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  • richardmitnick 12:49 pm on July 21, 2019 Permalink | Reply
    Tags: "A golden era of exploration: ATLAS highlights from EPS-HEP 2019", , , , Higgs boson, , ,   

    From CERN ATLAS: “A golden era of exploration: ATLAS highlights from EPS-HEP 2019” 

    CERN/ATLAS detector

    CERN ATLAS Higgs Event

    CERN ATLAS another view Image Claudia Marcelloni ATLAS CERN



    20th July 2019
    Katarina Anthony

    Event display of a Higgs boson candidate decaying in the four-lepton channel. (Image: ATLAS Collaboration/CERN)

    Eight years of operation. Over 10,000 trillion high-energy proton collisions. One critical new particle discovery. Countless new insights into our universe. The Large Hadron Collider (LHC) has been breaking records since data-taking began in 2010 – and yet, for ATLAS and its fellow LHC experiments, a golden era of exploration is only just beginning.

    Figure 1: New ATLAS measurement of the Higgs boson decaying in the four-lepton channel, using the full LHC Run-2 dataset. The distribution of the invariant mass of the four leptons (m4l) is shown. The Higgs boson corresponds to the excess of events (blue) over the non-resonant ZZ* background (red) at 125 GeV. (Image: ATLAS Collaboration/CERN)

    This week, the ATLAS Collaboration presented 25 new results at the European Physical Society’s High-Energy Physics conference (EPS-HEP) in Ghent, Belgium. The new analyses examine the largest-ever proton–proton collision dataset from the LHC, recorded during Run 2 of the accelerator (2015–2018) at the 13 TeV energy frontier.

    The new data have been fertile ground for ATLAS. New precision measurements of the Higgs boson, observations of key electroweak processes and high-precision tests of the Standard Model are among the highlights described below; find the full list of ATLAS public results using the full Run-2 dataset here.

    Studying the Higgs discovery channels

    Just over seven years ago, the Higgs boson was an elusive particle, out of reach from physicists for nearly five decades. Today, not only is the Higgs boson frequently observed, it is studied with such precision as to become a powerful tool for exploration.

    Key to these accomplishments are the so-called “Higgs discovery channels”: H→γγ, where the Higgs boson decays into two photons, and H→ZZ*→4l, where it decays via two Z bosons into four leptons. Though rare, these decays are easily identified in the ATLAS detector, making them essential to both the particle’s discovery and study.

    ATLAS presented new explorations of the Higgs boson in these channels (Figures 1 and 2), yielding greater insight into its behaviour. The new results benefit from the large full Run-2 dataset, as well as a number of new improvements to the analysis techniques. For example, ATLAS physicists now utilise Deep-Learning Neural Networks to assign the Higgs-boson events to specific production modes.

    All four Higgs-boson production modes can now be clearly identified in a single decay channel. ATLAS’ studies of the Higgs boson have advanced so quickly, in fact, that rare processes – such as its production in association with a top-quark pair, observed only just last year – can now been seen in just a single decay channel. The new sensitivity allowed physicists to measure kinematic properties of the Higgs boson with unprecedented precision (Figure 3). These are sensitive to new physics processes, making their exploration of particular interest to the collaboration.

    All four Higgs-boson production modes can now be clearly identified in a single decay channel. ATLAS’ studies of the Higgs boson have advanced so quickly, in fact, that rare processes – such as its production in association with a top-quark pair, observed only just last year – can now been seen in just a single decay channel. The new sensitivity allowed physicists to measure kinematic properties of the Higgs boson with unprecedented precision (Figure 3). These are sensitive to new physics processes, making their exploration of particular interest to the collaboration.

    Figure 2: Distribution of the invariant mass of the two photons in the ATLAS measurement of H→γγ using the full Run-2 dataset. The Higgs boson corresponds to the excess of events observed at 125 GeV with respect to the non-resonant background (dashed line). (Image: ATLAS Collaboration/CERN)

    Figure 3: Differential cross section for the transverse momentum (pT,H) of the Higgs boson from the two individual channels (H→ZZ*→4ℓ, H→γγ) and their combination. (Image: ATLAS Collaboration/CERN)

    Searching unseen properties of the Higgs boson

    Having accomplished the observation of Higgs boson interactions with third-generation quarks and leptons, ATLAS physicists are turning their focus to the lighter, second-generation of fermions: muons, charm quarks and strange quarks. While their interactions with the Higgs boson are described by the Standard Model, they have – so far – remained relegated to theory. Results from the ATLAS Collaboration are backing up these theories with real data.

    At EPS-HEP, ATLAS presented a new search for the Higgs boson decaying into muon pairs. This already-rare process is made all the more difficult to detect by background Standard Model processes, which produce muon pairs in abundance.

    Figure 4: ATLAS search for the Higgs boson decaying to two muons. The plot shows the weighted muon pair invariant mass spectrum (muu) summed over all categories. (Image: ATLAS Collaboration/CERN)

    The new result utilised novel machine learning techniques to provide ATLAS’ most sensitive result yet, with a moderate excess of 1.5 standard deviations expected for the predicted signal. In agreement with this prediction, only a small excess of 0.8 standard deviations is present around the Higgs-boson mass in the data (Figure 4).

    “This result shows that we are now close to the sensitivity required to test the Standard Model’s predictions for this very rare decay of the Higgs boson,” said ATLAS spokesperson Karl Jakobs from the University of Freiburg, Germany. “However, a definitive statement on the second generation will require the larger datasets that will be provided by the LHC in Run 3 and by the High-Luminosity LHC.”

    ATLAS’ growing sensitivity was also clearly on display in the collaboration’s new “di-Higgs” search, where two Higgs bosons are formed via the fusion of two vector bosons. Though one of the rarest Standard Model processes explored by ATLAS, its study gives unique insight into the previously-untested relationship between vector boson and Higgs-boson pairs. A small variation of this coupling relative to the Standard Model value would result in a dramatic rise in the measured cross section. The new search, despite being negative, successfully sets the first constraints on this relationship.

    Entering the Higgs sector

    The Higgs mechanism, giving mass to all elementary particles, is directly connected with profound questions about our universe, including the stability and energy of the vacuum, the “naturalness” of a world described by the Standard Model, and more. As such, the exploration of the Higgs sector is not limited to direct measurements of the Higgs boson – it instead requires a broad experimental programme that will extend over decades.

    A perfect example of this came in ATLAS’ new observation of the electroweak production of two jets in association with a pair of Z bosons. The Z and W bosons are the force carriers of weak interactions and, as they both have a spin of 1, are known as “vector bosons”. The Higgs boson is a vital mediator in “vector-boson scattering”, an electroweak process that contributes to the pair production of vector bosons (WW, WZ and ZZ) with jets. Measurements of these production processes are key for the study of electroweak symmetry breaking via the Higgs mechanism.

    The new ATLAS result – with a statistical significance of 5.5 standard deviations (Figure 5) – completes the experiment’s observation of vector-boson scattering in these critical processes, and sparks new ways to test the Standard Model.

    Figure 5: Observed and predicted distributions (BDT) in the signal regions of Z-boson pairs decaying to four leptons. The electroweak production of the Z-boson pair is shown in red; the error bars on the data points (black) show the statistical uncertainty on data. (Image: ATLAS Collaboration/CERN)

    Figure 6: Summary of the mass limits on supersymmetry models set by the ATLAS searches for Supersymmetry. Results are quoted for the nominal cross section in both a region of near-maximal mass reach and a demonstrative alternative scenario, in order to display the range in model space of search sensitivity. (Image: ATLAS Collaboration/CERN)

    Probing new physics

    As the community enters the tenth year of supersymmetry searches at the LHC, the ATLAS Collaboration continues to take a broad approach to the hunt. ATLAS is committed to providing results that are theory-independent as well as signature-based searches, in addition to the highly-targeted, model-dependent ones.

    Along with new, updated limits on various supersymmetry searches using the full Run-2 dataset (Figure 6), ATLAS once again highlighted new searches (first presented at the LHCP2019 conference) for superpartners produced through the electroweak interaction. Generated at extremely low rates at the LHC and decaying into Standard Model particles that are themselves difficult to reconstruct, such supersymmetry searches can only be described by the iconic quote: “not because it is easy, but because it is hard”.

    Overall, the results place strong constraints on important supersymmetric scenarios, which will inform theory developments and future ATLAS searches. Further, they provide examples of how advanced reconstruction techniques can help improve the ATLAS’ sensitivity of new physics searches.

    Asymmetric top-quark production

    The Standard Model continued to show its strength in ATLAS’ new precision measurement of charge asymmetry in top-quark pairs (Figure 7). This intriguing imbalance – where top and antitop quarks are not produced equally at all angles with respect to the proton beam direction – is among the most subtle, difficult and yet vital properties to measure in the study of top quarks.

    The effect of this asymmetry is predicted to be extremely small, however new physics processes interfering with the known production modes can lead to larger (or even smaller) values. ATLAS found evidence of this imbalance, with a significance of four standard deviations, with a value compatible with the Standard Model. The result marks an important milestone for the field, following decades of measurements which began at the Tevatron proton–antiproton collider, the predecessor of the LHC in the USA.


    FNAL/Tevatron map

    Figure 7: Measured values of the charge asymmetry (Ac) as a function of the invariant mass of the top quark pair system (mtt) in data. (Image: ATLAS Collaboration/CERN)

    Following the data

    As EPS-HEP 2019 drew to a close, it was clear that exploration of the high-energy frontier remains far from complete. With the LHC – and its upcoming HL-­LHC upgrade – set to continue apace, the future of high-energy physics will be guided by the results of ATLAS and its fellow experiments at the energy frontier.

    “Our community is living through data-driven times,” said ATLAS Deputy Spokesperson Andreas Hoecker from CERN. “Experimental results must guide the high-energy physics community to the next stage of exploration. This requires a broad and diverse particle physics research programme. The ATLAS Collaboration is up to taking this challenge!”

    See the full article here .

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  • richardmitnick 12:10 pm on July 15, 2019 Permalink | Reply
    Tags: , , , , , , Higgs boson, , ,   

    From CERN: “Exploring the Higgs boson “discovery channels” 

    Cern New Bloc

    Cern New Particle Event

    From CERN

    12th July 2019
    ATLAS Collaboration

    Event display of a two-electron two-muon ZH candidate. The Higgs candidate can be seen on the left with the two leading electrons represented by green tracks and green EM calorimeter deposits (pT = 22 and 120 GeV), and two subleading muons indicated by two red tracks (pT = 34 and 43 GeV). Recoiling against the four lepton candidate in the left hemisphere is a dimuon pair in the right hemisphere indicated by two red tracks (pT = 139 and 42 GeV) and an invariant mass of 91.5 GeV, which agrees well with the mass of the Z boson. (Image: ATLAS Collaboration/CERN)

    At the 2019 European Physical Society’s High-Energy Physics conference (EPS-HEP) taking place in Ghent, Belgium, the ATLAS and CMS collaborations presented a suite of new results. These include several analyses using the full dataset from the second run of CERN’s Large Hadron Collider (LHC), recorded at a collision energy of 13 TeV between 2015 and 2018. Among the highlights are the latest precision measurements involving the Higgs boson. In only seven years since its discovery, scientists have carefully studied several of the properties of this unique particle, which is increasingly becoming a powerful tool in the search for new physics.

    The results include new searches for transformations (or “decays”) of the Higgs boson into pairs of muons and into pairs of charm quarks. Both ATLAS and CMS also measured previously unexplored properties of decays of the Higgs boson that involve electroweak bosons (the W, the Z and the photon) and compared these with the predictions of the Standard Model (SM) of particle physics. ATLAS and CMS will continue these studies over the course of the LHC’s Run 3 (2021 to 2023) and in the era of the High-Luminosity LHC (from 2026 onwards).

    The Higgs boson is the quantum manifestation of the all-pervading Higgs field, which gives mass to elementary particles it interacts with, via the Brout-Englert-Higgs mechanism. Scientists look for such interactions between the Higgs boson and elementary particles, either by studying specific decays of the Higgs boson or by searching for instances where the Higgs boson is produced along with other particles. The Higgs boson decays almost instantly after being produced in the LHC and it is by looking through its decay products that scientists can probe its behaviour.

    In the LHC’s Run 1 (2010 to 2012), decays of the Higgs boson involving pairs of electroweak bosons were observed. Now, the complete Run 2 dataset – around 140 inverse femtobarns each, the equivalent of over 10 000 trillion collisions – provides a much larger sample of Higgs bosons to study, allowing measurements of the particle’s properties to be made with unprecedented precision. ATLAS and CMS have measured the so-called “differential cross-sections” of the bosonic decay processes, which look at not just the production rate of Higgs bosons but also the distribution and orientation of the decay products relative to the colliding proton beams. These measurements provide insight into the underlying mechanism that produces the Higgs bosons. Both collaborations determined that the observed rates and distributions are compatible with those predicted by the Standard Model, at the current rate of statistical uncertainty.

    Since the strength of the Higgs boson’s interaction is proportional to the mass of elementary particles, it interacts most strongly with the heaviest generation of fermions, the third. Previously, ATLAS and CMS had each observed these interactions. However, interactions with the lighter second-generation fermions – muons, charm quarks and strange quarks – are considerably rarer. At EPS-HEP, both collaborations reported on their searches for the elusive second-generation interactions.
    ATLAS presented their first result from searches for Higgs bosons decaying to pairs of muons (H→μμ) with the full Run 2 dataset. This search is complicated by the large background of more typical SM processes that produce pairs of muons. “This result shows that we are now close to the sensitivity required to test the Standard Model’s predictions for this very rare decay of the Higgs boson,” says Karl Jakobs, the ATLAS spokesperson. “However, a definitive statement on the second generation will require the larger datasets that will be provided by the LHC in Run 3 and by the High-Luminosity LHC.”
    CMS presented their first result on searches for decays of Higgs bosons to pairs of charm quarks (H→cc). When a Higgs boson decays into quarks, these elementary particles immediately produce jets of particles. “Identifying jets formed by charm quarks and isolating them from other types of jets is a huge challenge,” says Roberto Carlin, spokesperson for CMS. “We’re very happy to have shown that we can tackle this difficult decay channel. We have developed novel machine-learning techniques to help with this task.”

    An event recorded by CMS showing a candidate for a Higgs boson produced in association with two top quarks. The Higgs boson and top quarks decay leading to a final state with seven jets (orange cones), an electron (green line), a muon (red line) and missing transverse energy (pink line) (Image: CMS/CERN)

    The Higgs boson also acts as a mediator of physics processes in which electroweak bosons scatter or bounce off each other. Studies of these processes with very high statistics serve as powerful tests of the Standard Model. ATLAS presented the first-ever measurement of the scattering of two Z bosons. Observing this scattering completes the picture for the W and Z bosons as ATLAS has previously observed the WZ scattering process and both collaborations the WW processes. CMS presented the first observation of electroweak-boson scattering that results in the production of a Z boson and a photon.
    “The experiments are making big strides in the monumental task of understanding the Higgs boson,” says Eckhard Elsen, CERN’s Director of Research and Computing. “After observation of its coupling to the third-generation fermions, the experiments have now shown that they have the tools at hand to address the even more challenging second generation. The LHC’s precision physics programme is in full swing.”

    See the full article here .

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  • richardmitnick 12:04 pm on May 14, 2019 Permalink | Reply
    Tags: >Model-dependent vs model-independent research, , , , , , , Higgs boson, , , ,   

    From Symmetry: “Casting a wide net” 

    Symmetry Mag
    From Symmetry

    Jim Daley

    Illustration by Sandbox Studio, Chicago

    In their quest to discover physics beyond the Standard Model, physicists weigh the pros and cons of different search strategies.

    On October 30, 1975, theorists John Ellis, Mary K. Gaillard and D.V. Nanopoulos published a paper [Science Direct] titled “A Phenomenological Profile of the Higgs Boson.” They ended their paper with a note to their fellow scientists.

    “We should perhaps finish with an apology and a caution,” it said. “We apologize to experimentalists for having no idea what is the mass of the Higgs boson… and for not being sure of its couplings to other particles, except that they are probably all very small.

    “For these reasons, we do not want to encourage big experimental searches for the Higgs boson, but we do feel that people performing experiments vulnerable to the Higgs boson should know how it may turn up.”

    What the theorists were cautioning against was a model-dependent search, a search for a particle predicted by a certain model—in this case, the Standard Model of particle physics.

    Standard Model of Particle Physics

    It shouldn’t have been too much of a worry. Around then, most particle physicists’ experiments were general searches, not based on predictions from a particular model, says Jonathan Feng, a theoretical particle physicist at the University of California, Irvine.

    Using early particle colliders, physicists smashed electrons and protons together at high energies and looked to see what came out. Samuel Ting and Burton Richter, who shared the 1976 Nobel Prize in physics for the discovery of the charm quark, for example, were not looking for the particle with any theoretical prejudice, Feng says.

    That began to change in the 1980s and ’90s. That’s when physicists began exploring elegant new theories such as supersymmetry, which could tie up many of the Standard Model’s theoretical loose ends—and which predict the existence of a whole slew of new particles for scientists to try to find.

    Of course, there was also the Higgs boson. Even though scientists didn’t have a good prediction of its mass, they had good motivations for thinking it was out there waiting to be discovered.

    And it was. Almost 40 years after the theorists’ tongue-in-cheek warning about searching for the Higgs, Ellis found himself sitting in the main auditorium at CERN next to experimentalist Fabiola Gianotti, the spokesperson of the ATLAS experiment at the Large Hadron Collider who, along with CMS spokesperson Joseph Incandela, had just co-announced the discovery of the particle he had once so pessimistically described.

    CERN CMS Higgs Event

    CERN ATLAS Higgs Event

    Model-dependent vs model-independent

    Scientists’ searches for particles predicted by certain models continue, but in recent years, searches for new physics independent of those models have begun to enjoy a resurgence as well.

    “A model-independent search is supposed to distill the essence from a whole bunch of specific models and look for something that’s independent of the details,” Feng says. The goal is to find an interesting common feature of those models, he explains. “And then I’m going to just look for that phenomenon, irrespective of the details.”

    Particle physicist Sara Alderweireldt uses model-independent searches in her work on the ATLAS experiment at the Large Hadron Collider.

    CERN ATLAS Image Claudia Marcelloni CERN/ATLAS

    Alderweireldt says that while many high-energy particle physics experiments are designed to make very precise measurements of a specific aspect of the Standard Model, a model-independent search allows physicists to take a wider view and search more generally for new particles or interactions. “Instead of zooming in, we try to look in as many places as possible in a consistent way.”

    Such a search makes room for the unexpected, she says. “You’re not dependent on the prior interpretation of something you would be looking for.”

    Theorist Patrick Fox and experimentalist Anadi Canepa, both at Fermilab, collaborate on searches for new physics.

    In Canepa’s work on the CMS experiment, the other general-purpose particle detector at the LHC, many of the searches are model-independent.

    While the nature of these searches allows them to “cast a wider net,” Fox says, “they are in some sense shallower, because they don’t manage to strongly constrain any one particular model.”

    At the same time, “by combining the results from many independent searches, we are getting closer to one dedicated search,” Canepa says. “Developing both model-dependent and model-independent searches is the approach adopted by the CMS and ATLAS experiments to fully exploit the unprecedented potential of the LHC.”

    Driven by data and powered by machine learning

    Model-dependent searches focus on a single assumption or look for evidence of a specific final state following an experimental particle collision. Model-independent searches are far broader—and how broad is largely driven by the speed at which data can be processed.

    “We have better particle detectors, and more advanced algorithms and statistical tools that are enabling us to understand searches in broader terms,” Canepa says.

    One reason model-independent searches are gaining prominence is because now there is enough data to support them. Particle detectors are recording vast quantities of information, and modern computers can run simulations faster than ever before, she says. “We are able to do model-independent searches because we are able to better understand much larger amounts of data and extreme regions of parameter and phase space.”

    Machine-learning is a key part of this processing power, Canepa says. “That’s really a change of paradigm, because it really made us make a major leap forward in terms of sensitivity [to new signals]. It really allows us to benefit from understanding the correlations that we didn’t capture in a more classical approach.”

    These broader searches are an important part of modern particle physics research, Fox says.

    “At a very basic level, our job is to bequeath to our descendants a better understanding of nature than we got from our ancestors,” he says. “One way to do that is to produce lots of information that will stand the test of time, and one way of doing that is with model-independent searches.”

    Models go in and out of fashion, he adds. “But model-independent searches don’t feel like they will.”

    See the full article here .


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    Symmetry is a joint Fermilab/SLAC publication.

  • richardmitnick 3:02 pm on May 2, 2019 Permalink | Reply
    Tags: , , , , Higgs boson, , , ,   

    From University of Chicago: “Scientists invent way to trap mysterious ‘dark world’ particle at Large Hadron Collider” 

    U Chicago bloc

    From University of Chicago

    Apr 17, 2019 [Just found this via social media]
    Louise Lerner

    Courtesy of Zarija Lukic/Berkeley Lab

    A new paper outlines a method to directly detect particles from the ‘dark world’ using the Large Hadron Collider. Until now we’ve only been able to make indirect measurements and simulations, such as the visualization of dark matter above.

    CERN LHC Maximilien Brice and Julien Marius Ordan

    Higgs boson could be tied with dark particle, serve as ‘portal to the dark world’.

    Now that they’ve identified the Higgs boson, scientists at the Large Hadron Collider have set their sights on an even more elusive target.

    All around us is dark matter and dark energy—the invisible stuff that binds the galaxy together, but which no one has been able to directly detect. “We know for sure there’s a dark world, and there’s more energy in it than there is in ours,” said LianTao Wang, a University of Chicago professor of physics who studies how to find signals in large particle accelerators like the LHC.

    Wang, along with scientists from the University and UChicago-affiliated Fermilab, think they may be able to lead us to its tracks; in a paper published April 3 in Physical Review Letters, they laid out an innovative method for stalking dark matter in the LHC by exploiting a potential particle’s slightly slower speed.

    While the dark world makes up more than 95% of the universe, scientists only know it exists from its effects—like a poltergeist you can only see when it pushes something off a shelf. For example, we know there’s dark matter because we can see gravity acting on it—it helps keep our galaxies from flying apart.

    Theorists think there’s one particular kind of dark particle that only occasionally interacts with normal matter. It would be heavier and longer-lived than other known particles, with a lifetime up to one tenth of a second. A few times in a decade, researchers believe, this particle can get caught up in the collisions of protons that the LHC is constantly creating and measuring.

    “One particularly interesting possibility is that these long-lived dark particles are coupled to the Higgs boson in some fashion—that the Higgs is actually a portal to the dark world,” said Wang, referring to the last holdout particle in physicists’ grand theory of how the universe works, discovered at the LHC in 2012.

    Standard Model of Particle Physics

    CERN CMS Higgs Event

    CERN ATLAS Higgs Event

    “It’s possible that the Higgs could actually decay into these long-lived particles.”

    The only problem is sorting out these events from the rest; there are more than a billion collisions per second in the 27-kilometer LHC, and each one of these sends subatomic chaff spraying in all directions.

    Wang, UChicago postdoctoral fellow Jia Liu and Fermilab scientist Zhen Liu (now at the University of Maryland) proposed a new way to search by exploiting one particular aspect of such a dark particle. “If it’s that heavy, it costs energy to produce, so its momentum would not be large—it would move more slowly than the speed of light,” said Liu, the first author on the study.

    That time delay would set it apart from all the rest of the normal particles. Scientists would only need to tweak the system to look for particles that are produced and then decay a bit more slowly than everything else.

    The difference is on the order of a nanosecond—a billionth of a second—or smaller. But the LHC already has detectors sophisticated enough to catch this difference; a recent study using data collected from the last run and found the method should work, plus the detectors will get even more sensitive as part of the upgrade that is currently underway.

    “We anticipate this method will increase our sensitivity to long-lived dark particles by more than an order of magnitude—while using capabilities we already have at the LHC,” Liu said.

    Experimentalists are already working to build the trap: When the LHC turns back on in 2021, after boosting its luminosity by tenfold, all three of the major detectors will be implementing the new system, the scientists said. “We think it has great potential for discovery,” Liu said.


    CERN/CMS Detector

    CERN/ALICE Detector

    “If the particle is there, we just have to find a way to dig it out,” Wang said. “Usually, the key is finding the question to ask.”

    See the full article here .


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    U Chicago Campus

    An intellectual destination

    One of the world’s premier academic and research institutions, the University of Chicago has driven new ways of thinking since our 1890 founding. Today, UChicago is an intellectual destination that draws inspired scholars to our Hyde Park and international campuses, keeping UChicago at the nexus of ideas that challenge and change the world.

    The University of Chicago is an urban research university that has driven new ways of thinking since 1890. Our commitment to free and open inquiry draws inspired scholars to our global campuses, where ideas are born that challenge and change the world.

    We empower individuals to challenge conventional thinking in pursuit of original ideas. Students in the College develop critical, analytic, and writing skills in our rigorous, interdisciplinary core curriculum. Through graduate programs, students test their ideas with UChicago scholars, and become the next generation of leaders in academia, industry, nonprofits, and government.

    UChicago research has led to such breakthroughs as discovering the link between cancer and genetics, establishing revolutionary theories of economics, and developing tools to produce reliably excellent urban schooling. We generate new insights for the benefit of present and future generations with our national and affiliated laboratories: Argonne National Laboratory, Fermi National Accelerator Laboratory, and the Marine Biological Laboratory in Woods Hole, Massachusetts.

    The University of Chicago is enriched by the city we call home. In partnership with our neighbors, we invest in Chicago’s mid-South Side across such areas as health, education, economic growth, and the arts. Together with our medical center, we are the largest private employer on the South Side.

    In all we do, we are driven to dig deeper, push further, and ask bigger questions—and to leverage our knowledge to enrich all human life. Our diverse and creative students and alumni drive innovation, lead international conversations, and make masterpieces. Alumni and faculty, lecturers and postdocs go on to become Nobel laureates, CEOs, university presidents, attorneys general, literary giants, and astronauts.

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

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


    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.


    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.

    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.

    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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    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 3:00 pm on September 4, 2018 Permalink | Reply
    Tags: , , , , , , Higgs boson, , , ,   

    From University at Buffalo: “UB physicists awarded $1.45 million to study inner workings of the universe” 

    U Buffalo bloc.

    From University at Buffalo

    September 4, 2018
    Charlotte Hsu

    Photo illustration: Left to right: University at Buffalo physicists Avto Kharchilava, Ia Iashvili and Salvatore Rappoccio. Credit: Douglas Levere / University at Buffalo / CERN

    Funding comes as the field marks its latest big discovery — the observation of the Higgs boson’s most common mode of decay.

    University at Buffalo scientists have received $1.45 million from the National Science Foundation (NSF) for research in high-energy physics, a field that uses particle accelerators to smash beams of protons into one another at near-light speeds, generating data that illuminates the fundamental laws of nature.

    The grant was awarded to Salvatore Rappoccio, PhD, associate professor of physics in the UB College of Arts and Sciences, and UB physics professors Ia Iashvili, PhD, and Avto Kharchilava, PhD.

    The funding began Sept. 1, just days after the latest big discovery in high-energy physics.

    On Aug. 28, an international team of thousands of researchers — including Iashvili, Kharchilava and Rappoccio — announced that they had observed the Higgs boson, a subatomic particle, decaying into a pair of lighter particles called a bottom quark and antibottom quark.

    The sighting took place at the world’s most powerful particle accelerator, the Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN).


    CERN map

    CERN LHC Tunnel

    CERN LHC particles

    The finding deepens our understanding of why objects have mass. It also validates the Standard Model, a set of equations that physicists use to describe elementary particles and the way they behave (in essence, the way the universe works).

    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

    For Kharchilava, the discovery was over a decade in the making. He and his UB students had been searching for evidence of the Higgs boson transforming into bottom quarks since around 2005.

    “I was looking for this decay for almost 15 years, when we began the search at Fermilab, which operated the Tevatron collider,” he says. “We did not succeed back then because we did not have enough data and precision, so now we have more data and better precision and we have finally made the discovery.”

    FNAL/Tevatron map

    FNAL/Tevatron CDF detector

    FNAL/Tevatron DZero detector

    The new NSF funding will enable the UB scientists to continue their work on the Higgs boson, the Standard Model and the hunt for new phenomena in physics.

    The finding deepens our understanding of why objects have mass. It also validates the Standard Model, a set of equations that physicists use to describe elementary particles and the way they behave (in essence, the way the universe works).

    For Kharchilava, the discovery was over a decade in the making. He and his UB students had been searching for evidence of the Higgs boson transforming into bottom quarks since around 2005.

    “I was looking for this decay for almost 15 years, when we began the search at Fermilab, which operated the Tevatron collider,” he says. “We did not succeed back then because we did not have enough data and precision, so now we have more data and better precision and we have finally made the discovery.”

    See the full article here .


    Please help promote STEM in your local schools.

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    U Buffalo Campus

    UB is a premier, research-intensive public university and a member of the Association of American Universities. As the largest, most comprehensive institution in the 64-campus State University of New York system, our research, creative activity and people positively impact the world.

  • richardmitnick 12:47 pm on September 4, 2018 Permalink | Reply
    Tags: , , , , CISE-NSF's Office of Advanced Cyberinfrastructure in the Directorate for Computer and Information Science and Engineering, Higgs boson, IRIS-HEP-Institute for Research and Innovation in Software for High-Energy Physics, Molecular Sciences Software Institute and the Science Gateways Community Institute, MPS-NSF Division of Physics in the Directorate for Mathematical and Physical Sciences, , SCAILFIN-Scalable Cyberinfrastructure for Artificial Intelligence and Likelihood-Free Inference   

    From University of Illinois Physics: “University of Illinois part of $25 million software institute to enable discoveries in high-energy physics” 

    U Illinois bloc

    From University of Illinois Physics

    U Illinois Physics bloc

    Siv Schwink

    A data visualization from a simulation of collision between two protons that will occur at the High-Luminosity Large Hadron Collider (HL-LHC). On average, up to 200 collisions will be visible in the collider’s detectors at the same time. Shown here is a design for the Inner Tracker of the ATLAS detector, one of the hardware upgrades planned for the HL-LHC. Image courtesy of the ATLAS Experiment © 2018 CERN

    CERN/ATLAS detector

    Today, the National Science Foundation (NSF) announced its launch of the Institute for Research and Innovation in Software for High-Energy Physics (IRIS-HEP).

    The $25 million software-focused institute will tackle the unprecedented torrent of data that will come from the high-luminosity running of the Large Hadron Collider (LHC), the world’s most powerful particle accelerator located at CERN near Geneva, Switzerland.


    CERN map

    CERN LHC Tunnel

    CERN LHC particles

    The High-Luminosity LHC (HL-LHC) will provide scientists with a unique window into the subatomic world to search for new phenomena and to study the properties of the Higgs boson in great detail.

    CERN CMS Higgs Event

    CERN ATLAS Higgs Event

    The 2012 discovery at the LHC of the Higgs boson—a particle central to our fundamental theory of nature—led to the Nobel Prize in physics a year later and has provided scientists with a new tool for further discovery.

    The HL-LHC will begin operations around 2026, continuing into the 2030s. It will produce more than 1 billion particle collisions every second, from which only a tiny fraction will reveal new science, because the phenomena that physicists want to study have a very low probability per collision of occurring. The HL-LHC’s tenfold increase in luminosity—a measure of the number of particle collisions occurring in a given amount of time—will enable physicists to study familiar processes at an unprecedented level of detail and observe rare new phenomena present in nature.

    But the increased luminosity also leads to more complex collision data. A tenfold increase in the required data processing and storage can not be achieved without new software tools for intelligent data filtering that record only the most interesting collision events, to enable scientists to analyze the data more efficiently.

    Over the next five years, IRIS-HEP will focus on developing innovative software for use in particle physics research with the HL-LHC as the key science driver. It will also create opportunities for training and education in related areas of computational and data science and outreach to the general public. The institute will also work to increase participation from women and minorities who are underrepresented in high-energy physics research.

    IRIS-HEP brings together multidisciplinary teams of researchers and educators from 17 universities, including Mark Neubauer, a professor of physics at the University of Illinois at Urbana-Champaign and a faculty affiliate with the National Center for Supercomputing Applications (NCSA) in Urbana.


    Neubauer is a member of the ATLAS Experiment, which generates and analyzes data from particle collisions at the LHC. Neubauer will serve on the IRIS-HEP Executive Committee and coordinate the institute’s activities to develop and evolve the strategic vision of the institute.

    Neubauer, along with colleagues Peter Elmer (Princeton) and Michael Sokoloff (Cincinnati), led a community-wide effort to conceptualize the institute with funding from the NSF and was a key member of the group that developed the IRIS-HEP proposal. Through a process to conceptualize the institute involving 18 workshops over the last two years, key national and international partners from high-energy physics, computer science, industry, and data-science communities were brought together to generate more than eight community position papers, most notably a strategic plan for the institute and a roadmap for HEP software and computing R&D over the next decade. They reviewed two decades of approaches to LHC data processing and analysis and developed strategies to address the challenges and opportunities that lay ahead. IRIS-HEP emerged from that effort.

    “IRIS-HEP will serve as a new intellectual hub of software development for the international high-energy physics community,” comments Neubauer. “The founding of this Institute will do much more than fund software development to support the HL-LHC science; it will provide fertile ground for new ideas and innovation, empower early-career researchers interested in software and computing aspects of data-enabled science through mentoring and training to support their professional development, and will redefine the traditional boundaries of the high-energy physics community.”

    Neubauer will receive NSF funding through IRIS-HEP to contribute to the institute’s efforts in software research and innovation. He plans to collaborate with Daniel S. Katz, NCSA’s assistant director for scientific software and applications, to put together a team to research new approaches and systems for data analysis and innovative algorithms that apply machine learning and other approaches to accelerate computation on modern computing architectures.

    In related research also beginning in the current Fall semester, Neubauer and Katz through a separate NSF award with Kyle Cranmer (NYU), Heiko Mueller (NYU) and Michael Hildreth (Notre Dame) will be collaborating on the Scalable Cyberinfrastructure for Artificial Intelligence and Likelihood-Free Inference (SCAILFIN) Project. SCAILFIN aims to maximize the potential of artificial intelligence and machine learning to improve new physics searches at the LHC, while addressing current issues in software and data sustainability by making data analyses more reusable and reproducible.

    Katz says he is looking forward to delving into these projects: “How to build tools that make more sense of the data, how to make the software more sustainable so there is less rewriting, how to write software that is portable across different systems and compatible with future hardware changes—these are tremendous challenges. And these questions really are timely. They fit into the greater dialogue that is ongoing in both the computer science and the information science communities. I’m excited for this opportunity to meld the most recent work from these complementary fields together with work in physics.”

    Neubauer concludes, “The quest to understand the fundamental building blocks of nature and their interactions is one of the oldest and most ambitious of human scientific endeavors. The HL-LHC will represent a big step forward in this quest and is a top priority for the US particle physics community. As is common in frontier-science experiments pushing at the boundaries of knowledge, it comes with daunting challenges. The LHC experiments are making large investments to upgrade their detectors to be able to operate in the challenging HL-LHC environment.

    “A significant investment in R&D for software used to acquire, manage, process and analyze the huge volume of data that will be generated during the HL-LHC era will be critical to maximize the scientific return on investment in the accelerator and detectors. This is not a problem that could be solved by gains from hardware technology evolution or computing resources alone. The institute will support early-career scientists to develop innovative software over the next five to ten years, to get us where we need to be to do our science during the HL-LHC era. I am elated to see such a large investment by the NSF in this area for high-energy physics.”

    IRIS-HEP is co-funded by NSF’s Office of Advanced Cyberinfrastructure in the Directorate for Computer and Information Science and Engineering (CISE) and the NSF Division of Physics in the Directorate for Mathematical and Physical Sciences (MPS). IRIS-HEP is the latest NSF contribution to the 40-nation LHC effort. It is the third OAC software institute, following the Molecular Sciences Software Institute and the Science Gateways Community Institute.

    See the full University of Illinois article on this subject here .
    See the full Cornell University article on the subject here.
    See the full Princeton University article on this subject here.


    Please help promote STEM in your local schools.

    Stem Education Coalition

    U Illinois campus

    The University of Illinois at Urbana-Champaign community of students, scholars, and alumni is changing the world.

    With our land-grant heritage as a foundation, we pioneer innovative research that tackles global problems and expands the human experience. Our transformative learning experiences, in and out of the classroom, are designed to produce alumni who desire to make a significant, societal impact.

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