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  • richardmitnick 8:53 am on November 22, 2017 Permalink | Reply
    Tags: , , CERN LHC, , , , , ,   

    From Futurism: “Quantum Physicists Conclude Necessary Makeup of Elusive Tetraquarks” 

    futurism-bloc

    Futurism

    Mesons Baryons Tetraquarks

    , https://blog.cerebrodigital.org/tetraquark-particula-exotica-descubierta-en-fermilab/

    November 20, 2017
    Abby Norman

    Everything in the universe is made up of atoms — except, of course, atoms themselves. They’re made up of subatomic particles, namely, protons, neutrons, and electrons. While electrons are classified as leptons, protons and neutrons are in a class of particles known as quarks. Though, “known” may be a bit misleading: there is a lot more theoretical physicists don’t know about the particles than they do with any degree of certainty.

    As far as we know, quarks are the fundamental particle of the universe. You can’t break a quark down into any smaller particles. Imagining them as being uniformly minuscule is not quite accurate, however: while they are tiny, they are not all the same size. Some quarks are larger than others, and they can also join together and create mesons (1 quark + 1 antiquark) or baryons (3 quarks of various flavors).

    In terms of possible quark flavors, which are respective to their position, we’ve identified six: up, down, top, bottom, charm, and strange. As mentioned, they usually pair up either in quark-antiquark pairs or a quark threesome — so long as the charges ( ⅔, ⅔, and ⅓ ) all add up to positive 1.

    The so-called tetraquark pairing has long-eluded scientists; a hadron which would require 2 quark-antiquark pairs, held together by the strong force. Now, it’s not enough for them to simply pair off and only interact with their partner. To be a true tetraquark, all four quarks would need to interact with one another; behaving as quantum swingers, if you will.

    “Quarky” Swingers

    It might seem like a pretty straightforward concept: throw four quarks together and they’re bound to interact, right? Well, not necessarily. And that would be assuming they’d pair off stably in the first place, which isn’t a given. As Marek Karliner of Tel Aviv University explained to LiveScience, two quarks aren’t any more likely to pair off in a stable union than two random people you throw into an apartment together. When it comes to both people and quarks, close proximity doesn’t ensure chemistry.

    “The big open question had been whether such combinations would be stable,
    or would they instantly disintegrate into two quark-antiquark mesons,” Karliner told Futurism. “Many years of experimental searches came up empty-handed, and no one knew for sure whether stable tetraquarks exist.”

    Most discussions of tetraquarks up until recently involved those “ad-hoc” tetraquarks; the ones where four quarks were paired off, but not interacting. Finding the bona-fide quark clique has been the “holy grail” of theoretical physics for years – and we’re agonizingly close.

    Recalling that quarks are not something we can actually see, it probably goes without saying that predicting the existence of such an arrangement would be incredibly hard to do. The very laws of physics dictate that it would be impossible for four quarks to come together and form a stable hadron. But two physicists found a way to simplify (as much as you can “simplify” quantum mechanics) the approach to the search for tetraquarks.

    Several years ago, Karliner and his research partner, Jonathan Rosner of the University of Chicago, set out to establish the theory that if you want to know the mass and binding energy of rare hadrons, you can start by comparing them to the common hadrons you already know the measurements for. In their research [Nature] they looked at charm quarks; the measurements for which are known and understood (to quantum physicists, at least).

    Based on these comparisons, they proposed that a doubly-charged baryon should have a mass of 3,627 MeV, +/- 12 MeV [Physical Review Letters]. The next step was to convince CERN to go tetraquark-hunting, using their math as a map.

    For all the complex work it undertakes, the vast majority of which is nothing detectable by the human eye, The Large Hadron Collider is exactly what the name implies: it’s a massive particle accelerator that smashes atoms together, revealing their inner quarks.

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    If you’re out to prove the existence of a very tiny theoretical particle, the LHC is where you want to start — though there’s no way to know how long it will be before, if ever, the particles you seek appear.

    It took several years, but in the summer of 2017, the LHC detected a new baryon: one with a single up quark and two heavy charm quarks — the kind of doubly-charged baryon Karliner and Rosner were hoping for. The mass of the baryon was 3,621 MeV, give or take 1 MeV, which was extremely close to the measurement Karliner and Rosner had predicted. Prior to this observation physicists had speculated about — but never detected — more than one heavy quark in a baryon. In terms of the hunt for the tetraquark, this was an important piece of evidence: that more robust bottom quark could be just what a baryon needs to form a stable tetraquark.

    The perpetual frustration of studying particles is that they don’t stay around long. These baryons, in particular, disappear faster than “blink-and-you’ll-miss-it” speed; one 10/trillionth of a second, to be exact. Of course, in the world of quantum physics, that’s actually plenty of time to establish existence, thanks to the LHC.

    The great quantum qualm within the LHC, however, is one that presents a significant challenge in the search for tetraquarks: heavier particles are less likely to show up, and while this is all happening on an infinitesimal level, as far as the quantum scale is concerned, bottom quarks are behemoths.

    The next question for Rosner and Karliner, then, was did it make more sense to try to build a tetraquark, rather than wait around for one to show up? You’d need to generate two bottom quarks close enough together that they’d hook up, then throw in a pair of lighter antiquarks — then do it again and again, successfully, enough times to satisfy the scientific method.

    “Our paper uses the data from recently discovered double-charmed baryon to point, for the first time, that a stable tetraquark *must* exist,” Karliner told Futurism, adding that there’s “a very good chance” the LHCb at CERN would succeed in observing the phenomenon experimentally.

    That, of course, is still a theoretical proposition, but should anyone undertake it, the LHC would keep on smashing in the meantime — and perhaps the combination would arise on its own. As Karliner reminded LiveScience, for years the assumption has been that tetraquarks are impossible. At the very least, they’re profoundly at odds with the Standard Model of Physics. But that assumption is certainly being challenged. “The tetraquark is a truly new form of strongly-interacting matter,” Karliner told Futurism,” in addition to ordinary baryons and mesons.”

    If tetraquarks are not impossible, or even particularly improbable, thanks to the Karliner and Rosner’s calculations, at least now we have a better sense of what we’re looking for — and where it might pop up.

    Where there’s smoke there’s fire, as they say, and while the mind-boggling realm of quantum mechanics may feel more like smoke and mirrors to us, theoretical physicists aren’t giving up just yet. Where there’s a 2-bottom quark, there could be tetraquarks.

    See the full article here .

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    Futurism covers the breakthrough technologies and scientific discoveries that will shape humanity’s future. Our mission is to empower our readers and drive the development of these transformative technologies towards maximizing human potential.

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  • richardmitnick 3:22 pm on November 21, 2017 Permalink | Reply
    Tags: , , , CERN LHC, , , , , , , ,   

    From Symmetry: “Putting the puzzle together” 

    Symmetry Mag
    Symmetry

    11/21/17
    Ali Sundermier

    1
    Photos by Fermilab and CERN

    Successful physics collaborations rely on cooperation between people from many different disciplines.

    So, you want to start a physics experiment. Maybe you want to follow hints of an as yet unseen particle. Or maybe you want to learn something new about a mysterious process in the universe. Either way, your next step is to find people who can help you.

    In large science collaborations, such as the ATLAS and CMS experiments at the Large Hadron Collider; the Deep Underground Neutrino Experiment (DUNE); and Fermilab’s NOvA, hundreds to thousands of people spread out across many institutions and countries keep things operating smoothly. Whether they’re senior scientists, engineers, technicians or administrators, each of them has an important role to play.

    CERN/ATLAS detector

    CERN/CMS Detector

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

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


    FNAL DUNE Argon tank at SURF


    Surf-Dune/LBNF Caverns at Sanford



    SURF building in Lead SD USA

    FNAL NOvA Near Detector


    FNAL/NOvA experiment map

    Think of it like a jigsaw puzzle: This list will give you an idea about how their work fits together to create the big picture.

    Dreaming up the experiment

    Many particle physics experiments begin with a fundamental question. Why do objects have mass? Or, why is the universe made of matter?

    When scientists encounter these big, seemingly inscrutable questions, part of their job is to identify possible ways to answer them. A large part of this is breaking down the big questions into a program of smaller, answerable questions.

    In the case of the LHC, scientists who wondered about things such as undiscovered particles and the origin of mass designed a 27-kilometer particle collider and four giant detectors to learn more.

    Each scientist in a collaboration brings their own unique perspective and skill set to the table, whether it’s providing an understanding of the physics or offering expertise in operations or detector design.

    Perfecting the design

    Once scientists have an idea about the experiment they want to do and the approach they want to take, it’s the job of the engineers to turn the concepts into pieces of hardware that can be built, function and meet the experiment’s requirements.

    For example, engineers might have to figure out how the experiment should be supported mechanically or how to connect all the electrical systems and make signals available in a detector.

    In the case of NOvA, which investigates neutrino oscillations, scientists needed a detector that was huge and free of dense materials, which made conventional construction techniques unworkable. They had to work with engineers who could understand plastic as a building material so they could be confident about using it to build a gigantic, free-standing structure that fit the requirements.

    Keeping things running

    Technicians come in when the experimental apparatus and instrumentation are being built and often have complementary knowledge about what they’re working on. They build the hardware and coordinate the integration of components. It’s their work that, in the end, pulls everything together so the experiment functions.

    Once the experiment is built, technicians are responsible for keeping everything humming along at top performance. When physicists notice things going wrong with the detectors, the technicians usually have first eyes on it. It’s a vital task, since every second counts when it comes to collecting data.

    Doing the heavy lifting

    When designing and constructing the experiment, the scientists also recruit postdocs and grad students, who do the bulk of the data analysis.

    Grad students, who are still working on their PhDs, have to balance their own coursework with the real-world experiment, learning their way around running simulations, analyzing data and developing algorithms. They also make sure that every part of the detector is working up to par. In addition, they may work in instrumentation, developing new instruments and electronics.

    Postdocs, on the other hand, have already worked on experiments and obtained their PhDs, so they typically assume more of a leadership role in these collaborations. Part of their role is to guide the grad students in a sort of apprenticeship.

    Postdocs are often in charge of certain types of analysis or detector operations. Because they’ve worked on previous experiments, they have a tool kit and experience to draw on to solve problems when they crop up.

    Postdocs and grad students often work with technicians and engineers to ensure everything is properly built.

    Making the data accessible

    The LHC produces about 25 petabytes of data every year, or 25 billion megabytes. If the average size of an MP3 is about one megabyte per minute, then it would take almost 50,000 years to play 25 petabytes of songs. In physics collaborations, computer scientists and engineers have to organize the computing networks to ensure against bottlenecks or traffic jams when this massive amount of data is shared.

    They also maintain the software framework, which takes care of data handling and archiving. Say a scientist wants to know what happened on Feb. 27, 2015, at 3 a.m. Computing experts have to be able to go into the data catalogue and find, among the petabytes of data, where that event is stored.

    Sorting out the logistics

    One often overlooked group is the administrators.

    It’s up to the administrators to sequence all the different projects so they get the funds they need to make progress. They sort the logistics to make sure the right people are in the right places working on the right things.

    Administrators manage a group of people who are constantly coming and going. Is someone traveling to a site from a different institution? The administrators make sure that people get connected, work out itineraries and schedule where visiting scientists will live and work.

    Administrators also organize collaboration meetings, transfer money, and procure and ship equipment.

    Translating discoveries to the public

    While every single person involved in an experiment has a responsibility to effectively communicate with others, it can be challenging to communicate about research in a way that’s relatable to people from different backgrounds. That’s where the professional communicators come in.

    Communicators can translate a paper full of jargon and complicated science into a fascinating story that the rest of the world can get excited about.

    In addition to doing outreach for the public and writing press releases and pitching stories for the media, communicators offer coaching to people in a scientific collaboration on how to relay the science to a general audience, which is important for generating public interest.

    Fitting the pieces

    Now that you know many of the pieces that must fall into place for a large physics collaboration to be successful, also know that none of these roles is performed in a vacuum. For an experiment to work, there must be a synergy of tasks: Each relies on the success of the others. Now go start that experiment!

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 10:29 am on November 20, 2017 Permalink | Reply
    Tags: "A Model of Leptons", , , CERN LHC, , , ,   

    From CERN: “50 years since iconic ‘A Model of Leptons’ published” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    CERN

    20 Nov 2017
    Harriet Kim Jarlett

    1
    This event shows the real tracks produced in the 1200 litre Gargamelle bubble chamber that provided the first confirmation of a neutral current interaction. (Image: CERN)

    4
    Gargamelle

    1
    Steven Weinberg

    Today, 50 years ago, Steven Weinberg published the iconic paper A Model of Leptons [Physical Review Letters], which explains the profound link between mathematics and nature.

    2
    https://www.manhattanrarebooks.com/pages/books/222/steven-weinberg/a-model-of-leptons

    This paper lies at the core of the Standard Model, our most complete theory of how particles interact in our universe.

    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.

    Just two pages long, Weinberg’s elegant and simply written theory was revolutionary at the time, yet was virtually ignored for many years. But now, it is cited at least three times a week.

    The paper uses the idea of symmetry – that everything in our universe has a corresponding mirror image – between particles called pions to build Weinberg’s theory of the fundamental forces.

    From 1965 Weinberg had been building a mathematical structure and theorems based on this symmetry that explained why physicists had observed certain interactions between pions and nucleons and how pions behave when they are scattered from one another. This paved the way for a whole theory of hadronic physics at low energy.

    ____________________________________________________________________________
    “It’s what keeps you going as a theoretical physicist to hope that one of your squiggles will turn out to describe reality.”
    Steven Weinberg, Nobel prize winner and author of A Model of Leptons
    ____________________________________________________________________________

    Physicists had been using the concept of symmetry since the 1930’s, but had not yet been able to unite the electromagnetic and weak forces. Uniting the two forces would bring physicists closer to a single theory describing how and why all the fundamental interactions in our universe occur. The mathematics needed the particles carrying these two forces to be massless, but Weinberg and other physicists knew that if the particles really created these forces in nature, they had to be very heavy.

    One day, as the 34-year-old Weinberg was driving his red Camero to work, he had a flash of insight – he had been looking for massless particles in the wrong place. He applied his theory to a rarely mentioned and often disregarded particle, the massive W boson, and paired it with a massless photon. Theorists accounted for the mass of the W by introducing another unseen mechanism. This later became known as the Higgs mechanism, which calls for the existence of a Higgs boson.

    Proving the validity of Weinberg’s theory inspired one of the biggest experimental science programmes ever seen and CERN has built major projects with these discoveries at their heart: the Gargamelle bubble chamber found the first evidence of the electroweak current in 1973; the Super Proton Synchrotron showed, in 1982, the first evidence of the W boson; and most recently the Large Hadron Collider, in 2012, confirmed the existence of the Higgs Boson.

    CERN Super Proton Synchrotron

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    CERN CMS Higgs Event


    CERN/CMS Detector

    CERN ATLAS Higgs Event


    CERN/ATLAS detector

    3
    Steven Weinberg visiting the ATLAS collaboration in 2009. (Image: Maximilien Brice/CERN)

    Speaking to the CERN Courier Weinberg, now 84, describes what it’s like to see his work confirmed: “It’s what keeps you going as a theoretical physicist to hope that one of your squiggles will turn out to describe reality.” He received the Nobel Prize for this iconic, game-changing theory in 1979.

    Half a century after this publication, it’s hard to find a theory that explains fundamental physics as clearly as Weinberg’s, which brought together all the different pieces of the puzzle and assembled them into one, very simple idea.

    Read more about the original theory, and an interview with Steven Weinberg in this month’s CERN Courier.

    See the full article here.

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    Meet CERN in a variety of places:

    Quantum Diaries
    QuantumDiaries

    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 6:55 pm on November 18, 2017 Permalink | Reply
    Tags: , , CERN LHC, , , , ,   

    From Futurism: “Measurements From CERN Suggest the Possibility of a New Physics” 

    futurism-bloc

    Futurism

    November 18, 2017
    Brad Bergan

    A New Quantum Physics?

    2

    During the mid- to late-twentieth century, quantum physicists picked apart the unified theory of physics that Einstein’s theory of relativity offered. The physics of the large was governed by gravity, but only quantum physics could describe observations of the small. Since then, a theoretical tug-o-war between gravity and the other three fundamental forces has continued as physicists try to extend gravity or quantum physics to subsume the other as more fundamental.

    Recent measurements from the Large Hadron Collider show a discrepancy with Standard Model predictions that may hint at entirely new realms of the universe underlying what’s described by quantum physics.

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    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.

    Although repeated tests are required to confirm these anomalies, a confirmation would signify a turning point in our most fundamental description of particle physics to date.

    1
    Image credit: starsandspirals

    Quantum physicists found in a recent study [JHEP} that mesons don’t decay into kaon and muon particles often enough, according to the Standard Model predictions of frequency. The authors agree that enhancing the power [The Guardian] of the Large Hadron Collider (LHC) will reveal a new kind of particle responsible for this discrepancy. Although errors in data or theory may have caused the discrepancy, instead of a new particle, an improved LHC would prove a boon for several projects on the cutting edge of physics.

    The Standard Model

    The Standard Model is a well-established fundamental theory of quantum physics that describes three of the four fundamental forces believed to govern our physical reality. Quantum particles occur in two basic types, quarks and leptons. Quarks bind together in different combinations to build particles like protons and neutrons. We’re familiar with protons, neutrons, and electrons because they’re the building blocks of atoms.

    The “lepton family” features heavier versions of the electron — like the muon — and the quarks can coalesce into hundreds of other composite particles. Two of these, the Bottom and Kaon mesons, were culprits in this quantum mystery. The Bottom meson (B) decays to a Kaon meson (K) accompanied by a muon (mu-) and anti-muon (mu+) particle.

    The Anomaly

    They found a 2.5 sigma variance, or 1 in 80 probability, “which means that, in the absence of unexpected effects, i.e. new physics, a distribution more deviant than observed would be produced about 1.25 percent of the time,” Professor Spencer Klein, senior scientist at Lawrence Berkeley National Laboratory, told Futurism. Klein was not involved in the study.

    This means the frequency of mesons decaying into strange quarks during the LHC proton-collision tests fell a little below the expected frequency. “The tension here is that, with a 2.5 sigma [or standard deviation from the normal decay rate], either the data is off by a little bit, the theory is off by a little bit, or it’s a hint of something beyond the standard model,” Klein said. “I would say, naïvely, one of the first two is correct.”

    To Klein, this variance is inevitable considering the high volume of data run by computers for LHC operations. “With Petabyte-(1015 bytes)-sized datasets from the LHC, and with modern computers, we can make a very large number of measurements of different quantities,” Klein said. “The LHC has produced many hundreds of results. Statistically, some of them are expected to show 2.5 sigma fluctuations.” Klein noted that particle physicists usually wait for a 5-sigma fluctuation before crying wolf — corresponding to roughly a 1-in-3.5-million fluctuation in data [physics.org].

    These latest anomalous observations do not exist in a vacuum. “The interesting aspect of the two taken in combination is how aligned they are with other anomalous measurements of processes involving B mesons that had been made in previous years,” Dr. Tevong You, co-author of the study and junior research fellow in theoretical physics at Gonville and Caius College, University of Cambridge, told Futurism. “These independent measurements were less clean but more significant. Altogether, the chance of measuring these different things and having them all deviate from the Standard Model in a consistent way is closer to 1 in 16000 probability, or 4 sigma,” Tevong said.

    Extending the Standard Model

    Barring statistical or theoretical errors, Tevong suspects that the anomalies mask the presence of entirely new particles, called leptoquarks or Z prime particles. Inside bottom mesons, quantum excitations of new particles could be interfering with normal decay frequency. In the study, researchers conclude that an upgraded LHC could confirm the existence of new particles, making a major update to the Standard Model in the process.

    “It would be revolutionary for our fundamental understanding of the universe,” said Tevong. “For particle physics […] it would mean that we are peeling back another layer of Nature and continuing on a journey of discovering the most elementary building blocks. This would have implications for cosmology, since it relies on our fundamental theories for understanding the early universe,” he added. “The interplay between cosmology and particle physics has been very fruitful in the past. As for dark matter, if it emerges from the same new physics sector in which the Zprime or leptoquark is embedded, then we may also find signs of it when we explore this new sector.”

    The Power to Know

    So far, scientists at the LHC have only observed ghosts and anomalies hinting at particles that exist at higher energy levels. To prove their existence, physicists “need to confirm the indirect signs […], and that means being patient while the LHCb experiment gathers more data on B decays to make a more precise measurement,” Tevong said.

    CERN/LHCb

    “We will also get an independent confirmation by another experiment, Belle II, that should be coming online in the next few years. After all that, if the measurement of B decays still disagrees with the predictions of the Standard Model, then we can be confident that something beyond the Standard Model must be responsible, and that would point towards leptoquarks or Zprime particles as the explanation,” he added.

    To establish their existence, physicists would then aim to produce the particles in colliders the same way Bottom mesons or Higgs bosons are produced, and watch them decay. “We need to be able to see a leptoquark or Zprime pop out of LHC collisions,” Tevong said. “The fact that we haven’t seen any such exotic particles at the LHC (so far) means that they may be too heavy, and more energy will be required to produce them. That is what we estimated in our paper: the feasibility of directly discovering leptoquarks or Zprime particles at future colliders with higher energy.”

    Quantum Leap for the LHC

    Seeking out new particles in the LHC isn’t a waiting game. The likelihood of observing new phenomena is directly proportional to how many new particles pop up in collisions. “The more the particle appears the higher the chances of spotting it amongst many other background events taking place during those collisions,” Tevong explained. For the purposes of finding new particles, he likens it to searching for a needle in a haystack; it’s easier to find a needle if the haystack is filled with them, as opposed to one. “The rate of production depends on the particle’s mass and couplings: heavier particles require more energy to produce,” he said.

    This is why Tevong and co-authors B.C. Allanach and Ben Gripaios recommend either extending the LHC loop’s length, thus reducing the amount of magnetic power needed to accelerate particles, or replacing the current magnets with stronger ones.

    According to Tevong, the CERN laboratory is slated to keep running the LHC in present configuration until mid-2030s. Afterwards, they might upgrade the LHC’s magnets, roughly doubling its strength. In addition to souped-up magnets, the tunnel could see an enlargement from present 27 to 100 km (17 to 62 miles). “The combined effect […] would give about seven times more energy than the LHC,” Tevong said. “The timescale for completion would be at least in the 2040s, though it is still too early to make any meaningful projections.”

    If the leptoquark or Z prime anomalies are confirmed, the Standard Model has to change, Tevong reiterates. “It is very likely that it has to change at energy scales directly accessible to the next generation of colliders, which would guarantee us answers,” he added. While noting that there’s no telling if dark matter has anything to do with the physics behind Zprimes or leptoquarks, the best we can do is seek “as many anomalous measurements as possible, whether at colliders, smaller particle physics experiments, dark matter searches, or cosmological and astrophysical observations,” he said. “Then the dream is that we may be able to form connections between various anomalies that can be linked by a single, elegant theory.”

    See the full article here .

    Please help promote STEM in your local schools.

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    Futurism covers the breakthrough technologies and scientific discoveries that will shape humanity’s future. Our mission is to empower our readers and drive the development of these transformative technologies towards maximizing human potential.

     
  • richardmitnick 4:36 pm on November 6, 2017 Permalink | Reply
    Tags: A pair of physicists announced the discovery of a subatomic event so powerful that the researchers wondered if it was too dangerous to make public, , Bottom quarks, CERN LHC, , It's the first theoretical proof that it's possible to fuse subatomic particles together in ways that release energy, , , , , So much for tokamaks?, When two bottom quarks fuse the physicists found they produce a whopping 138 MeV. That's about eight times more powerful than one of the individual nuclear fusion events that takes place in hydrogen b   

    From SA: “The Subatomic Discovery That Physicists Considered Keeping Secret” 

    Scientific American

    Scientific American

    November 6, 2017
    Rafi Letzter

    A pair of physicists announced the discovery of a subatomic event so powerful that the researchers wondered if it was too dangerous to make public.

    The explosive event? The duo showed that two tiny particles known as bottom quarks could theoretically fuse together in a powerful flash. The result: a larger subatomic particle, a second, spare particle known as a nucleon, and a whole mess of energy spilling out into the universe. This “quarksplosion” would be an even more powerful subatomic analog of the individual nuclear fusion reactions that take place in the cores of hydrogen bombs.

    1
    The mushroom cloud from the 1952 explosion of Ivy Mike, the first thermonuclear fusion weapon ever detonated. Physicists have discovered an even more energetic subatomic reaction than thermonuclear fusion, taking place at the scale of quarks, but fortunately it seems ill-suited for weaponry. Credit: CTBTO Wikimedia (CC BY 2.0)

    Quarks are tiny particles that are usually found clinging together to make up the neutrons and protons inside atoms. They come in six versions or “flavors”: up, down, top, bottom, strange and charm.

    Energetic events at the subatomic level are measured in megaelectronvolts (MeV), and when two bottom quarks fuse, the physicists found, they produce a whopping 138 MeV. That’s about eight times more powerful than one of the individual nuclear fusion events that takes place in hydrogen bombs (a full-scale bomb blast consists of billions of these events). H-bombs fuse together tiny hydrogen nuclei known as deuterons and tritons to create helium nuclei, along with the most powerful explosions in the human arsenal. But each of those individual reactions inside the bombs releases only about 18 MeV, according to the Nuclear Weapon Archive, a website devoted to collecting research and data about nuclear weapons. That’s far less than the fusing bottom quarks’ 138 MeV.

    “I must admit that when I first realized that such a reaction was possible, I was scared,” co-researcher Marek Karliner of Tel Aviv University in Israel told Live Science. “But, luckily, it is a one-trick pony.”

    As powerful as fusion reactions are, a single instance of fusion on its own isn’t at all dangerous. Hydrogen bombs derive their enormous power from chain reactions — the cascading fusion of lots and lots of nuclei all at once.

    Karliner and Jonathan Rosner, of the University of Chicago, determined that such a chain reaction wouldn’t be possible with bottom quarks, and, before publishing, privately shared their insight with colleagues, who agreed.

    “If I thought for a microsecond that this had any military applications, I would not have published it,” Karliner said.

    To spark a chain reaction, nuclear bomb makers need large stockpiles of particles. And an important property of bottom quarks makes them impossible to stockpile: They wink out of existence just 1 picosecond after they’re created, or in about the time it takes light to travel half the length of a single grain of salt. After that time span, they decay into a far more common and less energetic kind of subatomic particle, known as the up quark.

    It might be possible to generate single fusion reactions of bottom quarks inside miles-long particle accelerators, the scientists said. But even inside an accelerator, one couldn’t assemble a large enough mass of quarks to do any damage out in the world, the researchers said. So there’s no need to worry about bottom quark bombs.

    The discovery is exciting, though, because it’s the first theoretical proof that it’s possible to fuse subatomic particles together in ways that release energy, Karliner said. That’s brand-new territory in the physics of very tiny particles, made possible by an experiment in the Large Hadron Collider at CERN, the massive particle-physics laboratory near Geneva.

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    Here’s how the physicists made this discovery.

    At CERN, particles zip around a 17-mile-long (27 kilometers) underground ring at near light speed before smashing into one another. The scientists then use powerful computers to sift through the data from those collisions, and strange particles sometimes emerge from that research. In June, something especially strange turned up in the data from one of those collisions: a “doubly charmed” baryon, or a bulky cousin of the neutron and proton, itself made up of two cousins of the “bottom” and “top” quarks known as “charm” quarks.

    Now, charm quarks are very heavy compared to the more common up and down quarks that make up protons and neutrons. And when heavy particles bind together, they convert a large chunk of their mass into binding energy, and in some cases, produce a bunch of leftover energy that escapes into the universe.

    When two charm quarks fuse, Karliner and Rosner found, the particles bind with an energy of about 130 MeV and spit out 12 MeV in leftover energy (about two-thirds of the energy of deuteron-triton fusion). That charmed fusion was the first reaction of particles on this scale ever found to emit energy in this way, and is the headline result of the new study, published Nov. 1 in the journal Nature.

    The even more energetic fusion of two bottom quarks, which bind with an energy of 280 MeV and spit out 138 MeV when they fuse, is the second, and more powerful of the two reactions discovered.

    So far, these reactions are entirely theoretical and haven’t been demonstrated in a lab. That next step should come soon though. Karliner said he expects to see the first experiments showing this reaction at CERN within the next couple years.

    See the full article here .

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    Scientific American, the oldest continuously published magazine in the U.S., has been bringing its readers unique insights about developments in science and technology for more than 160 years.

     
  • richardmitnick 10:22 am on October 24, 2017 Permalink | Reply
    Tags: A new chapter in Fermilab’s electron lens legacy, , CERN LHC, , , , Scientists at Fermilab invented and developed one novel collider component 20 years ago: the electron lens   

    From FNAL: “A new chapter in Fermilab’s electron lens legacy” 

    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.

    October 18, 2017
    Leah Poffenberger

    Sending bunches of protons speeding around a circular particle collider to meet at one specific point is no easy feat. Many different collider components work keep proton beams on course — and to keep them from becoming unruly.

    Scientists at Fermilab invented and developed one novel collider component 20 years ago: the electron lens. Electron lenses are beams of electrons formed into specific shapes that modify the motion of other particles — usually protons — that pass through them.

    The now retired Tevatron, a circular collider at Fermilab, and the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory have both benefited from electron lenses, a concept originally developed at Fermilab.

    FNAL Tevatron

    FNAL/Tevatron map


    FNAL/Tevatron DZero detector


    FNAL/Tevatron CDF detector

    BNL RHIC Campus

    BNL/RHIC Star Detector

    BNL RHIC PHENIX

    “Electron lenses are like a Swiss Army knife for accelerators: They’re relatively simple and inexpensive, but they can be applied in a wide variety of ways,” said Alexander Valishev, a Fermilab scientist who co-authored a recent study for a new electron lens application, which could be crucial to forthcoming colliders.

    The innovation is detailed in an article published on Sept. 27 in Physical Review Letters. (The article was also recently selected for presentation in the Physics Central’s Physics Buzz Blog.)

    “This little breakthrough in the physics of beams and accelerators is kind of a beginning of a bigger invention — it’s a new thing,” said Fermilab’s Vladimir Shiltsev, an author of the published paper. Shiltsev also played a major role in the origination of electron lenses in 1997. “Fermilab is known for inventions and developments that are, first, exciting, and then, functional. That’s what national labs are built for, and that’s what we’ve achieved.”

    1
    An electron lens introduces differences in the movement of particles that constitute a particle bunch. In the illustration, the perspective is looking down the beam pipe — down the path of the particle bunch. The bunch is seen as approaching the viewer (as the circle increases in size). Left: the particle bunch, represented as a uniformly blue circle, contains particles that all behave in the same way. Because the constituent particles follow the exact same trajectory, the bunch is more susceptible to wild deviations from its path, resulting from electromagnetic wake-fields. Right: Treated by an electron lens, the particle bunch, represented by red and blue, contains particles that move slightly differently from one another. For example, particles closer to the interior of the bunch move differently from those closer to the outside. This variegation helps confine the particle bunch to the more desirable straightforward path. Illustration: Diana Brandonisio

    A lens into the future

    This new type of electron lens, called the Landau damping lens, will be a critical part of a huge, prospective project in particle physics research: the Future Circular Collider at CERN.

    CERN Future Circular Collider

    The FCC would push the boundaries of traditional collider design to further study the particle physics beyond the Higgs boson, a fundamental particle discovered only five years ago.

    The proposed FCC has to be a high-luminosity machine: Its particle beams will need to be compact and densely packed. Compared with CERN’s Large Hadron Collider, the beams will also have a dramatic increase in energy — 50 trillion electronvolts, compared with the LHC’s beam energy of 7 trillion electronvolts. That involves an equally dramatic increase in the size of the accelerator. With a planned circumference of 100 kilometers, the FCC would dwarf the 27-kilometer LHC.

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    These high-energy, high-luminosity supercolliders all experience a problem, regardless of size: An intense beam of protons packed into the width of human hair traveling over a long distance can become unstable, especially if all the protons travel in exactly the same way.

    In a collider, particles arrive in packets called bunches — roughly foot-long streams packed with hundreds of billions of particles. A particle beam is formed of dozens, hundreds or thousands of these bunches.

    Imagine a circular collider as a narrow racetrack, with protons in a bunch as a tight pack of racecars. A piece of debris suddenly appears in the middle of the track, disrupting the flow of traffic. If every car reacts in the same way, say, by veering sharply to the left, it could lead to a major pileup.

    Inside the collider, it’s not a matter of avoiding just one bump on the track, but adjusting to numerous dynamic obstacles, causing the protons to change their course many times over. If an anomaly, such as a kink in the collider’s magnetic field, occurs unexpectedly, and if the protons in the beam all react to it in the same way at the same time, even a slight change of course could quickly go berserk.

    One could avoid the problem by thinning the particle beam from the get-go. By using lower-density proton beams, you provide less opportunity for protons to go off course. But that would mean removing protons and so missing out on potential for scientific discovery.

    Another, better way to address the problem is to introduce differences into the beam so that not all the protons in the bunches behave the same way.

    To return to the racetrack: If the drivers all react to the piece of debris different ways —some moving slightly to the right, others slightly to the left, one brave driver just skips over the top — the cars can all merge back together and continue the race, no accidents.

    Creating differentiations within a proton bunch would do essentially the same thing. Each proton follows its own, ever-so-slightly different course around the collider. This way, any departure from the course is isolated, rather than compounded by protons all misbehaving in concert, minimizing harmful beam oscillations.

    “Particles at the center of the bunch will move differently than particles around the outside,” Shiltsev said. “The protons will all be kind of messed up, but that’s what we want. If they all move together, they become unstable.”

    These differences are usually created with a special type of magnet called octupoles. The Tevatron, before its decommissioning in 2011, had 35 octupole magnets, and the LHC now has 336.

    But as colliders get larger and achieve greater energies, they need exponentially higher numbers of magnets: The FCC will require more than 10,000 octupole magnets, each a meter long, to achieve the same beam-stabilizing results as previous colliders.

    That many magnets take up a lot of space: as much as 10 of the FCC’s 100 kilometers.

    “That seems ridiculous,” Shiltsev said. “We’re looking for a way to avoid that.”

    The scientific community recognizes the Landau damping nonlinear lens as a likely solution to this problem: A single one-meter-long electron lens could replace all 10,000 octupole magnets and possibly do a better job keeping beams stable as they speed toward collision, without introducing any new problems.

    “At CERN they’ve embraced the idea of this new electron lens type, and people there will be studying them in further detail for the FCC,” Valishev said. “Given what we know so far about the issues that the future colliders will face, this would be a device of extremely high criticality. This is why we’re excited.”

    Electron Legos

    The Landau damping lens will join two other electron lens types in the repertoire of tools physicists have to modify or control beams inside a collider.

    “After many years of use, people are very happy with electron lenses: It’s one of the instruments used for modern accelerators, like magnets or superconducting cavities,” Shiltsev said. “Electron lenses are just one of the building blocks or Lego pieces.”

    Electron lenses are a lot like Legos: Lego pieces are made of the same material and can be the same color, but a different shape determines how they can be used. Electron lenses are all made of clouds of electrons, shaped by magnetic fields. The shape of the lens dictates how the lens influences a beam of protons.

    Scientists developed the first electron lens at Fermilab in 1997 for use to compensate for so-called beam-beam effects in the Tevatron, and a similar type of electron lens is still in use at the Brookhaven’s RHIC.

    In circular colliders, particle beams pass by each other, going in opposing directions inside the collider until they are steered into a collision at specific points. As the beams buzz by one another, they exert a small force on each other, which causes the proton bunches to expand slightly, decreasing their luminosity.

    That first electron lens, called the beam-beam compensation lens, was created to combat the interaction between the beams by squeezing them back to their original, compact state.

    After the success of this electron lens type in the Tevatron, scientists realized that electron beams could be shaped a second way to create another type of electron lens.

    Scientists designed the second lens to be shaped like a straw, allowing the proton beam to pass through the inside unaffected. The occasional proton might try to leave its group and stray from the center of the beam. In the LHC, losing even one-thousandth of the total number of protons in an uncontrolled way could be dangerous. The electron lens acts as a scraper, removing these rogue particles before they could damage the collider.

    “It’s extremely important to have the ability to scrape these particles because their energy is enormous,” Shiltsev said. “Uncontrolled, they can drill holes, break magnets or produce radiation.”

    Both types of electron lens have made their mark in collider design as part of the success of the Tevatron, RHIC and the LHC. The new Landau damping lens may help usher in the next generation of colliders.

    “The electron lens is an example of something that was invented here at Fermilab 20 years ago,” Shiltsev said. “This is a one of the rare technologies that wasn’t just brought to perfection at Fermilab: It was invented, developed and perfected and still continues to shine.”

    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 3:26 pm on October 23, 2017 Permalink | Reply
    Tags: , ATLAS and CMS join forces to tackle top-quark asymmetry, CERN LHC, , , ,   

    From CERN: “ATLAS and CMS join forces to tackle top-quark asymmetry” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    CERN

    20 Oct 2017
    Matthew Chalmers
    Henry Bennie

    1
    Event display of a tt̄ event candidate in the 2015 data (Image: ATLAS/CERN)

    2
    All matter around us is made of elementary particles called quarks and leptons. Each group consists of six particles, which are related in pairs, or “generations” – the up quark and the down quark form the first, lightest and most stable generation, followed by the charm quark and strange quark, then the top quark and bottom (or beauty) quark, the heaviest and least stable generation. (Image: Daniel Dombinguez/CERN)

    In their hunt for new particles and phenomena lurking in LHC collisions, the ATLAS and CMS experiments have joined forces to investigate the top quark. As the heaviest of all elementary particles, weighing almost as much as an atom of gold, the top quark is less well understood than its lighter siblings. With the promise of finding new physics hidden amongst the top quark’s antics, ATLAS and CMS have combined their top-quark data for the first time.

    There were already hints that the top quark didn’t play by the rules in data collected at the Tevatron collider at Fermilab in the US (the same laboratory that discovered the particle in 1995).

    FNAL Tevatron

    FNAL/Tevatron map


    FNAL/Tevatron DZero detector


    FNAL/Tevatron CDF detector

    Around a decade ago, researchers found that, when produced in pairs from the Tevatron’s proton-antiproton collisions, top quarks tended to be emitted in the direction of the proton beam, while anti-tops aligned in the direction of the antiproton beam. A small forward-backward asymmetry is predicted by the Standard Model, but the data showed the measured asymmetry to be tantalisingly bigger than expected, potentially showing that new particles or forces are influencing top-quark pair production.

    “As physicists, when we see something like this, we get excited,” says ATLAS researcher Frederic Deliot. If the asymmetry is much larger than predicted, it means “there could be lots of new physics to discover.”

    The forward-backward asymmetry measured at the Tevatron cannot be seen at the LHC because the LHC collides protons with protons, not antiprotons. But a related charge asymmetry, which causes top quarks to be produced preferentially in the centre of the LHC’s collisions, can be measured. The Standard Model predicts the effect to be small (around 1%) but, as with the forward-backward asymmetry, it could be made larger by new physics. The ATLAS and CMS experiments both measured the asymmetry by studying differences in the angular distributions of top quarks and antiquarks produced at the LHC at energies of 7 and 8 TeV.

    Alas, individually and combined, their results show no deviation from the latest Standard Model calculations.

    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.

    These calculations have in fact recently been improved, and show that the predicted asymmetry is slightly higher than previously thought. This, along with improvements in data analysis, even brings the earlier Tevatron result into line with the Standard Model.

    ATLAS and CMS will continue to subject the heavyweight top quark to tests at energies of 13 TeV to see if it deviates from its expected behaviour, including precision measurements of its mass and interactions with other Standard Model particles. But measuring the asymmetry will get even tougher, because the effect is predicted be half as big at a higher energy. “It’s going to be difficult,” says Deliot. “It will be possible to explore using the improved statistics at higher energy, but it is clear that the space for new physics has been severely restricted.”

    The successful combination of the charge-asymmetry measurements was achieved within the LHC top-quark physics working group, where scientists from ATLAS and CMS and theory experts work together intensively towards improving the interplay between theory and the two experiments, explains CMS collaborator Thorsten Chwalek. “Although the combination of ATLAS and CMS charge asymmetry results didn’t reveal any hints of new physics, the exercise of understanding all the correlations between the measurements was very important and paved the way for future ATLAS+CMS combinations in the top-quark sector.”

    See the full article here.

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    Meet CERN in a variety of places:

    Quantum Diaries
    QuantumDiaries

    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
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    CERN LHC particles

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  • richardmitnick 9:53 pm on October 12, 2017 Permalink | Reply
    Tags: , , CERN LHC, , , , , Xenon is a heavy noble gas that exists in trace quantities in the air, Xenon takes a turn in the LHC   

    From Symmetry: “Xenon takes a turn in the LHC” 

    Symmetry Mag
    Symmetry

    10/12/17
    Sarah Charley

    1
    For the first time, the Large Hadron Collider is accelerating xenon nuclei for experiments.

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    Most of the year, the Large Hadron Collider at CERN collides protons. LHC scientists have also accelerated lead nuclei stripped of their electrons. Today, for just about eight hours, they are experimenting with a different kind of nucleus: xenon.

    Xenon is a heavy noble gas that exists in trace quantities in the air. Xenon nuclei are about 40 percent lighter than lead nuclei, so xenon-xenon collisions have a different geometry and energy distribution than lead-lead collisions.

    “When two high-energy nuclei collide, they can momentarily form a droplet of quark gluon plasma, the primordial matter that filled our universe just after the big bang,” says Peter Steinberg, a physicist at the US Department of Energy’s Brookhaven National Laboratory and a heavy-ion coordinator for the ATLAS experiment at CERN. “The shape of the colliding nuclei influences the initial shape of this droplet, which in turn influences how the plasma flows and finally shows up in the angles of the particles we measure. We’re hoping that these smaller droplets from xenon-xenon collisions give us deeper insight into how this still-mysterious process works at truly subatomic length scales.”

    Not all particles that travel through CERN’s long chain of interconnected accelerators wind up in the LHC. Earlier this year, scientists were loading xenon ions into the accelerator and firing them at a fixed-target experiment instead.

    “We can have particles from two different sources feeding into CERN’s accelerator complex,” says Michaela Schaumann, a physicist in LHC operation working on the heavy-ion program. “The LHC’s injectors are so flexible that, once everything is set up properly, they can alternate between accelerating protons and accelerating ions a few times a minute.”

    Having the xenon beam already available provided an opportunity to send xenon into the LHC for first (and potentially only) time. It took some serious additional work to bring the beam quality up to collider levels, Schaumann says, but today it was ready to go.

    “We are keeping the intensities very low in order to fulfil machine protection requirements and be able to use the same accelerator configuration we apply during the proton-proton runs with xenon beams,” Schaumann says. “We needed to adjust the frequency of the accelerator cavities [because more massive xenon ions circulate more slowly than protons], but many of the other machine settings stayed roughly the same.”

    This novel run tests scientists’ knowledge of beam physics and shows the flexibility of the LHC. Scientists say they are hopeful it could reveal something new.

    “We can learn a lot about the properties of the hot, dense matter from smaller collision systems,” Steinberg says. “They are a valuable bridge to connect what we observe in lead-lead collisions to strikingly similar observations in proton-proton interactions.”

    3
    The LHC screen during the xenon-ion run. (Image: CERN)

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 12:56 pm on September 29, 2017 Permalink | Reply
    Tags: , , CERN LHC, CERN Open Data Portal, ,   

    From MIT: “First open-access data from large collider confirm subatomic particle patterns” 

    MIT News

    MIT Widget

    MIT News

    September 29, 2017
    Jennifer Chu

    1
    The Compact Muon Solenoid is a general-purpose detector at the Large Hadron Collider. Image courtesy of CERN

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    In November of 2014, in a first, unexpected move for the field of particle physics, the Compact Muon Solenoid (CMS) experiment — one of the main detectors in the world’s largest particle accelerator, the Large Hadron Collider — released to the public an immense amount of data, through a website called the CERN Open Data Portal.

    The data, recorded and processed throughout the year 2010, amounted to about 29 terabytes of information, yielded from 300 million individual collisions of high-energy protons within the CMS detector. The sharing of these data marked the first time any major particle collider experiment had released such an information cache to the general public.

    A new study by Jesse Thaler, an associate professor of physics at MIT and a long-time advocate for open access in particle physics, and his colleagues now demonstrates the scientific value of this move. In a paper published in Physical Review Letters, the researchers used the CMS data to reveal, for the first time, a universal feature within jets of subatomic particles, which are produced when high-energy protons collide. Their effort represents the first independent, published analysis of the CMS open data.

    “In our field of particle physics, there isn’t the tradition of making data public,” says Thaler. “To actually get data publicly with no other restrictions — that’s unprecedented.”

    Part of the reason groups at the Large Hadron Collider and other particle accelerators have kept proprietary hold over their data is the concern that such data could be misinterpreted by people who may not have a complete understanding of the physical detectors and how their various complex properties may influence the data produced.

    “The worry was, if you made the data public, then you would have people claiming evidence for new physics when actually it was just a glitch in how the detector was operating,” Thaler says. “I think it was believed that no one could come from the outside and do those corrections properly, and that some rogue analyst could claim existence of something that wasn’t really there.”

    “This is a resource that we now have, which is new in our field,” Thaler adds. “I think there was a reluctance to try to dig into it, because it was hard. But our work here shows that we can understand in general how to use this open data, that it has scientific value, and that this can be a stepping stone to future analysis of more exotic possibilities.”

    Thaler’s co-authors are Andrew Larkoski of Reed College, Simone Marzani of the State University of New York at Buffalo, and Aashish Tripathee and Wei Xue of MIT’s Center for Theoretical Physics and Laboratory for Nuclear Science.

    Seeing fractals in jets

    When the CMS collaboration publicly released its data in 2014, Thaler sought to apply new theoretical ideas to analyze the information. His goal was to use novel methods to study jets produced from the high-energy collision of protons.

    Protons are essentially accumulations of even smaller subatomic particles called quarks and gluons, which are bound together by interactions known in physics parlance as the strong force. One feature of the strong force that has been known to physicists since the 1970s describes the way in which quarks and gluons repeatedly split and divide in the aftermath of a high-energy collision.

    This feature can be used to predict the energy imparted to each particle as it cleaves from a mother quark or gluon. In particular, physicists can use an equation, known as an evolution equation or splitting function, to predict the pattern of particles that spray out from an initial collision, and therefore the overall structure of the jet produced.

    “It’s this fractal-like process that describes how jets are formed,” Thaler says. “But when you look at a jet in reality, it’s really messy. How do you go from this messy, chaotic jet you’re seeing to the fundamental governing rule or equation that generated that jet? It’s a universal feature, and yet it has never directly been seen in the jet that’s measured.”

    Collider legacy

    In 2014, the CMS released a preprocessed form of the detector’s 2010 raw data that contained an exhaustive listing of “particle flow candidates,” or the types of subatomic particles that are most likely to have been released, given the energies measured in the detector after a collision.

    The following year, Thaler published a theoretical paper with Larkoski and Marzani, proposing a strategy to more fully understand a complicated jet in a way that revealed the fundamental evolution equation governing its structure.

    “This idea had not existed before,” Thaler says. “That you could distill the messiness of the jet into a pattern, and that pattern would match beautifully onto that equation — this is what we found when we applied this method to the CMS data.”

    To apply his theoretical idea, Thaler examined 750,000 individual jets that were produced from proton collisions within the CMS open data. He looked to see whether the pattern of particles in those jets matched with what the evolution equation predicted, given the energies released from their respective collisions.

    Taking each collision one by one, his team looked at the most prominent jet produced and used previously developed algorithms to trace back and disentangle the energies emitted as particles cleaved again and again. The primary analysis work was carried out by Tripathee, as part of his MIT bachelor’s thesis, and by Xue.

    “We wanted to see how this jet came from smaller pieces,” Thaler says. “The equation is telling you how energy is shared when things split, and we found when you look at a jet and measure how much energy is shared when they split, they’re the same thing.”

    The team was able to reveal the splitting function, or evolution equation, by combining information from all 750,000 jets they studied, showing that the equation — a fundamental feature of the strong force — can indeed predict the overall structure of a jet and the energies of particles produced from the collision of two protons.

    While this may not generally be a surprise to most physicists, the study represents the first time this equation has been seen so clearly in experimental data.

    “No one doubts this equation, but we were able to expose it in a new way,” Thaler says. “This is a clean verification that things behave the way you’d expect. And it gives us confidence that we can use this kind of open data for future analyses.”

    Thaler hopes his and others’ analysis of the CMS open data will spur other large particle physics experiments to release similar information, in part to preserve their legacies.

    “Colliders are big endeavors,” Thaler says. “These are unique datasets, and we need to make sure there’s a mechanism to archive that information in order to potentially make discoveries down the line using old data, because our theoretical understanding changes over time. Public access is a stepping stone to making sure this data is available for future use.”

    This research was supported, in part, by the MIT Charles E. Reed Faculty Initiatives Fund, the MIT Undergraduate Research Opportunities Program, the U.S. Department of Energy, and the National Science Foundation.

    See the full article here .

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    The mission of MIT is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the MIT community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

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  • richardmitnick 3:36 pm on September 22, 2017 Permalink | Reply
    Tags: , ATLAS hunts for new physics with dibosons, , , CERN LHC, ,   

    From CERN Courier: “ATLAS hunts for new physics with dibosons” 


    CERN Courier

    Sep 22, 2017

    1
    WZ data

    Beyond the Standard Model of particle physics (SM), crucial open questions remain such as the nature of dark matter, the overabundance of matter compared to antimatter in the universe, and also the mass scale of the scalar sector (what makes the Higgs boson so light?). Theorists have extended the SM with new symmetries or forces that address these questions, and many such extensions predict new resonances that can decay into a pair of bosons (diboson), for example: VV, Vh, Vγ and γγ, where V stands for a weak boson (W and Z), h for the Higgs boson, and γ is a photon.

    The ATLAS collaboration has a broad search programme for diboson resonances, and the most recent results using 36 fb–1 of proton–proton collision data at the LHC taken at a centre-of-mass energy of 13 TeV in 2015 and 2016 have now been released. Six different final states characterised by different boson decay modes were considered in searches for a VV resonance: 4ℓ, ℓℓνν, ℓℓqq, ℓνqq, ννqq and qqqq, where ℓ, ν and q stand for charged leptons (electrons and muons), neutrinos and quarks, respectively. For the Vh resonance search, the dominant Higgs boson decay into a pair of b-quarks (branching fraction of 58%) was exploited together with four different V decays leading to ℓℓbb, ℓνbb, ννbb and qqbb final states. A Zγ resonance was sought in final states with two leptons and a photon.

    A new resonance would appear as an excess (bump) over the smoothly distributed SM background in the invariant mass distribution reconstructed from the final-state particles. The left figure shows the observed WZ mass distribution in the qqqq channel together with simulations of some example signals. An important key to probe very high-mass signals is to identify high-momentum hadronically decaying V and h bosons. ATLAS developed a new technique to reconstruct the invariant mass of such bosons combining information from the calorimeters and the central tracking detectors. The resulting improved mass resolution for reconstructed V and h bosons increased the sensitivity to very heavy signals.

    No evidence for a new resonance was observed in these searches, allowing ATLAS to set stringent exclusion limits. For example, a graviton signal predicted in a model with extra spatial dimensions was excluded up to masses of 4 TeV, while heavy weak-boson-like resonances (as predicted in composite Higgs boson models) decaying to WZ bosons are excluded for masses up to 3.3 TeV. Heavier Higgs partners can be excluded up to masses of about 350 GeV, assuming specific model parameters.

    See the full article here .

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    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

     
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