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  • richardmitnick 12:32 pm on April 18, 2019 Permalink | Reply
    Tags: "When Beauty Gets in the Way of Science", Accelerator Science, , , , , , , , , ,   

    From Nautilus: “When Beauty Gets in the Way of Science” 

    Nautilus

    From Nautilus

    April 18, 2019
    Sabine Hossenfelder

    Insisting that new ideas must be beautiful blocks progress in particle physics.

    When Beauty Gets in the Way of Science. Nautilus

    The biggest news in particle physics is no news. In March, one of the most important conferences in the field, Rencontres de Moriond, took place. It is an annual meeting at which experimental collaborations present preliminary results. But the recent data from the Large Hadron Collider (LHC), currently the world’s largest particle collider, has not revealed anything new.

    LHC

    CERN map


    CERN LHC Tunnel

    CERN LHC particles

    Forty years ago, particle physicists thought themselves close to a final theory for the structure of matter. At that time, they formulated the Standard Model of particle physics to describe the elementary constituents of matter and their interactions.

    Standard Model of Particle Physics (LATHAM BOYLE AND MARDUS OF WIKIMEDIA COMMONS)

    After that, they searched for the predicted, but still missing, particles of the Standard Model. In 2012, they confirmed the last missing particle, the Higgs boson.

    CERN CMS Higgs Event

    CERN ATLAS Higgs Event

    The Higgs boson is necessary to make sense of the rest of the Standard Model. Without it, the other particles would not have masses, and probabilities would not properly add up to one. Now, with the Higgs in the bag, the Standard Model is complete; all Pokémon caught.

    1
    HIGGS HANGOVER: After the Large Hadron Collider (above) confirmed the Higgs boson, which validated the Standard Model, it’s produced nothing newsworthy, and is unlikely to, says physicist Sabine Hossenfelder.Shutterstock

    The Standard Model may be physicists’ best shot at the structure of fundamental matter, but it leaves them wanting. Many particle physicists think it is simply too ugly to be nature’s last word. The 25 particles of the Standard Model can be classified by three types of symmetries that correspond to three fundamental forces: The electromagnetic force, and the strong and weak nuclear forces. Physicists, however, would rather there was only one unified force. They would also like to see an entirely new type of symmetry, the so-called “supersymmetry,” because that would be more appealing.

    2
    Supersymmetry builds on the Standard Model, with many new supersymmetric particles, represented here with a tilde (~) on them. ( From the movie “Particle fever” reproduced by Mark Levinson)

    Oh, and additional dimensions of space would be pretty. And maybe also parallel universes. Their wish list is long.

    It has become common practice among particle physicists to use arguments from beauty to select the theories they deem worthy of further study. These criteria of beauty are subjective and not evidence-based, but they are widely believed to be good guides to theory development. The most often used criteria of beauty in the foundations of physics are presently simplicity and naturalness.

    By “simplicity,” I don’t mean relative simplicity, the idea that the simplest theory is the best (a.k.a. “Occam’s razor”). Relying on relative simplicity is good scientific practice. The desire that a theory be simple in absolute terms, in contrast, is a criterion from beauty: There is no deep reason that the laws of nature should be simple. In the foundations of physics, this desire for absolute simplicity presently shows in physicists’ hope for unification or, if you push it one level further, in the quest for a “Theory of Everything” that would merge the three forces of the Standard Model with gravity.

    The other criterion of beauty, naturalness, requires that pure numbers that appear in a theory (i.e., those without units) should neither be very large nor very small; instead, these numbers should be close to one. Exactly how close these numbers should be to one is debatable, which is already an indicator of the non-scientific nature of this argument. Indeed, the inability of particle physicists to quantify just when a lack of naturalness becomes problematic highlights that the fact that an unnatural theory is utterly unproblematic. It is just not beautiful.

    Anyone who has a look at the literature of the foundations of physics will see that relying on such arguments from beauty has been a major current in the field for decades. It has been propagated by big players in the field, including Steven Weinberg, Frank Wilczek, Edward Witten, Murray Gell-Mann, and Sheldon Glashow. Countless books popularized the idea that the laws of nature should be beautiful, written, among others, by Brian Greene, Dan Hooper, Gordon Kane, and Anthony Zee. Indeed, this talk about beauty has been going on for so long that at this point it seems likely most people presently in the field were attracted by it in the first place. Little surprise, then, they can’t seem to let go of it.

    Trouble is, relying on beauty as a guide to new laws of nature is not working.

    Since the 1980s, dozens of experiments looked for evidence of unified forces and supersymmetric particles, and other particles invented to beautify the Standard Model. Physicists have conjectured hundreds of hypothetical particles, from “gluinos” and “wimps” to “branons” and “cuscutons,” each of which they invented to remedy a perceived lack of beauty in the existing theories. These particles are supposed to aid beauty, for example, by increasing the amount of symmetries, by unifying forces, or by explaining why certain numbers are small. Unfortunately, not a single one of those particles has ever been seen. Measurements have merely confirmed the Standard Model over and over again. And a theory of everything, if it exists, is as elusive today as it was in the 1970s. The Large Hadron Collider is only the most recent in a long series of searches that failed to confirm those beauty-based predictions.

    These decades of failure show that postulating new laws of nature just because they are beautiful according to human standards is not a good way to put forward scientific hypotheses. It’s not the first time this has happened. Historical precedents are not difficult to find. Relying on beauty did not work for Kepler’s Platonic solids, it did not work for Einstein’s idea of an eternally unchanging universe, and it did not work for the oh-so-pretty idea, popular at the end of the 19th century, that atoms are knots in an invisible ether. All of these theories were once considered beautiful, but are today known to be wrong. Physicists have repeatedly told me about beautiful ideas that didn’t turn out to be beautiful at all. Such hindsight is not evidence that arguments from beauty work, but rather that our perception of beauty changes over time.

    That beauty is subjective is hardly a breakthrough insight, but physicists are slow to learn the lesson—and that has consequences. Experiments that test ill-motivated hypotheses are at high risk to only find null results; i.e., to confirm the existing theories and not see evidence of new effects. This is what has happened in the foundations of physics for 40 years now. And with the new LHC results, it happened once again.

    The data analyzed so far shows no evidence for supersymmetric particles, extra dimensions, or any other physics that would not be compatible with the Standard Model. In the past two years, particle physicists were excited about an anomaly in the interaction rates of different leptons. The Standard Model predicts these rates should be identical, but the data demonstrates a slight difference. This “lepton anomaly” has persisted in the new data, but—against particle physicists’ hopes—it did not increase in significance, is hence not a sign for new particles. The LHC collaborations succeeded in measuring the violation of symmetry in the decay of composite particles called “D-mesons,” but the measured effect is, once again, consistent with the Standard Model. The data stubbornly repeat: Nothing new to see here.

    Of course it’s possible there is something to find in the data yet to be analyzed. But at this point we already know that all previously made predictions for new physics were wrong, meaning that there is now no reason to expect anything new to appear.

    Yes, null results—like the recent LHC measurements—are also results. They rule out some hypotheses. But null results are not very useful results if you want to develop a new theory. A null-result says: “Let’s not go this way.” A result says: “Let’s go that way.” If there are many ways to go, discarding some of them does not help much.

    To find the way forward in the foundations of physics, we need results, not null-results. When testing new hypotheses takes decades of construction time and billions of dollars, we have to be careful what to invest in. Experiments have become too costly to rely on serendipitous discoveries. Beauty-based methods have historically not worked. They still don’t work. It’s time that physicists take note.

    And it’s not like the lack of beauty is the only problem with the current theories in the foundations of physics. There are good reasons to think physics is not done. The Standard Model cannot be the last word, notably because it does not contain gravity and fails to account for the masses of neutrinos. It also describes neither dark matter nor dark energy, which are necessary to explain galactic structures.

    So, clearly, the foundations of physics have problems that require answers. Physicists should focus on those. And we currently have no reason to think that colliding particles at the next higher energies will help solve any of the existing problems. New effects may not appear until energies are a billion times higher than what even the next larger collider could probe. To make progress, then, physicists must, first and foremost, learn from their failed predictions.

    So far, they have not. In 2016, the particle physicists Howard Baer, Vernon Barger, and Jenny List wrote an essay for Scientific American arguing that we need a larger particle collider to “save physics.” The reason? A theory the authors had proposed themselves, that is natural (beautiful!) in a specific way, predicts such a larger collider should see new particles. This March, Kane, a particle physicist, used similar beauty-based arguments in an essay for Physics Today. And a recent comment in Nature Reviews Physics about a big, new particle collider planned in Japan once again drew on the same motivations from naturalness that have already not worked for the LHC. Even the particle physicists who have admitted their predictions failed do not want to give up beauty-based hypotheses. Instead, they have argued we need more experiments to test just how wrong they are.

    Will this latest round of null-results finally convince particle physicists that they need new methods of theory-development? I certainly hope so.

    As an ex-particle physicist myself, I understand very well the desire to have an all-encompassing theory for the structure of matter. I can also relate to the appeal of theories such a supersymmetry or string theory. And, yes, I quite like the idea that we live in one of infinitely many universes that together make up the “multiverse.” But, as the latest LHC results drive home once again, the laws of nature care heartily little about what humans find beautiful.

    See the full article here .

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    Please help promote STEM in your local schools.

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    Welcome to Nautilus. We are delighted you joined us. We are here to tell you about science and its endless connections to our lives. Each month we choose a single topic. And each Thursday we publish a new chapter on that topic online. Each issue combines the sciences, culture and philosophy into a single story told by the world’s leading thinkers and writers. We follow the story wherever it leads us. Read our essays, investigative reports, and blogs. Fiction, too. Take in our games, videos, and graphic stories. Stop in for a minute, or an hour. Nautilus lets science spill over its usual borders. We are science, connected.

     
  • richardmitnick 11:37 am on April 16, 2019 Permalink | Reply
    Tags: Accelerator Science, , , , , , ,   

    From Symmetry: “A collision of light” 

    Symmetry Mag
    From Symmetry

    04/16/19
    Sarah Charley

    1
    Natasha Hartono

    One of the latest discoveries from the LHC takes the properties of photons beyond what your electrodynamics teacher will tell you in class.

    Professor Anne Sickles is currently teaching a laboratory class at the University of Illinois in which her students will measure what happens when two photons meet.

    What they will find is that the overlapping waves of light get brighter when two peaks align and dimmer when a peak meets a trough. She tells her students that this is process called interference, and that—unlike charged particles, which can merge, bond and interact—light waves can only add or subtract.

    “We teach undergraduates the classical theory,” Sickles says. “But there are situations where effects forbidden in the classical theory are allowed in the quantum theory.”

    Sickles is a collaborator on the ATLAS experiment at CERN and studies what happens when particles of light meet inside the Large Hadron Collider.

    CERN ATLAS Credit CERN SCIENCE PHOTO LIBRARY

    LHC

    CERN map


    CERN LHC Tunnel

    CERN LHC particles

    For most of the year, the LHC collides protons, but for about a month each fall, the LHC switches things up and collides heavy atomic nuclei, such as lead ions. The main purpose of these lead collisions is to study a hot and dense subatomic fluid called the quark-gluon plasma, which is harder to create in collisions of protons. But these ion runs also enable scientists to turn the LHC into a new type of machine: a photon-photon collider.

    “This result demonstrates that photons can scatter off each other and change each other’s direction,” says Peter Steinberg, and ATLAS scientist at Brookhaven National Laboratory.

    When heavy nuclei are accelerated in the LHC, they are encased within an electromagnetic aura generated by their large positive charges.

    As the nuclei travel faster and faster, their surrounding fields are squished into disks, making them much more concentrated. When two lead ions pass closely enough that their electromagnetic fields swoosh through one another, the high-energy photons which ultimately make up these fields can interact. In rare instances, a photon from one lead ion will merge with a photon from an oncoming lead ion, and they will ricochet in different directions.

    However, according to Steinberg, it’s not as simple as two solid particles bouncing off each other. Light particles are both chargeless and massless, and must go through a quantum mechanical loophole (literally called a quantum loop) to interact with one another.

    “That’s why this process is so rare,” he says. “They have no way to bounce off of each other without help.”

    When the two photons see each other inside the LHC, they sometimes overreact with excitement and split themselves into an electron and positron pair. These electron-positron pairs are not fully formed entities, but rather unstable quantum fluctuations that scientists call virtual particles. The four virtual particles swirl into each other and recombine to form two new photons, which scatter off at weird angles into the detector.

    “It’s like a quantum-mechanical square dance,” Steinberg says.

    When ATLAS first saw hints of this process in 2017, they had only 13 candidate events with the correct characteristics (collisions that resulted in two low-energy photons inside the detector and nothing else).

    After another two years of data taking, they have now collected 59 candidate events, bumping this original observation into the statistical certainty of a full-fledged discovery.

    Steinberg sees this discovery as a big win for quantum electrodynamics, a theory about the quantum behavior of light that predicted this interaction. “This amazingly precise theory, which was developed in the first half of the 20th century, made a prediction that we are finally able to confirm many decades later.”

    Sickles says she is looking forward to exploring these kinds of light-by-light interactions and figuring out what else they could teach us about the laws of physics. “It’s one thing to see something,” she says. “It’s another thing to study it.”

    See the full article here .


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    Please help promote STEM in your local schools.


    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 11:26 am on April 12, 2019 Permalink | Reply
    Tags: Accelerator Science, , , , , , ,   

    From Fermi National Accelerator Lab: “Quarks, squarks, stops and charm at this year’s Moriond conference” 

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

    From Fermi National Accelerator Lab , an enduring source of strength for the US contribution to scientific research world wide.

    April 11, 2019
    Don Lincoln

    1
    Fermilab RAs Kevin Pedro and Nadja Strobbe presented a variety of CMS and ATLAS research results at the 53rd annual Recontres de Moriond conference.

    This March, scientists from around the world gathered in LaThuile, Italy, for the 53rd annual Recontres de Moriond conference, one of the longest running and most prestigious conferences in particle physics. This conference is broken into two distinct weeks, with the first week usually covering electroweak physics and the second covering processes involving quantum chromodynamics. Fermilab and the LHC Physics Center were well represented at the conference.

    Fermilab research associates Kevin Pedro and Nadja Strobbe from the CMS group both presented talks on LHC physics result. Pedro spoke on searches for new physics with unconventional signatures at both the ATLAS and CMS experiments. The interest in unusual signatures is driven by the fact that many researchers have already searched for more commonly accepted physical processes. Looking for the unconventional opens up the possibility of unanticipated discoveries. Pedro covered long-lived particles emerging from a complex dark matter sector. The signature for this possible physics result is a jet that originates far from the interaction vertex. He also covered long-lived particles that disappear in the detector. This is a signature for a form of supersymmetry.

    Strobbe presented a thorough overview of searches for strong-force-produced signatures of supersymmetry. She covered both ATLAS and CMS results, covering a broad range of signatures, including the associated production of b quarks and Higgs bosons, diphotons, several stop squark analyses, and the associated production of three bottom quarks and missing transverse momentum. In total, she presented 12 distinct analyses. The phenomenology of strong-force-produced supersymmetry is diverse, and it provides a rich source for the possible discovery of new physics. This is Strobbe’s last Moriond presentation as a Fermilab research associate, as she has recently accepted a faculty position at the University of Minnesota, where she will be starting in the fall.

    Strobbe and Pedro were not the only people associated with the LHC Physics Center presenting or involved at Moriond. Fermilab Senior Scientist Boaz Klima has long been a member of the organizing committee. Meng Xiao (Johns Hopkins) and Greg Landsberg (Brown) also presented.

    More broadly, many interesting physics topics were covered at the conference. The LHCb experiment announced the discovery of new pentaquarks containing charm quarks. They also reported that a peak in the data that was previously thought to be a single pentaquark was actually two distinct particles. Studies of mesons containing both bottom and charm quarks were very well-represented, with ATLAS, CMS and LHCb all making presentations. In the first week of the Moriond conference, both ATLAS and LHCb announced studies in the matter-antimatter asymmetry in decays of mesons containing both bottom and strange quarks. And in an example of very quick inter-collaboration cooperation, the experiments presented a combined result in the second week.

    While the LHC is best known for colliding two beams of protons (studies of which were well represented at Moriond), the LHC also collides lead ions to study the behavior of superhot quark matter – what is called quark-gluon plasma. ALICE presented studies of charmed mesons called J/psi, which showed that charm quarks are affected in quark-gluon plasmas, just like lighter quarks. The ALICE experiment presented data gathered in a special run of proton-proton collisions at an energy unusual for the LHC an observation of charmed baryons in LHC collisions. These particles occur more often in proton-proton collisions than in electron-positron ones.

    The Moriond conference is a fascinating one. It is small and cozy and allows for conversations and collaboration between researchers, with a storied history of over half a century. In its 53rd year, researchers are showing that its second half century will be just as exciting.

    Don Lincoln is a Fermilab scientist on the CMS experiment.

    See the full article here.


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    FNAL Icon

    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.

    FNAL MINERvA front face Photo Reidar Hahn

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    FNAL Short-Baseline Near Detector under construction

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    Dark Energy Camera [DECam], built at FNAL

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  • richardmitnick 12:58 pm on April 11, 2019 Permalink | Reply
    Tags: "LHCb results add clues to pentaquark mystery", Accelerator Science, , , , , ,   

    From Symmetry: “LHCb results add clues to pentaquark mystery” 

    Symmetry Mag
    From Symmetry

    04/11/19
    Sarah Charley

    A re-examination of a particle discovered in 2015 has scientists debating its true identity.

    Syracuse professor Tomasz Skwarnicki has been a physicist for 30 years. He and his collaborators have measured rare processes and even discovered new particles. But he says their recent re-examination of a particle they discovered in 2015 was one the few analyses that made him exclaim, “Oh my gosh.”

    CERN LHCb Pentaquark mystery

    Skwarnicki has been working on the LHCb experiment at CERN for more than a decade. He uses the collisions generated by the Large Hadron Collider to search for exotic combinations of quarks.

    LHC

    CERN map


    CERN LHC Tunnel

    CERN LHC particles

    LHCb
    CERN LHCb New II

    Quarks are fundamental particles that bond together to form hadrons—the most common ones being the protons and neutrons found in the atoms that make up almost everything around us.

    For decades scientists had only ever seen hadrons containing three quarks, or a quark and an antiquark. Recent observations of particles made from four and five quarks have begun to challenge this paradigm. A question that remains about these exotic particles, however, is how the quarks are structured within them.

    This interest in how quarks bond stems from the study of a fundamental property of quarks called color charge.

    A splash of color

    Color charge is similar to the electric charge in that it induces an attractive force between particles. Just as magnets with opposite electromagnetic charges stick together, quarks with different color charges stick together. There are three possible color charges: red, blue and green. (And for antiquarks, anti-red, anti-blue and anti-green.)

    It’s not a coincidence that quarks prefer to bond into groups of two and three. In nature, scientists have found only color-neutral objects. They have found hadrons made up of a quark and an antiquark of opposite color charges (for example, red and anti-red), and hadrons made up of three quarks of different color charges (a red quark, a blue quark and a green quark, which also neutralize one another).

    For decades scientists have been looking for new kinds of quark combinations that break this mold—specifically, two matter-quarks bound together into a diquark.

    Because the force between color-charged quarks is orders of magnitude stronger than that of an electric field, most experts think that only hadrons which are completely color neutral are possible. But some theorists hold out hope that with the right combination, pockets that maintain a non-neutral color charge could momentarily exist.

    If they could find a combination of quarks that are not completely color-neutral, “it would open a new world,” says Ahmed Ali, a theoretical physicist at DESY.

    And if they could find a way to harness that charge, he says, “the implications could be far-reaching.” The last time scientists figured out how to separate the charges fundamental particles, the result was electricity.

    Scientists think it’s physically impossible to isolate a non-neutral quark cluster. But some hope that in the collisions generated by the LHC, one of these theoretical diquark combinations could momentarily manifest itself. “Finding that experimentally would be a breakthrough,” Ali says.

    Scientists have made some promising observations that show complex combinations of quarks. Since 2003, numerous experiments have observed particles that appear to be made up of four quarks. And in 2015, LHCb announced the discovery of the first particle made up of five quarks—a pentaquark.

    But this latest analysis by the LHCb collaboration raises questions about the identity of this pentaquark—and may have taken scientists back to square one in the search for a particle that could shed light on questions about color.

    Seeing triple

    The first time Skwarnicki saw LHCb’s pentaquark, it appeared as a large and broad bump that unexpectedly showed up in data from collisions that produced protons and particles called J-psi. It wasn’t especially clear, he says: “It was like looking at an image that was far away and out of focus.”

    This year, Skwarnicki and his colleagues redid the analysis using 10 times as much data, and the difference was striking. “I was the first person to see the data,” he says. “It was beautiful.”

    And startling. Rather than a single bump, Skwarnicki was suddenly looking at three: three distinct pentaquarks. “The peaks were so sharp and narrow,” he says. “Each pentaquark has the same quark content, but they are in different quantum states, which gives them different masses.”

    The new result has reignited a debate about what pentaquarks actually look like. “The key question is how the quarks organize themselves,” Ali says.

    “There is a certain latent—but not so latent—competition between the different theoretical camps.”

    The atom camp

    Theorist Marek Karliner at Tel Aviv University, and his colleague Jon Rosner at the University of Chicago, were not surprised at the appearance of three separate pentaquarks.

    “The three masses just happen to sit right where you would expect them,” Karliner says.

    That is, right where you would expect them if the pentaquark isn’t a tightly bound pentaquark, but rather a new type of atomic nucleus, formed from two well-understood, color-neutral hadrons—one made up of two quarks, and one made up of three.

    Their reasoning? Simple addition. “We expect the mass of a nucleus to be very close to the sum of its constituent parts,” he says.

    The mass of the lightest pentaquark is suspiciously close to the combined masses of a two-quark particle called a D-meson and a three-quark particle called a Sigma-C baryon. The heavier two pentaquarks could be made of the same two particles, but with their internal quarks misaligned—a configuration that slightly bumps up their energy and therefore bumps up the overall mass of the pentaquark.

    Another feature that jumped out at Karliner is the lifetime of these particles. In this nuclear interpretation of the pentaquark, the two clusters of quarks are distinct and feel only a weak pull towards each other, forming a new type of meta-stable atomic nucleus.

    “They are long-lived compared to what we normally observe in composite unstable states made out of quarks,” Karliner says. “In the nuclear picture, the long lifetime is natural and very easy to understand.”

    3
    Some scientists think a tightly bound pentaquark could have pockets of non-neutral color charge. CERN

    The clustered quark camp

    To put it simply, Ali finds the nuclear model of the pentaquark a bit disappointing. Even though a molecular pentaquark is still a new discovery, “no new no new color structures are involved,” he says. “They are formed by the recombination of known hadrons.”

    What he really wants to find is evidence of a tightly bound pentaquark, in which the five quarks are held close together by the strong force. Ali suspects that within a true tightly bound pentaquark, the quark colors could mix in a way that would allow for some non-neutral color charge.

    He remains optimistic that more complex quark combinations are possible, he says. “The theory which describes quark behavior is rich, and there are many forms and representations which could still show themselves.”

    The LHC is currently shut down for upgrades that will allow the experiments to collect even more data, letting scientists take a closer look at the pentaquark. “I anticipate that this is not the end of the story,” Ali says. “It’s the beginning. We’re entering a new hadronic world, and I suspect that more objects will be found.”

    See the full article here .


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    Please help promote STEM in your local schools.


    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 3:21 pm on April 9, 2019 Permalink | Reply
    Tags: Accelerator Science, , , , , , , ,   

    From Symmetry: “A tiny new experiment at the LHC” 

    Symmetry Mag
    From Symmetry

    03/05/19 [Sorry, missed this one.]
    Caitlyn Buongiorno

    1
    Illustration by Sandbox Studio, Chicago with Ana Kova

    The story of the latest experiment approved for installation at the Large Hadron Collider starts with a theorist and a question about dark matter.

    Jonathan Feng originally described himself as a high-energy-collider guy, specifically a high-energy-collider theorist. Then a well-placed question at a talk started him on a winding path from colliders to cosmology, from theory to experiment, and finally right back to high-energy physics where he began.

    That path led to today, when the CERN Research Board approved the experiment Feng recently co-founded, called FASER, for installation at the Large Hadron Collider.

    2
    A 3D picture of the planned FASER detector as seen in the TI12 tunnel. The detector is precisely aligned with the collision axis in ATLAS, 480 m away from the collision point. (Image: FASER/CERN)

    Let’s start from the beginning. As a graduate student at SLAC National Accelerator Laboratory, Feng was studying supersymmetry, also called SUSY. SUSY predicts the existence of a whole host of massive new particles, which scientists continue to look for with experiments at accelerators like the LHC.

    Standard Model of Supersymmetry via DESY

    On a fateful visit to Fermi National Accelerator Laboratory, Feng gave a talk about his latest ideas for a model of supersymmetric particles. When he finished and transitioned into questions, someone in the audience pointed out a seemingly significant flaw: The existence of dark matter might have already negated his entire presentation.

    “As it turned out the model was okay, but that was really a wake-up call for me,” says Feng, now a professor at UC Irvine. “I realized I better start learning about dark matter and connecting it to supersymmetry.”

    Unlike evidence for supersymmetric particles, evidence for dark matter particles has already shown up in scientific observations. We know that dark matter is there because of the gravitational effects it has on galaxies, including our own. In fact, dark matter is five times as prevalent as visible matter and thought to make up the foundations upon which most galaxies are built.

    Caterpillar Project A Milky-Way-size dark-matter halo and its subhalos circled, an enormous suite of simulations . Griffen et al. 2016

    Fritz Zwicky discovered Dark Matter when observing the movement of the Coma Cluster. But Vera Rubin, Vera Rubin a Woman in STEM denied the Nobel, did most of the work on Dark Matter.

    Fritz Zwicky from http:// palomarskies.blogspot.com

    Coma cluster via NASA/ESA Hubble

    Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science)


    Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL)


    Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu

    Despite the abundance of dark matter in the universe, scientists have not yet been able to directly observe it. They think that’s because, other than through the force of gravity, dark matter rarely interacts with normal matter.

    For decades, scientists have searched for dark matter particles like this, ones that interact only weakly with known particles. One type of weakly interacting massive particles, called WIMPs, has a possible connection with supersymmetry.

    Like dark matter particles, SUSY particles could also be weakly interacting and massive, a fact that makes theorists wonder if dark matter particles are SUSY particles. Feng in particular was intrigued by the fact that the predicted number of SUSY particles left over from the Big Bang and the number required to account for all the dark matter in the universe were essentially the same.

    Suddenly, instead of negating models of supersymmetry, dark matter was bolstering them.

    “It’s just an amazing coincidence,” Feng says. “I still think that it’s almost too good to not be relevant to nature.”

    Feng spent the next 10 years focused on popularizing this coincidence, which supported theories behind the search for WIMPs. But as time went on and WIMPs continued to prove elusive, Feng grew restless. In 2008, he began also focusing on other possibilities.

    One such possibility was a different kind of weakly interacting particle—this one light, not massive. Such a dark matter particle would be even more difficult to detect than a WIMP. But it could be that there are other particles, called portal particles, that could be the bridge between normal matter and this light dark matter. Portal particles would be capable of communicating with both, and they would be easier to detect than dark matter particles.

    These portal particles could be produced in the decays of light particles like pions or kaons. As Feng and three postdocs thought about where to look for portal particles in 2017, they realized there’s a place where the pions and kaons they might come from are produced in droves: the LHC.

    Every second, millions of protons are collided in the LHC. The energy from those collisions transforms the protons into a multitude of other particles. Those particles then speed off in all directions.

    3
    Beams of particles are brought into collision at four different points along the Large Hadron Collider. The four large detectors—ATLAS, ALICE, CMS and LHCb—are built around those collision points. Artwork by Sandbox Studio, Chicago with Ana Kova.

    The LHC’s huge experiments are built to surround the places where the particle beams collide to give them the best chance of catching these particles. But Feng’s team realized that the LHC detectors had an important blind spot: straight down the beam pipes.

    4
    During collisions, it could be that portal particles (labeled A’) are escaping detection by traveling down the beam pipe.
    Artwork by Sandbox Studio, Chicago with Ana Kova

    The LHC beam pipes travel in a circle, not a straight line. Magnets turn the beams of particles inside them at a very, very slight angle so that they can travel around in a ring over and over and potentially collide at four locations.

    5
    The FASER collaboration discovered a disused tunnel, called TI12, in just the right location to intercept portal particles that could be escaping from collisions in the ATLAS detector. Artwork by Sandbox Studio, Chicago with Ana Kova.

    A portal particle coming from a kaon or pion created in a particle collision at the LHC would be neutral and therefore unaffected by the magnetic field, so it would continue in a straight line as the rest of the beam curved away. At a distance of 500 meters, the escaping particles would have spread out only 7 centimeters from one another, making it possible for a detector as small as a sheet of paper to catch almost all of them.

    6
    The portal particles would continue traveling straight, unaffected by the magnets that bend beams of particles around the ring of the LHC. They would travel through the earth and interact within the FASER detector. Artwork by Sandbox Studio, Chicago with Ana Kova.

    Feng and postdocs Iftah Galon, Felix Kling and Sebastian Trojanowski pulled out a map of CERN and traced a straight line from the collision point inside the ATLAS detector. Just in the spot where the portal particles would appear, they found a tunnel, TI12, left over from the LEP collider that had previously inhabited the LHC’s underground home.

    “That was really exciting,” says Galon, postdoctoral associate at the New High Energy Theory Center at Rutgers University. Suddenly, the idea to detect particles that had potentially been escaping the LHC for years unnoticed by the gigantic detectors around them wasn’t just a fantasy, “it was actually feasible.”

    In August of 2017, Feng and his postdocs excitedly published a paper proposing a new experiment, pointing out this unused tunnel as the perfect location. They called it FASER, a slightly forced acronym for ForwArd Search ExpeRiment at the LHC. They expected an experimentalist to jump on the idea within a few weeks, a month at the most.

    By the time two months had passed, Feng says he realized that wasn’t going to happen.

    Instead of being deterred, Feng, Galon, Kling and Trojanowski continued reaching out to their contacts and giving talks about FASER. If they couldn’t inspire the experimentalists to take on their idea, they were going to have to get involved themselves.

    In February of 2018, Feng met a CERN research physicist named Jamie Boyd.

    “That was the big break, when Jamie got wind of this and got on board,” Feng says. “He’s been extraordinarily effective at putting together the experimental side of FASER.”

    Before the LHC even started producing collisions, Boyd was working on ATLAS, one of the two largest experiments at LHC. For over 10 years, he cultivated relationships and experience, making him the perfect person to campaign for FASER.

    He also realized that FASER would need help from other experiments.

    “With any experiment, you create a number of back-up parts,” Boyd says. These back-ups are kept around in case something happens to the main equipment. Instead of halting the entire experiment, scientists can simply replace faulty parts and continue taking data. Boyd realized that a few of the many copies of back-up parts created early on for ATLAS and LHCb could safely be donated to FASER instead.

    “Other experiments’ generous contributions is partially why FASER could get off the ground so quickly,” he says.

    Somewhat unusually for a group of theorists, Feng, Galon, Kling and Trojanowski became founding members of the FASER experiment, with Feng and Boyd serving as co-spokespersons.

    From there, things came together at a whirlwind pace. In July they had a conceptual design and a collaboration of 14 people. In October, the ATLAS and LHCb collaboartaions donated essential parts. In November, their team had jumped up to 25 people and had produced a technical design to propose to CERN. In Febraury, they secured full funding for construction from the Heising-Simons and Simons Foundations. And on March 5, the group received the final go ahead from the CERN Research Board to integrate FASER into the LHC schedule.

    The LHC is down for upgrades until late 2020, so FASER will need to be built, tested, installed and ready for operation by then.

    “We have a very clear and very hard deadline,” Boyd says. “Because FASER is small, the LHC won’t stop its beam to wait for us. We have to match the beam shutdown schedule, not the other way around.”

    FASER’s main purpose is to detect portal particles produced by the LHC, but it also stands to provide other important insights. It could find heavy versions of hypothetical particles called axions. Less massive versions of axions are dark matter candidates, but the axions FASER could detect would be too heavy and unstable to be dark matter.

    “We look at the world, we look at physics, and we ask ourselves where new physics could be hiding,” Galon says. “If FASER finds any new particles, then we’ve done our job correctly.”

    FASER could also catch neutrinos, other weakly interacting particles that scientists already know about but have yet to directly observe in detectors at the LHC. This would provide scientists with an opportunity to study a previously unexplored energy range of neutrinos and test our current understanding of how neutrinos interact.

    FASER scientists expect to have data to analyze starting in 2021 and hope to make significant contributions to physics by the end of their first three-year run.

    See the full article here .


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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 11:55 am on April 8, 2019 Permalink | Reply
    Tags: "ATLAS sets strong constraints on supersymmetric dark matter", Accelerator Science, , , , , ,   

    From CERN ATLAS: “ATLAS sets strong constraints on supersymmetric dark matter” 

    CERN/ATLAS detector

    CERN ATLAS Higgs Event

    CERN ATLAS another view Image Claudia Marcelloni ATLAS CERN


    CERN ATLAS New II Credit CERN SCIENCE PHOTO LIBRARY


    From CERN ATLAS

    8th April 2019

    1
    Figure 1: A comparison of the significance for the signal plus background hypothesis (vertical axis) of a chosen supersymmetric model obtained by selecting events using the new object-based ETmiss significance variable (black line), compared to the previous approximation (ETmiss/ET, cyan) or to selecting events using only the measured missing transverse energy (ETmiss, mauve). Higher significance is found for the new variable. (Image: ATLAS Collaboration/CERN)

    One of the most complete theoretical frameworks that includes a dark matter candidate is supersymmetry. Dark matter is an unknown type of matter present in the universe, which could be of particle origin. Many supersymmetric models predict the existence of a new stable, invisible particle – the lightest supersymmetric particle (LSP) – which has the right properties to be a dark matter particle. The ATLAS Collaboration has recently reported two new results on searches for an LSP where it exploited the experiment’s full “Run 2” data sample taken at 13 TeV proton-proton collision energy. The analyses looked for the pair production of two heavy supersymmetric particles, each of which decays to observable Standard Model particles and an LSP in the detector.

    Identifying missing energy

    2
    Figure 2: 95% exclusion limits on chargino pair production. The grey shaded region shows the results from Run 1 of the LHC. The new results substantially extend previous limits. (Image: ATLAS Collaboration/CERN)

    A central challenge of these searches is that dark matter candidate particles would escape the ATLAS detector without leaving a visible signal. Their presence can only be inferred through the magnitude of the collision’s missing transverse momentum (ETmiss) – an imbalance in the momenta of detected particles in the plane perpendicular to the colliding protons. In the dense environment of numerous overlapping LHC collisions it can be difficult to separate genuine ETmiss from fake ETmiss originating from mismeasurement of the visible collision debris in the detector.

    To resolve this difficulty, ATLAS developed a new ETmiss significance variable, which quantifies the likelihood that the observed ETmiss originates from undetectable particles rather than from mismeasured objects. Unlike previous calculations based entirely on the reconstructed event kinematics, the new variable also considers the resolution and misidentification probability of each of the reconstructed particles used in the calculation. This helps discriminate more effectively between events with genuine and fake ETmiss, respectively, as shown in Figure 1, thus improving ATLAS’ ability to identify and partially reconstruct dark matter particles.

    Applying new reconstruction techniques

    3
    Figure 3: Distribution of object-based significance discriminant in SRC (upper). The final state is also pictorially represented (lower). (Image: ATLAS Collaboration/CERN)

    Both of the new ATLAS searches implement this new reconstruction technique to the full Run 2 dataset. One search looks for the pair production of charginos (the charged superpartners of bosons) and sleptons (superpartners of leptons), respectively, which decay to either two electrons or muons and give rise to large ETmiss due to the escaping LSPs. These signals are very challenging to extract as they look similar to Standard Model diboson processes, where some (although less) ETmiss is produced from invisible neutrinos. Events were selected at high ETmiss significance together with several other variables that help discriminate signal from background. In absence of a significant excess in the data over the background expectation, strong limits were placed on the considered supersymmetric scenarios, as shown in Figure 2.

    The second new search targets the pair production of supersymmetric bottom squarks (superpartners of bottom quarks), which both decay to a final state involving a Higgs boson and an LSP (plus an additional b-quark). Then – targeting Higgs boson decays to two b-quarks, as it is predicted to occur 58% of the time – the final state measured in the ATLAS detector would have a unique signature: large ETmiss associated with up to six “jets” of hadronic particles, originating from b-quarks. The measured and expected ETmiss significance distribution and expected event topology are shown in Figure 3. Again, no significant excess in data was found in this search.

    Both results place strong constraints on important supersymmetric scenarios, which will guide future ATLAS searches. Further, they provide an example how novel reconstruction techniques can help improve the sensitivity of new physics searches at the LHC.

    See the full article here .


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  • richardmitnick 10:37 am on April 8, 2019 Permalink | Reply
    Tags: A new scientific education and outreach centre targeting the general public of all ages, Accelerator Science, , CERN Science Gateway, , , ,   

    From CERN: “CERN unveils its Science Gateway project” 

    Cern New Bloc

    Cern New Particle Event


    From CERN

    8 April, 2019

    CERN is launching a new scientific education and outreach centre. The building will be designed by world-renowned architects, Renzo Piano Building Workshop and funded through external donations, with the leading contribution coming from FCA Foundation.

    1
    Artistic view of the Science Gateway. (Image: RPBW)

    CERN is launching the Science Gateway, a new scientific education and outreach centre targeting the general public of all ages. The building will be designed by world-renowned architects, Renzo Piano Building Workshop. The project will be funded through external donations, with the leading contribution coming from FCA Foundation, a charitable foundation created by Fiat Chrysler Automobiles. Construction is planned to start in 2020 and to be completed in 2022.

    As part of its mission to educate and engage the public in science, and to share knowledge and technology with society, CERN is launching the Science Gateway, a new facility for scientific education and outreach. The purpose of the project is to create a hub of scientific education and culture to inspire younger generations with the beauty of science. Aimed at engaging audiences of all ages, the Science Gateway will include inspirational exhibition spaces, laboratories for hands-on scientific experiments for children and students from primary to high-school level, and a large amphitheatre to host science events for experts and non-experts alike.

    With a footprint of 7000 square metres, the iconic Science Gateway building will offer a variety of spaces and activities, including exhibitions explaining the secrets of nature, from the very small (elementary particles) to the very large (the structure and evolution of the universe). The exhibitions will also feature CERN’s accelerators, experiments and computing, how scientists use them in their exploration and how CERN technologies benefit society. Hands-on experimentation will be a key ingredient in the Science Gateway’s educational programme, allowing visitors to get first-hand experience of what it’s like to be a scientist. The immersive activities available in the Science Gateway will foster critical thinking, evidence-based assessment and use of the scientific method, important tools in all walks of life.

    “The Science Gateway will enable CERN to expand significantly its education and outreach offering for the general public, in particular the younger generations. We will be able to share with everybody the fascination of exploring and learning how matter and the universe work, the advanced technologies we need to develop in order to build our ambitious instruments and their impact on society, and how science can influence our daily life,” says CERN Director-General Fabiola Gianotti. “I am deeply grateful to the donors for their crucial support in the fulfilment of this beautiful project.”

    The overall cost of the Science Gateway is estimated at 79 million Swiss Francs, entirely funded through donations. As of today, 57 million Swiss Francs have been already secured, allowing construction to start on schedule, thanks in particular to a very generous contribution of 45 million Swiss Francs from the FCA Foundation, which will support the project as it advances through the construction phases. Other donors include a private foundation in Geneva and Loterie Romande, which distributes its profits to public utility projects in various areas including research, culture and social welfare. CERN is looking for additional donations in order to cover the full cost of the project.

    John Elkann, Chairman of FCA and the FCA Foundation, said: “The new Science Gateway will satisfy the curiosity of 300,000 visitors every year – including many researchers and students, but also children and their families – providing them with access to tools that will help them understand the world and improve their lives, whatever career paths they eventually choose. At FCA we’re delighted to be supporting this project as part of our social responsibility which also allows us to honour the memory of Sergio Marchionne: in an open and stimulating setting, it will teach us how we can work successfully together, even though we may have diverse cultures and perspectives, to discover the answers to today’s big questions and to those of tomorrow”.

    As part of the educational portfolio of the Science Gateway, CERN and FCA Foundation will develop a programme for schools, with the advice of Fondazione Agnelli. The main goal will be to transmit concepts of science and technology in an engaging way, in order to encourage students to pursue careers in STEM (Science, Technology, Engineering and Mathematics). According to the approach of enquiry-based learning, students will be involved in hands-on educational modules and experiments in physics. Special kits will be delivered to classes, containing all necessary materials and instructions to run modules throughout the school year. As a follow-up, classes will be invited to take part in a contest, with the winners awarded a 2-3 day visit to the Science Gateway and CERN. There will be an initial period of experimentation, with a pilot programme in Italy focusing on junior high schools and involving up to 550,000 students. After the pilot, CERN plans to extend this initiative to all its Member States.

    The Science Gateway will be hosted in a new, iconic building, designed by world-renowned architects Renzo Piano Building Workshop, on CERN’s Meyrin site adjacent to another of CERN’s iconic buildings, the Globe of Science and Innovation. The vision for the Science Gateway is inspired by the fragmentation and curiosity already intrinsic to the nature of the CERN site and buildings, so it is made up of multiple elements, embedded in a green forest and interconnected by a bridge spanning the main road leading to Geneva. “It’s a place where people will meet,” says Renzo Piano. “Kids, students, adults, teachers and scientists, everybody attracted by the exploration of the Universe, from the infinitely vast to the infinitely small. It is a bridge, in the metaphorical and real sense, and a building fed by the energy of the sun, nestling in the midst of a newly grown forest.”

    Also inspired by CERN’s unique facilities, such as the Large Hadron Collider (LHC), the world’s largest particle accelerator, the architecture of the Science Gateway celebrates the inventiveness and creativity that characterise the world of research and engineering. Architectural elements such as tubes that seem to be suspended in space evoke the cutting-edge technology underpinning the most advanced research that is furthering our understanding of the origins of the universe.

    A bridge over the Route de Meyrin will dominate the brand-new Esplanade des Particules and symbolise the inseparable link between science and society. Construction is planned to start in 2020 and be completed in 2022.

    About FCA Foundation
    The FCA Foundation, the charitable arm of FCA, supports charitable organizations and initiatives that help empower people, build strong, resilient communities and generate meaningful and measurable societal impacts particularly in the field of education.

    See the full article here.


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    Meet CERN in a variety of places:

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    THE FOUR MAJOR PROJECT COLLABORATIONS

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  • richardmitnick 4:30 pm on April 2, 2019 Permalink | Reply
    Tags: Accelerator Science, , , Fermilab Integrable Optics Test Accelerator (IOTA), , Synchrotrons   

    From Fermi National Accelerator Lab: “Work at the Fermilab Integrable Optics Test Accelerator” 

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

    From Fermi National Accelerator Lab , an enduring source of strength for the US contribution to scientific research world wide.

    April 2, 2019
    Giulio Stancari

    1
    1/2) After the first electron beam was circulated in August 2018, the experimental program at the Fermilab Integrable Optics Test Accelerator (IOTA) continues with commissioning of machine and diagnostics and with the first beam-physics experiments. This view of IOTA was taken in November 2018. Photo: Giulio Stancari

    2
    (2/2) Jamie Santucci works on one of the synchrotron-light diagnostic stations in the Fermilab Integrable Optics Test Accelerator, or IOTA. Photo: Giulio Stancari

    See the full article here.


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    FNAL Icon

    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.

    FNAL MINERvA front face Photo Reidar Hahn

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  • richardmitnick 3:23 pm on April 2, 2019 Permalink | Reply
    Tags: "Moriond 2019 feels the strong force", Accelerator Science, , , , , ,   

    From CERN: “Moriond 2019 feels the strong force” 

    Cern New Bloc

    Cern New Particle Event


    From CERN

    2 April, 2019

    Pentaquarks, charmed beauty particles and more from the Moriond conference’s second week, which is devoted to studies of the strong nuclear force.

    Last week, physicists from all over the world gathered in La Thuile, Italy, for the second week of the Rencontres de Moriond conference. This second week of the annual meeting features new and recent findings in all things related to quantum chromodynamics (QCD) – the theory of the strong force that combines quarks into composite particles called hadrons – and to high-energy particle interactions. This year, results from the main experiments at the Large Hadron Collider (ALICE, ATLAS, CMS and LHCb) included new pentaquarks, new charmed beauty particles, a more precise measurement of matter–antimatter asymmetry in strange beauty particles, and new results from heavy-ion collisions.

    Discovery of new pentaquarks

    The LHCb collaboration announced the discovery of new five-quark hadrons, or “pentaquarks”. Quarks normally aggregate into groups of twos and threes, but in recent years the LHCb team has confirmed the existence of exotic tetraquarks and pentaquarks, which are also predicted by QCD. In a 2015 study, the LHCb researchers analysed data from the decay of the three-quark particle Λb into a J/ψ particle, a proton and a charged kaon and were able to see two new pentaquarks (dubbed Pc(4450)+ and Pc(4380)+) in intermediate decay states. After analysing a sample of nine times more Λb decays than in the 2015 study, the LHCb team has now discovered a new pentaquark, Pc(4312)+ as well as a two-peak pattern in the data that shows that the previously observed Pc(4450)+ structure is in fact two particles.

    2
    A Bs candidate decaying to a J/psi and a phi, where the J/psi decays to two opposite-charge muons (red lines) and the phi decays to two opposite-charge kaons (blue). The event was recorded by ATLAS on 16 August 2017 from proton–proton collisions at 13 TeV. (Image: CERN)

    Charmed beauty particles in focus

    Notwithstanding significant progress over the past two decades, researchers’ understanding of the QCD processes that make up hadrons is incomplete. One way to try and understand them is through the study of the little-known charmed beauty (Bc) particle family, which consists of hadrons made up of a beauty quark and a charm antiquark (or vice-versa). In 2014, using data from the LHC’s first proton–proton collision run, the ATLAS collaboration reported [Physical Review Letters]the observation of a Bc particle called Bc(2S). A very recent analysis by the CMS collaboration of the full LHC sample from the second run, published today in Physical Review Letters and presented at the meeting, has unambiguously observed a two-peak feature in this dataset that corresponds to Bc(2S) and to another Bc particle called Bc*(2S). Meanwhile, the LHCb team, which in 2017 reported no evidence for Bc(2S) in its 2012 data, has now analysed the full 2011–2018 data sample and has also observed the Bc(2S) and Bc*(2S), lending support to the CMS result.

    3
    An event recorded by CMS showing a candidate for the Bc(2S*). The signature for this new particle is the presence of two pions (green lines) and a Bc meson, that decays into a pion (yellow line) plus a J/psi that itself decays to two muons (red). (Image: CERN)

    Matter–antimatter asymmetry in strange beauty particles

    The meeting’s second week also saw the announcement of a new result concerning the amount of the matter–antimatter asymmetry known as CP violation in the system of strange beauty (Bs) particles, which are made of a bottom quark and a strange quark. Bs mesons have the special feature that they oscillate rapidly into their antiparticle and back, and these oscillations can lead to CP violation when the Bs decays into combinations of particles such as a J/ψ and a ϕ. The amount of CP violation predicted by the Standard Model and observed so far in experiments is too small to account for the observed imbalance between matter and antimatter in the universe, prompting scientists to search for additional, as-yet-unknown sources of CP violation and to measure the extent of the violation from known sources more precisely. Following hot on the heels of two independent measurements of the asymmetry in the Bs system reported by ATLAS and LHCb during the meeting’s first week, a new result that combined the two measurements was reported during the second week. The combined result is the most precise measurement yet of the asymmetry in the Bs system and is consistent with the small value precisely predicted by the Standard Model.

    Heavy-ion progress

    The ALICE collaboration specialises in collisions between heavy ions such as lead nuclei, which can recreate the quark–gluon plasma (QGP) that is believed to have occurred shortly after the Big Bang. ALICE highlighted its observation that three-quark particles (baryons) containing charm quarks (Λc) are produced more often in proton–proton collisions than in electron­–positron collisions. It also showed that its first measurements of such charmed baryons in lead–lead collisions suggest an even higher production rate in these collisions, similar to what has been observed for strange-quark baryons. These observations indicate that the presence of quarks in the colliding beams affects the hadron production rate, shedding new light on the QCD processes that form baryons. The collaboration also presented the first measurement of the triangle-shaped flow of J/psi particles, which contain heavy quarks, in lead–lead collisions. This measurement shows that even heavy quarks are affected by the quarks and gluons in the QGP and retain some memory of the collisions’ initial geometry. Finally, ALICE also presented measurements of particle jets in lead–lead collisions that probe the QGP at different length scales.

    For other results, check out the conference page.

    See the full article here.


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    THE FOUR MAJOR PROJECT COLLABORATIONS

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  • richardmitnick 11:37 am on April 1, 2019 Permalink | Reply
    Tags: "Highlights from the 2019 Moriond conference (electroweak physics)", Accelerator Science, , , , , ,   

    From CERN: “Highlights from the 2019 Moriond conference (electroweak physics)” 

    Cern New Bloc

    Cern New Particle Event


    From CERN

    29 March, 2019

    The latest experimental data provide more stringent tests of the Standard Model and of rare phenomena of the microworld.

    At the 66th Rencontres de Moriond conference, which is taking place in La Thuile, Italy, physicists working at CERN are presenting their most recent results. Since the start of the conference on 16 March, a wide range of topics from measurements of the Higgs boson and Standard Model processes to searches for rare and exotic phenomena have been presented.

    The Standard Model of particle physics is a successful theory that describes how elementary particles and forces govern the properties of the Universe, but it is incomplete as it cannot explain certain phenomena, such as gravity, dark matter and dark energy.

    Standard Model of Particle Physics (LATHAM BOYLE AND MARDUS OF WIKIMEDIA COMMONS)

    For this reason, physicists welcome any measurement that shows discrepancies with the Standard Model, as these give hints of new particles and new forces – of new physics, in other words. At the conference, the ATLAS and CMS collaborations have presented new results based on up to 140fb–1 of proton-proton collision data collected during Run 2 of the Large Hadron Collider (LHC) from 2015 to 2018. Many of these analyses benefited from novel machine-learning techniques used to extract data from background processes.

    Since the discovery of the Higgs boson in 2012, ATLAS and CMS physicists have made significant progress in understanding its properties, how it is formed and how it interacts with other known particles.

    CERN CMS Higgs Event


    CERN ATLAS Higgs Event

    Thanks to the large quantity of Higgs bosons produced in the collisions of Run 2, the collaborations were able to measure most of the Higgs boson’s main production and decay modes with a statistical significance far exceeding five standard deviations. In addition, many searches for new, additional Higgs bosons have been presented. From a combination of all Higgs boson measurements, ATLAS obtained new constraints on the Higgs self-coupling. CMS has presented updated results on the Higgs decay to two Z bosons and has also derived new information on the strength of the interaction between Higgs bosons and top quarks. This interaction is measured in two ways, using top quark pairs and using a rare process in which four top quarks are produced. The probability of four top quarks being produced at the LHC is about a factor of ten less likely than the production of Higgs bosons together with two top quarks, and about a factor of ten thousand less likely than the production of just a top quark pair.

    3
    ATLAS event display showing the clean signature of light-by-light scattering (Image: ATLAS/CERN)

    The ATLAS collaboration has also reported first evidence for the simultaneous production of three W or Z bosons, which are the mediator particles of the weak force. Tri-boson production is a rare process predicted by the Standard Model, and is sensitive to possible contributions from yet unknown particles or forces. The very large new dataset has also been used by the ATLAS and CMS collaborations to expand the searches for new particles beyond the Standard Model at the energy available at the LHC. One of the possible theories is supersymmetry, an extension of the Standard Model, which features a symmetry between matter and force and introduces many new particles, including possible candidates for dark matter. These hypothetical particles have not been detected in experiments so far, and the collaborations have set stronger lower limits on the possible range of masses that they could have.

    4
    A collision event recorded by CMS, containing a missing-transverse-energy signature, which is one of the characteristics sought in the search for SUSY (Image: CMS/CERN)

    The CMS collaboration has placed new limits on the parameters of new physics theories that describe hypothetical slowly moving heavy particles. These are detected by measuring how fast particles travel through the detector: while the regular particles propagate at speeds close to that of light, straight from the proton collisions, these heavy particles are expected to move measurably slower before decaying into a shower of other particles, creating a “delayed jet”. CMS has also presented first evidence for another rare process, the production of two W bosons in not one but two simultaneous interactions between the constituents of the colliding protons.

    In addition, ATLAS and CMS have presented new studies on the search for hypothetical Z′ (Z-prime) bosons. The existence of such neutral heavy particles is predicted by certain Grand Unified theories that could provide an elegant extension of the Standard Model. Although no significant signs of Z′ particles have been observed thus far, the results provide constraints on their production rate.

    The LHCb collaboration has presented several new measurements concerning particles containing beauty or charm quarks. Certain properties of these particles can be affected by the existence of new particles beyond the Standard Model. This allows LHCb to search for signs of new physics via a complementary, indirect route. One much anticipated result, shown for the first time at the conference, is a measurement using data taken from 2011 to 2016 of the ratio of two related rare decays of a B+ particle. These decays are predicted in the Standard Model to occur at the same rate to within 1%; the data collected are consistent with this prediction but favour a lower value. This follows a pattern of intriguing hints in other, similar decay processes; while none of these results are significant enough to constitute evidence of new physics on their own, they have captured the interest of physicists and will be investigated further with the full LHCb data set. LHCb also presented the first observation of matter–antimatter asymmetry known as CP violation in charm particle decays, as reported in a dedicated press release last week.

    Finally, using the results of lead-ion collisions taken in 2018, the ATLAS collaboration has been able to clearly observe a very rare phenomenon in which two photons – particles of light – interact, producing another pair of photons, with a significance of over 8 standard deviations. This process was among the earliest predictions of quantum electrodynamics (QED), the quantum theory of electromagnetism, and is forbidden by Maxwell’s classical theory of electrodynamics.

    See the full article here.


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    Meet CERN in a variety of places:

    Quantum Diaries
    QuantumDiaries

    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New
    ALICE

    CERN/ALICE Detector


    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    LHC

    CERN map

    CERN LHC Grand Tunnel

    CERN LHC particles

    OTHER PROJECTS AT CERN

    CERN AEGIS

    CERN ALPHA

    CERN ALPHA


    CERN ALPHA-g Detector

    CERN ALPHA-g Detector


    CERN AMS

    CERN ACACUSA

    CERN ASACUSA

    CERN ATRAP

    CERN ATRAP

    CERN AWAKE

    CERN AWAKE

    CERN CAST

    CERN CAST Axion Solar Telescope

    CERN CLOUD

    CERN CLOUD

    CERN COMPASS

    CERN COMPASS

    CERN DIRAC

    CERN DIRAC

    CERN GBAR

    CERN GBAR

    CERN ISOLDE

    CERN ISOLDE

    CERN LHCf

    CERN LHCf

    CERN NA62

    CERN NA62

    CERN NTOF

    CERN TOTEM

    CERN UA9

    CERN Proto Dune

    CERN Proto Dune

     
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