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  • richardmitnick 2:42 pm on April 10, 2018 Permalink | Reply
    Tags: , , , Higgs, Now the question is what if there is a whole sector of undiscovered particles that cannot communicate with our standard particles but can interact with the Higgs boson?, , , , , Theorists predict that about 90 percent of Higgs bosons are created through gluon fusion   

    From Symmetry: “How to make a Higgs boson” 

    Symmetry Mag
    Symmetry

    04/10/18
    Sarah Charley

    CERN CMS Higgs Event


    CERN ATLAS Higgs Event

    It doesn’t seem like collisions of particles with no mass should be able to produce the “mass-giving” boson, the Higgs. But every other second at the LHC, they do.

    Einstein’s most famous theory, often written as E=mc2, tells us that energy and matter are two sides of the same coin.

    The Large Hadron Collider uses this principle to convert the energy contained within ordinary particles into new particles that are difficult to find in nature—particles like the Higgs boson, which is so massive that it almost immediately decays into pairs of lighter, more stable particles.

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    But not just any collision can create a Higgs boson.

    “The Higgs is not just created from a ‘poof’ of energy,” says Laura Dodd, a researcher at the University of Wisconsin, Madison. “Particles follow a strict set of laws that dictate how they can form, decay and interact.”

    One of these laws states that Higgs bosons can be produced only by particles that interact with the Higgs field—in other words, particles with mass.

    The Higgs field is like an invisible spider’s web that permeates all of space. As particles travel through it, some get tangled in the sticky tendrils, a process that makes them gain mass and slow down. But for other particles—such as photons and gluons—this web is completely transparent, and they glide through unhindered.

    Given enough energy, the particles wrapped in the Higgs field can transfer their energy into it and kick out a Higgs boson. Because massless particles do not interact with the Higgs field, it would make sense to say that they can’t create a Higgs. But scientists at the LHC would beg to differ.

    The LHC accelerates protons around its 17-mile circumference to just under the speed of light and then brings them into head-on collisions at four intersections along its ring. Protons are not fundamental particles, particles that cannot be broken down into any smaller constituent pieces. Rather they are made up of gluons and quarks.

    As two pepped-up protons pass through each other, it’s usually pairs of massless gluons that infuse invisible fields with their combined energy and excite other particles into existence—and that includes Higgs bosons.

    __________________________________________________________

    We know that particles follow strict rules about who can talk to whom.
    __________________________________________________________

    How? Gluons have found a way to cheat.

    “It would be impossible to generate Higgs bosons with gluons if the collisions in the LHC were a simple, one-step processes,” says Richard Ruiz, a theorist at Durham University’s Institute for Particle Physics Phenomenology.

    Luckily, they aren’t.

    Gluons can momentarily “launder” their energy to a virtual particle, which converts the gluon’s energy into mass. If two gluons produce a pair of virtual top quarks, the tops can recombine and annihilate into a Higgs boson.

    To be clear, virtual particles are not stable particles at all, but rather irregular disturbances in quantum mechanical fields that exist in a half-baked state for an incredibly short period of time. If a real particle were a thriving business, then a virtual particle would be a shell company.

    Theorists predict that about 90 percent of Higgs bosons are created through gluon fusion. The probability of two gluons colliding, creating a top quark-antitop pair and propitiously producing a Higgs is roughly one in 2 billion. However, because the LHC generates 10 million proton collisions every second, the odds are in scientists’ favor and the production rate for Higgs bosons is roughly one every two seconds.

    Shortly after the Higgs discovery, scientists were mostly focused on what happens to Higgs bosons after they decay, according to Dodd.

    “But now that we have more data and a better understanding of the Higgs, we’re starting to look closer at the collision byproducts to better understand how frequently the Higgs is produced through the different mechanisms,” she says.

    The Standard Model of particle physics predicts that almost all Higgs bosons are produced through one of four possible processes.

    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.


    Standard Model of Particle Physics from Symmetry Magazine

    What scientists would love to see are Higgs bosons being created in a way that the Standard Model of particle physics does not predict, such as in the decay of a new particle. Breaking the known rules would show that there is more going on than physicists previously understood.

    “We know that particles follow strict rules about who can talk to whom because we’ve seen this time and time again during our experiments,” Ruiz says. “So now the question is, what if there is a whole sector of undiscovered particles that cannot communicate with our standard particles but can interact with the Higgs boson?”

    Scientists are keeping an eye out for anything unexpected, such as an excess of certain particles radiating from a collision or decay paths that occur more or less frequently than scientists predicted. These indicators could point to undiscovered heavy particles morphing into Higgs bosons.

    At the same time, to find hints of unexpected ingredients in the chain reactions that sometimes make Higgs bosons, scientists must know very precisely what they should expect.

    “We have fantastic mathematical models that predict all this, and we know what both sides of the equations are,” Ruiz says. “Now we need to experimentally test these predictions to see if everything adds up, and if not, figure out what those extra missing variables might be.”

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


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  • richardmitnick 10:45 am on April 5, 2018 Permalink | Reply
    Tags: A Second 'Big Bang' Could End Our Universe in an Instant, , , , , Higgs, , , , , Thanks to The Higgs Boson   

    From Harvard via Science Alert: “A Second ‘Big Bang’ Could End Our Universe in an Instant, Thanks to The Higgs Boson” 

    Harvard University
    Harvard University

    ScienceAlert

    Science Alert

    Well, that’s just great.

    1
    A Black Hole Artist Concept. (NASA/JPL-Caltech)

    5 APR 2018
    JEREMY BERKE, BUSINESS INSIDER

    Our universe may end the same way it was created: with a big, sudden bang. That’s according to new research from a group of Harvard physicists, who found that the destabilization of the Higgs boson – a tiny quantum particle that gives other particles mass – could lead to an explosion of energy that would consume everything in the known universe and upend the laws of physics and chemistry.

    As part of their study, published last month in the journal Physical Review D, the researchers calculated when our universe could end.

    It’s nothing to worry about just yet. They settled on a date 10139 years from now, or 10 million trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion years in the future. And they’re at least 95 percent sure – a statistical measure of certainty – that the universe will last at least another 1058 years.

    The Higgs boson, discovered in 2012 by researchers smashing subatomic protons together at the Large Hadron Collider, has a specific mass.

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    CERN CMS Higgs Event

    CERN ATLAS Higgs Event

    If the researchers are correct, that mass could change, turning physics on its head and tearing apart the elements that make life possible, according to the New York Post.

    And rather than burning slowly over trillions of years, an unstable Higgs boson could create an instantaneous bang, like the Big Bang that created our universe.

    The researchers say a collapse could be driven by the curvature of space-time around a black hole, somewhere deep in the universe. When space-time curves around super-dense objects, like a black hole, it throws the laws of physics out of whack and causes particles to interact in all sorts of strange ways.

    The researchers say the collapse may have already begun – but we have no way of knowing, as the Higgs boson particle may be far away from where we can analyse it, within our seemingly infinite universe. “It turns out we’re right on the edge between a stable universe and an unstable universe,” Joseph Lykken, a physicist from the Fermi National Accelerator Laboratory who was not involved in the study, told the Post.

    He added: “We’re sort of right on the edge where the universe can last for a long time, but eventually, it should go ‘boom.'”

    See the full article here .

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    Harvard University campus
    Harvard is the oldest institution of higher education in the United States, established in 1636 by vote of the Great and General Court of the Massachusetts Bay Colony. It was named after the College’s first benefactor, the young minister John Harvard of Charlestown, who upon his death in 1638 left his library and half his estate to the institution. A statue of John Harvard stands today in front of University Hall in Harvard Yard, and is perhaps the University’s best known landmark.

    Harvard University has 12 degree-granting Schools in addition to the Radcliffe Institute for Advanced Study. The University has grown from nine students with a single master to an enrollment of more than 20,000 degree candidates including undergraduate, graduate, and professional students. There are more than 360,000 living alumni in the U.S. and over 190 other countries.

     
  • richardmitnick 5:34 pm on March 22, 2018 Permalink | Reply
    Tags: , , , , Higgs, , , , Rutgers Physics, ,   

    From Rutgers: “Physicists at Crossroads in Trying to Understand Universe” 

    Rutgers smaller
    Our once and future Great Seal.

    Rutgers University

    March 21, 2018
    Todd Bates
    848-932-0550
    todd.bates@rutgers.edu

    1
    This image shows the evolution of the universe from its Big Bang birth (on the left) to the present (on the right), a timespan of nearly 14 billion years. By producing the world’s highest energy collisions, CERN’s Large Hadron Collider in Switzerland acts as a time machine that takes Rutgers physics professors Scott Thomas and Sunil Somalwar all the way back to the first trillionth of a second after the Big Bang.
    Image: NASA/WMAP Science Team

    Scientists at Rutgers University–New Brunswick and elsewhere are at a crossroads in their 50-year quest to go beyond the Standard Model in physics.

    Rutgers Today asked professors Sunil Somalwar and Scott Thomas in the Department of Physics and Astronomy at the School of Arts and Sciences to discuss mysteries of the universe. Somalwar’s research focuses on experimental elementary particle physics, or high energy physics, which involves smashing particles together at large particle accelerators such as the one at CERN in Switzerland. Thomas’s research focuses on theoretical particle physics.

    The duo, who collaborate on experiments, and other Rutgers physicists – including Yuri Gershtein – contributed to the historic 2012 discovery of the Higgs boson, a subatomic particle responsible for the structure of all matter and a key component of the Standard Model.

    CERN CMS Higgs Event


    CERN ATLAS Higgs Event


    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.


    Standard Model of Particle Physics from Symmetry Magazine

    Rutgers Today: What is the Standard Model?

    Thomas: It is a theory started about 50 years ago. It should be called “the most fantastically successful theory of everything ever” because it’s a triumph of human intellect. It explains, in a theoretical structure and in great quantitative detail, every single experiment ever done in the laboratory. And no experiment so far conflicts with this theory. The capstone to the Standard Model experimentally was the discovery of the Higgs boson. It predicted the existence and interactions of lots of different particles, all of which were found. The problem is that as theorists, we are victims of our own success. The Standard Model is so successful that the theory does not point to answers to some of the questions we still have. The Higgs boson answered many questions, but we don’t get clues directly from this theoretical structure how the remaining questions might be answered, so we’re at a crossroads in this 50-year quest. We need some hints from experiments and then, hopefully, the hints will be enough to tell us the next theoretical structure that underlies the Standard Model.

    Rutgers Today: What questions remain?

    Somalwar: The Standard Model says that matter and antimatter should be nearly equal. But after the Big Bang about 13.8 billion years ago, matter amounted to one part in 10 billion and antimatter dropped to virtually zero. A big mystery is what happened to all the antimatter. And why are neutrinos (also subatomic particles) so light? Is the Higgs boson particle by itself or is there a Higgs zoo? There are good reasons that the Higgs boson could not possibly be alone. There’s got to be more to the picture.

    Rutgers Today: What are you focusing on?

    Somalwar: I am looking for evidence of heavy particles that might have existed a picosecond after the Big Bang. These particles don’t exist anymore because they degenerate. They’re very unstable. They could explain why neutrinos are so light and why virtually all antimatter disappeared but not all matter disappeared. What we do is called frontier science – it’s at the forefront of physics: the smallest distances and highest energies. Once you get to the frontier, you occupy much of the area and start prospecting. But at some point, things are mined out and you need a new frontier. We’ve just begun prospecting here. We don’t have enough mined areas and we may have some gems lying there and more will come in the next year or two. So, it’s a very exciting time right now because it’s like we’ve gotten to the gold rush.

    Thomas: I am trying to understand the physics underlying the Higgs sector of the Standard Model theory, which must include at least one particle – the Higgs boson. This sector is very important because it determines the size of atoms and the mass of elementary particles. The physics underlying the Higgs sector is a roadblock to understanding physics at a more fundamental scale. Are there other species of Higgs particles? What are their interactions and what properties do they have? That would start to give us clues and then maybe we could reconstruct a theory of what underlies the Standard Model. The real motivation is to understand the way the universe works at its most fundamental level. That’s what drives us all.

    See the full article here.

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    rutgers-campus

    Rutgers, The State University of New Jersey, is a leading national research university and the state’s preeminent, comprehensive public institution of higher education. Rutgers is dedicated to teaching that meets the highest standards of excellence; to conducting research that breaks new ground; and to providing services, solutions, and clinical care that help individuals and the local, national, and global communities where they live.

    Founded in 1766, Rutgers teaches across the full educational spectrum: preschool to precollege; undergraduate to graduate; postdoctoral fellowships to residencies; and continuing education for professional and personal advancement.

    As a ’67 graduate of University college, second in my class, I am proud to be a member of

    Alpha Sigma Lamda, National Honor Society of non-tradional students.

     
  • richardmitnick 12:30 pm on March 4, 2018 Permalink | Reply
    Tags: , Higgs, , , ,   

    From Quanta Magazine: “Elusive Higgs-Like State Created in Exotic Materials” 

    Quanta Magazine
    Quanta Magazine

    February 28, 2018
    Sophia Chen

    Two teams of physicists have created the “Higgs mode” – a link between particle physics and the physics of matter. The work could help researchers understand the strange behavior of deeply quantum systems.

    1
    Camille Chew for Quanta Magazine

    CERN CMS Higgs Event


    CERN ATLAS Higgs Event

    If you want to understand the personality of a material, study its electrons. Table salt forms cubic crystals because its atoms share electrons in that configuration; silver shines because its electrons absorb visible light and reradiate it back. Electron behavior causes nearly all material properties: hardness, conductivity, melting temperature.

    Of late, physicists are intrigued by the way huge numbers of electrons can display collective quantum-mechanical behavior. In some materials, a trillion trillion electrons within a crystal can act as a unit, like fire ants clumping into a single mass to survive a flood. Physicists want to understand this collective behavior because of the potential link to exotic properties such as superconductivity, in which electricity can flow without any resistance.

    Last year, two independent research groups designed crystals, known as two-dimensional antiferromagnets, whose electrons can collectively imitate the Higgs boson. By precisely studying this behavior, the researchers think they can better understand the physical laws that govern materials — and potentially discover new states of matter. It was the first time that researchers have been able to induce such “Higgs modes” in these materials. “You’re creating a little mini universe,” said David Alan Tennant, a physicist at Oak Ridge National Laboratory who led one of the groups along with Tao Hong, his colleague there.

    Both groups induced electrons into Higgs-like activity by pelting their material with neutrons. During these tiny collisions, the electrons’ magnetic fields begin to fluctuate in a patterned way that mathematically resembles the Higgs boson.

    2
    A crystal made of copper bromide was used to construct the Oak Ridge team’s two-dimensional antiferromagnet. Genevieve Martin/Oak Ridge National Laboratory, U.S. Dept. of Energy.

    The Higgs mode is not simply a mathematical curiosity. When a crystal’s structure permits its electrons to behave this way, the material most likely has other interesting properties, said Bernhard Keimer, a physicist at the Max Planck Institute for Solid State Research who coleads the other group.

    That’s because when you get the Higgs mode to appear, the material should be on the brink of a so-called quantum phase transition. Its properties are about to change drastically, like a snowball on a sunny spring day. The Higgs can help you understand the character of the quantum phase transition, says Subir Sachdev, a physicist at Harvard University. These quantum effects often portend bizarre new material properties.

    For example, physicists think that quantum phase transitions play a role in certain materials, known as topological insulators, that conduct electricity only on their surface and not in their interior. Researchers have also observed quantum phase transitions in high-temperature superconductors, although the significance of the phase transitions is still unclear. Whereas conventional superconductors need to be cooled to near absolute zero to observe such effects, high-temperature superconductors work at the relatively balmy conditions of liquid nitrogen, which is dozens of degrees higher.

    Over the past few years, physicists have created the Higgs mode in other superconductors, but they can’t always understand exactly what’s going on. The typical materials used to study the Higgs mode have a complicated crystal structure that increases the difficulty of understanding the physics at work.

    So both Keimer’s and Tennant’s groups set out to induce the Higgs mode in simpler systems. Their antiferromagnets were so-called two-dimensional materials: While each crystal exists as a 3-D chunk, those chunks are built out of stacked two-dimensional layers of atoms that act more or less independently. Somewhat paradoxically, it’s a harder experimental challenge to induce the Higgs mode in these two-dimensional materials. Physicists were unsure if it could be done.

    Yet the successful experiments showed that it was possible to use existing theoretical tools to explain the evolution of the Higgs mode. Keimer’s group found that the Higgs mode parallels the behavior of the Higgs boson. Inside a particle accelerator like the Large Hadron Collider, a Higgs boson will quickly decay into other particles, such as photons. In Keimer’s antiferromagnet, the Higgs mode morphs into different collective-electron motion that resembles particles called Goldstone bosons. The group experimentally confirmed that the Higgs mode evolves according to their theoretical predictions.

    Tennant’s group discovered how to make their material produce a Higgs mode that doesn’t die out. That knowledge could help them determine how to turn on other quantum properties, like superconductivity, in other materials. “What we want to understand is how to keep quantum behavior in systems,” said Tennant.

    Both groups hope to go beyond the Higgs mode. Keimer aims to actually observe a quantum phase transition in his antiferromagnet, which may be accompanied by additional weird phenomena. “That happens quite a lot,” he said. “You want to study a particular quantum phase transition, and then something else pops up.”

    They also just want to explore. They expect that more weird properties of matter are associated with the Higgs mode — potentially ones not yet envisioned. “Our brains don’t have a natural intuition for quantum systems,” said Tennant. “Exploring nature is full of surprises because it’s full of things we never imagined.”

    No science papers cited in this article.

    See the full article here .
    Re-released at Wired, Sophia Chen 3.4.18 Science.

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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 10:12 am on March 1, 2018 Permalink | Reply
    Tags: , , , , , Higgs, , MIT physicists observe electroweak production of same-sign W boson pairs, , ,   

    From MIT: “MIT physicists observe electroweak production of same-sign W boson pairs” 

    MIT News

    MIT Widget

    MIT News

    February 27, 2018
    Scott Morley | Laboratory for Nuclear Science

    1
    Vector-boson scattering processes are characterized by two high-energetic jets in the forward regions of the detector. The Figure shows a significant excess of events in the distribution of the mass of the two tagging jets in yellow, labelled as EW WW. Image: Markus Klute

    In research conducted by a group led by MIT Laboratory for Nuclear Science researcher and associate professor of physics Markus Klute, electroweak productions of same-sign W boson pairs were observed, the first such observation of its kind and a milestone toward precision testing of vector boson scattering (W and Z bosons) at the Large Hadron Collider (LHC).

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    The LHC at CERN in Geneva, Switzerland, was proposed in the 1980s as a machine to either find the Higgs boson or discover yet unknown particles or interactions.

    CERN CMS Higgs Event


    CERN ATLAS Higgs Event

    This idea, that the LHC would be able to make a discovery, whatever that might be, is called by theorists No-lose Theorem, and is connected to probing the scattering of W boson pairs at energies above 1 teraelectronvolt (TeV). In 2012, only two years after the first high-energy collision at the LHC, this proposal paid huge dividends when the Higgs boson was discovered by the ATLAS and Compact Muon Solenid (CMS) collaborations.

    According to CERN, the CMS detector at the LHC utilizes a massive solenoid magnet to study everything from the Higgs boson to dark matter to the Standard Model.

    CERN/CMS Detector

    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.

    CMS is capable of generating a magnetic field that is approximately 100,000 times that of Earth. It resides in an underground cavern near Cessy, France, which is northwest of Geneva.

    The main goal of a recent measurement by CMS was to identify W boson pairs with the same sign (W+W+ or W-W-) produced purely via the electroweak interaction and probing the scattering of W bosons. The result does not unveil physics beyond the Standard Model, but this first observation of this process marks a starting point for a field of study to independently test whether the discovered Higgs boson is or is not the particle predicted by Robert Brout, François Englert, and Peter Higgs. It is anticipated that the rapidly growing data sets available at the LHC will further knowledge along these lines. Studies show that the high luminosity LHC will likely allow the direct study of longitudinal W boson scattering.

    “The measurement of vector-boson scattering processes, like the one studied in this paper, is an important test bench of the nature of the Higgs boson, as small deviations from the Standard Model expectation can have a large impact on event rates,” Klute says. “While challenging new physics models, these processes also allow a unique model-independent measurement of Higgs boson couplings to the W and Z boson at the LHC.”

    “The observation of this vector-boson scattering process is an important milestone toward future precision measurements,” Klute says. “These measurements are very challenging experimentally and require theoretical predictions with high precision. Both areas are pushed forward by the published results.”

    The work, while within CMS, was performed by MIT and included Klute, his students Andrew Levin and Xinmei Nui, and research scientist Guillelmo Gomez-Ceballos, along with University of Antwerp colleague Xavier Janssen and his student Jasper Lauwers.

    The work has been published in Physical Review Letters.

    This research was funded with support from U.S. Department of Energy.

    See the full article here .

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

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  • richardmitnick 3:18 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.


     
  • 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 .

    Please help promote STEM in your local schools.

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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 .

    Please help promote STEM in your local schools.

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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

    Please help promote STEM in your local schools.

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    CERN Courier

    QuantumDiaries


    Quantum Diaries

     
  • 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.

    STEM Icon

    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


     
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