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  • richardmitnick 3:18 pm on February 20, 2018 Permalink | Reply
    Tags: , , DarkMatter, , Higgs, , ,   

    From Symmetry: “The secret life of Higgs bosons” 

    Symmetry Mag

    Symmetry

    02/20/18
    Sarah Charley

    Are these mass-giving particles hanging out with dark matter?

    CERN CMS Higgs Event


    CERN ATLAS Higgs Event


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

    The Higgs boson has existed since the earliest moments of our universe. Its directionless field permeates all of space and entices transient particles to slow down and burgeon with mass. Without the Higgs field, there could be no stable structures; the universe would be cold, dark and lifeless.

    Many scientists are hoping that the Higgs boson will help them understand phenomena not predicted by the Standard Model, physicists’ field guide to the subatomic world. While the Standard Model is an ace at predicting the the properties of all known subatomic particles, it falls short on things like gravity, the accelerating expansion of the universe, the supernatural speeds of spinning galaxies, the absurd excess of matter over antimatter, and beyond.

    “We can use the Higgs boson as a tool to look for new physics that might not readily interact with our standard set of particles,” says Darin Acosta, a physicist at the University of Florida.

    In particular, there’s hope that the Higgs boson might interact with dark matter, thought to be a widespread but never directly detected kind of matter that outnumbers regular matter five to one. This theoretical massive particle makes itself known through its gravitational attraction. Physicists see its fingerprint all over the cosmos in the rotational speed of galaxies, the movements of galaxy clusters and the bending of distant light. Even though dark matter appears to be everywhere, scientists have yet to find a tool that can bridge the light and dark sectors.

    Dark matter halo. Image credit: Virgo consortium / A. Amblard / ESA

    If the Higgs field is the only vendor of mass in the cosmos, then dark matter must be a client. This means that the Higgs boson, the spokesparticle of the Higgs field, must have some relationship with dark matter particles.

    “It could be that dark matter aids in the production of Higgs bosons, or that Higgs bosons can transform into dark matter particles as they decay,” Acosta says. “It’s simple on paper, but the challenge is finding evidence of it happening, especially when so many parts of the equation are completely invisible.”

    The particle that wasn’t there

    To find evidence of the Higgs boson flirting with dark matter, scientists must learn how to see the invisible. Scientists never see the Higgs boson directly; in fact, they discovered the Higgs boson by tracing the particles it produces as it decays. Now, they want to precisely measure how frequently the Higgs boson transforms into different types of particles. It’s not easy.

    “All we can see with our detector is the last step of the decay, which we call the final state,” says Will Buttinger, a CERN research fellow. “In many cases, the Higgs is not the parent of the particles we see in the final state, but the grandparent.”

    The Standard Model not only predicts all the different possible decays of Higgs bosons, but how favorable each decay is. For instance, it predicts that about 60 percent of Higgs bosons will transform into a pair of bottom quarks, whereas only 0.2 percent will transform into a pair of photons. If the experimental results show Higgs bosons decaying into certain particles more or less often than predicted, it could mean that a few Higgs bosons are sneaking off and transforming into dark matter.

    Of course, these kinds of precision measurements cannot tell scientists if the Higgs is evolving into dark matter as part of its decay path—only that it is behaving strangely. To catch the Higgs in the act, scientists need irrefutable evidence of the Higgs schmoozing with dark matter.

    “How do we see invisible things?” asks Buttinger. “By the influence it has on what we can see.”

    For example, humans cannot see the wind, but we can look outside our windows and immediately know if it’s windy based whether or not trees are swaying. Scientists can look for dark matter particles in a similar way.

    “For every action, there is an equal and opposite reaction,” Buttinger says. “If we see particles shooting off in one direction, we know that there must be something shooting off in the other direction.”

    If a Higgs boson transforms into a visible particle paired with a dark matter particle, the solitary tracks of the visible particles will have an odd and inexplicable trajectory—an indication that, perhaps, a dark matter particle is escaping.

    The Higgs boson is the newest tool scientists have to explore the uncharted terrain within and beyond the Standard Model. The continued research at the LHC and its future upgrades will enable scientists to characterize this reticent particle and learn its close-held secrets.

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


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  • richardmitnick 12:30 pm on December 31, 2017 Permalink | Reply
    Tags: “The universe is inevitable” he declared. “The universe is impossible.”Nima Arkani-Hamed, , Complications in Physics - "Is Nature Unnatural?", , Higgs, Nima Arkani-Hamed of the Institute for Advanced Study, , , , The universe might not make sense   

    From Quanta Magazine: Complications in Physics – “Is Nature Unnatural?” 2013 

    Quanta Magazine
    Quanta Magazine

    May 24, 2013 [Just brought forward in social media.]
    Natalie Wolchover

    Decades of confounding experiments have physicists considering a startling possibility: The universe might not make sense.

    1
    Is the universe natural or do we live in an atypical bubble in a multiverse? Recent results at the Large Hadron Collider have forced many physicists to confront the latter possibility. Illustration by Giovanni Villadoro.

    On an overcast afternoon in late April, physics professors and students crowded into a wood-paneled lecture hall at Columbia University for a talk by Nima Arkani-Hamed, a high-profile theorist visiting from the Institute for Advanced Study in nearby Princeton, N.J.

    6
    Nima Arkani-Hamed, Institute for Advanced Study Princeton, N.J., USA
    With his dark, shoulder-length hair shoved behind his ears, Arkani-Hamed laid out the dual, seemingly contradictory implications of recent experimental results at the Large Hadron Collider in Europe.

    3
    “The universe is impossible,” said Nima Arkani-Hamed, 41, of the Institute for Advanced Study, during a recent talk at Columbia University. Natalie Wolchover/Quanta Magazine

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    “The universe is inevitable,” he declared. “The universe is impossible.”

    The spectacular discovery of the Higgs boson in July 2012 confirmed a nearly 50-year-old theory of how elementary particles acquire mass, which enables them to form big structures such as galaxies and humans.

    CERN CMS Higgs Event

    CERN ATLAS Higgs Event

    “The fact that it was seen more or less where we expected to find it is a triumph for experiment, it’s a triumph for theory, and it’s an indication that physics works,” Arkani-Hamed told the crowd.

    However, in order for the Higgs boson to make sense with the mass (or equivalent energy) it was determined to have, the LHC needed to find a swarm of other particles, too. None turned up.

    With the discovery of only one particle, the LHC experiments deepened a profound problem in physics that had been brewing for decades. Modern equations seem to capture reality with breathtaking accuracy, correctly predicting the values of many constants of nature and the existence of particles like the Higgs. Yet a few constants — including the mass of the Higgs boson — are exponentially different from what these trusted laws indicate they should be, in ways that would rule out any chance of life, unless the universe is shaped by inexplicable fine-tunings and cancellations.

    In peril is the notion of “naturalness,” Albert Einstein’s dream that the laws of nature are sublimely beautiful, inevitable and self-contained. Without it, physicists face the harsh prospect that those laws are just an arbitrary, messy outcome of random fluctuations in the fabric of space and time.

    The LHC will resume smashing protons in 2015 in a last-ditch search for answers. But in papers, talks and interviews, Arkani-Hamed and many other top physicists are already confronting the possibility that the universe might be unnatural. (There is wide disagreement, however, about what it would take to prove it.)

    “Ten or 20 years ago, I was a firm believer in naturalness,” said Nathan Seiberg, a theoretical physicist at the Institute, where Einstein taught from 1933 until his death in 1955. “Now I’m not so sure. My hope is there’s still something we haven’t thought about, some other mechanism that would explain all these things. But I don’t see what it could be.”

    Physicists reason that if the universe is unnatural, with extremely unlikely fundamental constants that make life possible, then an enormous number of universes must exist for our improbable case to have been realized. Otherwise, why should we be so lucky? Unnaturalness would give a huge lift to the multiverse hypothesis, which holds that our universe is one bubble in an infinite and inaccessible foam. According to a popular but polarizing framework called string theory, the number of possible types of universes that can bubble up in a multiverse is around 10^500. In a few of them, chance cancellations would produce the strange constants we observe.

    In such a picture, not everything about this universe is inevitable, rendering it unpredictable. Edward Witten, a string theorist at the Institute, said by email, “I would be happy personally if the multiverse interpretation is not correct, in part because it potentially limits our ability to understand the laws of physics. But none of us were consulted when the universe was created.”

    “Some people hate it,” said Raphael Bousso, a physicist at the University of California at Berkeley who helped develop the multiverse scenario. “But I just don’t think we can analyze it on an emotional basis. It’s a logical possibility that is increasingly favored in the absence of naturalness at the LHC.”

    What the LHC does or doesn’t discover in its next run is likely to lend support to one of two possibilities: Either we live in an overcomplicated but stand-alone universe, or we inhabit an atypical bubble in a multiverse.

    Multiverse. Image credit: public domain, retrieved from https://pixabay.com/

    “We will be a lot smarter five or 10 years from today because of the LHC,” Seiberg said. “So that’s exciting. This is within reach.

    Cosmic Coincidence

    Einstein once wrote that for a scientist, “religious feeling takes the form of a rapturous amazement at the harmony of natural law” and that “this feeling is the guiding principle of his life and work.” Indeed, throughout the 20th century, the deep-seated belief that the laws of nature are harmonious — a belief in “naturalness” — has proven a reliable guide for discovering truth.

    “Naturalness has a track record,” Arkani-Hamed said in an interview. In practice, it is the requirement that the physical constants (particle masses and other fixed properties of the universe) emerge directly from the laws of physics, rather than resulting from improbable cancellations. Time and again, whenever a constant appeared fine-tuned, as if its initial value had been magically dialed to offset other effects, physicists suspected they were missing something. They would seek and inevitably find some particle or feature that materially dialed the constant, obviating a fine-tuned cancellation.

    This time, the self-healing powers of the universe seem to be failing. The Higgs boson has a mass of 126 giga-electron-volts, but interactions with the other known particles should add about 10,000,000,000,000,000,000 giga-electron-volts to its mass. This implies that the Higgs’ “bare mass,” or starting value before other particles affect it, just so happens to be the negative of that astronomical number, resulting in a near-perfect cancellation that leaves just a hint of Higgs behind: 126 giga-electron-volts.

    Physicists have gone through three generations of particle accelerators searching for new particles, posited by a theory called supersymmetry, that would drive the Higgs mass down exactly as much as the known particles drive it up. But so far they’ve come up empty-handed.

    The upgraded LHC will explore ever-higher energy scales in its next run, but even if new particles are found, they will almost definitely be too heavy to influence the Higgs mass in quite the right way. The Higgs will still seem at least 10 or 100 times too light. Physicists disagree about whether this is acceptable in a natural, stand-alone universe. “Fine-tuned a little — maybe it just happens,” said Lisa Randall, a professor at Harvard University. But in Arkani-Hamed’s opinion, being “a little bit tuned is like being a little bit pregnant. It just doesn’t exist.”

    If no new particles appear and the Higgs remains astronomically fine-tuned, then the multiverse hypothesis will stride into the limelight. “It doesn’t mean it’s right,” said Bousso, a longtime supporter of the multiverse picture, “but it does mean it’s the only game in town.”

    A few physicists — notably Joe Lykken of Fermi National Accelerator Laboratory in Batavia, Ill., and Alessandro Strumia of the University of Pisa in Italy — see a third option. They say that physicists might be misgauging the effects of other particles on the Higgs mass and that when calculated differently, its mass appears natural. This “modified naturalness” falters when additional particles, such as the unknown constituents of dark matter, are included in calculations — but the same unorthodox path could yield other ideas. “I don’t want to advocate, but just to discuss the consequences,” Strumia said during a talk earlier this month at Brookhaven National Laboratory.


    4
    Brookhaven Forum 2013 David Curtin, left, a postdoctoral researcher at Stony Brook University, and Alessandro Strumia, a physicist at the National Institute for Nuclear Physics in Italy, discussing Strumia’s “modified naturalness” idea, which questions longstanding assumptions about how to calculate the natural value of the Higgs boson mass. Thomas Lin/Quanta Magazine.

    However, modified naturalness cannot fix an even bigger naturalness problem that exists in physics: The fact that the cosmos wasn’t instantly annihilated by its own energy the moment after the Big Bang.

    Dark Dilemma

    The energy built into the vacuum of space (known as vacuum energy, dark energy or the cosmological constant) is a baffling trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion times smaller than what is calculated to be its natural, albeit self-destructive, value. No theory exists about what could naturally fix this gargantuan disparity. But it’s clear that the cosmological constant has to be enormously fine-tuned to prevent the universe from rapidly exploding or collapsing to a point. It has to be fine-tuned in order for life to have a chance.

    To explain this absurd bit of luck, the multiverse idea has been growing mainstream in cosmology circles over the past few decades. It got a credibility boost in 1987 when the Nobel Prize-winning physicist Steven Weinberg, now a professor at the University of Texas at Austin, calculated that the cosmological constant of our universe is expected in the multiverse scenario [Physical Review Letters].

    5
    Steven Weinberg, University of Texas at Austin

    Of the possible universes capable of supporting life — the only ones that can be observed and contemplated in the first place — ours is among the least fine-tuned. “If the cosmological constant were much larger than the observed value, say by a factor of 10, then we would have no galaxies,” explained Alexander Vilenkin, a cosmologist and multiverse theorist at Tufts University. “It’s hard to imagine how life might exist in such a universe.”

    Most particle physicists hoped that a more testable explanation for the cosmological constant problem would be found. None has. Now, physicists say, the unnaturalness of the Higgs makes the unnaturalness of the cosmological constant more significant. Arkani-Hamed thinks the issues may even be related. “We don’t have an understanding of a basic extraordinary fact about our universe,” he said. “It is big and has big things in it.”

    The multiverse turned into slightly more than just a hand-waving argument in 2000, when Bousso and Joe Polchinski, a professor of theoretical physics at the University of California at Santa Barbara, found a mechanism that could give rise to a panorama of parallel universes. String theory, a hypothetical “theory of everything” that regards particles as invisibly small vibrating lines, posits that space-time is 10-dimensional. At the human scale, we experience just three dimensions of space and one of time, but string theorists argue that six extra dimensions are tightly knotted at every point in the fabric of our 4-D reality. Bousso and Polchinski calculated that there are around 10500 different ways for those six dimensions to be knotted (all tying up varying amounts of energy), making an inconceivably vast and diverse array of universes possible. In other words, naturalness is not required. There isn’t a single, inevitable, perfect universe.

    “It was definitely an aha-moment for me,” Bousso said. But the paper sparked outrage.

    “Particle physicists, especially string theorists, had this dream of predicting uniquely all the constants of nature,” Bousso explained. “Everything would just come out of math and pi and twos. And we came in and said, ‘Look, it’s not going to happen, and there’s a reason it’s not going to happen. We’re thinking about this in totally the wrong way.’ ”

    Life in a Multiverse

    The Big Bang, in the Bousso-Polchinski multiverse scenario, is a fluctuation. A compact, six-dimensional knot that makes up one stitch in the fabric of reality suddenly shape-shifts, releasing energy that forms a bubble of space and time. The properties of this new universe are determined by chance: the amount of energy unleashed during the fluctuation. The vast majority of universes that burst into being in this way are thick with vacuum energy; they either expand or collapse so quickly that life cannot arise in them. But some atypical universes, in which an improbable cancellation yields a tiny value for the cosmological constant, are much like ours.

    In a paper posted last month to the physics preprint website arXiv.org, Bousso and a Berkeley colleague, Lawrence Hall, argue that the Higgs mass makes sense in the multiverse scenario, too. They found that bubble universes that contain enough visible matter (compared to dark matter) to support life most often have supersymmetric particles beyond the energy range of the LHC, and a fine-tuned Higgs boson. Similarly, other physicists showed in 1997 that if the Higgs boson were five times heavier than it is, this would suppress the formation of atoms other than hydrogen, resulting, by yet another means, in a lifeless universe.

    Despite these seemingly successful explanations, many physicists worry that there is little to be gained by adopting the multiverse worldview. Parallel universes cannot be tested for; worse, an unnatural universe resists understanding. “Without naturalness, we will lose the motivation to look for new physics,” said Kfir Blum, a physicist at the Institute for Advanced Study. “We know it’s there, but there is no robust argument for why we should find it.” That sentiment is echoed again and again: “I would prefer the universe to be natural,” Randall said.

    But theories can grow on physicists. After spending more than a decade acclimating himself to the multiverse, Arkani-Hamed now finds it plausible — and a viable route to understanding the ways of our world. “The wonderful point, as far as I’m concerned, is basically any result at the LHC will steer us with different degrees of force down one of these divergent paths,” he said. “This kind of choice is a very, very big deal.”

    Naturalness could pull through. Or it could be a false hope in a strange but comfortable pocket of the multiverse.

    As Arkani-Hamed told the audience at Columbia, “stay tuned.”

    See the full article here .

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    Formerly known as Simons Science News, Quanta Magazine is an editorially independent online publication launched by the Simons Foundation to enhance public understanding of science. Why Quanta? Albert Einstein called photons “quanta of light.” Our goal is to “illuminate science.” At Quanta Magazine, scientific accuracy is every bit as important as telling a good story. All of our articles are meticulously researched, reported, edited, copy-edited and fact-checked.

     
  • richardmitnick 2:12 pm on November 28, 2017 Permalink | Reply
    Tags: , , Higgs, Protons,   

    From Symmetry: “LHC data: how it’s made” 

    Symmetry Mag
    Symmetry

    11/28/17
    Sarah Charley

    1
    Photo by Silvia Biondi; Matteo Franchini, CERN

    In the Large Hadron Collider, protons become new particles, which become energy and light, which become data.

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    Scientists have never actually seen the Higgs boson.

    CERN CMS Higgs Event


    CERN ATLAS Higgs Event

    They’ve never seen the inside of a proton, either, and they’ll almost certainly never see dark matter. Many of the fundamental patterns woven into the fabric of nature are completely imperceptible to our clunky human senses.

    But scientists don’t need to see particles to learn about their properties and interactions. Physicists can study the subatomic world with particle detectors, which gather information from events that occur much faster and are much smaller than the eye can see.

    But what is this information, and how exactly do detectors gather it? At experiments at the Large Hadron Collider, the world’s largest and most powerful particle accelerator, it all begins with a near-light-speed race.

    Starting with a bang

    The LHC is built in a ring 17 miles in circumference. Scientists load bunches of protons into this ring and send them hurtling around in opposite directions, gaining more and more energy with each pass.

    By the time the LHC has boosted the proton beams to their maximum energy, they will have traveled a distance equivalent to a round-trip journey between Earth and the sun. They will be moving so fast that they no longer convert energy into speed but in effect swell with mass instead.

    Once the protons are ramped up to their final energy, the LHC’s magnets nudge the two beams into a collision course at four intersections around the ring.

    CERN/ATLAS detector

    CERN/CMS Detector

    CERN/LHCb detector

    CERN ALICE detector

    “When two protons traveling at near light speeds collide head-on, the impact releases a surge of energy unimaginably quickly in an unimaginably small volume of space,” says Dhiman Chakraborty, a professor of Physics at Northern Illinois University working on the ATLAS experiment. “In that miniscule volume, conditions are similar to those that prevailed when the universe was a mere tenth of a nanosecond old.”

    This energy is often converted directly into mass according to Einstein’s famous equation, E=mc2, resulting in birth of exotic particles not to be found anywhere else on Earth. These particles, which can include Higgs bosons, are extremely short-lived.

    “They decay instantaneously and spontaneously into less massive, more stable ‘daughter’ particles,” Chakraborty says. “The large mass of the exotic parent particle, being converted back into energy, sends its much lighter daughters flying off at near light speeds.”

    Even though these rare particles are short-lived, they give scientists a peek at the texture of spacetime and the ubiquitous fields woven into it.

    “So much so that the existence of the entire universe we see today—ourselves as observers included—is owed to [the particles and fields we cannot see],” he says.

    3
    This CMS experiment event display identifies an electron and a muon passing through the detector. Courtesy of CMS Collaboration

    Enter the detector

    All of this happens in less than a millionth of a trillionth of a second. Even though the LHC’s detectors encompass the beampipe and are only a few centimeters away from the collison, it is impossible for them to see the new heavy particles, which often disintegrate before they can move a distance equal to the diameter of an atomic nucleus.

    But the detectors can “see” the byproducts of their decay. The Higgs bosons can transform into pairs of photons, for example. When those photons hit the atoms and molecules that make up the detector material, they radiate sparkles of light and jolts of energy like meteorites blazing through the atmosphere. Sensors inhale these dim twinkles and transform them into electrical signals, recording where and when they arrived.

    “Each pulse is a snapshot of space and time,” Chakraborty says. “They tell us exactly where, when and how fast those daughter particles traversed our detector.”

    A single proton-proton collision can generate several high-energy daughter particles, some of which produce showers of hundreds more. These streams of particles release detectable energy as they hit the detectors and generate electrical pulses. The time, location, length, shape, height and total energy of each electrical pulse are directly translated into data bits by an electronic readout card.

    Much the way biologists chart animal tracks to study the speed, direction and size of a herd, physicists study the shape of these electrical pulses to characterize the passing particles. A long, broad electrical pulse indicates that a large stream of particles grazed across the detector, but a pulse with a sharp peak suggests that a small pack cut straight through.

    These electrical pulses create a multifaceted connect-the-dots. Algorithms quickly identify patterns in the cascade of hits and rapidly reconstruct particle energies and tracks.

    “We only have a few microseconds to reconstruct what happened before the next batch of collisions arrives,” says Tulika Bose, an associate professor at Boston University working on the CMS experiment. “We can’t keep all the data, so we use automated systems to crudely reconstruct particles like muons and electrons.

    “If the event looks interesting enough based on this limited amount of information, we keep all the data from that snapshot in time and save them for further analysis.”

    These interesting events are packaged and dispatched upstairs to a second series of automated gatekeepers that further evaluate the quality and characteristics of these collision snapshots. Preprogrammed algorithms identify more particles in the snapshot. This entire process takes less than a millisecond, faster than the blink of a human eye.

    Even then, humans won’t lay eyes on the data until after it undergoes a strenuous suite of processing and preparation for analysis.

    Humans can’t see the Higgs boson, but by tracing its byproducts back to a single Higgs-like origin, they were able to gather enough evidence to discover it.

    “In the five years since that discovery, we’ve produced hundreds of thousands more Higgs bosons and reconstructed a good number of them,” Chakraborty says. “They’re being studied intensely with the goal of gaining insight into deeper mysteries of nature.”

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 7:00 am on July 7, 2017 Permalink | Reply
    Tags: , , , Higgs, ,   

    From ATLAS: “Why should there be only one? Searching for additional Higgs Bosons beyond the Standard Model” 

    CERN ATLAS Higgs Event

    CERN/ATLAS
    ATLAS

    6th July 2017
    ATLAS Collaboration

    1
    Figure 1: Feynman diagram for leading order production of a neutral MSSM Higgs boson in association with b-quarks. (Image: ATLAS Collaboration/CERN)

    CERN CMS Higgs Event

    Since the discovery of the elusive Higgs boson in 2012, researchers have been looking beyond the Standard Model to answer many outstanding questions. An attractive extension to the Standard Model is Supersymmetry (SUSY), which introduces a plethora of new particles, some of which may be candidates for Dark Matter.

    Standard model of Supersymmetry DESY

    One of the most popular SUSY models – the Minimal Supersymmetric Standard Model (MSSM) – predicts the existence of five Higgs bosons. In this model, the recently discovered Higgs boson (h) would be considered to be the lightest of the set. Two charged Higgs (H+, H–) and two neutral Higgs (A/H) would complete the set, and could exist within a wide range of masses above that of the discovered Higgs boson. The LHC experiments are poised to search for these additional bosons using techniques similar to those used in the initial Higgs searches.

    In July 2017, the ATLAS collaboration presented a new result on the search for neutral (A/H) Higgs bosons decaying to two tau leptons. Taus are particularly interesting to the search as there is a stronger coupling between A/H and down-type fermions (e, μ, τ, d, s, b) for certain values of the MSSM parameter-space. This will enhance the probability of decays to tau leptons, as well as the production of A/H in association with b-quarks (Figure 1), providing a larger cross-section. Like with the Standard Model Higgs boson, gluon-fusion production of A/H remains an important production process in the MSSM to varying degrees (depending on the chosen model parameters). Thus, by classifying events by their probability of containing b-flavoured jets, the ATLAS search has been optimised for both b-associated and gluon-fusion production of A/H, respectively.

    2
    Figure 2 (left): The observed and expected 95% CL upper limits on the production cross section times di-tau branching fraction for a scalar boson produced via b-associated production. Figure 3 (right): The observed and expected 95% CL limits on tanβ as a function of the mass of the A boson in the hMSSM scenario. The area above the black curve has been excluded. The exclusion arising from the Standard Model Higgs boson coupling measurements and the exclusion limit from the ATLAS 2015 H/A→ ττ search are shown. (Images: ATLAS Collaboration/CERN)

    See the full article here .

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

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  • richardmitnick 9:00 pm on July 3, 2017 Permalink | Reply
    Tags: , , , , Higgs, Joe Incandela, , What comes next?   

    From Symmetry: “When was the Higgs actually discovered?” 

    Symmetry Mag

    Symmetry

    07/03/17
    Sarah Charley

    The announcement on July 4 was just one part of the story. Take a peek behind the scenes of the discovery of the Higgs boson.

    1
    Maximilien Brice, Laurent Egli, CERN

    Joe Incandela UCSB and Cern CMS

    Joe Incandela sat in a conference room at CERN and watched with his arms folded as his colleagues presented the latest results on the hunt for the Higgs boson. It was December 2011, and they had begun to see the very thing they were looking for—an unexplained bump emerging from the data.

    “I was far from convinced,” says Incandela, a professor at the University of California, Santa Barbara and the former spokesperson of the CMS experiment at the Large Hadron Collider.

    CERN CMS Higgs Event

    CERN/CMS Detector

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    For decades, scientists had searched for the elusive Higgs boson: the holy grail of modern physics and the only piece of the robust and time-tested Standard Model that had yet to be found.

    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 construction of the LHC was motivated in large part by the absence of this fundamental component from our picture of the universe. Without it, physicists couldn’t explain the origin of mass or the divergent strengths of the fundamental forces.

    “Without the Higgs boson, the Standard Model falls apart,” says Matthew McCullough, a theorist at CERN. “The Standard Model was fitting the experimental data so well that most of the theory community was convinced that something playing the role of Higgs boson would be discovered by the LHC.”

    The Standard Model predicted the existence of the Higgs but did not predict what the particle’s mass would be. Over the years, scientists had searched for it across a wide range of possible masses. By 2011, there was only a tiny region left to search; everything else had been excluded by previous generations of experimentation.

    FNAL in the Tevatron research had ruled out many of the possible levels of energy that could have been the home of Higgs.

    FNAL Tevatron

    FNAL/Tevatron map


    FNAL/Tevatron DZero detector


    FNAL/Tevatron CDF detector

    If the predicted Higgs boson were anywhere, it had to be there, right where the LHC scientists were looking.

    But Incandela says he was skeptical about these preliminary results. He knew that the Higgs could manifest itself in many different forms, and this particular channel was extremely delicate.

    “A tiny mistake or an unfortunate distribution of the background events could make it look like a new particle is emerging from the data when in reality, it’s nothing,” Incandela says.

    A common mantra in science is that extraordinary claims require extraordinary evidence. The challenge isn’t just collecting the data and performing the analysis; it’s deciding if every part of the analysis is trustworthy. If the analysis is bulletproof, the next question is whether the evidence is substantial enough to claim a discovery. And if a discovery can be claimed, the final question is what, exactly, has been discovered? Scientists can have complete confidence in their results but remain uncertain about how to interpret them.

    In physics, it’s easy to say what something is not but nearly impossible to say what it is. A single piece of corroborated, contradictory evidence can discredit an entire theory and destroy an organization’s credibility.

    “We’ll never be able to definitively say if something is exactly what we think it is, because there’s always something we don’t know and cannot test or measure,” Incandela says. “There could always be a very subtle new property or characteristic found in a high-precision experiment that revolutionizes our understanding.”

    With all of that in mind, Incandela and his team made a decision: From that point on, everyone would refine their scientific analyses using special data samples and a patch of fake data generated by computer simulations covering the interesting areas of their analyses. Then, when they were sure about their methodology and had enough data to make a significant observation, they would remove the patch and use their algorithms on all the real data in a process called unblinding.

    “This is a nice way of providing an unbiased view of the data and helps us build confidence in any unexpected signals that may be appearing, particularly if the same unexpected signal is seen in different types of analyses,” Incandela says.

    A few weeks before July 4, all the different analysis groups met with Incandela to present a first look at their unblinded results. This time the bump was very significant and showing up at the same mass in two independent channels.

    “At that point, I knew we had something,” Incandela says. “That afternoon we presented the results to the rest of the collaboration. The next few weeks were among the most intense I have ever experienced.”

    Meanwhile, the other general-purpose experiment at the LHC, ATLAS, was hot on the trail of the same mysterious bump.

    CERN/ATLAS detector

    CERN ATLAS Higgs Event

    Andrew Hard was a graduate student at The University of Wisconsin, Madison working on the ATLAS Higgs analysis with his PhD thesis advisor Sau Lan Wu.

    “Originally, my plan had been to return home to Tennessee and visit my parents over the winter holidays,” Hard says. “Instead, I came to CERN every day for five months—even on Christmas. There were a few days when I didn’t see anyone else at CERN. One time I thought some colleagues had come into the office, but it turned out to be two stray cats fighting in the corridor.”

    Hard was responsible for writing the code that selected and calibrated the particles of light the ATLAS detector recorded during the LHC’s high-energy collisions. According to predictions from the Standard Model, the Higgs can transform into two of these particles when it decays, so scientists on both experiments knew that this project would be key to the discovery process.

    “We all worked harder than we thought we could,” Hard says. “People collaborated well and everyone was excited about what would come next. All in all, it was the most exciting time in my career. I think the best qualities of the community came out during the discovery.”

    At the end of June, Hard and his colleagues synthesized all of their work into a single analysis to see what it revealed. And there it was again—that same bump, this time surpassing the statistical threshold the particle physics community generally requires to claim a discovery.

    “Soon everyone in the group started running into the office to see the number for the first time,” Hard says. “The Wisconsin group took a bunch of photos with the discovery plot.”

    Hard had no idea whether CMS scientists were looking at the same thing. At this point, the experiments were keeping their latest results secret—with the exception of Incandela, Fabiola Gianotti (then ATLAS spokesperson) and a handful of CERN’s senior management, who regularly met to discuss their progress and results.

    Fabiola Gianotti, then the ATLAS spokesperson, now the General Director of CERN

    “I told the collaboration that the most important thing was for each experiment to work independently and not worry about what the other experiment was seeing,” Incandela says. “I did not tell anyone what I knew about ATLAS. It was not relevant to the tasks at hand.”

    Still, rumors were circulating around theoretical physics groups both at CERN and abroad. Mccullough, then a postdoc at the Massachusetts Institute of Technology, was avidly following the progress of the two experiments.

    “We had an update in December 2011 and then another one a few months later in March, so we knew that both experiments were seeing something,” he says. “When this big excess showed up in July 2012, we were all convinced that it was the guy responsible for curing the ails of the Standard Model, but not necessarily precisely that guy predicted by the Standard Model. It could have properties mostly consistent with the Higgs boson but still be not absolutely identical.”

    The week before announcing what they’d found, Hard’s analysis group had daily meetings to discuss their results. He says they were excited but also nervous and stressed: Extraordinary claims require extraordinary confidence.

    “One of our meetings lasted over 10 hours, not including the dinner break halfway through,” Hard says. “I remember getting in a heated exchange with a colleague who accused me of having a bug in my code.”

    After both groups had independently and intensely scrutinized their Higgs-like bump through a series of checks, cross-checks and internal reviews, Incandela and Gianotti decided it was time to tell the world.

    “Some people asked me if I was sure we should say something,” Incandela says. “I remember saying that this train has left the station. This is what we’ve been working for, and we need to stand behind our results.”

    On July 4, 2012, Incandela and Gianotti stood before an expectant crowd and, one at a time, announced that decades of searching and generations of experiments had finally culminated in the discovery of a particle “compatible with the Higgs boson.”

    Science journalists rejoiced and rushed to publish their stories. But was this new particle the long-awaited Higgs boson? Or not?

    Discoveries in science rarely happen all at once; rather, they build slowly over time. And even when the evidence overwhelmingly points in a clear direction, scientists will rarely speak with superlatives or make definitive claims.

    “There is always a risk of overlooking the details,” Incandela says, “and major revolutions in science are often born in the details.”

    Immediately after the July 4 announcement, theorists from around the world issued a flurry of theoretical papers presenting alternative explanations and possible tests to see if this excess really was the Higgs boson predicted by the Standard Model or just something similar.

    “A lot of theory papers explored exotic ideas,” McCullough says. “It’s all part of the exercise. These papers act as a straw man so that we can see just how well we understand the particle and what additional tests need to be run.”

    For the next several months, scientists continued to examine the particle and its properties. The more data they collected and the more tests they ran, the more the discovery looked like the long-awaited Higgs boson. By March, both experiments had twice as much data and twice as much evidence.

    “Amongst ourselves, we called it the Higgs,” Incandela says, “but to the public, we were more careful.”

    It was increasingly difficult to keep qualifying their statements about it, though. “It was just getting too complicated,” Incandela says. “We didn’t want to always be in this position where we had to talk about this particle like we didn’t know what it was.”

    On March 14, 2013—nine months and 10 days after the original announcement—CERN issued a press release quoting Incandela as saying, “to me, it is clear that we are dealing with a Higgs boson, though we still have a long way to go to know what kind of Higgs boson it is.”​

    To this day, scientists are open to the possibility that the Higgs they found is not exactly the Higgs they expected.

    “We are definitely, 100 percent sure that this is a Standard-Model-like Higgs boson,” Incandela says. “But we’re hoping that there’s a chink in that armor somewhere. The Higgs is a sign post, and we’re hoping for a slight discrepancy which will point us in the direction of new physics.”

    See the full article here .

    Please help promote STEM in your local schools.

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 11:11 am on May 24, 2017 Permalink | Reply
    Tags: , , , , , Higgs, Our failure in resolve,   

    From FNAL: “Fermilab scientists set upper limit for Higgs boson mass” 

    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.

    In 1977, theoretical physicists at Fermilab — Ben Lee and Chris Quigg, along with Hank Thacker — published a paper setting an upper limit for the mass of the Higgs boson. This calculation helped guide the design of the Large Hadron Collider by setting the energy scale necessary for it to discover the particle. The Large Hadron Collider turned on in 2008, and in 2012, the LHC’s ATLAS and CMS discovered the long-sought Higgs boson — 35 years after the seminal paper.

    1

    CERN CMS Higgs Event


    CERN/CMS Detector


    CERN ATLAS Higgs Event


    CERN/ATLAS detector

    Where it all started:

    FNAL Tevatron

    FNAL/Tevatron map


    FNAL/Tevatron DZero detector


    FNAL/Tevatron CDF detector

    Where we failed and handed it to Europe:

    3
    Sight of the planned Superconducting Super Collider, in the vicinity of Waxahachie, Texas. Cancelled by our idiot Congress under Bill Clinton in 1993. We could have had it all.

    See the full article here .

    Please help promote STEM in your local schools.

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    FNAL Icon
    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 12:37 pm on November 29, 2016 Permalink | Reply
    Tags: , , , Higgs,   

    From Don Lincoln at FNAL: Higgs Boson 2016 Video 

    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.

    FNAL Don Lincoln
    From Don Lincoln of FNAL

    Published on Nov 16, 2016

    CERN CMS Higgs Event
    CERN CMS Higgs Event

    The Higgs boson burst into the public arena on July 4, 2012, when scientists working at the CERN laboratory announced the particle’s discovery. However the initial discovery was a bit tentative, with the need to verify that the discovered particle was, indeed, the Higgs boson. In this video, Fermilab’s Dr. Don Lincoln looks at the data from the perspective of 2016 and shows that more recent analyses further supports the idea that the Higgs boson is what was discovered.

    Watch, enjoy, learn.

    The data presented in this video can be seen in a technical form in this paper: http://cds.cern.ch/record/2158863/fil…. Figure 19 is a more accurate version.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

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    FNAL Icon
    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 9:22 am on November 21, 2016 Permalink | Reply
    Tags: , , , Higgs, , ,   

    From Symmetry- “Q and A: What more can we learn about the Higgs?” 

    Symmetry Mag

    Symmetry

    11/17/16
    Angela Anderson

    1
    Illustration by Sandbox Studio, Chicago with Ana Kova

    Four physicists discuss Higgs boson research since the discovery.

    CERN CMS Higgs Event
    CERN CMS Higgs Event

    CERN ATLAS Higgs Event
    CERN ATLAS Higgs Event

    More than two decades before the discovery of the Higgs boson, four theoretical physicists wrote a comprehensive handbook called The Higgs Hunter’s Guide. The authors—Sally Dawson of the Department of Energy’s Brookhaven National Laboratory; John F. Gunion from the University of California, Davis; Howard E. Haber from the University of California, Santa Cruz; and Gordon Kane from the University of Michigan—were recently recognized for “instrumental contributions to the theory of the properties, reactions and signatures of the Higgs boson” as recipients of the American Physical Society’s 2017 J.J. Sakurai Prize for Theoretical Physics.

    They are still investigating the particle that completed the Standard Model, and some are hunting different Higgs bosons that could take particle physics beyond that 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.

    Dawson, Gunion and Haber recently attended the Higgs Couplings 2016 workshop at SLAC National Accelerator Laboratory, where physicists gathered to talk about the present and future of Higgs research. Symmetry interviewed all four to find out what’s on the horizon.

    S: What is meant by “Higgs couplings”?
    JG: The Higgs is an unstable particle that lasts a very short time in the detector before it decays into pairs of things like top quarks, gluons, and photons. The rates and relative importance of these decays is determined by the couplings of the Higgs boson to these different particles. And that’s what the workshop is all about, trying to determine whether or not the couplings predicted in the Standard Model agree with the couplings that are measured experimentally.

    SD: Right, we can absolutely say how much of the time we expect the Higgs to decay to the known particles, so a comparison of our predictions with the experimental measurements tells us whether there’s any possible deviation from our Standard Model.

    JG: For us what would be really exciting is if we did see deviations. However, that probably requires more precision than we currently have experimentally.

    GK: But we don’t all agree on that, in the sense that I would prefer that it almost exactly agree with the Standard Model predictions because of a theory that I like that says it should. But most of the people in the world would prefer what John and Sally said.

    S.How many people are working in Higgs research now worldwide?

    GK: I did a search for “Higgs” in the title of scientific papers after 2011 on arXiv.org and came up with 5211 hits; there are several authors per paper, of course, and some have written multiple papers, so we can only estimate.

    SD: There are roughly 5000 people on each experiment, ATLAS and CMS, and some fraction of those work on Higgs research, but it’s really too hard to calculate. They all contribute in different ways. Let’s just say many thousands of experimentalists and theorists worldwide.
    What are Higgs researchers hoping to accomplish?

    HH: There are basically two different avenues. One is called the precision Higgs program designed to improve precision in the current data. The other direction addresses a really simple question: Is the Higgs boson a solo act or not? If additional Higgs-like particles exist, will they be discovered in future LHC experiments?

    SD: I think everybody would like to see more Higgs bosons. We don’t know if there are more, but everybody is hoping.

    JG: If you were Gordy [Kane] who only believes in one Higgs boson, you would be working to confirm with greater and greater precision that the Higgs boson you see has precisely the properties predicted in the Standard Model. This will take more and more luminosity and maybe some future colliders like a high luminosity LHC or an e+e- collider.

    HH: The precision Higgs program is a long-term effort because the high luminosity LHC is set to come online in the mid 2020s and is imagined to continue for another 10 years. There are a lot of people trying to predict what precision could you ultimately achieve in the various measurements of Higgs boson properties that will be made by the mid 2030s. Right now we have a set of measurements with statistical and systematic errors of about 20 percent. By the end of the high luminosity LHC, we anticipate that the size of the measurement errors can be reduced to around 10 percent and maybe in some cases to 5 percent.

    S. How has research on the topic changed since the Higgs discovery?

    SD: People no longer build theoretical models that don’t have a Higgs in them. You have to make sure that your model is consistent with what we know experimentally. You can’t just build a crazy model; it has to be a model with a Higgs with roughly the properties we’ve observed, and that is actually pretty restrictive.

    JG: Many theoretical models have either been eliminated or considerably constrained. For example, the supersymmetric models that are theoretically attractive kind of expect a Higgs boson of this mass, but only after pushing parameters to a bit of an extreme. There’s also an issue called naturalness: In the Standard Model alone there is no reason why the Higgs boson should have such a light mass as we see, whereas in some of these theories it is natural to see the Higgs boson at this mass. So that’s a very important topic of research—looking for those models that are in a certain sense naturally predicting what we see and finding additional experimental signals associated with such models.

    GK: For example, the supersymmetric theories predict that there will be five Higgs bosons with different masses. The extent to which the electroweak symmetry is broken by each of the five depends on their couplings, but there should be five discovered eventually if the others exist.

    HH: There’s also a slightly different attitude to the research today. Before the Higgs boson was discovered it was known that the Standard Model was theoretically inconsistent without the Higgs boson. It had to be there in some form. It wasn’t going to be that we ran the LHC and saw nothing—no Higgs boson and nothing else. This is called a no-lose theorem. Now, having discovered the Higgs boson, you cannot guarantee that additional new phenomenon exists that must be discovered at the LHC. In other words, the Standard Model itself, with the Higgs boson, is a theoretically consistent theory. Nevertheless, not all fundamental phenomena can be explained by Standard Model physics (such as neutrino masses, dark matter and the gravitational force), so we know that new phenomena beyond the Standard Model must be present at some very high-energy scale. However, there is no longer a no-lose theorem that states that this new phenomena must appear at the energy scale that is probed at the LHC.

    S. How have the new capabilities of the LHC changed the game?

    SD: We have way more Higgs bosons; that’s really how it’s changed. Since the energy is higher we can potentially make heavier new particles.

    GK: There were about a million Higgs bosons produced in the first run of the LHC, and there will be more than twice that in the second run, but they only can find a small fraction of those in the detector because of background noise and some other things. It’s very hard. It takes clever experimenters. To find a couple of hundred Higgs you need to produce a million.

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

    SD: Most of the time the Higgs decays into something we can’t see in our detector. But as the measurements get better and better, experimentalists who have been extracting the couplings are quantifying more properties of the Higgs decays. So instead of just counting how many Higgs bosons decay to two Z bosons, they will look at where the two Z bosons are in the detector or the energy of the Z bosons.

    S. Are there milestones you are looking forward to?

    GK: Confirming the Standard Model Higgs with even more precision. The decay the Higgs boson was discovered in—two photons—could happen in any other kind of particle. But the decay to W boson pairs is the one that you need for it to break the electroweak symmetry [a symmetry between the masses of the particles associated with the electromagnetic and weak forces], which is what it should do according to the Standard Model.

    SD: So, one of the things we will see a lot of in the next year or two is better measurements of the Higgs decay into the bottom quarks. Within a few years, we should learn whether or not there are more Higgs bosons. Measuring the couplings to the desired precision will take 20 years or more.

    JG: There’s another thing people are thinking about, which is how the Higgs can be connected to the important topic of dark matter. We are working on models that establish such a connection, but most of these models, of course, have extra Higgs bosons. It’s even possible that one of those extra Higgs bosons might be invisible dark matter. So the question is whether the Higgs we can see tells us something about dark matter Higgs bosons or other dark matter particles, such as the invisible particles that are present in supersymmetry.

    S. Are there other things still to learn?

    JG: There are many possible connections between Higgs bosons, in a generic sense and the history of the universe. For example, it could be that a Higgs-like particle called the inflaton is responsible for the expansion of the universe. As a second example, generalized Higgs boson models could explain the preponderance of matter over antimatter in the current universe.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 10:01 am on August 17, 2016 Permalink | Reply
    Tags: , , , CERN: Facts & Figures, Higgs   

    From CERN: “Facts & Figures” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    CERN

    The Large Hadron Collider (LHC) is the most powerful particle accelerator ever built. The accelerator sits in a tunnel 100 metres underground at CERN, the European Organization for Nuclear Research, on the Franco-Swiss border near Geneva, Switzerland.

    What is the LHC?

    The LHC is a particle accelerator that pushes protons or ions to near the speed of light. It consists of a 27-kilometre ring of superconducting magnets with a number of accelerating structures that boost the energy of the particles along the way.

    Why is it called the “Large Hadron Collider”?

    “Large” refers to its size, approximately 27km in circumference
    “Hadron” because it accelerates protons or ions, which belong to the group of particles called hadrons
    “Collider” because the particles form two beams travelling in opposite directions, which are made to collide at four points around the machine

    How does the LHC work?

    The CERN accelerator complex is a succession of machines with increasingly higher energies. Each machine accelerates a beam of particles to a given energy before injecting the beam into the next machine in the chain. This next machine brings the beam to an even higher energy and so on. The LHC is the last element of this chain, in which the beams reach their highest energies.

    1
    The CERN accelerator complex (Image: CERN)

    Inside the LHC, two particle beams travel at close to the speed of light before they are made to collide. The beams travel in opposite directions in separate beam pipes – two tubes kept at ultrahigh vacuum. They are guided around the accelerator ring by a strong magnetic field maintained by superconducting electromagnets. Below a certain characteristic temperature, some materials enter a superconducting state and offer no resistance to the passage of electrical current. The electromagnets in the LHC are therefore chilled to ‑271.3°C (1.9K) – a temperature colder than outer space – to take advantage of this effect. The accelerator is connected to a vast distribution system of liquid helium, which cools the magnets, as well as to other supply services.

    What are the main goals of the LHC?

    The Standard Model of particle physics – a theory developed in the early 1970s that describes the fundamental particles and their interactions – has precisely predicted a wide variety of phenomena and so far successfully explained almost all experimental results in particle physics..

    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.

    But the Standard Model is incomplete. It leaves many questions open, which the LHC will help to answer.

    What is the origin of mass? The Standard Model does not explain the origins of mass, nor why some particles are very heavy while others have no mass at all. However, theorists Robert Brout, François Englert and Peter Higgs made a proposal that was to solve this problem. The Brout-Englert-Higgs mechanism gives a mass to particles when they interact with an invisible field, now called the “Higgs field”, which pervades the universe.
    Particles that interact intensely with the Higgs field are heavy, while those that have feeble interactions are light. In the late 1980s, physicists started the search for the Higgs boson, the particle associated with the Higgs field. In July 2012, CERN announced the discovery of the Higgs boson, which confirmed the Brout-Englert-Higgs mechanism.

    CERN ATLAS Higgs Event
    CERN ATLAS Higgs Event

    CERN CMS Higgs Event
    CERN CMS Higgs Event

    However, finding it is not the end of the story, and researchers have to study the Higgs boson in detail to measure its properties and pin down its rarer decays.

    Will we discover evidence for supersymmetry? The Standard Model does not offer a unified description of all the fundamental forces, as it remains difficult to construct a theory of gravity similar to those for the other forces. Supersymmetry – a theory that hypothesises the existence of more massive partners of the standard particles we know – could facilitate the unification of fundamental forces.

    Standard model of Supersymmetry DESY
    Standard model of Supersymmetry DESY

    What are dark matter and dark energy? The matter we know and that makes up all stars and galaxies only accounts for 4% of the content of the universe. The search is then still open for particles or phenomena responsible for dark matter (23%) and dark energy (73%).

    Why is there far more matter than antimatter in the universe? Matter and antimatter must have been produced in the same amounts at the time of the Big Bang, but from what we have observed so far, our Universe is made only of matter.

    How does the quark-gluon plasma give rise to the particles that constitute the matter of our Universe?

    Quark gluon plasma. Duke University
    Quark gluon plasma. Duke University

    For part of each year, the LHC provides collisions between lead ions, recreating conditions similar to those just after the Big Bang. When heavy ions collide at high energies they form for an instant the quark-gluon plasma, a “fireball” of hot and dense matter that can be studied by the experiments.

    How was the LHC designed?

    Scientists started thinking about the LHC in the early 1980s, when the previous accelerator, the LEP, was not yet running. In December 1994, CERN Council voted to approve the construction of the LHC and in October 1995, the LHC technical design report was published.

    Contributions from Japan, the USA, India and other non-Member States accelerated the process and between 1996 and 1998, four experiments (ALICE, ATLAS, CMS and LHCb) received official approval and construction work started on the four sites.

    LHC Run 2

    What are the detectors at the LHC?

    There are seven experiments installed at the LHC: ALICE, ATLAS, CMS, LHCb, LHCf, TOTEM and MoEDAL. They use detectors to analyse the myriad of particles produced by collisions in the accelerator. These experiments are run by collaborations of scientists from institutes all over the world. Each experiment is distinct, and characterized by its detectors.

    What is the data flow from the LHC experiments?

    The CERN Data Centre stores more than 30 petabytes of data per year from the LHC experiments, enough to fill about 1.2 million Blu-ray discs, i.e. 250 years of HD video. Over 100 petabytes of data are permanently archived, on tape.

    Costs for Run 1
    Exploitation costs of the LHC when running (direct and indirect costs) represent about 80% of the CERN annual budget for operation, maintenance, technical stops, repairs and consolidation work in personnel and materials (for machine, injectors, computing, experiments).
    The directly allocated resources for the years 2009-2012 were about 1.1 billion CHF.

    Costs for LS1
    The cost of the Long Shutdown 1 (22 months) is estimated at 150 Million CHF. The maintenance and upgrade works represent about 100 MCHF for the LHC and 50 MCHF for the accelerator complex without the LHC.

    What is the LHC power consumption?

    The total power consumption of the LHC (and experiments) is equivalent to 600 GWh per year, with a maximum of 650 GWh in 2012 when the LHC was running at 4 TeV. For Run 2, the estimated power consumption is 750 GWh per year.
    The total CERN energy consumption is 1.3 TWh per year while the total electrical energy production in the world is around 20000 TWh, in the European Union 3400 TWh, in France around 500 TWh, and in Geneva canton 3 TWh.

    What are the main achievements of the LHC so far?

    10 September 2008: LHC first beam (see press release)

    23 November 2009: LHC first collisions (see press release)

    30 November 2009: world record with beam energy of 1.18 TeV (see press release)

    16 December 2009: world record with collisions at 2.36 TeV and significant quantities of data recorded (see press release)

    March 2010: first beams at 3.5 TeV (19 March) and first high energy collisions at 7 TeV (30 March) (see press release)

    8 November 2010: LHC first lead-ion beams (see press release)

    22 April 2011: LHC sets new world record beam intensity (see press release)

    5 April 2012: First collisions at 8 TeV (see press release)

    4 July 2012: Announcement of the discovery of a Higgs-like particle at CERN (see press release)

    For more information about the Higgs boson:
    The Higgs boson
    CERN and the Higgs boson
    The Basics of the Higgs boson
    How standard is the Higgs boson discovered in 2012?
    Higgs update 4 July

    28 September 2012: Tweet from CERN: “The LHC has reached its target for 2012 by delivering 15 fb-1 (around a million billion collisions) to ATLAS and CMS ”

    14 February 2013: At 7.24 a.m, the last beams for physics were absorbed into the LHC, marking the end of Run 1 and the beginning of the Long Shutdown 1 (see press release)

    8 October 2013: Physics Nobel prize to François Englert and Peter Higgs “for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments at CERN’s Large Hadron Collider” (see press release)

    See LHC Milestones.

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Meet CERN in a variety of places:

    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New

    ALICE
    CERN ALICE New

    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    LHC

    CERN LHC Map
    CERN LHC Grand Tunnel

    CERN LHC particles

    Quantum Diaries

     
  • richardmitnick 2:02 pm on July 14, 2016 Permalink | Reply
    Tags: , , , Higgs   

    From FNAL: “Importance of multivariate analysis” 

    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.

    July 14, 2016
    Andy Beretvas
    Giorgio Chiarelli

    During the hunt for the Higgs boson, scientists had to investigate and study a number of predicted processes.

    Science proceeds step by step, looking for the unknown and the unexplored. Higgs production is rare, and as many different processes contribute to the background against which the Higgs signal must be distinguished, physicists have to reduce that background piece by piece to bring it to an acceptable level.

    1
    The left plot show the distribution of the dijet mass. The right plot shows the neural network output. Both plots are for the one-tag candidates where events from all lepton categories are added together. The best fit to the data is shown.

    One of the ways in which the Higgs was hunted is through its associated production with W bosons.

    W boson properties are well known and provide a way to select events in which a Higgs boson can be searched through its decays into two b quarks.

    Unfortunately there are processes that can mimic our signal. One of them is the production of a W and a Z boson together, with the Z boson decaying into two heavy flavor quarks (two charm or two beauty quarks) and the W decaying into leptons (one charged and one neutral). A second is the production of a WW boson pair, in which the second W decays into heavy flavor quark.

    These processes are predicted in the Standard Model, but until now, they escaped a clear observation in this final state.

    Scientists at CDF have looked into the full data set collected during the 10 years of Tevatron Run II to identify these processes. During this search, they developed a number of techniques to disentangle events containing real W’s from events in which its presence was mimicked by other processes.

    The separation of signal and background is shown in the left plot of the above figure. Among the techniques used as part of this analysis was that of a neural network. Its output is shown on the right side of the figure. This technique is modeled on the central nervous system.

    CDF also looked for events containing a W or a Z decaying into heavy quarks, and we used the know-how developed in the Higgs experiment. The evidence for the Higgs boson was obtained in part thanks to an earlier version of this study.

    In the end, the measuring of WZ (W→lepton and neutrino; Z→bb or cc) and WW (W→lepton and neutrino; W→c or s) is an interesting check of the Standard Model prediction, with the two signals never measured separately so far at a hadron collider. CDF measured a production cross section for WW of 9.4 ± 4.2 picobarns and WZ of 3.7 +2.5 -2.2 picobarns with and evidence of 2.87 sigma for the first process and 2.12 for the second one.

    Learn more.

    See the full article here .

    Please help promote STEM in your local schools.

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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.

     
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