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  • richardmitnick 10:42 am on July 31, 2015 Permalink | Reply
    Tags: , , , , Higgs, , ,   

    From FNAL- “Frontier Science Result: CMS Shedding light on the invisible Higgs” 

    FNAL II photo

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

    July 31, 2015
    Jim Pivarski

    1
    Event recorded with the CMS detector in 2012 at a proton-proton center of mass energy of 8 TeV. The event shows characteristics expected from the decay of the Standard Model Higgs boson to a pair of photons (dashed yellow lines and green towers). The event could also be due to known standard model background processes..

    There are basically two types of detectors used in collider experiments: trackers, which are sensitive to any particles that interact electromagnetically, and calorimeters, which are sensitive to any particles that interact electromagnetically or through the strong force. That’s only two of the four forces — there’s also the weak force and gravity. Anything that interacts exclusively through the latter two forces would be invisible.

    This is not a speculative point. Neutrinos are effectively invisible in collider experiments. Even specialized neutrino detectors can detect only a small fraction of the neutrinos that pass through them. Dark matter is known purely through its gravitational effect on galaxies; no one even knows if it interacts via the weak force as well. Invisible particles could be slipping through detectors at the LHC right now.

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

    But if you can’t see them, how can you find them? Fortunately, physicists have developed a few tricks, mostly involving conservation laws. For instance, conservation of charge forces some particles and antiparticles to be produced in pairs, and one may be detected while the other decays invisibly. Conservation of momentum requires particles to be produced symmetrically around the beamline; if the observed distribution is highly asymmetric, that’s an indication of an unseen particle.

    In a recent study, CMS physicists used the latter technique to determine how often Higgs bosons decay into invisible particles and also a photon.

    CERN CMS Detector
    CMS in the LHC at CERN

    This is interesting because Higgs bosons have been observed only in a few of their predicted decay modes — the rest could be wildly different from expectations. In particular, Higgs bosons could interact with new phenomena like dark matter or supersymmetry, and most of these particles would be invisible.

    Supersymmetry standard model
    Standard Model of Supersymmetry

    One of the ways supersymmetry might be hiding is by decaying into gravitinos (gravity only), neutralinos (gravity and weak only) and a visible photon.

    Through this analysis, the mostly invisible signature has been partially ruled out: At most 7 to 13 percent of Higgs bosons might decay this way, if any at all. Before the measurement, it could have been as much as 57 percent. That’s a lot for one bite!

    See the full article here.

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    Fermilab Campus

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

     
  • richardmitnick 2:54 pm on June 1, 2015 Permalink | Reply
    Tags: , , Higgs,   

    From Quanta: “A New Theory to Explain the Higgs Mass” 

    Quanta Magazine
    Quanta Magazine

    May 27, 2015
    Natalie Wolchover

    1
    Skip Sterling for Quanta Magazine

    Three physicists who have been collaborating in the San Francisco Bay Area over the past year have devised a new solution to a mystery that has beleaguered their field for more than 30 years. This profound puzzle, which has driven experiments at increasingly powerful particle colliders and given rise to the controversial multiverse hypothesis, amounts to something a bright fourth-grader might ask: How can a magnet lift a paperclip against the gravitational pull of the entire planet?

    Despite its sway over the motion of stars and galaxies, the force of gravity is hundreds of millions of trillions of trillions of times weaker than magnetism and the other microscopic forces of nature. This disparity shows up in physics equations as a similarly absurd difference between the mass of the Higgs boson, a particle discovered in 2012 that controls the masses and forces associated with the other known particles, and the expected mass range of as-yet-undiscovered gravitational states of matter.

    In the absence of evidence from Europe’s Large Hadron Collider (LHC) supporting any of the theories previously proposed to explain this preposterous mass hierarchy — including the seductively elegant “supersymmetry” — many physicists have come to doubt the very logic of nature’s laws.

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

    Increasingly, they worry that our universe might just be a random, rather bizarre permutation among uncountable other possible universes — an effective dead end in the quest for a coherent theory of nature.

    This month, the LHC launched its eagerly anticipated second run at nearly double its previous operating energy, continuing its pursuit of new particles or phenomena that would solve the hierarchy problem. But the very real possibility that no new particles lie around the corner has left theoretical physicists facing their “nightmare scenario.” It has also gotten them thinking.

    “It is in moments of crisis that new ideas develop,” said Gian Giudice, a theoretical particle physicist at the CERN laboratory near Geneva, which houses the LHC.

    The new proposal offers a possible way forward. The trio is “super excited,” said David Kaplan, 46, a theoretical particle physicist from Johns Hopkins University in Baltimore, Md., who developed the model during a West Coast sabbatical with Peter Graham, 35, of Stanford University and Surjeet Rajendran, 32, of the University of California, Berkeley.

    2
    David Kaplan of Johns Hopkins University. Will Kirk

    Their solution traces the hierarchy between gravity and the other fundamental forces back to the explosive birth of the cosmos, when, their model suggests, two variables that were evolving in tandem suddenly deadlocked. At that instant, a hypothetical particle called the “axion” locked the Higgs boson into its present-day mass, far below the scale of gravity. The axion has appeared in theoretical equations since 1977 and is deemed likely to exist. Yet no one, until now, noticed that axions could be what the trio calls “relaxions,” solving the hierarchy problem by “relaxing” the value of the Higgs mass.

    “It’s a very, very clever idea,” said Raman Sundrum, a theoretical particle physicist at the University of Maryland in College Park who was not involved in developing it. “Possibly some version of that is the way the world works.”

    In the weeks since the trio’s paper appeared online, it has opened up “a new playground” populated with researchers eager to revise its weaknesses and take its basic premise in different directions, said Nathaniel Craig, a theoretical physicist at the University of California, Santa Barbara.

    “This just seems like a pretty simple possibility,” Rajendran said. “We’re not standing on our heads to do something crazy here. It just wants to work.”

    However, as several experts noted, in its current form the idea has shortcomings that will need to be carefully considered. And even if it survives this scrutiny, it could take more than a decade to test experimentally. For the time being, experts said, the relaxion is shaking up longheld views and encouraging some physicists to see the hierarchy problem in a new light. The lesson, said Michael Dine, a physicist at the University of California, Santa Cruz, and a veteran of the hierarchy problem, is “not to just give up and assume that we won’t be able to figure it out.”

    An Unnatural Balance

    For all the revelry surrounding the 2012 discovery of the Higgs boson, which completed the “Standard Model” of particle physics and earned Peter Higgs and François Englert the 2013 Nobel Prize in physics, it came as little surprise; the particle’s existence and measured mass of 125 giga-electron volts (GeV) agreed with years of indirect evidence.

    4
    Standard Model of Particle Physics. The diagram shows the elementary particles of the Standard Model (the Higgs boson, the three generations of quarks and leptons, and the gauge bosons), including their names, masses, spins, charges, chiralities, and interactions with the strong, weak and electromagnetic forces. It also depicts the crucial role of the Higgs boson in electroweak symmetry breaking, and shows how the properties of the various particles differ in the (high-energy) symmetric phase (top) and the (low-energy) broken-symmetry phase (bottom).

    It’s what wasn’t found at the LHC that left experts baffled. Nothing showed up that could reconcile the Higgs mass with the predicted mass scale associated with gravity, which lies beyond experimental reach at 10,000,000,000,000,000,000 GeV.

    3
    The mass-energy scale associated with gravity (right) lies 17 orders of magnitude beyond the scale of the known particles (left), where 1 GeV = 1,000 MeV. The tendency of particle masses to equalize in calculations makes this a puzzling hierarchy. Nelson Hsu for Quanta Magazine

    “The issue is that in quantum mechanics, everything influences everything else,” Giudice explained. The super-heavy gravitational states should mingle quantum mechanically with the Higgs boson, contributing huge factors to the value of its mass. Yet somehow, the Higgs boson ends up lightweight. It’s as if all the gargantuan factors affecting its mass — some positive, others negative, but all dozens of digits long — have magically canceled out, leaving an extraordinarily tiny value behind. The improbably fine-tuned cancellation of these factors seems “suspicious,” Giudice said. “You think, well, there must be something else behind it.”

    Experts often compare the finely tuned Higgs mass to a pencil standing on its lead tip, nudged this way and that by powerful forces like air currents and table vibrations that have somehow struck a perfect balance. “It is not a state of impossibility; it is a state of extremely small likelihood,” said Savas Dimopoulos of Stanford. If you came across such a pencil, he said, “you would first move your hand over the pencil to see if there was any string holding it from the ceiling. [Next] you would look at the tip to see if there is chewing gum.”

    Physicists have similarly sought a natural explanation for the hierarchy problem since the 1970s, confident that the search would lead them toward a more complete theory of nature, perhaps even turning up the particles behind “dark matter,” the invisible substance that permeates galaxies. “Naturalness has really been the leitmotif of that research,” Giudice said.

    4
    Surjeet Rajendran of the University of California, Berkeley. Sarah Wittmer

    Since the 1980s, the most popular proposal has been supersymmetry. It solves the hierarchy problem by postulating a yet-to-be-discovered twin for each elementary particle: for the electron, a hypothetical “selectron,” for each quark, a “squark,” and so on. Twins contribute opposite terms to the mass of the Higgs boson, rendering it immune to the effects of super-heavy gravity particles (since they are nullified by the effects of their twins).

    Supersymmetry standard model
    Standard Model of Supersymmetry

    But no evidence for supersymmetry or for any competing ideas — such as “technicolor” and “warped extra dimensions” — turned up during the first run of the LHC from 2010 to 2013. When the collider shut down for upgrades in early 2013 without having found a single “sparticle” or any other sign of physics beyond the Standard Model, many experts felt they could no longer avoid contemplating a stark alternative. What if the Higgs mass, and by implication the laws of nature, are unnatural? Calculations show that if the mass of the Higgs boson were just a few times heavier and everything else stayed the same, protons could no longer assemble into atoms, and there would be no complex structures — no stars or living beings. So, what if our universe really is as accidentally fine-tuned as a pencil balanced on its tip, singled out as our cosmic address from an inconceivably vast array of bubble universes inside an eternally frothing “multiverse” sea simply because life requires such an outrageous accident to exist?

    This multiverse hypothesis, which has loomed over discussions of the hierarchy problem since the late 1990s, is seen as a bleak prospect by most physicists. “I just don’t know what to do with it,” Craig said. “We don’t know what the rules are.” Other bubbles of the multiverse, if they exist, lie beyond the boundaries of light communication, forever limiting theories about the multiverse to what we can observe from within our lonely bubble. With no way to tell where our data point lies on the vast spectrum of possibilities in a multiverse, it becomes difficult or impossible to construct multiverse-based arguments about why our universe is the way it is. “I don’t know at what point we would ever be convinced,” Dine said. “How would you settle it? How would you know?”

    The Higgs and the Relaxion

    Kaplan visited the Bay Area last summer to collaborate with Graham and Rajendran, whom he knew because all three had worked at various times under Dimopoulos, who was one of the key developers of supersymmetry. Over the past year the trio split their time between Berkeley and Stanford — and the various coffee shops, lunch spots and ice cream parlors bordering both campuses — exchanging “embryonic bits of the idea,” Graham said, and gradually developing a new origin story for the laws of particle physics.

    Inspired by a 1984 attempt by Larry Abbott to address a different naturalness problem in physics, they sought to recast the Higgs mass as an evolving parameter, one that could dynamically “relax” to its tiny value during the birth of the cosmos rather than starting out as a fixed, seemingly improbable constant. “Though it took six months of dead ends and really stupid models and very baroque, complicated things, we ended up landing on this very simple picture,” Kaplan said.

    In their model, the Higgs mass depends on the numerical value of a hypothetical field that permeates space and time: an axion field. To picture it, “we think of the totality of space as being this 3-D mattress,” Dimopoulos said. The value at each point in the field corresponds to how compressed the mattress springs are there. It has long been recognized that the existence of this mattress — and its vibrations in the form of axions — could solve two deep mysteries: First, the axion field would explain why most interactions between protons and neutrons run both forward and backward, solving what’s known as the “strong CP” problem. And axions could make up dark matter. Solving the hierarchy problem would be a third impressive achievement.

    The story of the new model begins when the cosmos was an energy-infused dot. The axion mattress was extremely compressed, which made the Higgs mass enormous. As the universe expanded, the springs relaxed, as if their energy were spreading through the springs of the newly created space. As the energy dissipated, so did the Higgs mass. When the mass fell to its present value, it caused a related variable to plunge past zero, switching on the Higgs field, a molasseslike entity that gives mass to the particles that move through it, such as electrons and quarks. Massive quarks in turn interacted with the axion field, creating ridges in the metaphoric hill that its energy had been rolling down. The axion field got stuck. And so did the Higgs mass.

    5
    Peter Graham of Stanford University. Courtesy of Peter Graham

    In what Sundrum called a radical break from past models, the new one shows how the modern-day mass hierarchy might have been sculpted by the birth of the cosmos. “The fact that they’ve put equations to this in a realistic sense is really remarkable,” he said.

    Dimopoulos remarked on the striking minimalism of the model, which employs mostly pre-established ideas. “People like myself who have invested quite a bit on these other approaches to the hierarchy problem were very happily surprised that you don’t have to look very far,” he said. “In the backyard of the Standard Model, the solution was there. It took very clever young people to realize that.

    “This elevates the stock price of the axion,” he added. Recently, the Axion Dark Matter eXperiment at the University of Washington in Seattle began looking for the rare conversions of dark matter axions into light inside strong magnetic fields.

    AXION DME
    Axion Dark Matter eXperiment

    Now, Dimopoulos said, “We should look even harder to find it.”

    However, like many experts, Nima Arkani-Hamed of the Institute for Advanced Study in Princeton, N.J., noted that it’s early days for this proposal. While “it’s definitely clever,” he said, its current implementation is far-fetched. For example, in order for the axion field to have gotten stuck on the ridges created by the quarks rather than rolling past them, cosmic inflation must have progressed much more slowly than most cosmologists have assumed. “You add 10 billion years of inflation,” he said. “You have to wonder why all of cosmology arranges itself just to make this happen.”

    And even if the axion is discovered, that alone wouldn’t prove it is the “relaxion” — that it relaxes the value of the Higgs mass. As Kaplan’s stay in the Bay Area winds down, he, Graham and Rajendran are beginning to develop ideas for how to test that aspect of their model. It might eventually be possible to oscillate an axion field, for example, to see whether this affects the masses of nearby elementary particles, by way of the Higgs mass. “You would see the electron mass wiggling,” Graham said.

    These tests of the proposal will not happen for many years. (The model doesn’t predict any new phenomena that the LHC would detect.) And realistically, several experts said, it faces long odds. So many clever proposals have failed over the years that many physicists are reflexively skeptical. Still, the intriguing new model is delivering a timely dose of optimism.

    “We thought we had thought of everything and there was nothing new under the sun,” Sundrum said. “What this shows is that humans are pretty smart and there’s still room for new breakthroughs.”

    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 12:10 pm on March 3, 2015 Permalink | Reply
    Tags: , , Higgs,   

    From BBC: “New Higgs detection ‘closes circle’” 

    BBC
    BBC

    3 March 2015
    Jonathan Webb

    1
    The low energy work is separate from studies at the Large Hadron Collider

    Physicists who detected a version of the Higgs Boson in a superconductor say their discovery closes a “historical circuit”.

    They also stressed that the low-energy work was “completely separate” from the famous evidence gathered by the Large Hadron Collider.

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

    Superconductivity was the field of study where the idea for the Higgs originated in the 1960s. But the particle proved impossible to witness because it decays so fast. This new signature was glimpsed as very thin, chilled layers of metal compounds were pushed very close to the boundary of their superconducting state. This process creates a “mode” in the material that is analogous to the Higgs Boson but lasts much longer.

    Rather than the study of particles, it belongs in the field known condensed matter physics; it also uses much less energy than experiments at the LHC, where protons are smashed together at just under the speed of light. It was at the LHC in 2012 that the Higgs Boson, believed to give all the other subatomic particles their mass, was detected for the very first time.

    The new superconductor discovery was presented amid much discussion at this week’s March Meeting of the American Physical Society in San Antonio, Texas. It also appeared in the journal Nature Physics in January. Speaking at the meeting, Prof Aviad Frydman from Bar Ilan University in Israel responded in no uncertain terms to the suggestion that his work could substitute for the LHC. “That’s complete nonsense,” he told the BBC. “In fact it’s kind of embarrassing.”

    2
    The team used superconducting films made from compounds of niobium (pictured here as a fibre) and indium

    Prof Frydman said the convergence of results from “two extremes of physics” was the most striking aspect of his findings, which were the fruit of a collaboration spanning Israel, Germany, Russia, India and the USA. “You take the high energy physics, which works in gigaelectronvolts. And then you take superconductivity, which is low energy, low temperature, one millivolt. “You have 10 to the 15 (one quadrillion) orders of magnitude between them, and the same physics governs both! That is the nice thing.”

    “It’s not that our experiment can replace the LHC. It’s completely separate.”

    Superconductors are materials that, when under critical conditions including temperatures near absolute zero (-273C), allow electrons to move with complete freedom. It was attempts to understand this property that ultimately led to Peter Higgs and others proposing the now-famous boson. “In the 1960s there were two distinct, basic problems. One was superconductivity and one was the mass of particles,” Prof Frydman explained.

    “People like Phil Anderson developed this mechanism for understanding superconductivity. And the guys from high energy saw this kind of solution, and applied it to high energy physics. That’s where the Higgs actually came from.” So the detection of a superconducting Higgs, he added, is “closing a historical circuit”. This closure was a long time coming. Detecting the Higgs in a superconductor had seemed almost impossible. This was because the energy required to excite (and detect) the Higgs mode – even though vastly less than that needed to generate its analogous particle inside the LHC – would destroy the very property of superconductivity. The Higgs mode would vanish almost before it arose. But when Prof Frydman and his colleagues held their thin films in conditions very close to the “critical transition” between being a superconductor and an insulator, they created a longer-lived, lower-energy Higgs mode.

    Other claims of a superconducting Higgs have been made in the past, including one in 2014. They have all faced criticism. Indeed, Prof Frydman’s conference presentation was also greeted with intense questions from others in the field. “Like any physical finding, there are different interpretations,” he said. “The Cern experiment is also being contested.”

    See the full article here.

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  • richardmitnick 5:18 pm on January 23, 2015 Permalink | Reply
    Tags: , Higgs,   

    From Wired: “How Three Guys With $10K and Decades-Old Data Almost Found the Higgs Boson First” An Absolutely Great Story 

    Wired logo

    Wired

    1
    The Large Electron-Positron collider’s ALEPH detector was disassembled in 2001 to make room for the Large Hadron Collider. ALEPH collaboration/CERN

    On a fall morning in 2009, a team of three young physicists huddled around a computer screen in a small office overlooking Broadway in New York. They were dressed for success—even the graduate student’s shirt had buttons—and a bottle of champagne was at the ready. With a click of the mouse, they hoped to unmask a fundamental particle that had eluded physicists for decades: the Higgs boson.

    Of course, these men weren’t the only physicists in pursuit of the Higgs boson. In Geneva, a team of hundreds of physicists with an $8 billion machine called the Large Hadron Collider, and the world’s attention, also was in the hunt. But shortly after starting for the first time, the LHC had malfunctioned and was offline for repairs, opening a window three guys at NYU hoped to take advantage of.

    The key to their strategy was a particle collider that had been dismantled in 2001 to make room for the more powerful LHC. For $10,000 in computer time, they would attempt to show that the Large Electron-Positron collider had been making dozens of Higgs bosons without anybody noticing.

    “Two possible worlds stood before us then,” said physicist Kyle Cranmer, the leader of the NYU group. “In one, we discover the Higgs and a physics fairy tale comes true. Maybe the three of us share a Nobel prize. In the other, the Higgs is still hiding, and instead of beating the LHC, we have to go back to working on the LHC.”

    Cranmer had spent years working on both colliders, beginning as a graduate student at the Large Electron-Positron collider. He had been part of a 100-person statistical team that combed through terabytes of LEP data for evidence of new particles. “Everyone thought we had been very thorough,” he said. “But our worldview was colored by the ideas that were popular at the time.” A few years later, he realized the old data might look very different through the lens of a new theory.

    So, like detectives poring through evidence in a cold case, the researchers aimed to prove that the Higgs, and some supersymmetric partners in crime, had been at the scene in disguise.

    Dreaming up the Higgs

    The Higgs boson is now viewed as an essential component of the Standard Model of physics, a theory that describes all known particles and their interactions. But back in the 1960s, before the Standard Model had coalesced, the Higgs was part of a theoretical fix for a radioactive problem.

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    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.

    Here’s the predicament they faced. Sometimes an atom of one element will suddenly transform into an atom of a different element in a process called radioactive decay. For example, an atom of carbon can decay into an atom of nitrogen by emitting two light subatomic particles. (The carbon dating of fossils is a clever use of this ubiquitous process.) Physicists trying to describe the decay using equations ran into trouble—the math predicted that a sufficiently hot atom would decay infinitely quickly, which isn’t physically possible.

    To fix this, they introduced a theoretical intermediate step into the decay process, involving a never-before-seen particle that blinks into existence for just a trillionth of a trillionth of a second. As if that weren’t far-fetched enough, in order for the math to work, the particle—called the W boson—would need to weigh 10 times as much as the carbon atom that kicked off the process.
    “Figuring out what happened in a collider is like trying to figure out what your dog ate at the park yesterday. You can find out, but you have to sort through a lot of shit to do it.”

    To explain the bizarrely large mass of the W boson, three teams of physicists independently came up with the same idea: a new physical field. Just as your legs feel sluggish and heavy when you wade through deep water, the W boson seems heavy because it travels through what became known as the Higgs field (named after physicist Peter Higgs, who was a member of one of the three teams). The waves kicked up by the motion of this field, by way of a principle known as wave-particle duality, become particles called Higgs bosons.

    Their solution boiled down to this: Radioactive decay requires a heavy W boson, and a heavy W boson requires the Higgs field, and disturbances in the Higgs field produce Higgs bosons. “Explaining” radioactive decay in terms of one undetected field and two undiscovered particles may seem ridiculous. But physicists are conspiracy theorists with a very good track record.

    Forensic physics

    How do you find out if a theoretical particle is real? By the time Cranmer came of age, there was an established procedure. To produce evidence of new particles, you smash old ones together really, really hard. This works because E = mc2 means energy can be exchanged for matter; in other words, energy is the fungible currency of the subatomic world. Concentrate enough energy in one place and even the most exotic, heavy particles can be made to appear. But, they explode almost immediately. The only way to figure out they were there is to catch and analyze the detritus.

    How particle detectors work

    The innermost layer of a modern detector is made of thin silicon strips, like in a camera. A zooming particle, such as an electron, leaves a track of activated pixels. The track curves slightly, thanks to a magnetic field, and the degree of curvature reveals the electron’s momentum. Next the electron enters a series of chambers of excitable gas, where it ionizes little trails behind it. An electric field pulls the charged trails over to an array of wire sensors. Finally, the electron enters an iron or steel calorimeter which slows the particle to a halt, gathering and recording all of it’s energy.

    Modern particle accelerators like the LEP and LHC are like high-tech surveillance states. Thousands of electronic sensors, photoreceptors, and gas chambers monitor the collision site. Particle physics has become a forensic science.

    It’s also a messy science. “Figuring out what happened in a collider is like trying to figure out what your dog ate at the park yesterday,” said Jesse Thaler, the MIT physicist who first told me of Cranmer’s quest. “You can find out, but you have to sort through a lot of shit to do it.”

    The situation may be even worse than that. To reason backward from the particles that live long enough to detect to the short-lived undetected ones, requires detailed knowledge of each intermediate decay—almost like an exact description of all the chemical reactions in the dog’s gut. Complicating matters further, small changes in the theory you’re working with can affect the whole chain of reasoning, causing big changes in what you conclude really happened.
    The fine-tuning problem

    While the LEP was running, the Standard Model was the theory used to interpret its data. A panoply of particles were made, from the beauty quark to the W boson, but Cranmer and others had found no sign of a Higgs. They started to get worried: If the Higgs wasn’t real, how much of the rest of the Standard Model was also a convenient fiction?

    The model had at least one troubling feature beyond a missing Higgs: For matter to be capable of forming planets and stars, for the fundamental forces to be strong enough to hold things together but weak enough to avoid total collapse, an absurdly lucky cancellation (where two equivalent units of opposite sign combine to make zero) had to occur in some foundational formulas. This degree of what’s known as “fine-tuning” has a snowball’s chance in hell of happening by coincidence, according to physicist Flip Tanedo of the University of California, Irvine. It’s like a snowball never melting because every molecule of scorching hot air whizzing through hell just happens to avoid it by chance.

    So Cranmer was quite excited when he got wind of a new model that could explain both the fine-tuning problem and the hiding Higgs. The Nearly-Minimal Supersymmetric Standard Model has a host of new fundamental particles. The cancellation which seemed so lucky before is explained in this model by new terms corresponding to some of the new particles. Other new particles would interact with the Higgs, giving it a covert way to decay that would have gone unnoticed at the LEP.

    Supersymmetry standard model
    Standard Model of Supersymmetry

    If this new theory was correct, evidence for the Higgs boson was likely just sitting there in the old LEP data. And Cranmer had just the right tools to find it: He had experience with the old collider, and he had two ambitious apprentices. So he sent his graduate student James Beacham to retrieve the data from magnetic tapes sitting in a warehouse outside Geneva, and tasked NYU postdoctoral researcher Itay Yavin with working out the details of the new model. After laboriously deciphering dusty FORTRAN code from the original experiment and loading and cleaning information from the tapes, they brought the data back to life.

    This is what the team hoped to see evidence of in the LEP data:

    First, an electron and positron smash into each other, and their energy converts into the matter of a Higgs boson. The Higgs then decays into two ‘a’ particles—predicted by supersymmetry but never before seen—which fly in opposite directions. After a fraction of a second, each of the two ‘a’ particles decays into two tau particles. Finally each of the four tau particles decays into lighter particles, like electrons and pions, which survive long enough to strike the detector.

    As light particles hurtled through the detector’s many layers, detailed information on their trajectory was gathered (see sidebar). A tau particle would appear in the data as a common origin for a few of those trails. Like a firework shot into the sky, a tau particle can be identified by the brilliant arcs traced by its shrapnel. A Higgs, in turn, would appear as a constellation of light particles indicating the simultaneous explosion of four taus.

    Unfortunately, there are almost guaranteed to be false positives. For example, if an electron and a positron collide glancingly, they could create a quark with some of their energy. The quark could explode into pions, mimicking the behavior of a tau that came from a Higgs.

    1
    A computer simulation of a Higgs decaying into more elementary particles. The colored tracks show what the detector would see. ALEPH Collaboration/CERN

    To claim that a genuine Higgs had been made, rather than a few impostors, Beacham and Yavin needed to be extremely careful. Electronics sensitive enough to measure a single particle will often misfire, so there are countless decisions about which events to count and which to discard as noise. Confirmation bias makes it too dangerous to set those thresholds while looking at actual data from the LEP, as Beachem and Yavin would have been tempted to shade things in favor of a Higgs discovery. Instead, they decided to build two simulations of the LEP. In one, collisions took place in a universe governed by the Standard Model; in the other, the universe followed the rules of the Nearly-Minimal Supersymmetric Model. After carefully tuning their code on the simulated data, the team concluded that they had enough power to proceed: If the Higgs had been made by the LEP, they would detect significantly more four-tau events than if it had not.
    Moment of theoretical truth

    The team was hopeful and nervous as the moment of truth approached. Yavin had hardly been sleeping, checking and re-checking the code. A bottle of champagne was ready. With one click, the count of four-tau events at the LEP would come onscreen. If the Standard Model was correct, there would be around six, an expected number of false positives. If the Nearly-Minimal Supersymmetric Standard Model was correct, there would be around 30, a big enough excess to conclude that there really had been a Higgs.

    “I had done my job,” Cranmer said. “Now it was up to nature.”

    4
    Kyle Cranmer clicks for the Higgs! Also pictured: Itay Yavin (standing), James Beacham (sitting), and Veuve Clicquot (boxed). Courtesy Particle Fever

    There were just two tau quartets.

    “Honey, we didn’t find the Higgs,” Cranmer told his wife on the phone. Yavin collapsed in his chair. Beacham was thrilled the code had worked at all, and drank the champagne anyway.

    If Cranmer’s little team had found the Higgs boson before the multi-billion-dollar LHC and unseated the Standard Model, if the count had been 32 instead of 2, their story would have been front-page news. Instead, it was a typical success for the scientific method: A theory was carefully developed, rigorously tested, and found to be false.

    “With one keystroke, we rendered over a hundred theory papers null and void,” Beacham said.

    Three years later, a huge team of physicists at the LHC announced they had found the Higgs and that it was entirely consistent with the Standard Model. This was certainly a victory—for massive engineering projects, for international collaborations, for the theorists who dreamt up the Higgs field and boson 50 years ago. But the Standard Model probably won’t stand forever. It still has problems with fine-tuning and with integrating general relativity, problems that many physicists hope some new model will resolve. The question is, which one?

    “There are a lot of possibilities for how nature works,” said physicist Matt Strassler, a visiting scholar at Harvard University. “Once you go beyond the Standard Model, there are a gazillion ways to try to fix the fine-tuning problem.” Each proposed model has to be tested against nature, and each test invariably requires months or years of labor to do right, even if you’re cleverly reusing old data. The adrenaline builds until the moment of truth—will this be the new law of physics? But the vast number of possible models means that almost every test ends with the same answer: No. Try again.

    See the full article here.

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  • richardmitnick 11:21 am on July 25, 2014 Permalink | Reply
    Tags: , , , Higgs, ,   

    From Fermilab: “The Higgs gives mass to matter, too” 


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

    Friday, July 25, 2014
    Jim Pivarski

    Nearly 50 years before its discovery, the Higgs field was proposed as a way to explain why particles have mass. The Standard Model would be internally inconsistent if particles could have mass on their own (that is, as an intrinsic property like charge), but it would not be inconsistent to propose a new field that gives them an effective mass by interacting with them. That new field has come to be known as the Higgs field, and particles of this field are called Higgs bosons.

    sm
    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.

    sim
    Higgs Field simulation

    This story is well known, and it was told in many ways when the Higgs boson was discovered in 2012. What is less well known is that the problem of mass was not a single problem. The reason that force particles (such as W and Z bosons) cannot have intrinsic mass is different from the reason that matter particles (such as electrons and quarks) cannot have intrinsic mass. The effective mass of force particles and matter particles could come from different sources. There could be two Higgs fields, one that only interacts with and gives mass to force particles, the other to matter particles, or perhaps the mechanisms themselves could be completely different.

    higgs cms
    CMS depiction of the higgs boson

    Many physicists expected that a single Higgs field would pull double duty and give mass to all the particles. This, however, was a hypothesis, based on the expectation that nature is simple and elegant.

    As it turns out, nature seems to be simple and elegant. CMS scientists recently published a study of Higgs boson decays to matter particles, complementing its discovery, which was through its decays to force particles. The same Higgs field interacts with both types of particles in the expected way.

    Specifically, the study focused on Higgs to tau pairs (tau is a heavy cousin of the electron) and Higgs to b quarks (the b quark is a heavy cousin of the quarks found in the protons and neutrons of an atom). Since this interaction is responsible for mass, it is stronger for more massive particles. Both of these decay products are hard to distinguish from backgrounds, especially the b quarks, so the statistical significance is weak (3.8 sigma, equivalent to a one in 14,000 chance that the combined observation is spurious). However, these decays and all the decays to force particles point back to a single Higgs boson. The basic principles of physics may yet be simple enough to fit on the front of a T-shirt.

    proton
    The quark structure of the proton. (The color assignment of individual quarks is not important, only that all three colors are present.)

    neut
    The quark structure of the neutron. (The color assignment of individual quarks is not important, only that all three colors are present.)

    See the full article here.

    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.


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  • richardmitnick 4:58 am on October 10, 2013 Permalink | Reply
    Tags: , , Higgs,   

    From CERN: “Watch CERN physicists react to Nobel announcement” 

    CERN New Masthead

    Cameras were rolling in CERN’s building 40 on Tuesday when members of the ATLAS and CMS collaborations heard the news from the Swedish Academy of Sciences that François Englert and Peter W. Higgs had received the 2013 Nobel prize in physics. Watch their reaction in the video above.

    The Nobel prize was awarded to Englert and 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.” The ATLAS and CMS collaborations announced their discovery of the particle at CERN on 4 July 2012.

    As the news came through from Stockholm, CERN physicists burst into applause, and CERN Director-General Rolf Heuer gave a spontaneous speech congratulating the theoretical physicists for the award and the experimental physicists at CERN for their discovery.

    The ATLAS and CMS collaborations each involves more than 3000 people from all around the world. They have constructed sophisticated instruments – particle detectors – to study proton collisions at CERN’s Large Hadron Collider (LHC), itself a highly complex instrument involving many people and institutes in its construction.

    See the full article here.

    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

    LHC

    CERN LHC New

    LHC particles

    Quantum Diaries


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  • richardmitnick 9:23 am on October 9, 2013 Permalink | Reply
    Tags: , , , Higgs,   

    From Livermore Lab: “U.S. scientists celebrate Nobel Prize for Higgs discovery” 


    Lawrence Livermore National Laboratory

    10/08/2013
    Donald B Johnston, LLNL, (925) 423-4902, johnston19@llnl.gov

    The Royal Swedish Academy of Sciences awarded the Nobel Prize in physics today to theorists Peter Higgs and Francois Englert to recognize their work developing the theory of what is now known as the Higgs field, which gives elementary particles mass.

    U.S. scientists, including researchers at Lawrence Livermore National Laboratory (LLNL), played a significant role in advancing the theory and in discovering the particle that proves the existence of the Higgs field, the Higgs boson.

    Nearly 2,000 physicists from U.S. institutions — including 89 U.S. universities and seven U.S. Department of Energy laboratories — participate in the ATLAS and CMS experiments, making up about 23 percent of the ATLAS collaboration and 33 percent of CMS at the time of the Higgs discovery. Brookhaven National Laboratory serves as the U.S. hub for the ATLAS experiment, and Fermi National Accelerator Laboratory serves as the U.S. hub for the CMS experiment. U.S. scientists provided a significant portion of the intellectual leadership on Higgs analysis teams for both experiments.

    Lawrence Livermore joined the Compact Muon Solenoid (CMS) experiment in 2005. LLNL contributions include: assisted in development of the trigger system that captures Higgs and other phenomena for the CMS experiment; and a leadership role in developing the software that reconstructs raw data into the physics objects that form the basis of all analyses. Lab researchers are now working on a novel physics analysis and leading a detector upgrade that can discover new particles and reveal information about the Higgs.

    cms
    Lowering of the final element (YE-1) of the Compact Muon Solenoid (CMS) detector into its underground experimental cavern.

    The LLNL team on CMS is Doug Wright, David Lange, Jeff Gronberg and postdoc Finn Rebassoo. Former LLNL postdocs currently on CMS are Jonathan Hollar (now at University of Louvain, Belgium) and Bryan Dahmes (now at University of Minnesota).

    Support for the U.S. effort comes from the U.S. Department of Energy Office of Science and the National Science Foundation.

    See the full article here.

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  • richardmitnick 12:48 pm on March 26, 2013 Permalink | Reply
    Tags: , , Higgs,   

    From CERN: “Edinburgh Medal honours Higgs and CERN” 

    CERN New Masthead

    March 26, 2013
    Marina Giampietro

    two
    CERN Director-General Rolf Heuer accepts an Edinburgh Medal on behalf of CERN at a ceremony on Saturday. Also honoured was Peter Higgs (right) (Image: Joshua Smythe)

    “In a ceremony on 24 March, the 2013 Edinburgh Medal was awarded to Peter Higgs and CERN. The Director-General received the medal on behalf of CERN [See video].

    The Edinburgh Medal, now in its 25th year, is awarded by the Edinburgh International Science Festival to scientists whose achievements have made a significant contribution to the understanding and well-being of humanity.

    The first Edinburgh Medal was awarded to Abdus Salam who received the Nobel prize in physics for theoretical work that became a fundamental part of the Standard Model of particles and forces. Salam’s work incorporated what is now known as the Brout-Englert-Higgs mechanism, which gives mass to elementary particles. The mechanism introduced a new field, which like all fundamental fields has an associated particle, in this case called the Higgs boson.

    This year the award comes full circle, being awarded to Higgs and to CERN, where the ATLAS and CMS experiments at the Large Hadron Collider tracked down a particle last summer that look increasingly like a Higgs boson.

    And now, a neat video of the awards.

    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

    LHC

    CERN LHC New

    LHC particles

    Quantum Diaries


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  • richardmitnick 8:20 am on March 8, 2013 Permalink | Reply
    Tags: , , Higgs   

    A New Video about the Higgs Boson 

    Take the six minutes to watch this video. In the video you will be brought up to date on where the new particle stands. Also, there is an explanation of Higgs by Dr. Don Lincoln of Fermilab.

     
  • richardmitnick 4:26 pm on March 6, 2013 Permalink | Reply
    Tags: , , , Higgs,   

    From CERN: “A question of spin for the new boson” 

    CERN New Masthead

    6 Mar 2013
    James Gillies

    “Physicists speaking today at the Moriond conference in La Thuile, Italy, have announced that the new particle discovered at CERN last year is looking more and more like a Higgs boson. However, more analysis is still required before a definitive statement can be made. The key to a positive identification of the particle is a detailed analysis of its properties and the way that it interacts with other particles. Since the announcement last July, much more data has been analysed, and these properties are becoming clearer.

    The key property that will allow us to say whether or not it is a Higgs particle is called spin. If this particle has spin-zero, then it is a Higgs particle. If not, then it is something different, possibly linked to the way gravity works. All the analysis conducted so far strongly indicates spin-zero, but is not yet able to rule out entirely the possibility that the particle has spin-two.

    ‘Until we can confidently tie down the particle’s spin,’ said CERN Research Director Sergio Bertolucci, ‘the particle will remain Higgs-like. Only when we know that is has spin-zero will we be able to call it a Higgs.’

    Even then, the work will be far from over. If the new particle is a Higgs, it could be the Higgs as predicted in the 1960s, which would complete the Standard Model of particle physics, or it could be a more exotic particle that would lead us beyond the Standard Model. The stakes are high. The Standard Model accounts for all the visible matter in the Universe, including the stuff that we are made of, but it does not account for the 96% of the Universe that is invisible to us – the dark universe. Finding out what kind of Higgs it is will rely on carefully measuring the particle’s interactions with other particles, and that may take several years to resolve.

    sm
    Standard Model with proposed Higgs boson

    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

    LHC

    CERN LHC New

    LHC particles

    Quantum Diaries


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