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  • richardmitnick 12:36 pm on June 15, 2019 Permalink | Reply
    Tags: Accelerator Science, , , FNAL Muon G-2 experiment, Muon g-2 anomaly, ,   

    From Fermi National Accelerator Lab: “Physicists are out to unlock the muon’s secret” 

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

    From Fermi National Accelerator Lab , an enduring source of strength for the US contribution to scientific research world wide.

    June 13, 2019
    Sabine Hossenfelder

    FNAL Muon G-2 studio

    Physicists count 25 elementary particles that, for all we presently know, cannot be divided any further. They collect these particles and their interactions in what is called the Standard Model of particle physics.

    Standard Model of Particle Physics

    But the matter around us is made of merely three particles: up and down quarks (which combine to protons and neutrons, which combine to atomic nuclei) and electrons (which surround atomic nuclei). These three particles are held together by a number of exchange particles, notably the photon and gluons.

    What’s with the other particles? They are unstable and decay quickly. We only know of them because they are produced when other particles bang into each other at high energies, something that happens in particle colliders and when cosmic rays hit Earth’s atmosphere. By studying these collisions, physicists have found out that the electron has two bigger brothers: The muon (μ) and the tau (τ).

    The muon and the tau are pretty much the same as the electron, except that they are heavier. Of these two, the muon has been studied closer because it lives longer – about 2 x 10^-6 seconds.

    The muon turns out to be… a little odd.

    Physicists have known for a while, for example, that cosmic rays produce more muons than expected. This deviation from the predictions of the standard model is not hugely significant, but it has stubbornly persisted. It has remained unclear, though, whether the blame is on the muons, or the blame is on the way the calculations treat atomic nuclei.

    Next, the muon (like the electron and tau) has a partner neutrino, called the muon-neutrino. The muon neutrino also has some anomalies associated with it. No one currently knows whether those are real or measurement errors.

    The Large Hadron Collider has seen a number of slight deviations from the predictions of the standard model which go under the name lepton anomaly. They basically tell you that the muon isn’t behaving like the electron, which (all other things equal) really it should. These deviations may just be random noise and vanish with better data. Or maybe they are the real thing.

    And then there is the gyromagnetic moment of the muon, usually denoted just g. This quantity measures how muons spin if you put them into a magnetic field. This value should be 2 plus quantum corrections, and the quantum corrections (the g-2) you can calculate very precisely with the standard model. Well, you can if you have spent some years learning how to do that because these are hard calculations indeed. Thing is though, the result of the calculation doesn’t agree with the measurement.

    This is the so-called muon g-2 anomaly, which we have known about since the 1960s when the first experiments ran into tension with the theoretical prediction. Since then, both the experimental precision as well as the calculations have improved, but the disagreement has not vanished.

    The most recent experimental data comes from a 2006 experiment at Brookhaven National Lab, and it placed the disagreement at 3.7σ. That’s interesting for sure, but nothing that particle physicists get overly excited about.

    A new experiments is now following up on the 2006 result: The muon g-2 experiment at Fermilab. The collaboration projects that (assuming the mean value remains the same) their better data could increase the significance to 7σ, hence surpassing the discovery standard in particle physics (which is somewhat arbitrarily set to 5σ).

    For this experiment, physicists first produce muons by firing protons at a target (some kind of solid). This produces a lot of pions (composites of two quarks) which decay by emitting muons. The muons are then collected in a ring equipped with magnets in which they circle until they decay. When the muons decay, they produce two neutrinos (which escape) and a positron that is caught in a detector. From the direction and energy of the positron, one can then infer the magnetic moment of the muon.

    The Fermilab g-2 experiment, which reuses parts of the hardware from the earlier Brookhaven experiment, is already running and collecting data. In a recent paper [ https://arxiv.org/abs/1905.00497 ], Alexander Keshavarzi, on behalf of the collaboration reports they successfully completed the first physics run last year. He writes we can expect a publication of the results from the first run in late 2019. After some troubleshooting (something about an underperforming kicker system), the collaboration is now in the second run.

    Another experiment to measure more precisely the muon g-2 is underway in Japan, at the J-PARC muon facility. This collaboration too is well on the way.

    J-PARC Facility Japan Proton Accelerator Research Complex , located in Tokai village, Ibaraki prefecture, on the east coast of Japan

    While we don’t know exactly when the first data from these experiments will become available, it is clear already that the muon g-2 will be much talked about in the coming years. At present, it is our best clue for physics beyond the standard model. So, stay tuned.

    See the full article here.


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    FNAL Icon

    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.

    FNAL MINERvA front face Photo Reidar Hahn

    FNAL DAMIC

    FNAL Muon g-2 studio

    FNAL Short-Baseline Near Detector under construction

    FNAL Mu2e solenoid

    Dark Energy Camera [DECam], built at FNAL

    FNAL DUNE Argon tank at SURF

    FNAL/MicrobooNE

    FNAL Don Lincoln

    FNAL/MINOS

    FNAL Cryomodule Testing Facility

    FNAL MINOS Far Detector in the Soudan Mine in northern Minnesota

    FNAL LBNF/DUNE from FNAL to SURF, Lead, South Dakota, USA

    FNAL/NOvA experiment map

    FNAL NOvA Near Detector

    FNAL ICARUS

    FNAL Holometer

     
  • richardmitnick 12:24 pm on June 13, 2019 Permalink | Reply
    Tags: Accelerator Science, , , Compact particle accelerators, ,   

    From DESY: “Laser trick produces high-energy terahertz pulses” 

    DESY
    From DESY

    2019/06/13

    Milestone for compact particle accelerators.

    A team of scientists from DESY and the University of Hamburg has achieved an important milestone in the quest for a new type of compact particle accelerator. Using ultra-powerful pulses of laser light, they were able to produce particularly high-energy flashes of radiation in the terahertz range having a sharply defined wavelength (colour). Terahertz radiation is to open the way for a new generation of compact particle accelerators that will find room on a lab bench. The team headed by Andreas Maier and Franz Kärtner from the Hamburg Center for Free-Electron Laser Science (CFEL) is presenting its findings in the journal Nature Communications. CFEL is jointly run by DESY, the University of Hamburg and the Max Planck Society.

    1
    From the colour difference of two slightly delayed laser flashes (left) a non-linear crystal generates an energetic terahertz pulse (right). Credit: DESY, Lucid Berlin

    The terahertz range of electromagnetic radiation lies between the infrared and microwave frequencies. Air travellers may be familiar with terahertz radiation from the full-body scanners used by airport security to search for objects hidden beneath a person’s garments. However, radiation in this frequency range might also be used to build compact particle accelerators. “The wavelength of terahertz radiation is about a thousand times shorter than the radio waves that are currently used to accelerate particles,” says Kärtner, who is a lead scientist at DESY. “This means that the components of the accelerator can also be built to be around a thousand times smaller.” The generation of high-energy terahertz pulses is therefore also an important step for the AXSIS (frontiers in Attosecond X-ray Science: Imaging and Spectroscopy) project at CFEL, funded by the European Research Council (ERC), which aims to open up completely new applications with compact terahertz particle accelerators.

    However, chivvying along an appreciable number of particles calls for powerful pulses of terahertz radiation having a sharply defined wavelength. This is precisely what the team has now managed to create. “In order to generate terahertz pulses, we fire two powerful pulses of laser light into a so-called non-linear crystal, with a minimal time delay between the two,” explains Maier from the University of Hamburg. The two laser pulses have a kind of colour gradient, meaning that the colour at the front of the pulse is different from that at the back. The slight time shift between the two pulses therefore leads to a slight difference in colour. “This difference lies precisely in the terahertz range,” says Maier. “The crystal converts the difference in colour into a terahertz pulse.”

    The method requires the two laser pulses to be precisely synchronised. The scientists achieve this by splitting a single pulse into two parts and sending one of them on a short detour so that it is slightly delayed before the two pulses are eventually superimposed again. However, the colour gradient along the pulses is not constant, in other words the colour does not change uniformly along the length of the pulse. Instead, the colour changes slowly at first, and then more and more quickly, producing a curved outline. As a result, the colour difference between the two staggered pulses is not constant. The difference is only appropriate for producing terahertz radiation over a narrow stretch of the pulse.

    That was a big obstacle towards creating high-energy terahertz pulses,” as Maier reports. “Because straightening the colour gradient of the pulses, which would have been the obvious solution, is not easy to do in practice.” It was co-author Nicholas Matlis who came up with the crucial idea: he suggested that the colour profile of just one of the two partial pulses should be stretched slightly along the time axis. While this still does not alter the degree with which the colour changes along the pulse, the colour difference with respect to the other partial pulse now remains constant at all times. “The changes that need to be made to one of the pulses are minimal and surprisingly easy to achieve: all that was necessary was to insert a short length of a special glass into the beam,” reports Maier. “All of a sudden, the terahertz signal became stronger by a factor of 13.” In addition, the scientists used a particularly large non-linear crystal to produce the terahertz radiation, specially made for them by the Japanese Institute for Molecular Science in Okazaki.

    “By combining these two measures, we were able to produce terahertz pulses with an energy of 0.6 millijoules, which is a record for this technique and more than ten times higher than any terahertz pulse of sharply defined wavelength that has previously been generated by optical means,” says Kärtner. “Our work demonstrates that it is possible to produce sufficiently powerful terahertz pulses with sharply defined wavelengths in order to operate compact particle accelerators.”

    See the full article here .


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    desi

    DESY is one of the world’s leading accelerator centres. Researchers use the large-scale facilities at DESY to explore the microcosm in all its variety – from the interactions of tiny elementary particles and the behaviour of new types of nanomaterials to biomolecular processes that are essential to life. The accelerators and detectors that DESY develops and builds are unique research tools. The facilities generate the world’s most intense X-ray light, accelerate particles to record energies and open completely new windows onto the universe. 
That makes DESY not only a magnet for more than 3000 guest researchers from over 40 countries every year, but also a coveted partner for national and international cooperations. Committed young researchers find an exciting interdisciplinary setting at DESY. The research centre offers specialized training for a large number of professions. DESY cooperates with industry and business to promote new technologies that will benefit society and encourage innovations. This also benefits the metropolitan regions of the two DESY locations, Hamburg and Zeuthen near Berlin.

    DESY Petra III interior


    DESY Petra III

    DESY/FLASH

    H1 detector at DESY HERA ring

    DESY DORIS III

     
  • richardmitnick 8:38 am on June 12, 2019 Permalink | Reply
    Tags: Accelerator Science, , , , , , , ,   

    From Science Magazine: “Exotic particles called pentaquarks may be less weird than previously thought” 

    AAAS
    From Science Magazine

    Jun. 5, 2019
    Adrian Cho

    1
    The Large Hadron Collider beauty experiment has discovered three new pentaquarks. Peter Ginter/CERN

    Four years ago, when experimenters spotted pentaquarks—exotic, short-lived particles made of five quarks—some physicists thought they had glimpsed the strong nuclear force, which binds the atomic nucleus, engaging in a bizarre new trick. New observations have now expanded the zoo of pentaquarks, but suggest a tamer explanation for their structure. The findings, from the Large Hadron Collider beauty experiment (LHCb), a particle detector fed by the LHC at CERN, the European particle physics laboratory near Geneva, Switzerland, suggest pentaquarks are not bags of five quarks binding in a new way, but are more like conventional atomic nuclei.

    “I’m really excited that the new data send such a clear message,” says Tomasz Skwarnicki, an LHCb physicist at Syracuse University in New York who led the study. But, he notes, “It may not be the message some people had hoped for.”

    Pentaquarks are heavier cousins of protons and neutrons, which are also made of quarks. In ordinary matter, quarks come in two types, up and down. Atom smashers can blast four heavier types of quarks into brief existence: charm, strange, top, and bottom. Quarks cling to one another through the strong force so mightily they cannot be isolated. Instead, they are almost always found in groups of three in particles known as baryons—including the proton and neutron—or in pairs called mesons, which consist of a quark and an antimatter quark.

    But for decades, some theorists have hypothesized the existence of larger bundles of quarks. In recent years, experimenters have found evidence for four-quark particles, or tetraquarks. Then, in 2015, LHCb reported signs of two pentaquarks.

    Some theorists argue that the new particles are bags of four and five quarks, bound together through the exchange of quantum particles called gluons, adding a new wrinkle to the often intractable theory of the strong force. Others argue they’re more like an atomic nucleus. In this “molecular” picture a pentaquark is a three-quark baryon stuck to a two-quark meson the same way that protons and neutrons bind in a nucleus—by exchanging short-lived pi mesons.

    LHCb’s new pentaquarks, reported today in Physical Review Letters (PRL), bolster the molecular picture. In 2015, LHCb researchers reported a pentaquark with a mass of 4450 megaelectron volts (MeV), 4.74 times the mass of the proton. With nine times more data, they now find in that mass range two nearly overlapping but separate pentaquarks with masses of 4440 MeV and 4457 MeV. They also find a lighter pentaquark at 4312 MeV. Each contains the same set of quarks: charm, anticharm, two ups, and a down. (Previous hints of a pentaquark at 4380 MeV have faded.)

    3
    Pentaquark depiction

    5
    New Large Hadron Collider data reveal that exotic quark quintets, discovered in 2016, are composites of quark-antiquark mesons and three-quark baryons.

    The lightest pentaquark has a mass just below the sum of a particular baryon and meson that together contain the correct quark ingredients. The heavier pentaquarks have masses just below the sum of the same baryon and a related meson with extra internal energy. That suggests each pentaquark is just a baryon bound to a meson, with a tiny bit of mass taken up in binding energy. “This is a no-brainer explanation,” says Marek Karliner, a theorist at Tel Aviv University in Israel.

    The molecular picture also helps explain why the pentaquarks, although fleeting, appear to be more stable than expected, Karliner says. That’s because packaging the charm quark in the baryon and anticharm quark in the meson separates them, keeping them from annihilating each other.

    Other theorists rushed to a similar conclusion when LHCb researchers discussed their results at a conference in La Thuile, Italy, in March. For example, within a day, Li-Sheng Geng, a theorist at Beihang University in Beijing, and colleagues posted a paper, in press at PRL, that uses the molecular picture to predict the existence of four more pentaquarks that should be within LHCb’s reach.

    But the bag-of-quarks picture is not dead. Pentaquarks should occasionally form when protons are bombarded with gamma ray photons, as physicists at Thomas Jefferson National Accelerator Facility in Newport News, Virginia, are trying to do. But they have yet to spot any pentaquarks. That undermines the molecular picture because it predicts higher rates for such photoproduction than the bag-of-quarks model does, says Ahmed Ali, a theorist at DESY, the German accelerator laboratory in Hamburg. “They are already almost excluding the molecular interpretation,” he says. Others say it’s too early to draw such conclusions.

    The structure of pentaquarks isn’t necessarily an either/or proposition, notes Feng-Kun Guo, a theorist at the Chinese Academy of Sciences in Beijing. Quantum mechanics allows a tiny object to be both a particle and a wave, or to be in two places at once. Similarly, a pentaquark could have both structures simultaneously. “It’s just a question of which one is dominant,” Guo says.

    Regardless of the binding mechanism, the new pentaquarks are exciting because they suggest the existence of a whole new family of such particles, Karliner says. “It’s like a whole new periodic table.”

    See the full article here .


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  • richardmitnick 12:38 pm on May 25, 2019 Permalink | Reply
    Tags: "CMS hunts for dark photons coming from the Higgs boson", Accelerator Science, , , , One idea is that dark matter comprises dark particles that interact with each other through a mediator particle called the dark photon, , ,   

    From CERN CMS: “CMS hunts for dark photons coming from the Higgs boson” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    From CERN CMS

    24 May, 2019
    Ana Lopes

    1
    A proton–proton collision event featuring a muon–antimuon pair (red), a photon (green), and large missing transverse momentum. (Image: CERN)

    They know it’s there but they don’t know what it’s made of. That pretty much sums up scientists’ knowledge of dark matter.

    Fritz Zwicky discovered Dark Matter when observing the movement of the Coma Cluster., Vera Rubin a Woman in STEM denied the Nobel, did most of the work on Dark Matter.

    Fritz Zwicky from http:// palomarskies.blogspot.com

    Coma cluster via NASA/ESA Hubble

    Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science)


    Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL)


    Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu

    This knowledge comes from observations of the universe, which indicate that the invisible form matter is about five to six times more abundant than visible matter.

    One idea is that dark matter comprises dark particles that interact with each other through a mediator particle called the dark photon, named in analogy with the ordinary photon that acts as a mediator between electrically charged particles. A dark photon would also interact weakly with the known particles described by the Standard Model of particle physics, including the Higgs boson.

    Standard Model of Particle Physics (LATHAM BOYLE AND MARDUS OF WIKIMEDIA COMMONS)

    CERN CMS Higgs Event


    CERN ATLAS Higgs Event

    At the Large Hadron Collider Physics (LHCP) conference, happening this week in Puebla, Mexico, the CMS collaboration reported the results of its latest search for dark photons.

    The collaboration used a large proton–proton collision dataset, collected during the Large Hadron Collider’s second run, to search for instances in which the Higgs boson might transform, or “decay”, into a photon and a massless dark photon. They focused on cases in which the boson is produced together with a Z boson that itself decays into electrons or their heavier cousins known as muons.

    Such instances are expected to be extremely rare, and finding them requires deducing the presence of the potential dark photon, which particle detectors won’t see. For this, researchers add up the momenta of the detected particles in the transverse direction – that is, at right angles to the colliding beams of protons – and identify any missing momentum needed to reach a total value of zero. Such missing transverse momentum indicates an undetected particle.

    But there’s another step to distinguish between a possible dark photon and known particles. This entails estimating the mass of the particle that decays into the detected photon and the undetected particle. If the missing transverse momentum is carried by a dark photon produced in the decay of the Higgs boson, that mass should correspond to the Higgs-boson mass.

    The CMS collaboration followed this approach but found no signal of dark photons. However, the collaboration placed upper bounds on the likelihood that a signal would have been seen.

    Another null result? Yes, but results such as these and the ATLAS results on supersymmetry also presented this week in Puebla, while not finding new particles or ruling out their existence, are much needed to guide future work, both experimental and theoretical.

    For more details about this result, see the CMS website.

    See the full article here.


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    Meet CERN in a variety of places:

    Quantum Diaries
    QuantumDiaries

    Cern Courier

    CMS
    CERN CMS New

     
  • richardmitnick 7:29 am on May 23, 2019 Permalink | Reply
    Tags: "Atom smasher could be making new particles that are hiding in plain sight", Accelerator Science, , CERN FASER experiment, , Compact Detector for Exotics at LHCb, ,   

    From Science Magazine: “Atom smasher could be making new particles that are hiding in plain sight” 

    AAAS
    From Science Magazine

    May. 22, 2019
    Adrian Cho

    1
    In a simulated event, the track of a decay particle called a muon (red), displaced slightly from the center of particle collisions, could be a sign of new physics.
    ATLAS EXPERIMENT © 2019 CERN

    Are new particles materializing right under physicists’ noses and going unnoticed? The world’s great atom smasher, the Large Hadron Collider (LHC), could be making long-lived particles that slip through its detectors, some researchers say.

    LHC

    CERN map


    CERN LHC Maximilien Brice and Julien Marius Ordan


    CERN LHC particles

    Next week, they will gather at the LHC’s home, CERN, the European particle physics laboratory near Geneva, Switzerland, to discuss how to capture them.


    They argue the LHC’s next run should emphasize such searches, and some are calling for new detectors that could sniff out the fugitive particles.

    It’s a push born of anxiety. In 2012, experimenters at the $5 billion LHC discovered the Higgs boson, the last particle predicted by the standard model of particles and forces, and the key to explaining how fundamental particles get their masses.

    CERN CMS Higgs Event


    CERN ATLAS Higgs Event

    But the LHC has yet to blast out anything beyond the standard model.

    Standard Model of Particle Physics (LATHAM BOYLE AND MARDUS OF WIKIMEDIA COMMONS)

    “We haven’t found any new physics with the assumptions we started with, so maybe we need to change the assumptions,” says Juliette Alimena, a physicist at Ohio State University (OSU) in Columbus who works with the Compact Muon Solenoid (CMS), one of the two main particle detectors fed by the LHC.

    CERN/CMS Detector


    For decades, physicists have relied on a simple strategy to look for new particles: Smash together protons or electrons at ever-higher energies to produce heavy new particles and watch them decay instantly into lighter, familiar particles within the huge, barrel-shaped detectors. That’s how CMS and its rival detector, A Toroidal LHC Apparatus (ATLAS), spotted the Higgs, which in a trillionth of a nanosecond can decay into, among other things, a pair of photons or two “jets” of lighter particles.

    CERN ATLAS Credit CERN SCIENCE PHOTO LIBRARY

    Long-lived particles, however, would zip through part or all of the detector before decaying. That idea is more than a shot in the dark, says Giovanna Cottin, a theorist at National Taiwan University in Taipei. “Almost all the frameworks for beyond-the-standard-model physics predict the existence of long-lived particles,” she says. For example, a scheme called supersymmetry posits that every standard model particle has a heavier superpartner, some of which could be long-lived. Long-lived particles also emerge in “dark sector” theories that envision undetectable particles that interact with ordinary matter only through “porthole” particles, such as a dark photon that every so often would replace an ordinary photon in a particle interaction.

    CMS and ATLAS, however, were designed to detect particles that decay instantaneously. Like an onion, each detector contains layers of subsystems—trackers that trace charged particles, calorimeters that measure particle energies, and chambers that detect penetrating and particularly handy particles called muons—all arrayed around a central point where the accelerator’s proton beams collide. Particles that fly even a few millimeters before decaying would leave unusual signatures: kinked or offset tracks, or jets that emerge gradually instead of all at once.

    Standard data analysis often assumes such oddities are mistakes and junk, notes Tova Holmes, an ATLAS member from the University of Chicago in Illinois who is searching for the displaced tracks of decays from long-lived supersymmetric particles. “It’s a bit of a challenge because the way we’ve designed things, and the software people have written, basically rejects these things,” she says. So Holmes and colleagues had to rewrite some of that software.

    More important is ensuring that the detectors record the odd events in the first place. The LHC smashes bunches of protons together 400 million times a second. To avoid data overload, trigger systems on CMS and ATLAS sift interesting collisions from dull ones and immediately discard data about 1999 of every 2000 collisions. The culling can inadvertently toss out long-lived particles. Alimena and colleagues wanted to look for particles that live long enough to get stuck in CMS’s calorimeter and decay only later. So they had to put in a special trigger that occasionally reads out the entire detector between the proton collisions.

    Long-lived particle searches had been fringe efforts, says James Beacham, an ATLAS experimenter from OSU. “It’s always been one guy working on this thing,” he says. “Your support group was you in your office.” Now, researchers are joining forces. In March, 182 of them released a 301-page white paper on how to optimize their searches.

    Some want ATLAS and CMS to dedicate more triggers to long-lived particle searches in the next LHC run, from 2021 through 2023. In fact, the next run “is probably our last chance to look for unusual rare events,” says Livia Soffi, a CMS member from the Sapienza University of Rome. Afterward, an upgrade will increase the intensity of the LHC’s beams, requiring tighter triggers.

    Others have proposed a half-dozen new detectors to search for particles so long-lived that they escape the LHC’s existing detectors altogether. Jonathan Feng, a theorist at the University of California, Irvine, and colleagues have won CERN approval for the Forward Search Experiment (FASER), a small tracker to be placed in a service tunnel 480 meters down the beamline from ATLAS.

    CERN FASER experiment schematic

    Supported by $2 million from private foundations and built of borrowed parts, FASER will look for low-mass particles such as dark photons, which could spew from ATLAS, zip through the intervening rock, and decay into electron-positron pairs.

    Another proposal calls for a tracking chamber in an empty hall next to the LHCb, a smaller detector fed by the LHC.

    CERN/LHCb detector

    The Compact Detector for Exotics at LHCb would look for long-lived particles, especially those born in Higgs decays, says Vladimir Gligorov, an LHCb member from the Laboratory for Nuclear Physics and High Energies in Paris.

    3
    The Compact Detector for Exotics at LHCb. https://indico.cern.ch/event/755856/contributions/3263683/attachments/1779990/2897218/PBC2019_CERN_CodexB_report.pdf

    Even more ambitious would be a detector called MATHUSLA, essentially a large, empty building on the surface above the subterranean CMS detector.

    5
    MATHUSLA. http://cds.cern.ch/record/2653848

    Tracking chambers in the ceiling would detect jets spraying up from the decays of long-lived particles created 70 meters below, says David Curtin, a theorist at the University of Toronto in Canada and project co-leader. Curtin is “optimistic” MATHUSLA would cost less than €100 million. “Given that it has sensitivity to this broad range of signatures—and that we haven’t seen anything else—I’d say it’s a no-brainer.”

    Physicists have a duty to look for the odd particles, Beacham says. “The nightmare scenario is that in 20 years, Jill Theorist says, ‘The reason you didn’t see anything is you didn’t keep the right events and do the right search.’”

    See the full article here .


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  • richardmitnick 4:43 pm on May 20, 2019 Permalink | Reply
    Tags: "Searching for Electroweak SUSY: not because it is easy but because it is hard", Accelerator Science, , , , ,   

    From CERN ATLAS: “Searching for Electroweak SUSY: not because it is easy, but because it is hard” 

    CERN/ATLAS detector

    CERN ATLAS Higgs Event

    CERN ATLAS another view Image Claudia Marcelloni ATLAS CERN


    CERN ATLAS New II Credit CERN SCIENCE PHOTO LIBRARY


    From CERN ATLAS

    20th May 2019
    ATLAS Collaboration

    The Standard Model is a remarkably successful but incomplete theory.

    Standard Model of Particle Physics

    Supersymmetry (SUSY) offers an elegant solution to the Standard Model’s limitations, extending it to give each particle a heavy “superpartner” with different “spin” properties (an important “quantum number”, distinguishing matter particles from force particles and the Higgs boson). For example, “sleptons” are the spin 0 superpartners of spin 1/2 electrons, muons and tau leptons, while “charginos” and “neutralinos” are the spin 1/2 counterparts of the spin 0 Higgs bosons (SUSY postulates a total of five Higgs bosons) and spin 1 gauge bosons.

    If these superpartners exist and are not too massive, they will be produced at CERN’s Large Hadron Collider (LHC) and could be hiding in data collected by the ATLAS detector. However, unlike most processes at the LHC, which are governed by strong force interactions, these superpartners would be created through the much weaker electroweak interaction, thus lowering their production rates. Further, most of these new SUSY particles are expected to be unstable. Physicists can only search for them by tracing their decay products – typically into a known Standard Model particle and a “lightest supersymmetric particle” (LSP), which could be stable and non-interacting, thus forming a natural dark matter candidate.

    ______________________________________________
    If sleptons, charginos and neutralinos exist, they will be produced at the LHC and could be hiding in Run 2 data. New searches from the ATLAS Collaboration look for these particles around unexplored corners.
    ______________________________________________

    Today, at the Large Hadron Collider Physics (LHCP) conference in Puebla, Mexico, and at the SUSY2019 conference in Corpus Christi, USA, the ATLAS Collaboration presented numerous new searches for SUSY based on the full Run-2 dataset (taken between 2015 and 2018), including two particularly challenging searches for electroweak SUSY. Both searches target particles that are produced at extremely low rates at the LHC, and decay into Standard Model particles that are themselves difficult to reconstruct. The large amount of data successfully collected by ATLAS in Run 2 provides a unique opportunity to explore these scenarios with new analysis techniques.

    Search for the “stau”

    Collider and astroparticle physics experiments have set limits on the mass of various SUSY particles. However, one important superpartner – the tau slepton, known as the “stau” – has yet to be searched for beyond the exclusion limit of around 90 GeV found at the LHC’s predecessor at CERN, the Large Electron-Positron collider (LEP). A light stau, if it exists, could play a role in neutralino co-annihilation, moderating the amount of dark matter in the visible universe, which otherwise would be too abundant to explain astrophysical measurements.

    The search for a light stau is experimentally challenging due to its extremely low production rate in LHC proton-proton collisions, requiring advanced techniques to reconstruct the Standard Model tau leptons it can decay into. In fact, during Run 1, only a narrow parameter region around a stau mass of 109 GeV and a massless lightest neutralino could be excluded by LHC experiments.

    2
    Figure 1: Observed (expected) limits on the combined left and right stau pair production are shown by the red line (black dashed line). The mass of stau is shown on the x-axis, while the mass of the LSP is shown on the y-axis. (Image: ATLAS Collaboration/CERN)

    3
    Figure 2: Observed (expected) limits on the stau-left pair production are shown by the red line (black dashed line). The mass of stau is shown on the x-axis, while the mass of the LSP is shown on the y-axis. (Image: ATLAS Collaboration/CERN)

    This first ATLAS Run 2 stau search targets the direct production of a pair of staus, each decaying into one tau lepton and one invisible LSP. Each tau lepton further decays into hadrons and an invisible neutrino. Signal events would thus be characterised by the presence of two sets of close-by hadrons and large missing transverse energy (ETmiss) originating from the invisible LSP and neutrinos. Events are further categorized into regions with medium and high ETmiss, to examine different stau mass scenarios.

    The ATLAS data did not reveal hints for stau pair production and thus new exclusion limits were set on the mass of staus. These limits are shown in Figures 1 and 2 using different assumptions on the presence of both possible stau types (left and right, referring to the two different spin states of the tau partner lepton). The limits obtained are the strongest obtained so far in these scenarios.

    Compressed search

    One of the reasons physicists have yet to see charginos and neutralinos may be because their masses are “compressed”. In other words, they are very close to the mass of the LSP. This is expected in scenarios where these particles are “higgsinos”, the superpartners of the Higgs bosons.

    Compressed higgsinos decay to pairs of electrons or muons with very low momenta. It is challenging to identify and reconstruct these particles in an environment with more than a billion high-energy collisions every second and a detector designed to measure high-energy particles – like trying to locate a whispering person in a very crowded and noisy room.

    3
    Figure 3: The distribution of the electron/muon and track pair mass, where the signal events tend to cluster at low mass values. The solid histogram indicates the Standard Model background process, the points with error bars indicate the data, and the dashed lines indicate hypothetical Higgsino events. The bottom plot shows the ratio of the data to the total Standard Model background. (Image: ATLAS Collaboration/CERN)

    4
    Figure 4: Observed (expected) limits on higgsino production are shown by the red line (blue dashed line). The mass of the produced higgsino is shown on the x-axis, while the mass difference to the LSP is shown on the y-axis. The grey region represents the models excluded by the LEP experiments. The blue region represents the constraint from the previous ATLAS search for higgsinos.(Image: ATLAS Collaboration/CERN)

    A new search for higgsinos utilizes muons measured with unprecedentedly low – for ATLAS, so far – momenta. It also benefits from new and unique analysis techniques that allow physicists to look for higgsinos in areas that were previously inaccessible. For example, the search uses charged particle tracks, which can be reconstructed with very low momentum, as a proxy for one of the electrons or muons in the decay pair. Because of the small mass difference between the higgsinos, the mass of the electron/muon and track pair is also expected to be small, as shown in Figure 3.

    Once again, no signs of higgsinos were found in this search. As shown in Figure 4, the results were used to extend constraints on higgsino masses set by ATLAS in 2017 and by the LEP experiments in 2004.

    Overall, both sets of results place strong constraints on important supersymmetric scenarios, which will guide future ATLAS searches. Further, they provide examples of how advanced reconstruction techniques can help improve the sensitivity of new physics searches.

    See the full article for further reseach materials.

    See the full article here .


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  • richardmitnick 2:20 pm on May 14, 2019 Permalink | Reply
    Tags: Accelerator Science, , , , LS2, , , , Superconducting magnet circuits   

    From CERN: “LS2 Report: consolidating the energy extraction systems of LHC superconducting magnet circuits” 

    Cern New Bloc

    Cern New Particle Event


    From CERN

    13 May, 2019
    Anaïs Schaeffer

    1
    The LS2 team from the NRC Kurchatov-IHEP Institute, Protvino, Russia, with a 13 kA energy extraction system (Image: NRC Kurchatov-IHEP Institute)

    In the LHC, 1232 superconducting dipole magnets and 392 quadrupole magnets guide and focus the beams around the accelerator’s 27-kilometre ring, which is divided into eight sectors. These magnets operate at very low temperatures – 1.9 K or −271.3 °C – where even a tiny amount of energy released inside a magnet can warm its windings to above the critical temperature, causing the loss of superconductivity: this is called a quench. When this happens, the energy stored in the affected magnet has to be safely extracted in a short time to avoid damage to the magnet coil.

    To do so, two protection elements are activated: at the level of the quenching magnet, a diode diverts the current into a parallel by-pass circuit in less than a second; at the level of the circuit, 13 kA energy extraction systems absorb the energy of the whole magnet circuit in a few minutes. There are equivalent extraction systems installed for about 200 corrector circuits with currents up to 600 A.

    “In the framework of a long-lasting and fruitful collaboration between CERN and the Russian Federation, energy extraction systems for quench protection of the LHC superconducting magnets were designed in close partnership with two Russian institutes, the NRC Kurchatov-IHEP Institute in Protvino for the 13 kA systems and the Budker Institute in Novosibirsk for the 600 A systems. Russian industry was involved in the manufacturing of the parts of these systems,” explains Félix Rodríguez Mateos, leader of the Electrical Engineering (EE) section in the Machine Protection and Electrical Integrity (MPE) group of CERN’s Technology department.

    With a wealth of expertise and know-how, the Russian teams have continuously provided invaluable support to the MPE group. “Our Russian colleagues come to CERN for every year-end technical stop (YETS) and long shutdown to help us perform preventive maintenance and upgrade activities on the energy extraction systems,” says Rodríguez Mateos.

    During LS2, an extensive maintenance campaign is being performed on the 13 kA systems, which already count 10 years of successful operation in the LHC. “We are currently replacing an element, the arcing contact, in each one of the 256 electromechanical switches of the energy extraction systems to ensure their continuous reliable operation throughout the next runs,” adds Rodríguez Mateos. “In February, we fully replaced 32 switches at Point 8 of the accelerator in anticipation of consolidation for the future HL-LHC.”

    During LS2, the Electrical Engineering section is involved in many other activities that will be the subject of future articles.

    See the full article here.


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  • richardmitnick 12:04 pm on May 14, 2019 Permalink | Reply
    Tags: >Model-dependent vs model-independent research, Accelerator Science, , , , , , , , , ,   

    From Symmetry: “Casting a wide net” 

    Symmetry Mag
    From Symmetry

    05/14/19
    Jim Daley

    1
    Illustration by Sandbox Studio, Chicago

    In their quest to discover physics beyond the Standard Model, physicists weigh the pros and cons of different search strategies.

    On October 30, 1975, theorists John Ellis, Mary K. Gaillard and D.V. Nanopoulos published a paper [Science Direct] titled “A Phenomenological Profile of the Higgs Boson.” They ended their paper with a note to their fellow scientists.

    “We should perhaps finish with an apology and a caution,” it said. “We apologize to experimentalists for having no idea what is the mass of the Higgs boson… and for not being sure of its couplings to other particles, except that they are probably all very small.

    “For these reasons, we do not want to encourage big experimental searches for the Higgs boson, but we do feel that people performing experiments vulnerable to the Higgs boson should know how it may turn up.”

    What the theorists were cautioning against was a model-dependent search, a search for a particle predicted by a certain model—in this case, the Standard Model of particle physics.

    Standard Model of Particle Physics

    It shouldn’t have been too much of a worry. Around then, most particle physicists’ experiments were general searches, not based on predictions from a particular model, says Jonathan Feng, a theoretical particle physicist at the University of California, Irvine.

    Using early particle colliders, physicists smashed electrons and protons together at high energies and looked to see what came out. Samuel Ting and Burton Richter, who shared the 1976 Nobel Prize in physics for the discovery of the charm quark, for example, were not looking for the particle with any theoretical prejudice, Feng says.

    That began to change in the 1980s and ’90s. That’s when physicists began exploring elegant new theories such as supersymmetry, which could tie up many of the Standard Model’s theoretical loose ends—and which predict the existence of a whole slew of new particles for scientists to try to find.

    Of course, there was also the Higgs boson. Even though scientists didn’t have a good prediction of its mass, they had good motivations for thinking it was out there waiting to be discovered.

    And it was. Almost 40 years after the theorists’ tongue-in-cheek warning about searching for the Higgs, Ellis found himself sitting in the main auditorium at CERN next to experimentalist Fabiola Gianotti, the spokesperson of the ATLAS experiment at the Large Hadron Collider who, along with CMS spokesperson Joseph Incandela, had just co-announced the discovery of the particle he had once so pessimistically described.

    CERN CMS Higgs Event


    CERN ATLAS Higgs Event

    Model-dependent vs model-independent

    Scientists’ searches for particles predicted by certain models continue, but in recent years, searches for new physics independent of those models have begun to enjoy a resurgence as well.

    “A model-independent search is supposed to distill the essence from a whole bunch of specific models and look for something that’s independent of the details,” Feng says. The goal is to find an interesting common feature of those models, he explains. “And then I’m going to just look for that phenomenon, irrespective of the details.”

    Particle physicist Sara Alderweireldt uses model-independent searches in her work on the ATLAS experiment at the Large Hadron Collider.

    CERN ATLAS Image Claudia Marcelloni CERN/ATLAS

    Alderweireldt says that while many high-energy particle physics experiments are designed to make very precise measurements of a specific aspect of the Standard Model, a model-independent search allows physicists to take a wider view and search more generally for new particles or interactions. “Instead of zooming in, we try to look in as many places as possible in a consistent way.”

    Such a search makes room for the unexpected, she says. “You’re not dependent on the prior interpretation of something you would be looking for.”

    Theorist Patrick Fox and experimentalist Anadi Canepa, both at Fermilab, collaborate on searches for new physics.


    In Canepa’s work on the CMS experiment, the other general-purpose particle detector at the LHC, many of the searches are model-independent.

    While the nature of these searches allows them to “cast a wider net,” Fox says, “they are in some sense shallower, because they don’t manage to strongly constrain any one particular model.”

    At the same time, “by combining the results from many independent searches, we are getting closer to one dedicated search,” Canepa says. “Developing both model-dependent and model-independent searches is the approach adopted by the CMS and ATLAS experiments to fully exploit the unprecedented potential of the LHC.”

    Driven by data and powered by machine learning

    Model-dependent searches focus on a single assumption or look for evidence of a specific final state following an experimental particle collision. Model-independent searches are far broader—and how broad is largely driven by the speed at which data can be processed.

    “We have better particle detectors, and more advanced algorithms and statistical tools that are enabling us to understand searches in broader terms,” Canepa says.

    One reason model-independent searches are gaining prominence is because now there is enough data to support them. Particle detectors are recording vast quantities of information, and modern computers can run simulations faster than ever before, she says. “We are able to do model-independent searches because we are able to better understand much larger amounts of data and extreme regions of parameter and phase space.”

    Machine-learning is a key part of this processing power, Canepa says. “That’s really a change of paradigm, because it really made us make a major leap forward in terms of sensitivity [to new signals]. It really allows us to benefit from understanding the correlations that we didn’t capture in a more classical approach.”

    These broader searches are an important part of modern particle physics research, Fox says.

    “At a very basic level, our job is to bequeath to our descendants a better understanding of nature than we got from our ancestors,” he says. “One way to do that is to produce lots of information that will stand the test of time, and one way of doing that is with model-independent searches.”

    Models go in and out of fashion, he adds. “But model-independent searches don’t feel like they will.”

    See the full article here .


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  • richardmitnick 9:09 am on May 13, 2019 Permalink | Reply
    Tags: Accelerator Science, , , CLIC, , , , , , Roadmap for the future of the discipline, The European Strategy Group   

    From CERN: “In Granada, the European particle physics community prepares decisions for the future of the field” 

    Cern New Bloc

    Cern New Particle Event


    From CERN

    13 May, 2019

    The European particle physics community is meeting this week in Granada, Spain, to discuss the roadmap for the future of the discipline.

    1

    Geneva and Granada. The European particle physics community is meeting this week in Granada, Spain, to discuss the roadmap for the future of the discipline. The aim of the symposium is to define scientific priorities and technological approaches for the coming years and to consider plans for the medium- and long-term future. An important focus of the discussions will be assessing the various options for the period beyond the lifespan of the Large Hadron Collider.

    “The Granada symposium is an important step in the process of updating the European Strategy for Particle Physics and aims to prioritise our scientific goals and prepare for the upcoming generation of facilities and experiments,” said the President of the CERN Council, Ursula Bassler. “The discussions will focus on the scientific reach of potential new projects, the associated technological challenges and the resources required.”

    The European Strategy Group, which was established to coordinate the update process, has received 160 contributions from the scientific community setting out their views on possible future projects and experiments. The symposium in Granada will provide an opportunity to assess and discuss them.

    “The intent is to make sure that we have a good understanding of the science priorities of the community and of all the options for realising them,” said the Chair of the European Strategy Group, Professor Halina Abramowicz. “This will ensure that the European Strategy Group is well informed when deciding about the strategy update.”

    The previous update of the European Strategy, approved in May 2013, recommended that design and feasibility studies be conducted in order for Europe “to be in a position to propose an ambitious post-LHC accelerator project.” Over the last few years, in collaboration with partners from around the world, Europe has therefore been engaging in R&D and design projects for a range of ambitious post-LHC facilities under the CLIC and FCC umbrellas.


    CLIC collider

    CERN FCC Future Circular Collider details of proposed 100km-diameter successor to LHC

    A study to investigate the potential to build projects that are complementary to high-energy colliders, exploiting the opportunities offered by CERN’s unique accelerator complex, was also launched by CERN in 2016. These contributions will feed into the discussion, which will also take into account the worldwide particle physics landscape and developments in related fields.

    “At least two decades will be needed to design and build a new collider to succeed the LHC. Such a machine should maximise the potential for new discoveries and enable major steps forward in our understanding of fundamental physics” said CERN Director-General, Fabiola Gianotti. “It is not too early to start planning for it as it will take time to develop the new technologies needed for its implementation.”

    The Granada symposium will be followed up with the compilation of a “briefing book” and with a Strategy Drafting Session, which will take place in Bad Honnef, Germany, from 20 to 24 January 2020. The update of the European Strategy for Particle Physics is due to be completed and approved by the CERN Council in May 2020.

    An online Q&A session will be held on Thursday 16 May – 4pm CEST

    Reporters interested in participating are invited to register by sending an e-mail to press@cern.ch

    https://europeanstrategy.cern/

    See the full article here.


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  • richardmitnick 12:54 pm on May 10, 2019 Permalink | Reply
    Tags: Accelerator Science, “Belle II will accumulate more than 50 times the data sample of the original Belle experiment at KEK”, “We are developing the data-distribution software working not only with Belle II colleagues but also with colleagues at CERN., “We store an entire copy of the Belle II data and we have the computing resources to process that data and make it available to collaborators around the world”, , Belle II detector, Benefitting from our own experience at the RHIC & ATLAS Computing Center, , Brookhaven’s magnet division constructed 43 custom-designed corrector magnets., , , , Physicists and engineers in the Laboratory’s Superconducting Magnet Division made contributions essential to upgrading the KEK accelerator helping to transform it into SuperKEKB., Physicists will search for signs of “new physics”—something that cannot be explained by the particles and forces already included in the Standard Model., , SuperKEKB accelerator, SuperKEKB collides electrons with their antimatter counterparts known as positrons, The corrector magnets are installed on each side of the Belle II detector   

    From Brookhaven National Lab: “Brookhaven Lab and the Belle II Experiment” 

    From Brookhaven National Lab

    May 7, 2019
    Karen McNulty Walsh
    kmcnulty@bnl.gov

    Tracking particle smashups and detector conditions from half a world away, scientists seek answers to big physics mysteries.

    1
    SuperKEKB accelerator and Belle II detector at the interaction region.(Credit: Belle II/KEK)

    If you think keeping track of the photos on your mobile phone is a challenge, imagine how daunting the job would be if your camera were taking thousands of photos every second. That’s the task faced by particle physicists working on the Belle II experiment at Japan’s SuperKEKB particle accelerator, which started its first physics run in late March. Belle II physicists will sift through “snapshots” of millions of subatomic smashups per day—as well as data on the conditions of the “camera” at the time of each collision—to seek answers to some of the biggest questions in physics.

    A key part of the experiment is taking place half a world away, using computing resources and expertise at the U.S. Department of Energy’s Brookhaven National Laboratory, the lead laboratory for U.S. collaborators on Belle II.

    “We store an entire copy of the Belle II data, and we have the computing resources to process that data and make it available to collaborators around the world,” said Benedikt Hegner, a physicist in Brookhaven Lab’s Computational Sciences Initiative. To date, Brookhaven’s Scientific Data and Computing Center (SDCC) has handled up to 95 percent of the experiment’s entire computing workload—reconstructing particles from simulated events prior to the experiment’s startup, and since late March, from live collision events. SDCC will continue that role for the experiment’s first three years, thereafter maintaining some 30 percent of the data-transfer and storage responsibility while transitioning the rest to other Belle II member nations that have powerful GRID computing capabilities.

    “We are developing the data-distribution software, working not only with Belle II colleagues but also with colleagues at CERN, the European laboratory for particle physics research, learning from their experience managing datasets from the Large Hadron Collider (LHC)—as well as our own experience at the RHIC & ATLAS Computing Center,” Hegner said.

    2
    Benedikt Hegner in the Scientific Data and Computing Center at Brookhaven Lab, which stores and processes Belle II data and makes it available to collaborators around the world.

    Brookhaven also hosts Belle II’s “conditions database”—an archive of the detector’s conditions at the time of each recorded collision. This database tracks millions of variables—for example, the detector’s level of electronic noise, millimeter-scale movements of the detector due to the strong magnetic field, and variations in electronic response due to small temperature changes—all of which need to be properly taken into account to make sense of Belle II’s measurements.

    “This is the first time a particle physics experiment’s conditions database is being hosted at a distant location,” Hegner noted. Tracking the conditions helps calibrate the detector and even feeds input to the “trigger” systems that decide which collisions to record. “If we’re having trouble with our system, Belle II will eventually see that during data collection. So, the reliability of our services is essential,” Hegner said.

    But Brookhaven’s involvement in Belle II goes beyond cataloging collisions and crunching the numbers. Physicists and engineers in the Laboratory’s Superconducting Magnet Division made contributions essential to upgrading the KEK accelerator, helping to transform it into SuperKEKB, and members of Brookhaven Lab’s physics department are looking forward to analyzing Belle II data and being part of the upgraded facility’s discoveries.

    Improved magnets, more collisions, “new physics”?

    Like its predecessor, SuperKEKB collides electrons with their antimatter counterparts, known as positrons. To keep collision rates high, these beams must be tightly focused. But the magnetic fields guiding the particles in one beam can have unwanted effects in the adjacent beam, causing the particles to spread. To fine-tune the fields of the accelerator magnets and counteract these adjacent-beam effects, Brookhaven’s magnet division constructed 43 custom-designed corrector magnets. These corrector magnets are installed on each side of the Belle II detector, making adjustments to both the incoming and outgoing beams to maintain high beam intensity, or “luminosity.” High luminosity results in higher collision rates, so physicists at Brookhaven and around the world will have more data to analyze.

    4
    Corrector magnets: Leak field cancel coil being wound by Brookhaven Lab magnet division technician Thomas Van Winckel.

    “Belle II will accumulate more than 50 times the data sample of the original Belle experiment at KEK,” said Brookhaven physicist David Jaffe, who is coordinating Brookhaven Lab scientists’ involvement in the project.

    By scouring reconstructed images of the particles emerging from these electron-positron collisions, physicists will search for signs of “new physics”—something that cannot be explained by the particles and forces already included in the Standard Model, the world’s reigning (and well-tested) theory of particle physics.

    One particular area of interest is the decay of beauty and charm mesons—particles made of two quarks, one of which is a heavy “beauty” or “charm” quark. These “heavy flavor” mesons are created in abundance in electron-positron collisions at the SuperKEKB accelerator.

    “SuperKEKB is called a ‘B factory’ because it is optimized for the production of beauty mesons. It also produces an abundance of charm mesons,” Jaffe said. “While many physicists on Belle II will be investigating the behavior of beauty mesons, the Brookhaven team will be exploiting the huge sample of charm mesons to look for possible discoveries.”

    For example, if heavy flavor mesons measured by Belle II decay (transform into other particles) differently than predicted by the Standard Model, such a discrepancy would be an indication that some new, previously undiscovered particle might be taking part in the action.

    Evidence of new particles might help account for the mysterious dark matter that makes up some 27 percent of the universe, or offer clues about dark energy, which accounts for another 68 percent (with the remaining 5 percent made of the ordinary matter we see around us). Such a discovery might also help explain why today’s universe is made of matter rather than a mix of matter and antimatter, even though scientists believe both were created in equal amounts at the very beginning of time.

    To grasp how shocking this matter-antimatter asymmetry is, think of the common laundry experience of losing a random sock in the dryer. But imagine if every time you did the laundry—even a billion loads, each with a billion pairs of socks labeled “left” and “right”—you always ended up with a single unpaired left sock and never a lone right sock. That’s what it’s like for physicists trying to understand why the universe ended up with only matter. There must be some difference in the way matter and antimatter behave to explain this anomaly.

    There is evidence that matter and antimatter behave differently from several well-known experiments studying meson decays. These include a Nobel Prize-winning experiment at Brookhaven’s Alternating Gradient Synchrotron, which studied the decay of mesons containing a strange quark in the 1960s. More recently, several experiments studying beauty meson decays at other B factories—the original Belle at KEK, the BaBar experiment at the SLAC National Accelerator Laboratory in the U.S., and the LHCb experiment at CERN—observed similar asymmetries. But thus far, the matter-antimatter asymmetry observed in beauty and strange mesons follows the pattern predicted by the Standard Model, and is not sufficient to explain the matter-antimatter asymmetry of the universe.

    LHCb also recently observed a smaller level of matter-antimatter asymmetry in charm meson decays for the first time. It is unclear if this new observation is consistent with the Standard Model or due to new particles that preferentially interact with charm quarks. Additional measurements are needed to solve this mystery.

    5
    Physicist David Jaffe is coordinating Brookhaven Lab’s contributions to Belle II.

    “What we’ll do at Belle II is like many, many trips to the laundromat where we carefully launder our `charmed’ socks and use different methods to dry them. We’ll use our observations from these different loads of charmed laundry to map out what happens in charm meson decays to higher precision than ever before,” explained Jaffe. “Then we’ll compare those observations to our expectations from the Standard Model to see if we’ve found evidence for new particles.”

    The Belle II experiment, Jaffe noted, complements LHCb. “Belle II has a different range of features that enable contrasting studies of the charm mesons,” he said. “We are starting to accumulate large data samples to help us make the precision measurements we need to resolve these questions. Once we’ve confirmed the technical capabilities of the experiment, we will move on to data analysis and the possibility of discovery.”

    See the full article here .


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