her students in Illinois and pieces constructed by an outside contractor.

    Next, the physicists added components of a “hadronic” calorimeter for tracking hadrons (particles made of more than one quark), which Connors and her team had been working on. They placed the hadron detectors directly behind the electromagnetic calorimeter—just as the two components will be arranged in the actual detector. This outer layer is designed to catch the larger hadron particles that make it through the first layer so physicists can account for the full energy of each jet.

    Building the calorimeter thick enough to “catch” all the particles is one way that the design of sPHENIX benefits from the 16 years of operating RHIC and several years experience at LHC.

    “Before RHIC was built, we didn’t even know how many particles would be produced. We had to build the detectors to cover a wide range of possibilities,” Morrison said. “Now, knowing what the collisions look like and the kinds of particles produced, we can build a detector tailored to do the measurements that are focused on the specific important questions we’d like to answer.”

    Mighty magnet

    Testing is also underway on a 20-ton solenoid magnet acquired from a former physics experiment at DOE’s SLAC National Accelerator Laboratory. This magnet would form the heart of the sPHENIX detector, completely surrounding the collision zone like the cylindrical magnet at the center of RHIC’s STAR detector. Like STAR’s, the sPHENIX magnet would bend the trajectories of charged particles as they emerge from the collisions. But with three times the bending power of STAR, sPHENIX should be able to separate out the signals from the three types of upsilon particles, whose masses differ by only a few percent.

    “Upsilons don’t make it all the way to the magnet,” Morrison explained. “These are heavy particles that decay, often into an electron and an antielectron, which have a lot of energy when they come out. You need a powerful magnetic field to bend these charged particles so you can get a better measurement of their velocity and momentum, and tease out small differences to separate the electrons that come from the different-size upsilons.”

    So far, a team of engineers and physicists in Brookhaven’s Superconducting Magnet Division, Collider-Accelerator Department, and Physics Department has cooled the superconducting magnet down to its near-absolute-zero operating temperature of 4.2 Kelvin and tested it with 100 amperes of current.

    “We needed to test the overall health and integrity of the magnet to make sure all the joints and couplings are in place, in case they got jostled while being transported cross-country,” said lead magnet engineer Piyush Joshi. They also tested systems Joshi designed to shut the magnet down in a controlled manner if the field between the magnet’s two layers of coils ever gets out of balance. “You want to detect any imbalance very quickly so you can extract the energy before it causes any damage to the magnet,” he said. He originally wrote the algorithms for an LHC magnet project, but they proved to be just as useful for the sPHENIX tests.

    With the initial, low-field tests complete, the group will next use steel recycled from another older experiment at Brookhaven to surround the magnet to contain its most powerful field—and ramp it up to a full 4,600 amps.

    5
    Engineers and physicists involved in testing the 20-ton superconducting solenoid expected to form the heart of the sPHENIX upgrade: Kin Yip, Collider-Accelerator Department (CAD); Piyush Joshi, Superconducting Magnet Division (SMD); Richard Meier, CAD cryo group; Brian Van Kuik, CAD main control room operations coordinator; Ray Ceruti, SMD; Sonny Dimaiuta, SMD; Dominick Milidantri, SMD.

    Path forward

    By reusing equipment and tools developed with funding for RHIC and the LHC, and inspiring university collaborators to chip in their expertise, the nascent collaboration has taken these early steps on the path toward transforming PHENIX into sPHENIX. But the team hopes to get an official seal of approval—and, eventually, a budget—from DOE.

    The 2015 Long Range Plan for Nuclear Science—a set of recommendations made by the nation’s Nuclear Science Advisory Committee to leaders at DOE and the National Science Foundation—identifies the sPHENIX “state-of-the-art jet detector” as “essential” to probing the inner workings of QGP at shorter and shorter length scales, one of two “central goals” noted in the report for completing the scientific mission at RHIC. The report also notes that there is significant international interest in sPHENIX.

    “Right now we have a collaboration of 183 people, and growing,” Morrison said, with those scientists representing 58 institutions in 10 countries.

    Looking ahead and continuing the tradition of making the most of our nation’s investments in science, the physicists designing the sPHENIX upgrades say this transformed detector could largely be reused as a detector for a future Electron Ion Collider—the next priority nuclear physics project identified in the Long Range Plan.

    “Transforming PHENIX into sPHENIX would maximize the benefits derived from the investments already made to build RHIC by allowing us to fully understand the quark-gluon plasma,” Morrison said. “It’s what we need to do to complete the story of QGP discovery and to prepare for the coming research directions in nuclear physics.”

    sPHENIX R&D is supported by the DOE Office of Science and also by Brookhaven Lab’s Laboratory Directed Research and Development program, BNL Program Development, and in-kind contributions from collaborating universities.

    See the full article here .

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    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.
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  • richardmitnick 5:25 pm on June 14, 2016 Permalink | Reply
    Tags: , , , , Particle Accelerators, , SuperKEKB detector   

    From CMU: “CMU Researchers Aid in Japan’s Search for Anti-matter 

    Carnegie Mellon University logo
    Carnegie Mellon University

    June 13, 2016
    Jocelyn Duffy,
    jhduffy@andrew.cmu.edu

    1
    View of the SuperKEKB collision point in late 2015. The accelerator beam line is now covered with a concrete shield. The Belle II detector can be seen in the background.

    The hunt to solve an anti-matter mystery may have new clues, thanks to an upgrade of the SuperKEKB, an electron-positron colliding accelerator at the High Energy Accelerator Research Organization (KEK) in Japan.

    SuperKEKB accelerator Japan
    SuperKEKB accelerator Japan

    Test operations started earlier this year, and Carnegie Mellon University Physics Professor Roy Briere has been a member of KEK’s Belle II collaboration since 2013.

    When fully operational, the rate of collisions produced by SuperKEKB will be several tens of times larger than that of its predecessor, KEKB.

    “By producing collisions with much higher intensity, we hope to accumulate 50 times more data. And that means our measurements are going to be very precise,” Briere said.

    Scientists will use the collision data to pursue the mystery of the disappearance of anti-matter during the early, developmental processes of the universe, and to discover and clarify new physical laws that go beyond the Standard Model of particle physics.

    “When you have 50 times the data, you can test things much more accurately and try to find the little chink in the Standard Model’s armor, so to speak,” Briere said.

    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.
    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.

    The Belle II collaboration, named after the collider’s detector, is an international research organization hosted by KEK’s Institute of Particle and Nuclear Studies. The group is assembling the Belle II detector, which will gather data at the point where the beams of electrons and positrons smash into each other. Briere and postdoctoral researcher Jake Bennett are working on the software infrastructure needed to calibrate one portion of the massive detector.

    While SuperKEKB and Belle II physicists continue to optimize the collider and the detector, Briere also is working with members of the collaboration to anticipate what they may see when the collider records its first collisions and how to plan their analyses accordingly. Briere assisted Professor Vladimir Savinov and colleagues at the University of Pittsburgh in organizing a conference in May, which brought together theorists and experimentalists for workshops on this topic.

    Briere also is a member of the BESIII experiment at the BEPCII collider in Beijing, and was a member and former co-spokesperson for the CLEO detector collaboration at Cornell University.

    See the full article here .

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    Carnegie Mellon University (CMU) is a global research university with more than 12,000 students, 95,000 alumni, and 5,000 faculty and staff.
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  • richardmitnick 10:55 am on June 14, 2016 Permalink | Reply
    Tags: , , , Particle Accelerators, , Stacking the building blocks of the 2016 ATLAS Physics Programme   

    From ATLAS at CERN: “Stacking the building blocks of the 2016 ATLAS Physics Programme” 

    CERN ATLAS Higgs Event

    CERN/ATLAS
    ATLAS

    13th June 2016
    ATLAS Collaboration

    1
    Figure 1: The increase in the number of reconstructed vertices showing an improvement in the reconstruction algorithms for the 2016 data.

    2016 is set to be an outstanding year for the ATLAS experiment and the Large Hadron Collider (LHC). We’re expecting up to 10 times more data compared to 2015, which will allow us to make precise measurements of many known physics processes and to search for new physics.

    Many exotic and unusual particles decay almost immediately after being produced. Therefore, what is actually measured is a set of fundamental building blocks including electrons, muons, taus and other charged particles, as well as jets (collimated sprays of hadrons), b-jets (jets containing bottom quarks) and undetected missing energy. These are all reconstructed from the information recorded in the detectors using sophisticated software algorithms. Thus the quality of our physics results depends on how accurately and efficiently we can measure these building blocks.

    2
    Figure 2: The mass of the Z boson reconstructed from pairs of electrons. Good agreement is observed in the mass between the data from 2015 and 2016.

    ATLAS scientists have used the recent LHC downtime to improve the performance of the reconstruction algorithms. Figure 1 shows the increase in the number of reconstructed primary vertices, due to an improvement in the reconstruction algorithm. Primary vertices are reconstructed from the charged tracks and indicate the number of interactions (or collisions) between pairs of protons. The average number of interactions in this dataset is 15.

    Reconstruction algorithms need to be tuned and evaluated using data. Well-known particles provide an essential component of detector calibration, using their mass as a known reference. Figure 2 shows the mass of the Z boson reconstructed from an electron and an anti-electron. Electrons are reconstructed using the energy measured in the calorimeter and the momentum of the track in the inner detector. There is good agreement between the data taken in 2015 and 2016, which demonstrates that the quality of the detector and the reconstruction algorithms is already very high.

    3
    Figure 3: The b-tagging discriminant used to distinguish b-jets from jets containing charm and other light flavours. Good performance is observed with agreement within uncertainties between the data and the simulated data.

    The ability to identify jets containing b-quarks is critical for identifying the signatures of specific particles such as top quarks, Higgs boson and other more exotic particles. These b-jets are reconstructed using multivariate algorithms, which exploit techniques from machine learning to identify the characteristics of b-jets compared to other jets. These algorithms are trained using simulated data, and the output is a discriminating variable with the signal having high values and the background having low values. Figure 3 shows the output of this algorithm and the components from the different flavours of jets are indicated with different colours. The signal from the b-jets is very well separated from the background, which demonstrates that the algorithm is performing with high efficiency.

    These excellent results from the early 2016 data show that ATLAS is performing very well. We look forward to exciting results to come!

    Links

    First 2016 vertex reconstruction in data and comparison between 2015 and 2016 software release (Figure 1): https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PLOTS/IDTR-2016-003/
    Reconstructed invariant mass of Z->ee candidates in early 2016 and 2015 data (Figure 2): https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PLOTS/EGAM-2016-001/
    b-tagging performance plots in a ttbar-dominated sample from early 2016 ATLAS data (Figure 3): http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PLOTS/FTAG-2016-001/

    See the full article here .

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

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  • richardmitnick 9:43 am on June 6, 2016 Permalink | Reply
    Tags: , , , , Particle Accelerators,   

    From FNAL: “Exclusive production: shedding light with grazing protons” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

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

    June 3, 2016
    Bo Jayatilaka

    1
    When two protons approaching each other pass close enough together, they can “feel” each other, similar to the way that two magnets can be drawn closely together without necessarily sticking together. According to the Standard Model, at this grazing distance, the protons can produce a pair of W bosons. No image credit.

    As its name implies, the primary mission of the Large Hadron Collider is to generate collisions of protons for study by physicists at experiments such as CMS.

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

    CERN/CMS Detector
    CERN/CMS Detector

    It may surprise you to find out that the vast majority of protons accelerated by the LHC never collide with one another. Some of these fly-by protons, however, still interact with each other in such a way as to help physicists shed light on the nature of the universe.

    The LHC accelerates bunches of protons, with more than 10 billion protons in each bunch, in opposite directions around the ring. As those protons arrive at a detector, such as CMS, magnets focus the beams to increase the density of protons and thus increase the chance of a coveted collision. Despite what seems like overwhelming odds, only a few of these protons actually collide with each other: tens to hundreds per each beam “crossing.” An even smaller fraction of the remaining protons pass close enough to other protons to “feel” each other, even if they do not directly collide.

    Think of two toy magnets on a tabletop: A north end and a south end moved close enough to each other will rather firmly stick to each other. However, you can also move one magnet just close enough to the other that you can make it wiggle without drawing it all the way over. This exchange of energy is mediated by the exchange of photons, the carrier particle of the electromagnetic force. Similarly, two protons in the LHC that get just the right distance from each other will exchange photons without colliding.

    Now for the part that gets really interesting to particle physicists. The photons generated by these near-miss proton interactions can be billions of times more energetic than those of visible light, and as a result they carry enough energy to create particles in their own right. The Standard Model predicts the production of massive particles, such as pairs of W bosons, from these interacting photons without any of the additional activity that is seen in the messier proton-proton collision events.

    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.
    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.

    In a detector such as CMS, this pair of W bosons is said to be produced “exclusively.” However, “exclusive production” is an apt name in another way – creating a pair of W bosons from interacting photons is a rare occurrence in an even rarer sample of photons generated from near-miss proton interactions.

    CMS scientists performed such a search for such W boson pairs emanating from interacting photons. In a data set consisting of 7- and 8-TeV collisions, 15 candidate events for this process were observed. While it may not seem like much, the expected background was considerably smaller, allowing the CMS team to claim that they have evidence of the process. (In the particle physics world, evidence is a three-standard-deviation departure from background, as explained here). Furthermore, these results helped place stringent results on a number of models which predict a greater rate of this process.

    See the full article here .

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    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

     
  • richardmitnick 7:31 am on June 5, 2016 Permalink | Reply
    Tags: , , , Particle Accelerators, , , Poles and masses at the Tevatron   

    From FNAL: “Poles and masses” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

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

    June 2, 2016
    Leo Bellantoni

    3
    From top left to bottom right: Andreas Jung (Fermilab, now at Purdue University), Jiri Franc (Czech Technical University, Prague, Czech Republic), Slava Shary and Frederic Deloit (CEA Irfu SPP, Saclay, France), Yegor Aushev and Mykola Savitskyi (Taras Shevchenko National University, Kiev, Ukraine) and Michal Stepanek (Czech Technical University, Prague, Czech Republic) are the primary analysts for this measurement.

    1
    This is the Feynman diagram for a quark-antiquark pair on the left combining to form a gluon (marked g), which breaks into a top and antitop that decay on the right. As described in the text, it is possible from the diagram to calculate the rate at which this type of event occurs.

    The figure [above], called a Feynman diagram, shows a quark and an antiquark on the left merging to form a gluon; then the gluon turns into a top quark and a top antiquark, each of which decays into some other particles on the right. In a very simple and intuitive way, this depicts a certain type of event that was measured in the Tevatron.

    FNAL/Tevatron map
    FNAL/Tevatron tunnel
    FNAL/Tevatron DZero detector
    FNAL/Tevatron CDF detector
    Tevatron map; Tevatron tunnel; DZero; CDF

    But the diagram also is a symbol for a number. You see, this whole process is quantum mechanical; one can only give a probability for that type of event to happen. The really nifty thing about the diagram is that it is a shorthand code for how to compute that probability. From the diagram, using a table for decoding it, you can write down the mathematical expression that gives you the probability.

    In this particular case, for the gluon you write down igαβ/ (p2 + ie) or some such thing; I won’t go into the definitions of g and p and such, but the point is that this is in the end some specific number. And you will multiply this by some other numbers for the initial quarks and for the antiquark, and for the top quark and so on. The resulting product will tell you how frequently this type of event occurs.

    The number that you write for the top quark depends on the mass of the top quark. You might think then, “Oh, go measure the mass, and then you know that number.”

    Unfortunately, subatomic particle physics isn’t that simple. Top quarks, or indeed, any quarks, exist only in a sea of other particles that wink in and out of existence. They aren’t part of the top quark, but they can’t be separated from it, either. Should they be counted as contributing to the mass of the top? The mass that is usually measured in collider experiments is different still, since it comes from measuring what the top quark decays into. It’s called the MC mass, and it isn’t necessarily the same as what we want for the number that goes with the diagram. After all, the number that goes with the diagram (called the pole mass) is involved in how often the event occurs, not what comes out of it.

    So there is this long-standing theoretical question: How does the MC mass relate to, say, the pole mass? Y’know, clearly they are related, but how, exactly?

    Here comes the trick: Measure the pole mass directly. We can do this by measuring how often the event occurs and knowing all the other numbers that you read off the diagram. Then you know the number for the top quark and therefore you know the pole mass. The result isn’t as precise as measuring what the top quark decays into and figuring the MC mass, but at least you know the number that goes with the diagram.

    Recently, DZero measured the rate at which top-antitop pairs were created in the Tevatron; specifically, we measured the production cross section with a refined strategy to improve the accuracy of the measurement. The result is picobarns. From that, we then went and obtained the pole mass of the top quark. The result, GeV, is the most precise determination of the top quark’s pole mass at the Tevatron. Despite the lower precision than the MC mass taken from the decay products, it is a more powerful measure of the top quark’s role in the world.

    See the full article here .

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    Fermilab Campus

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.

     
  • richardmitnick 3:34 pm on May 22, 2016 Permalink | Reply
    Tags: , , , , , Particle Accelerators,   

    From HuffPost: “Meet The Most Powerful Woman In Particle Physics” Women in Science 

    Huffington Post
    The Huffington Post

    05/18/2016
    David Freeman

    1
    Fabiola Gianotti, CERN’s new director-general. Christian Beutler

    Fabiola Gianotti isn’t new to CERN, the Geneva, Switzerland-based research organization that operates the Large Hadron Collider (LHC), the world’s biggest particle collider.

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

    In fact, the Italian particle physicist was among the CERN scientists who made history in 2012 with the discovery of the Higgs boson.

    CERN CMS Higgs Event
    CERN CMS Higgs Event

    CERN/CMS Detector
    CERN/CMS Detector

    But now Gianotti isn’t just working at CERN. As the organization’s new director-general — the first woman ever to hold the position — she’s running the show. And though expanding our knowledge of the subatomic realm remains her main focus, she’s acutely aware that she is now a high-visibility role model for women around the world.

    “Physics is widely regarding as a male-dominated field, and it’s true that there are more men in our community than women,” Gianotti told The Huffington Post in an email. “So I am glad if in my new role I can contribute to encourage young women to undertake a job in scientific research with the certitude that they have the same opportunities as men.”

    Recently, HuffPost Science posed a few questions to Gianotti via email. Here, lightly edited, are her answers.

    How will things be different for you in your new role?

    My new role is very interesting and stimulating, and I feel very honored to have been offered it. The range of issues I have to deal with is much broader than before and includes scientific strategy and planning, budget, personnel aspects, relations with a large variety of stakeholders, etc. Days are long and full, and I am learning many new things. And there is nothing more enriching and gratifying than learning.

    What’s a typical day like for you?

    Super-hectic, super-speedy and … atypical!

    What do you think explains the gender gap in science generally and in physics particularly?

    There are many factors. There’s no difference in ability between men and women, that’s for sure. And in my experience, the more diverse a team is, the stronger it is. There is the baggage of history, of course, which takes a long time to overcome. There is the question of the lack of role models, and there is the question of making workplaces more family friendly. We need to enable parents, men or women, to take breaks to raise families and we need to support parents with infrastructure and facilities.

    2
    The Large Hadron Collider, Geneva, Switzerland.

    Your term as CERN’s director-general is scheduled to last five years. What are your goals for CERN during this period?

    The second run of the LHC is the top priority for CERN in the coming years. We got off to a very good start in 2015, and have three years of data-taking ahead of us before we go into the accelerator’s second long shutdown. The experiments are expected to record at least three times more data than in Run 1 at an energy almost twice as large. It will be a long time before another such step in energy will be made in the future.

    So, the coming years are going to be an exciting period for high-energy physics. But CERN is not just the LHC. We have a variety of experiments and facilities, including precise measurements of rare decays and detailed studies of antimatter, to mention just a couple of them. In parallel with the ongoing program, we will be working to ensure a healthy long-term future for CERN, at first with the high-luminosity LHC upgrade scheduled to come on stream in the middle of the next decade, and also through a range of design studies looking at the post-LHC era — from 2035 onwards.

    CERN HL-LHC bloc

    What discoveries can we reasonably expect from CERN during your term?

    I’m afraid that I don’t have a crystal ball to hand. There will be a wealth of excellent physics results from the LHC Run 2 and from other CERN experiments. We’ll certainly get to know the Higgs boson much better and expand our exploration of physics beyond the Standard Model.

    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.
    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.

    Whether we find any hints of the new physics everyone is so eagerly waiting for, however, I don’t know. We know there’s new physics to be found. Good as it is, the Standard Model explains only the 5 percent of the universe that is visible. There are so many exciting questions still waiting to be answered.

    What are the biggest opportunities at CERN? The biggest challenges?

    These two questions have a single answer. Over the coming years, the greatest opportunities and challenges, not only for CERN but for the global particle physics community as a whole, come from the changing nature of the field. Collaboration between regions is growing. CERN recently signed a set of agreements with the U.S. outlining U.S. participation in the upgrade of the LHC and CERN participation in neutrino projects at Fermilab in the U.S.

    FNAL LBNF/DUNE
    FNAL LBNF/DUNE

    There are also emerging players in the field, notably China, whose scientific community has expressed ambitious goals for a potential future facility. All this represents a great opportunity for particle physics. The challenge for all of us in the field is to advance in a globally coordinated manner, so as to be able to carry out as many exciting and complementary projects as possible.

    Were you always interested in being a scientist? If you couldn’t be a scientist, what would you be/do?

    I was always interested in science, and I was always interested in music. I pursued both for as long as I could, but when the time came to make a choice, I chose science. I suppose that as a professional physicist, it is still possible to enjoy music — I still play the piano from time to time. But as a professional musician, it would be harder to engage in science.

    What do you do in your spare time?

    I spend my little spare time with family and friends. I do some sport, I listen to music, I read.

    What do you think is the biggest misconception nonscientists have about particle physics?

    That it’s hard to understand! Of course, if you want to be a particle physicist, you have to master the language of mathematics and be trained to quite a high level. But if you want to understand the field conceptually, it’s almost child’s play. All children are natural scientists. They are curious, and they want to take things apart to see how they work.

    Particle physics is just like that. We study the fundamental building blocks of matter from which everything is made, and the forces at work between them. And the equations that describe the building blocks and their interactions are simple and elegant. They can be written on a small piece of paper.

    See the full article here .

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  • richardmitnick 8:28 am on May 22, 2016 Permalink | Reply
    Tags: , , , , , Particle Accelerators,   

    From livescience: “LHC [Particle] Smasher Opens Quantum Physics Floodgates” 

    Livescience

    May 20, 2016
    Ian O’Neill, Discovery News

    1
    A display of a proton-proton collision taken in the LHCb detector in the early hours of May 9.
    Credit: CERN/LHCB

    CERN/LHCb
    CERN/LHCb

    A display of a proton-proton collision taken in the LHCb detector in the early hours of May 9. Credit: CERN/LHCb

    The Large Hadron Collider is the most complex machine ever built by humankind and it is probing into deep quantum unknown, revealing never-before-seen detail in the matter and forces that underpin the foundations of our universe.

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

    In its most basic sense, the LHC is a time machine; with each relativistic proton-on-proton collision, the particle accelerator is revealing energy densities and states of matter that haven’t existed in our universe since the moment after the Big Bang, nearly 14 billion years ago.

    The collider, which is managed by the European Organization for Nuclear Research (CERN) is located near Geneva, Switzerland.

    With the countless billions of collisions between ions inside the LHC’s detectors comes a firehose of data that needs to be recorded, deciphered and stored. Since the 27 kilometer (17 mile) circumference ring of supercooled electromagnets started smashing protons together once more after its winter break, LHC scientists are expecting a lot more data this year than what the experiment produced in 2015.

    “The LHC is running extremely well,” said CERN Director for Accelerators and Technology Frédérick Bordry in a statement. “We now have an ambitious goal for 2016, as we plan to deliver around six times more data than in 2015.”

    And this data will contain ever more detailed information about the elusive Higgs boson that was discovered in 2012 and possibly even details of “new” or “exotic” physics that physicists could spend decades trying to understand. Key to the LHC’s aims is to attempt to understand what dark matter is and why the universe is composed of matter and not antimatter.

    In fact, there was already a buzz surrounding an unexpected signal that was recorded in 2015 that could represent something amazing, but as is the mantra of any scientist: more data is needed. And it looks like LHC physicists are about to be flooded with the stuff.

    Central to the LHC’s recent upgrades is the sheer density of accelerated “beams” of protons that are accelerated to close to the speed of light. The more concentrated or focused the beams, the more collisions can be achieved. More collisions means more data and the more likelihood of revealing new and exciting things about our universe. This year, LHC engineers hope to magnetically squeeze the beams of protons when they collide inside the detectors, generating up to one billion proton collisions per second.

    Add these advances in extreme beam control with the fact the LHC will be running at a record-breaking collision energy of 13 TeV and we have the unprecedented opportunity to make some groundbreaking discoveries.

    “In 2015, we opened the doors to a completely new landscape with unprecedented energy. Now we can begin to explore this landscape in depth,” said CERN Director for Research and Computing, Eckhard Elsen.

    The current plan is to continue proton-proton collisions for six months and then carry out a four-week run using much heavier lead ions.

    So the message is clear: Hold onto your hats. We’re in for an incredible year of discovery that could confirm or deny certain models of our universe and revel something completely unexpected and, possibly, something very exotic.

    See the full article here .

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  • richardmitnick 9:07 am on May 14, 2016 Permalink | Reply
    Tags: , Boston U, Boston U Bump Hunters, , , Particle Accelerators, ,   

    From BU: “Bump Hunters” 

    Boston University Bloc

    Boston University

    5.14.16
    Elizabeth Dougherty

    Boston U Bump Hunters Steve Ahlen, Kenneth Lane, Tulika Bose, Kevin Black, Sheldon Glashow
    Bump Hunters Steve Ahlen, Kenneth Lane, Tulika Bose, Kevin Black, Sheldon Glashow

    Tulika Bose stands guard over the printer.

    She’s carried her laptop down the hall and submitted her print job on arrival to be certain that she will intercept her papers before anyone else has a chance to see them. Her documents contain secrets.

    Bose is a physicist working at the Large Hadron Collider (LHC) in Switzerland.

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

    Her work has nothing to do with weapons or national defense or space exploration or any of the usual top-secret stuff physicists work on. What her files contain are ideas about what we—everything under the sun and beyond it—are made of. Her documents could contain the secrets of the universe.


    Access mp4 video here .
    When Protons Collide: A proton collision is like a car accident—except when it isn’t. Physicist Kevin Black explains why. (Watch out for the kitchen sink!) Video by Joe Chan

    An associate professor of physics at Boston University, Bose is part of a cadre of physicists at BU committed to understanding matter down to its smallest particles and most intricate interactions. BU is unusual, one of only a small handful of US universities with researchers working on multiple experiments at the LHC.

    These experiments are looking for signs of particles that have never been seen before. The particles familiar from high school physics—electrons, protons, and neutrons—were just the beginning. Over the past several decades, physicists have confirmed that there are six kinds of quarks; three types of leptons; and assorted bosons, including photons, gluons, and the famed Higgs. These particles only exist in high-energy environments, such as the LHC, where protons are sent hurtling around a ring at speeds very close to the speed of light, colliding together spectacularly. All of the particles that are predicted to exist by the accepted theory of particle physics, called the Standard Model, have been found through experiments like those done at the LHC.

    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.
    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.

    2
    A theoretical physicist since the 1960s and a Nobel Laureate, Glashow came to BU in 2000 because of the physics department’s emphasis on experiments like those at the LHC. Photo by Gina Manning

    U also happens to have on its faculty Sheldon Glashow, a BU College of Arts & Sciences physics professor, who won the Nobel Prize in Physics in 1979 for his work developing the foundations of the Standard Model. Theorists like Glashow and Kenneth Lane, also a BU professor of physics, and experimental physicists like Bose have become masters of the Standard Model and are spending their careers trying to figure out one thing: Is there more to the universe than what we know right now?

    The answer, almost surely, is yes.

    When physicists look for new particles, they are really looking for “bumps” in the data produced by their experiments. A bump indicates that something appeared with energy or mass that was different than expected. “We call it ‘bump hunting,’” says Steve Ahlen, BU professor of physics, who represents yet another flavor of physicist. A hardware physicist, Ahlen has built muon detector chambers with his own hands and led their construction in Boston. Those built in Boston were auspiciously placed at the LHC and captured a good portion of the particles that allowed researchers to confirm the existence of the Higgs boson in 2012.

    The hunt is on, at a time like no other in physics. The quest reached a pinnacle with the Higgs boson, but finding it wasn’t the end. It was just the beginning.

    “Before the Higgs was discovered, people were absolutely convinced that it was there. The challenge was finding it,” says Glashow. “The trouble now is that we theorists don’t know what else is out there. We are no longer so confident that we know what to look for. But we hope that something interesting will show up.”

    On Colliders and Detectors

    The Large Hadron Collider is currently the world’s highest energy particle collider. It is also the largest machine ever built. The circular tunnel around which proton beams fly is 17 miles wide and buried 574 feet underground in a rural area on the border of France and Switzerland at the European Organization for Nuclear Research (CERN). The collider’s job is to smash particles together at high speeds and record the spray of shrapnel that results, so that physicists can look for signs of new particles. If they find something that looks interesting, they piece the data back together again, retracing the paths of all the particles in the spray back to the collision that caused them.

    “I think of it as if a murder has happened, and you have all these clues,” says Bose. “The detective comes in and uses all these clues to reconstruct the scene and figure out who committed the crime.”

    In 2015, the LHC operated at 13 tera-electron-volts (TeV), the highest energy level yet. One TeV is a trillion electron-volts, which sounds like a lot. It is, but it is small compared to the energy consumed by light bulbs and laptops and other things of daily life. A tera-electron-volt is approximately equal to the energy of a single flying mosquito. What the LHC does, beyond multiplying that energy by 13, is compress it into the space of a proton beam, a million million times smaller than a mosquito.

    At this energy level, the LHC can accelerate protons to speeds extremely close to the speed of light. Further, it bundles those protons, with each beam containing a thousand bunches of about a hundred billion protons per bunch. Packing far more punch than a mosquito, the total energy of a beam is more like a 17-ton plane flying over 460 miles per hour.

    In March 2016, the collider began running again, this time with more intense beams. This increased brightness will make for more collisions per second, so the LHC will produce approximately six times more data than in 2015. “We’re just beginning to tap its potential,” says Kevin Black, an associate professor of physics at BU, and also Bose’s husband. Bose and her students work on an experiment called CMS at LHC. Black works on a different experiment there called ATLAS.

    The CMS and ATLAS experiments are, at their core, two different pieces of hardware that detect particles.

    CERN/CMS Detector
    CERN CMS Higgs Event
    CERN/CMS and Higgs event at CMS

    CERN/ATLAS
    CERN ATLAS Higgs Event
    CERN/ATLAS andHiggs event at ATLAS

    They sit at opposite sides of the beam ring surrounding two separate beam intersections, where they capture all of the shrapnel from the proton-proton collisions that occur at their centers.

    The ATLAS detector, which Ahlen helped build, is a 75-foot-high, 140-foot-long machine in which five layers of detection hardware measure the momentum and mass of particles produced when protons smash together. CMS, for Compact Muon Solenoid, is considerably smaller and more dense. It captures the same types of particles as ATLAS, just in a different way.

    2
    A hands-on physicist, Ahlen likes to build things. He is currently building dark energy detectors and climbing mountains to install them on telescopes. Photo by Gina Manning

    These machines can detect all of the particles defined in the Standard Model. Take muons as an example. A muon is a tiny particle, even by the standards of particle physicists, that is produced inside colliders and also when cosmic rays strike the atmosphere. When Ahlen got involved with the development of detectors for particle colliders in the 1990s, it wasn’t clear how to detect muons affordably. He came up with a simple solution: A twelve-foot-long, two-inch-diameter aluminum tube, crimped at both ends and filled with gas, with a wire stretched under tension from end to end. “If you pressurize it, it can localize the trajectory of a particle that passes through the tube,” he says, waving around a spare tube he keeps behind the door in his office.

    The ATLAS detector, which has several layers of specialized particle detectors, contains about 500,000 of these tubes. They were built all over the world to exacting standards, many in Boston by Ahlen, who borrowed and bartered equipment and materials to get the job done.

    While the tubes themselves might not seem so special, keep in mind that each tube in the ATLAS detector must be precisely placed. “We know where each wire is to less than the width of a human hair,” says Ahlen.

    Not only that, every particle that whizzes by must be recorded, along with the exact time it flew through. So every tube and every other sensor in the detector—tens of millions of them in total—is connected to a clock. The clocks are set to the beam crossing, which occurs every 25 nanoseconds. The first crossing is one. “The second, two, the third, three,” says Ahlen. “Every 25 nanoseconds, boom, boom.”

    There were 40 million beam crossings per second, and about a billion proton-proton collisions per second, in the last run of the LHC.

    The time-stamped data flows from each detector down an electrical pipe to join with others in a raging river of data. Carefully coded computer algorithms determine which events to keep and which to throw away. Bose, who is the “trigger” in charge of this gatekeeping for CMS, saves only about a thousand events per second. A lot, but still just a tiny fraction of the data produced.

    Secret Keepers

    CMS and ATLAS produce and save independent sets of data and have independent teams analyzing it. Bose, for example, is one of nearly 4,000 people working on the CMS experiment, while Black is part of a team of 3,000 people working on ATLAS.

    The teams sift through their data in secret, without sharing early results. At a time when data sharing in science is all the rage, secrecy seems to go against the grain, but it is a necessity in physics. In the past, there have been cases where rumors about the early sightings of new particles lead to false discoveries. In one case, physicists started looking for signs of a new particle people were buzzing about. “Any run that had a little bump in the rumored location, they kept,” says Black. “Anything that didn’t, they found a reason to throw out the data. Inadvertently, they self-selected the particle into existence.” In the end, an unbiased look at the data proved that the particle did not exist.

    3
    For Black (PhD ’05), who is currently stationed at the LHC in Switzerland, patience is a virtue. The phenomena he studies occur so rarely that even with millions of collisions per second, he might not see them. Photo by Darrin Vanselow

    So experimentalists like Bose and Black try not to share data. In fact, they try extra hard, since the two are married. “We don’t talk about the details,” says Black. “I think we actually have more of a dividing line there because we are worried that if there is any leak, people might look to us first.”

    In practice, though, that line is a bit murky. The thousands of scientists at the LHC work side-by-side. The offices of scientists on different experiments are intermeshed. They share cafeterias and printers and hold open-door seminars to discuss ideas. Despite all this openness, no one wants to undermine the credibility of the science they are doing. “From a pure science point of view, the result is much stronger when two independent experiments come up with the same answer without biasing each other,” says Bose. “We try to keep an open mind. You look everywhere and you see what you see.”

    In the end, it isn’t just secrecy that keeps the science pure. Particle physicists have also set a very high bar for discovery. For a new particle to be accepted, scientists must be confident that it is not a statistical fluctuation. They’ve agreed on a number, 5-sigma, which means that the chance of the data being a statistical fluctuation is 1 in 3.5 million.

    The concept of sigma might be familiar from basic statistics—or from tests graded on a curve. One standard deviation from the mean on a bell curve is called one-sigma. Students scoring two- or three-sigma above (or below) are rare and end up with the grades to prove it.

    But the LHC doesn’t make its findings based on a single test. A bump at the LHC stands out against the bell curves of all the tests ever run. This mass of data all taken together, says Bose, is called “background.” It forms a landscape that has become familiar to physicists. A bump like the Higgs appears as a blot on this predictable landscape, a little like the unexpected genius who shows up for test after test and busts the curve.

    The bump that physicists recognized as the first sign of the Higgs boson was produced by data from about 10 collisions. Even with such scant data, the confidence level was about 4-sigma because the Higgs stood out so starkly against the familiar background. Later, when all of the data came together, about 40 events produced a more pronounced bump with a confidence level of 8-sigma. “That’s a very clean discovery,” says Ahlen.

    From Old Physics, New

    The LHC fired up its proton beams again in March 2016, and saw its first collisions on April 23. The hope is that at the planned higher energy level, it will produce more dramatic collisions that will allow physicists to discover something new.

    “The best thing that could happen is that we’ll discover a whole set of new particles that don’t make any sense at all,” says Black. “I’m hopeful that sort of thing will happen, that we’ll discover something that truly doesn’t make sense and we’ll really learn something from it.”

    Physicists refer to their quest as a search for “new physics,” begging the question: What’s wrong with the old physics? It’s not so much that the old physics doesn’t work—it does, amazingly well—but ask any particle physicist, and they will tell you there’s something about it that just isn’t satisfying. Parameters have to line up in very specific ways for some calculations to work out. If something is off by a smidgen, everything falls apart.

    “This kind of special balancing out of parameters in the current theory gives us the impression that there has to be some underlying principle that we’re missing,” says Black.

    So it is and so it has always been in physics. It all started back when the Greeks came up with the solid but incomplete idea of the atom. Centuries later, Newton’s experiments resulted in Newtonian mechanics, which brilliantly explain the day-to-day physics of the movements of planets in space and objects on Earth. Things got heady in the late 1800s when scientists started to understand electrical currents and magnetic fields. The early 20th century gave rise to quantum theory, which explains the world of tiny, energetic things, like photons. According to Lane, every successful theory has engulfed its predecessor. “Quantum mechanics ate the physics of the 18th and 19th centuries alive,” he says.

    The most recent meal, so to speak, was devoured in the 1960s and 70s by the Standard Model. By 1960, physicists knew about weak nuclear forces, which govern how particles decay into other particles. But no one knew how this force was related to existing theories of electromagnetism. Glashow worked out a new model for weak nuclear forces that relied on three new particles.

    “No one cared,” he says, until 1967, when Glashow’s idea morphed, in a confluence of other ideas, into a theory that made sense: The Standard Model. “Experimenters went out of their way to verify the predictions of the theory,” says Glashow, who won the Nobel Prize alongside Steven Weinberg and Abdus Salam for their work. “Lo and behold, the theory was right.”

    For theorists like Glashow and Lane, the observations of experiments lend credence to theory, and theory provides a rationale for understanding and deciphering what is seen in experiments. “Physics is an experimental science,” says Lane. “It’s not mathematics or philosophy. If it can’t be tested by experiment, it ain’t physics.”

    The most recent piece of experimental data confirming the Standard Model was the discovery of the Higgs boson in 2012. For Lane, the Higgs was a bit of a disappointment. “It’s kind of a simple-minded solution to a big problem,” he says. “Some people still feel burned by this discovery. Me, for example.”

    But ultimately, Lane is interested in figuring out what the most basic, fundamental particles are and how they interact with one another. “Right now, we have a story for that, but there’s always been a story for that,” he says.

    As long as people have been curious about the world they live in, they’ve been coming up with theories, testing them, and making them better. “This,” says Lane, “is an enterprise that need have no end.”

    See the full article here .

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