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  • richardmitnick 10:48 am on July 9, 2016 Permalink | Reply
    Tags: , , CERN LHC,   

    From Ethan Siegel: “Did The LHC Discover A New Type Of Particle?” 

    From Ethan Siegel

    Jul 9, 2016

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

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    The CMS detector at CERN, one of the two most powerful particle detectors ever assembled. Image credit: CERN.

    In the quest to advance our knowledge of the Universe, the biggest advances always seem to come when an experiment or measurement indicates something new: something our best theories to that date hadn’t predicted before. We all know that the LHC is looking for fundamental particles beyond the Standard Model, including hints of supersymmetry, technicolor, extra dimensions and more. Is it possible that the LHC just discovered a new type of particle, and the results just got buried in the news? That’s the question of Andrea Lelli, who wants to know why

    ” the news about tetraquark particles discovered in the LHC was published in some scientific feeds, but it seems the news did not catch mainstream attention. Isn’t this a valuable discovery, even though tetraquarks were already theorized? What does it mean for the standard model exactly?”

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    Let’s find out.

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    The particles and antiparticles of the Standard Model. Image credit: E. Siegel.

    When it comes to the particles we know in the Universe, we have:

    the quarks, which make up protons and neutrons (among other things)
    the leptons, including the electron and the very light neutrinos,
    the antiquarks and antileptons, the antiparticle counterparts of the above two classes,

    we have the photon, the particle version of what we call light,
    we have the gluons, which bind the quarks together and are responsible for the strong nuclear force,
    we have the heavy gauge bosons — the W+, W- and the Z0 — which mediate the weak interactions and radioactive decays,
    and the Higgs boson.

    The main goal of the LHC was to find the Higgs, which it did, completing the gamut of expected particles in the Standard Model.

    CERN CMS Higgs Event
    CERN CMS Higgs Event

    CERN ATLAS Higgs Event
    CERN ATLAS Higgs Event

    The stretch goal, however, was to find new particles beyond the ones we expected. We hopes to find clues to the greatest unsolved problems in theoretical physics at these high energies. To find something that could provide a hint to dark matter, the matter-antimatter asymmetry of the Universe, the reason particles have the masses they do, the reason strong decays don’t occur in certain fashions, etc. To find a new fundamental particle, and to give us either experimental support for a speculative theoretical idea or to surprise us, and push us in a new direction entirely.

    The closest we’ve gotten to that is a “hint” of a new particle whose decay shows up in the two-photon channel at 750 GeV. The threshold for discovery, however, requires a significance indicating there’s less than a 0.00003% chance of a fluke; the CMS and ATLAS data are at a 3% and a 10% chance of a fluke, respectively. That’s a pretty tenuous hint.

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    The ATLAS and CMS diphoton bumps, displayed together, clearly correlating at ~750 GeV. Image credit: CERN, CMS/ATLAS collaborations, image generated by Matt Strassler at https://profmattstrassler.com/2015/12/16/is-this-the-beginning-of-the-end-of-the-standard-model/.

    But the LHC does have a few new discoveries under its belt, although they aren’t quite fundamental discoveries in the “new particle” sense. What we got instead, however, was an announcement about the discovery of tetraquarks.

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    New Tetraquark Particle Found At Fermilab

    These aren’t new particles that are additions or extensions to the standard model: they don’t represent new forces, new interactions, or potential solutions to any of the great, outstanding problems of theoretical physics today. Rather, they’re entirely combinations of the existing particles that have never been seen before.

    The way quarks work is they come with a color: red, green or blue. (Antiquarks are cyan, magenta and yellow, respectively: the anti-colors of the quarks.) Gluons are exchanged between quarks to mediate the strong nuclear force, and they change the quark (or antiquark) colors when they do. But here’s the kicker: in order to exist in nature, any combination of quarks or antiquarks must be completely colorless. So you can have:

    Three quarks, since red+green+blue = colorless.
    Three antiquarks, since cyan+magenta+yellow = colorless.
    Or a quark-antiquark combination, since red+cyan (i.e., anti-red) = colorless.

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    Image credit: Wikipedia / Wikimedia Commons user Qashqaiilove.

    (You can also think of colors as “arrow” vectors in particular directions, and you have to get back to the origin to make something colorless.)

    The three quark combinations are known as baryons, and protons and neutrons are two such examples, along with more exotic combinations involving heavier quarks. Combinations of three antiquarks are known as anti-baryons, and include anti-protons and anti-neutrons. And the quark-antiquark combinations are known as mesons, which mediate the forces between atomic nuclei and have interesting life-and-decay properties on their own. Meson examples include the pion, the kaon, charmonium and the upsilon.

    But why stop there? Why not envision other color-free combinations? Why not something like:

    Two quarks and two antiquarks, a tetraquark?
    Or four quarks and one antiquark, a pentaquark?
    Or even something like five quarks and two antiquarks, a septaquark?

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    A pentaquark mass state discovered at the LHCb collaboration in 2015. The “spike” corresponds to the pentaquark. Image credit: CERN on behalf of the LHCb collaboration.

    (Having six quarks isn’t interesting or new: we already know how to make deuterium, a heavy isotope of hydrogen.) According to the Standard Model, this is not only possible, this is predicted. It’s a natural consequence of quantum chromodynamics: the science behind the strong nuclear force and those interactions.

    In the early 2000s, it was claimed that pentaquarks — these five quark/antiquark combinations — were discovered. Unfortunately, this was premature, as the 2003 result from Japan’s Laser Electron Photon Experiment at SPring-8 (LEPS) was unable to be reproduced and the other mid-2000s results were of poor significance. Tetraquark states were coming out at right around the same time. In 2003, the Belle experiment (also in Japan) announced a very controversial result: the discovery of a particle with a mass of 3872 MeV/c2 whose quantum numbers did not match any feasible baryon or meson-like states. For the first time, we had a tetraquark candidate.

    KEK Belle detector
    KEK Belle detector

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    Colour flux tubes produced by a configuration of four static quark-and-antiquark charges, representing calculations done in lattice QCD. Image credit: Wikimedia Commons user Pedro.bicudo, under a c.c.a.-s.a.-4.0 license.

    Belle went on, in 2007, to discover two other tetraquark candidates, including the first one with charm quarks inside of it, while Fermilab also uncovered a number of tetraquark candidates. But the biggest breakthrough in these “other” combination states came in 2013, when both Belle and the BES III experiment (in China) independently reported the discovery of the first confirmed tetraquark state.

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    BESIII detector

    It was the first tetraquark to be directly observed experimentally. Just like pions, it comes in positively charged, negatively charged and also neutral versions.

    Since then, the LHC has taken the lead, collecting more data on high-energy hadrons than any other experiment before it. The LHCb experiment, in particular, is the one designed to observe these particles. Some tetraquark candidates — like Fermilab’s bottom-quark containing candidate from the DØ experiment — were disfavored by the LHC. But others were directly observed, like Belle’s 2007 charm-containing tetraquark along with many new ones. And the latest tetraquark results that you allude to, reported here in Symmetry Magazine, detail four new tetraquark particles.

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    The LHCb detector room at CERN. Image credit: CERN.

    Symmetry Mag
    Symmetry, a journal of FNAL and SLAC, both USA

    The cool thing about these four new particles is that they’re made up of two charm and two strange quarks apiece (with two always being the “anti” version), making these the first tetraquarks to have no light (up and down) quarks in them. And just like you can have a single electron within an atom exist in many different unique states, the way these quarks are configured means that each of these particles have unique quantum numbers, including mass, spin, parity, and charge conjugation. Physicist Thomas Britton, who did much of this work for his Ph.D., detailed:

    We looked at every known particle and process to make sure these four structures couldn’t be explained by any pre-existing physics. It was like baking a six-dimensional cake with 98 ingredients and no recipe—just a picture of a cake.

    In other words, we’re 100% positive these aren’t any normal hadrons the Standard Model could have predicted, and pretty sure these really are tetraquarks!

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    B mesons can decay directly into a J/Ψ (psi) particle and a Φ (phi) particle. The CDF scientists found evidence that some B mesons unexpectedly decay into an intermediate quark structure identified as a Y particle. Image credit: Symmetry Magazine.

    The way they normally show up — as the picture details above — is by showing up in an intermediate stage (indicated by Y) of some decays. This is completely allowed by the Standard Model, but it’s a very rare process and so, in some sense, it’s amazing that we have the sheer amount of data and can measure it precisely enough to detect these classes of particles at all. Tetraquarks, pentaquarks and even higher combinations are expected to be real. Perhaps most oddly of all, the Standard Model predicts the existence of glueballs, which are bound states of gluons.

    It’s important to remember that in doing these tests, and in looking for these incredibly rare and difficult-to-find states of nature, we are doing the highest-precision tests of QCD — the theory underlying the strong force — of all-time. If these predicted states of quarks, antiquarks and gluons fail to materialize, then something about QCD is wrong, and that would be a way of going beyond the Standard Model, too! Finding these states is the first step; understanding the details of how they fit together, what their hierarchies are and how our known physics applies to these more and more complex systems is what comes next. As with everything in nature, the payoff for human advancement is hard to see when the initial discovery is made, but the joy of finding things out is always its own reward.

    See the full article here .

    Please help promote STEM in your local schools.

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    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 8:02 am on July 6, 2016 Permalink | Reply
    Tags: CERN LHC, , , Sabine Hossenfelder, The future of Particle Physics   

    From Ethan Siegel: “Could no new particles at the LHC be exactly what physics needs?” 

    From Ethan Siegel

    7.5.16

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    The ATLAS and CMS diphoton bumps, displayed together, clearly correlating at ~750 GeV. Image credit: CERN, CMS/ATLAS collaborations, image generated by Matt Strassler at https://profmattstrassler.com/2015/12/16/is-this-the-beginning-of-the-end-of-the-standard-model/.

    This article was authored by Sabine Hossenfelder. Sabine is a theoretical physicist specialized in quantum gravity and high energy physics. She also freelance writes about science. Her blog, Backreaction, can be found here.

    “We have made the discovery of a new particle — a completely new particle — which is most probably very different from all the other particles. It’s nearly a once in a lifetime experience, I would say.” -Rolf-Dieter Heuer

    At the end of the LHC’s first run at high energies, both the CMS and ATLAS collaborations reported a particularly interesting “bump” in the diphoton channel. Based on what’s known and predicted of the Standard Model, there should be a particular pattern to two-photon signals with a given particular energy. A bump is the most surefire indication we can look for in the search for a new particle, and a bump of a particular size, width and energy could either indicate a completely new, fundamental, beyond-the-standard-model particle, the first of its kind — or a new standard model feature — or it could simply be statistical noise. Despite the fact that it would be the nightmare of most of my colleagues, I’m hoping the diphoton bump turns out to be nothing more than noise.

    I finished high school in 1995. It was the year the top quark was discovered, a prediction dating back to 1973. As I read the articles in the news, I was fascinated by the mathematics that allowed physicists to reconstruct the structure of elementary matter. It wouldn’t have been difficult to predict in 1995 that I’d go on to earn a PhD in theoretical high energy physics.

    Little did I realize that for more than 20 years the so-provisional-looking standard model would remain the undefeated world champion of accuracy, irritatingly successful in its arbitrariness and yet impossible to surpass. We added neutrino masses in the late 1990s, but the idea that they wouldn’t be massless dates back to the 1950s. The prediction of the Higgs, discovered 2012, originated in the early 1960s. And while the poor standard model has been discounted as “ugly” by everyone from Stephen Hawking to Michio Kaku to Paul Davies, it’s still the best we can do.

    Since I entered physics, I’ve seen grand unified models proposed and falsified. I’ve seen loads of dark matter candidates not being found, followed by a ritual parameter adjustment to explain the lack of detection. I’ve seen supersymmetric particles being “predicted” with constantly increasing masses, from some GeV to some 100 GeV to LHC energies of some TeV. And now that it looks like the LHC isn’t going to see any superpartners either, my colleagues in particle physicists are more than willing to once again move the goalposts.

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    The Standard Model particles and their supersymmetric counterparts. Exactly 50% of these particles have been discovered, and 50% have never showed a trace that they exist. Image credit: Claire David, of http://davidc.web.cern.ch/davidc/index.php?id=research.

    During my professional career, all I have seen is failure. A failure, that is, of particle physicists to uncover a more powerful mathematical framework that improves upon the theories we already have. Yes, failure is part of science — it’s frustrating, but not worrisome. What worries me much more is our failure to learn from those failures. Rather than trying something new, we’ve been trying the same thing over and over again, expecting different results.

    When I look at the data what I see is that our reliance on gauge-symmetry and the attempt at unification, the use of naturalness as guidance, and the trust in beauty and simplicity aren’t working. The cosmological constant isn’t natural. The Higgs mass isn’t natural. The standard model isn’t pretty, and the concordance model isn’t simple. Grand unification failed. It failed again. And yet we haven’t drawn any consequences from this: Particle physicists are still playing today by the same rules as in 1973.

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    The various decay channels of the observed Standard Model Higgs, along with their error bars. The parameter mu = 1 corresponds to a Standard Model Higgs only. Image credit: The ATLAS collaboration, 2015. Via https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2015-007/.

    For the last ten years you’ve been told that the LHC must see some new physics besides the Higgs because otherwise nature isn’t “natural” — a technical term invented to describe the degree of numerical coincidence of a theory. I’ve been laughed at when I explained that I don’t buy into naturalness because it’s a philosophical criterion, not a scientific one. But on that matter I got the last laugh: nature, it turns out, doesn’t like to be told what’s presumably natural.

    The idea of naturalness that has been preached for so long is not compatible with the LHC data — the Higgs but no further new physics — regardless of what else will be found in the data yet to come. And now naturalness is in the way of moving predictions for so-far undiscovered particles — yet again — to higher energies. Particle physicists, opportunistic as always, are suddenly more than willing to discard of naturalness to justify the next larger collider.

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    Inside the magnet upgrades on the LHC, that have it running at nearly double the energies of the first (2010–2013) run. Image credit: Richard Juilliart/AFP/Getty Images.

    The LHC so far hasn’t seen evidence for physics beyond the standard model, except possibly for the diphoton bump. That not-quite-robust hint is the only remaining anomaly in the LHC data that might signal new physics, the resort of last hope. The statistical significance isn’t remarkable — we have seen many fluctuations of this size come and go. But if the bump doesn’t disappear with the data from the next run, the standard model might fall.

    Broadly speaking, there are three options for what the anomaly could be:

    it might be new physics,
    it might be a little understood aspect of standard model physics,
    or it might simply be a statistical fluctuation that turns out to be nothing novel at all.

    The first option is arguably the more exciting one and it has attracted the bulk of attention in the last couple of months. Indeed, there have been so many proposals for what the diphoton bump could be I’m unable to survey them, but a brief summary is: it doesn’t look like anything that anybody expected before they saw the data. Most importantly, it neither looks like a fourth generation nor like supersymmetry. If you have any respect left for particle physicists at this point, this should actually tell you that the bump is likely to join the nirvana of statistical flukes.

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    The previous anomaly — a diboson “bump” at around 2,000 GeV — that went away and was found to be mere statistical noise with the accumulation of more data. Images credit: ATLAS collaboration (L), via http://arxiv.org/abs/1506.00962; CMS collaboration (R), via http://arxiv.org/abs/1405.3447.

    The last word on the diphoton anomaly hasn’t been spoken, and it’s too early to jump to conclusions, so I won’t. The only rumors I have heard are the same rumors that have already circulated on Twitter, I’m no wiser than you and have thus nothing to add about the significance of the bump. But I want to spend a few words on the significance of no-bump.

    If the bump goes away, this would catapult us into what has become known as the “nightmare scenario” for the LHC: The Higgs and nothing else. Many particle physicists are afraid of this scenario because, if it comes true, it will leave them without guidance, lost in a thicket of rapidly multiplying models that threaten to block out sunlight. Without some new physics, everyone is concerned we’ll have nothing to work with that we haven’t had already for 50 years. Without any new inputs that can tell us which direction to look towards in the ultimate goal of unification and/or quantum gravity, we’d finally have to admit the truth: we’re completely lost.

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    A proton-antiproton interaction at 540 GeV, showing particle tracks in a streamer chamber. Without any new physics at the LHC, there’s no guidance towards what particles or interactions might lie beyond the Standard Model. Image credit: UA5 collaboration, CERN, from 1982.

    That’s why I’d love it if the bump goes away. Because it would be a clear signal that we’ve been doing something seriously wrong, that our experience from constructing the standard model is no longer a promising direction to continue.

    We already know we’ve been doing something wrong — bump or no bump — because naturalness has gone out the window. But if the bump stays, chances are we’d try to absorb it into the mathematics we already have rather than look for something really new. Sometimes things have to get really bad before they can get better. That’s why for me no-bump is the most hopeful outcome.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 3:51 pm on June 23, 2016 Permalink | Reply
    Tags: , CERN LHC, , ORNL Cray Titan,   

    From DEIXIS via ORNL: “Early-universe soup” 

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    Oak Ridge National Laboratory

    DEIXIS

    June 22nd, 2016
    Sarah Webb

    ORNL’s Titan supercomputer is helping Brookhaven physicists understand the matter that formed microseconds after the Big Bang.

    ORNL Titan Supercomputer
    ORNL Crfay Titan Supercomputer

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    An experimental and theoretical exploration of the quantum chromodynamics (QCD) phase diagram. The matter produced in collisions at the highest energies and the smallest baryon chemical potentials can change from quark-gluon plasma (QGP) to a hadron gas through a smooth crossover. But lower energy collisions can access higher baryon chemical potentials where a first-order phase transition line is thought to exist. The reach of the future DOE Basic Energy Sciences program at RHIC is shown, as are the trajectories on the phase diagram followed by the cooling droplets of QGP produced in collisions with varying energy. The present reach of lattice QCD calculations is illustrated by the yellow band. (Illustration: Swagato Mukherjee, Brookhaven National Laboratory.)

    At the dawn of the universe – just after the Big Bang – all matter was in the form of a hot-flowing soup called quark-gluon plasma, or QGP. Though a few ambitious, atom-smashing experiments have produced transient samples of this extreme phase of matter, researchers still have much to learn about its fundamental behavior.

    Experimental physicists have tried to produce quark-gluon plasma since the 1980s and first reported observing it in 2000. Over the past 45 years, theorists have outlined the equations that govern QGP and many have combined theory and experiment to describe it.

    Large-scale computations have been critical to the theoretical study of QGP’s novel characteristics. As part of a theoretical effort funded by the Department of Energy, Brookhaven National Laboratory’s Swagato Mukherjee and his colleagues are using an allotment of 167 million processor hours from the ASCR Leadership Computing Challenge (ALCC) to better understand QGP. Their findings will help physicists plan the next wave of experiments. “Neither theory nor experiment can do this alone,” Mukherjee says.

    At the heart of every atom lies the nucleus, a super-tight ball of subatomic protons and neutrons. Those particles are made of even smaller parts, including quarks, which comprise just one thousandth of the mass. Gluons, the adhesive particles that hold quarks together, carry the strong interaction, a fundamental physical force that binds the atomic nucleus and generates the other 99.9 percent of all matter’s mass.

    But at temperature extremes 70,000 times hotter than the center of the sun, even tightly packed quarks and gluons begin to flow. The transition to the flowing state is much like phase changes in matter such as water. Water exists as liquid, steam or ice, based on how much heat and pressure are applied. Scientists long ago carefully mapped the underlying conditions and boundaries between water’s different forms as a phase diagram, information that’s been critical for understanding water’s behavior. If researchers can understand how changes in temperature and density affect QGP, physicists can create a similar roadmap documenting conditions that form it.

    Because of the extreme conditions required for QGP creation, the only way to observe it on Earth is to bombard matter with high-energy particles at either the Relativistic Heavy Ion Collider (RHIC) at Brookhaven or the Large Hadron Collider at CERN in Switzerland.

    BNL/RHIC
    BNL/RHIC

    CERN LHC Grand Tunnel
    CERN/LHC

    Fast-moving nuclei of lead and gold collide at high energy, briefly producing the plasma-soup researchers can study.

    Experiments aren’t the only way to study QGP’s properties. Physicists have worked out the theory of how quarks and gluons interact, known as quantum chromodynamics, or QCD. However, the complexity of these interactions, with billions of variables, requires sophisticated parallel computing resources to solve, Mukherjee says.

    Using their ALCC allotment, Mukherjee and his colleagues have concentrated on a version of this theory, lattice QCD, to computationally study the plasma on Titan, a Cray XK7 at Oak Ridge National Laboratory. The calculations line up quarks at the intersection points on a grid, with gluons positioned on each of the crossbars between them. Initially, the researchers omitted the density component and solely calculated how increasing heat eventually produces the flowing QGP. Now they’ll need to consider the density component as well. With their ongoing ALCC allotment, they’re simulating how increasing density changes the phase diagram and eventually the plasma’s behavior.

    These types of computations will be critical for future experiments at the big colliders. In 2019 and 2020, DOE will support a large collaborative effort, the Beam Energy Scan II at RHIC, to observe the full phase diagram of quark-gluon plasma, including the density component, Mukherjee says, an effort that will cost hundreds of millions of dollars. The calculations Mukherjee and his colleagues perform will provide information that helps the experimental physicists plan those experiments. The calculations will provide temperature benchmarks – a range needed to generate QGP.

    In large particle accelerators, researchers can’t control the temperature or density, only the energy of the atomic collisions, Mukherjee says. So calculations will help researchers translate that collision energy into the heat and density parameters they need to observe the full range of changes in the phase diagram of quark-gluon plasma.

    Ultimately, the exercise is about fundamental discovery and collaboration between theorists and experimentalists to discover the quark-gluon soup recipe. Mukherjee is part of a larger Brookhaven theoretical team, the Nuclear Physics Lattice Gauge Theory group led by Fritjof Karsch. This work is an integral part of the BEST collaboration – for Beam Energy Scan Theory – a DOE-funded, multi-institutional Topical Collaboration in Nuclear Theory, looking at the phases and properties of hot-dense QCD matter. Mukherjee’s research is supported by DOE Office of Science’s Nuclear Physics program.

    See the full article here .

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    ORNL is managed by UT-Battelle for the Department of Energy’s Office of Science. DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time.

    i2

     
  • richardmitnick 3:27 pm on June 23, 2016 Permalink | Reply
    Tags: CERN LHC, , , Where are the bottom quarks?   

    From Symmetry: “The Higgs-shaped elephant in the room” 

    Symmetry Mag

    Symmetry

    06/23/16
    Sarah Charley

    Higgs bosons should mass-produce bottom quarks. So why is it so hard to see it happening?

    1
    Maximilien Brice, CERN

    Higgs bosons are born in a blob of pure concentrated energy and live only one-septillionth of a second before decaying into a cascade of other particles. In 2012, these subatomic offspring were the key to the discovery of the Higgs boson.

    Higgs Boson Event

    So-called daughter particles stick around long enough to show up in the CMS and ATLAS detectors at the Large Hadron Collider. Scientists can follow their tracks and trace the family trees back to the Higgs boson they came from.

    CERN/CMS Detector
    CMS

    CERN/ATLAS detector
    ATLAS

    But the particles that led to the Higgs discovery were actually some of the boson’s less common progeny. After recording several million collisions, scientists identified a handful of Z bosons and photons with a Higgs-like origin. The Standard Model of particle physics predicts that Higgs bosons produce those particles 2.5 and 0.2 percent of the time.

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth

    Physicists later identified Higgs bosons decaying into W bosons, which happens about 21 percent of the time.

    According to the Standard Model, the most common decay of the Higgs boson should be a transformation into a pair of bottom quarks. This should happen about 60 percent of the time.

    The strange thing is, scientists have yet to discover it happening (though they have seen evidence).

    According to Harvard researcher John Huth, a member of the ATLAS experiment, seeing the Higgs turning into bottom quarks is priority No. 1 for Higgs boson research.

    “It would behoove us to find the Higgs decaying to bottom quarks because this is the largest interaction,” Huth says, “and it darn well better be there.”

    If the Higgs to bottom quarks decay were not there, scientists would be left completely dumbfounded.

    “I would be shocked if this particle does not couple to bottom quarks,” says Jim Olsen, a Princeton researcher and Physics Coordinator for the CMS experiment. “The absence of this decay would have a very large and direct impact on the relative decay rates of the Higgs boson to all of the other known particles, and the recent ATLAS and CMS combined measurements are in excellent agreement with expectations.”

    To be fair, the decay of a Higgs to two bottom quarks is difficult to spot.

    When a dying Higgs boson produces twin Z or W bosons, they each decay into a pair of muons or electrons. These particles leave crystal clear signals in the detectors, making it easy for scientists to spot them and track their lineage. And because photons are essentially immortal beams of light, scientists can immediately spot them and record their trajectory and energy with electromagnetic detectors.

    But when a Higgs births a pair of bottom quarks, they impulsively marry other quarks, generating huge unstable families which bourgeon, break and reform. This chaotic cascade leaves a messy ancestry.

    Scientists are developing special tools to disentangle the Higgs from this multi-generational subatomic soap opera. Unfortunately, there are no cheek swabs or Maury Povich to announce, Higgs, you are the father! Instead, scientists are working on algorithms that look for patterns in the energy these jets of particles deposit in the detectors.

    “The decay of Higgs bosons to bottom quarks should have different kinematics from the more common processes and leave unique signatures in our detector,” Huth says. “But we need to deeply understand all the variables involved if we want to squeeze the small number of Higgs events from everything else.”

    Physicist Usha Mallik and her ATLAS team of researchers at the University of Iowa have been mapping the complex bottom quark genealogies since shortly after the Higgs discovery in 2012.

    “Bottom quarks produce jets of particles with all kinds and colors and flavors,” Mallik says. “There are fat jets, narrow gets, distinct jets and overlapping jets. Just to find the original bottom quarks, we need to look at all of the jet’s characteristics. This is a complex problem with a lot of people working on it.”

    This year the LHC will produce five times more data than it did last year and will generate Higgs bosons 25 percent faster. Scientists expect that by August they will be able to identify this prominent decay of the Higgs and find out what it can tell them about the properties of this unique particle.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 5:45 pm on June 17, 2016 Permalink | Reply
    Tags: CERN LHC, ,   

    From Pauline Gagnon in Quantum Diaries: “Enough data to explore the unknown” 

    6.17.16

    Pauline Gagnon
    Pauline Gagnon

    The Large Hadron Collider (LHC) at CERN has already delivered more high energy data than it had in 2015. To put this in numbers, the LHC has produced 4.8 fb-1, compared to 4.2 fb-1 last year, where fb-1 represents one inverse femtobarn, the unit used to evaluate the data sample size. This was achieved in just one and a half month compared to five months of operation last year.

    With this data at hand, and the projected 20-30 fb-1 until November, both the ATLAS and CMS experiments can now explore new territories and, among other things, cross-check on the intriguing events they reported having found at the end of 2015. If this particular effect is confirmed, it would reveal the presence of a new particle with a mass of 750 GeV, six times the mass of the Higgs boson. Unfortunately, there was not enough data in 2015 to get a clear answer. The LHC had a slow restart last year following two years of major improvements to raise its energy reach. But if the current performance continues, the discovery potential will increase tremendously. All this to say that everyone is keeping their fingers crossed.

    If any new particle were found, it would open the doors to bright new horizons in particle physics. Unlike the discovery of the Higgs boson in 2012, if the LHC experiments discover a anomaly or a new particle, it would bring a new understanding of the basic constituents of matter and how they interact. The Higgs boson was the last missing piece of the current theoretical model, called the Standard Model. This model can no longer accommodate new particles. However, it has been known for decades that this model is flawed, but so far, theorists have been unable to predict which theory should replace it and experimentalists have failed to find the slightest concrete signs from a broader theory. We need new experimental evidence to move forward.

    Although the new data is already being reconstructed and calibrated, it will remain “blinded” until a few days prior to August 3, the opening date of the International Conference on High Energy Physics. This means that until then, the region where this new particle could be remains masked to prevent biasing the data reconstruction process. The same selection criteria that were used for last year data will then be applied to the new data. If a similar excess is still observed at 750 GeV in the 2016 data, the presence of a new particle will make no doubt.

    Even if this particular excess turns out to be just a statistical fluctuation, the bane of physicists’ existence, there will still be enough data to explore a wealth of possibilities. Meanwhile, you can follow the LHC activities live or watch CMS and ATLAS data samples grow. I will not be available to report on the news from the conference in August due to hiking duties, but if anything new is announced, even I expect to hear its echo reverberating in the Alps.

    See the full article here .

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  • richardmitnick 5:11 pm on June 17, 2016 Permalink | Reply
    Tags: , CERN LHC, , , ,   

    From Don Lincoln at FNAL: “The triumphant Standard Model” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

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

    June 17, 2016

    FNAL Don Lincoln
    Don Lincoln

    In high-end research, there are a couple of deeply compelling types of data analyses that scientists do. There are those that break the existing scientific understanding and rewrite the textbooks. Those are exciting. But there are also those in which a highly successful theory is tested in a regime never before explored. There can also be two types of outcome. If the theory fails to explain the data, we have a discovery of the type I mentioned first. But it is also possible that the theory explains the data perfectly well. If so, that means that you’ve proven that the existing theory is even more successful than was originally known. That’s a different kind of success. It means that predictions made in one realm taught scientists enough to understand far more.

    In the LHC, pairs of protons are collided together with the unprecedented energy of 13 trillion electronvolts of energy.

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

    Before 2015, when the data in this analysis was recorded, the highest energy ever studied by humanity was only 8 trillion electronvolts. So, already we know that the new data is 63 percent higher in terms of energy reach as compared to the old data. To get a visceral sense of what that means, imagine that your bank told you that they made a mistake and that for every dollar you thought you had in your account, you actually had $1.63. I’m guessing you’d start planning for an awesome vacation or perhaps an earlier retirement.

    When the protons collide, most commonly, a quark or gluon from each proton hits a quark or gluon from the other proton and knocks them out of the collision area into the detector. As the quarks and gluons leave the collision area, they convert into sprays of particles that travel in roughly the same direction. These are called jets. Physicists study the location and energy of the jets in the detector and compare them to the predicted distribution.

    CMS scientists studied the production patterns of jets at a collision energy of 13 trillion electronvolts and found that they agreed with the predictions of the Standard Model with the same level of precision seen at lower energy measurements.

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth

    This result comes with a small sadness because this means that new physics hasn’t been discovered. On the other hand, it is a resounding endorsement of the theory of quantum chromodynamics, or QCD, which is the portion of the Standard Model that deals explicitly with quark and gluon scattering. QCD, first worked out nearly half a century ago, continues its decades-long track record of success.

    2
    Scientists are constantly exploring the universe, seeing what happens when existing theories are tested in new realms. In today’s analysis, scientists put the leading theory of quark scattering to the test, studying what happens when it is compared to data taken at energies over 60 percent higher than ever before achieved.

    See the full article here .

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    collaborate at Fermilab on experiments at the frontiers of discovery.

     
  • richardmitnick 10:55 am on June 14, 2016 Permalink | Reply
    Tags: , CERN LHC, , , , Stacking the building blocks of the 2016 ATLAS Physics Programme   

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

    CERN ATLAS Higgs Event

    CERN/ATLAS
    ATLAS

    13th June 2016
    ATLAS Collaboration

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

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

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

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

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

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

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

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

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

    Links

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

    See the full article here .

    CERN LHC Map
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    CERN LHC particles
    LHC at CERN

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  • richardmitnick 9:43 am on June 6, 2016 Permalink | Reply
    Tags: , CERN LHC, , , ,   

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

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

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

    June 3, 2016
    Bo Jayatilaka

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

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

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

    CERN/CMS Detector
    CERN/CMS Detector

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

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

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

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

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

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

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

    See the full article here .

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    collaborate at Fermilab on experiments at the frontiers of discovery.

     
  • richardmitnick 3:34 pm on May 22, 2016 Permalink | Reply
    Tags: , , CERN LHC, , , ,   

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

    Huffington Post
    The Huffington Post

    05/18/2016
    David Freeman

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

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

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

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

    CERN CMS Higgs Event
    CERN CMS Higgs Event

    CERN/CMS Detector
    CERN/CMS Detector

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

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

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

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

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

    What’s a typical day like for you?

    Super-hectic, super-speedy and … atypical!

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

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

    2
    The Large Hadron Collider, Geneva, Switzerland.

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

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

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

    CERN HL-LHC bloc

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

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

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

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

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

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

    FNAL LBNF/DUNE
    FNAL LBNF/DUNE

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

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

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

    What do you do in your spare time?

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

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

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

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

    See the full article here .

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  • richardmitnick 8:28 am on May 22, 2016 Permalink | Reply
    Tags: , , CERN LHC, , , ,   

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

    Livescience

    May 20, 2016
    Ian O’Neill, Discovery News

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

    CERN/LHCb
    CERN/LHCb

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    See the full article here .

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