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  • richardmitnick 10:10 am on July 9, 2017 Permalink | Reply
    Tags: , , CERN LHC LHCb, CERN Physicists Find a Particle With a Double Dose of Charm, FNAL Tevatron, , , ,   

    From NYT: “CERN Physicists Find a Particle With a Double Dose of Charm” 

    New York Times

    The New York Times

    JULY 6, 2017
    KENNETH CHANG

    3
    The new particle, awkwardly known as Xi-cc++ (pronounced ka-sigh-see-see-plus-plus)

    1
    The Vertex Locator detector is part of an experiment at CERN’s Large Hadron Collider that discovered a particle that contains two charm quarks. Credit CERN

    Physicists have discovered a particle that is doubly charming.

    Researchers reported on Thursday that in debris flying out from the collisions of protons at the CERN particle physics laboratory outside Geneva, they had spotted a particle that has long been predicted but not detected until now.

    The new particle, awkwardly known as Xi-cc++ (pronounced ka-sigh-see-see-plus-plus), could provide new insight into how tiny, whimsically named particles known as quarks, the building blocks of protons and neutrons, interact with each other.

    Protons and neutrons, which account for the bulk of ordinary matter, are made of two types of quarks: up and down. A proton consists of two up quarks and one down quark, while a neutron contains one up quark and two down quarks. These triplets of quarks are known as baryons.

    There are also heavier quarks with even quirkier names — strange, charm, top, bottom — and baryons containing permutations of heavier quarks also exist.

    An experiment at CERN, within the behemoth Large Hadron Collider, counted more 300 Xi-cc++ baryons, each consisting of two heavy charm quarks and one up quark.

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    The discovery fits with the Standard Model, the prevailing understanding of how the smallest bits of the universe behave, and does not seem to point to new physics.

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

    “The existence of these particles has been predicted by the Standard Model,” said Patrick Spradlin, a physicist at the University of Glasgow who led the research. “Their properties have also been predicted.”

    Dr. Spradlin presented the findings on Thursday at a European Physical Society conference in Venice, and a paper describing them has been submitted to the journal Physical Review Letters.

    Up and down quarks have almost the same mass, so in protons and neutrons, the three quarks swirl around each other in an almost uniform pattern. In the new particle, the up quark circulates around the two heavy charm quarks at the center. “You get something far more like an atom,” Dr. Spradlin said.

    Quark interactions are complex and difficult to calculate, and the structure of the new particles will enable physicists to check the assumptions and approximations they use in their calculations. “It’s a new regime in quark-quark dynamics,” said Jonathan L. Rosner, a retired theoretical physicist at the University of Chicago.

    The mass of the Xi-cc++ is about 3.8 times that of a proton. The particle is not stable. Dr. Spradlin said the scientists had not yet figured out its lifetime precisely, but it falls apart after somewhere between 50 millionths of a billionth of a second and 1,000 millionths of a billionth of a second.

    For Dr. Rosner, the CERN results appear to match predictions that he and Marek Karliner of Tel Aviv University made.

    What is less clear is how the new particle fits in with findings from 2002, when physicists working at Fermilab outside Chicago made the first claim of a doubly charmed baryon, one consisting of two charm quarks plus a down quark (instead of the up quark seen in the CERN experiment).

    FNAL Tevatron

    FNAL/Tevatron map


    FNAL/Tevatron DZero detector


    FNAL/Tevatron CDF detector

    The two baryons should be very close in mass, but the Fermilab one was markedly lighter than what the CERN researchers found for Xi-cc++, and it appeared to decay instantaneously, in less than 30 millionths of a billionth of a second.

    Theorists like Dr. Rosner had difficulty explaining the behavior of the Fermilab particle within the Standard Model. “I didn’t have an honest alternative to allow me to believe that result,” he said.

    Peter S. Cooper, a deputy spokesman for the Fermilab experiment, congratulated the CERN researchers on their discovery. “That paper smells sweet,” he said. “From an experimental point of view, there’s nothing wrong. They definitely have something.”

    But he said the Fermilab findings still stood, too. He acknowledged that the two results do not readily make sense together.

    “I consider this a problem for my theoretical brethren to work out,” Dr. Cooper said. He added that it was a textbook example of the scientific method: “Our theoretical colleagues make a prediction. We go out and make a measurement and see if it’s right. If it isn’t, they go back and think harder.”

    It is possible one of the experiments is wrong. Researchers at other laboratories, including at CERN, have sought to detect the Fermilab baryon without success. Dr. Spradlin said he and his colleagues are searching the same data that revealed the Xi-cc++ for the baryon with two charm quarks and one down quark. That could confirm the Fermilab findings or reveal a mass closer to theorists’ expectations.

    “We should be able to see it with the data we have,” Dr. Spradlin said. “I think we are very close to resolving this controversy.”

    I presented an earlier post from LHCb, but it contained no reference to the paper in Physical Review Letters.

    See the full article here .

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  • richardmitnick 12:11 pm on June 10, 2017 Permalink | Reply
    Tags: , , FNAL Tevatron, , , , Tevatron first accelerator to use electron lens   

    From FNAL: “Tevatron first accelerator to use electron lens” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

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

    accelerator to use electron lens

    June 10, 2017
    Troy Rummler
    1

    Tevatron is the first accelerator to use an electron lens

    Fermilab’s Tevatron was the first particle accelerator to make use of an electron lens, a technique that allowed the machine to compensate for destabilizing forces unavoidably generated by the colliding beams. Proposed in 1997, the lenses were installed in 2001 and 2004 in the Tevatron, where they demonstrated beam-beam compensation. They were also used in the removal of unwanted particles. The innovation earned Fermilab scientist Vladimir Shiltsev a European Physical Society Accelerator Prize.

    FNAL Tevatron

    FNAL/Tevatron map


    FNAL/Tevatron DZero detector


    FNAL/Tevatron CDF detector

    See the full article here .

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    Fermilab Campus

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

     
  • richardmitnick 3:46 pm on May 24, 2017 Permalink | Reply
    Tags: , , Early days, FNAL Tevatron, , ,   

    From FNAL: “Early Tevatron design days” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

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

    May 24, 2017
    Tom Nicol

    1
    Fermilab technicians assemble a magnet spool piece for the Tevatron. Photo: Fermilab

    When I started at the lab in December 1977, work on the dipole magnets for the Tevatron was well under way in what was then called the Energy Doubler Department in the Technical Services Section.

    My first project was to work on the quadrupole magnets and spools, which hadn’t really been started yet. The spool is a special unit that attaches to each quadrupole and the adjacent dipole. It contains what we used to call “the stuff that wouldn’t fit anywhere else” – correction magnets and their power leads, quench stoppers to dump the energy from all the magnets, beam position monitors, relief valves, things like that.

    At the time, we were located in the Village in the old director’s complex, which now houses the daycare center. We had a large open area where the engineers, designers and drafters worked and a small conference room where we kept up-to-date models of some of the things we were working on.

    2
    A team tests a magnet spool piece. Photo: Fermilab

    For several weeks we worked feverishly on the design of the quadrupole and spool combination — we in the design room and the model makers in the model shop on their full-scale models. We would work all week, then have a meeting with the lab director, Bob Wilson. Dr. Wilson would come out to see how we were doing, but more importantly to see what our designs looked like.

    It turns out he was very interested in that and very fussy that things — even those buried in the tunnel — looked just so.

    After every one of those meetings we’d walk back into the design room and tell everyone to tear up what we’d been working on and start over. The same would hold for the model makers. This went on for several weeks until Dr. Wilson was happy. We began to really dread going into those meetings, but in the end they served us very well.

    FNAL Tevatron

    FNAL/Tevatron map


    FNAL/Tevatron DZero detector


    FNAL/Tevatron CDF detector

    See the full article here .

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    Fermilab Campus

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

     
  • richardmitnick 1:55 pm on May 24, 2017 Permalink | Reply
    Tags: , , Charm mesons and baryons, FNAL Tevatron, , , ,   

    From FNAL: ” Fermilab measures lifetimes and properties of charm mesons and baryons” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

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

    properties of charm mesons and baryons

    May 24, 2017
    Troy Rummler

    1

    Heavy quarks produced in high-energy collisions decay within a tiny fraction of a second, traveling less than a few centimeters from the collision point. To study properties of these particles, Fermilab began using microstrip detectors in the late 1970s. These detectors are made of thin slices of silicon and placed close to the interaction point in order to take advantage of the microstrip’s tremendous position resolution. Over time, Fermilab developed this technology, improving our understanding of silicon’s capabilities and adapting the technology to other detectors, including those at CDF and DZero.

    FNAL Tevatron

    FNAL/Tevatron map


    FNAL/Tevatron DZero detector


    FNAL/Tevatron CDF detector

    See the full article here .

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    Fermilab Campus

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

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

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

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

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

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

    1

    CERN CMS Higgs Event


    CERN/CMS Detector


    CERN ATLAS Higgs Event


    CERN/ATLAS detector

    Where it all started:

    FNAL Tevatron

    FNAL/Tevatron map


    FNAL/Tevatron DZero detector


    FNAL/Tevatron CDF detector

    Where we failed and handed it to Europe:

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

    See the full article here .

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    Fermilab Campus

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

     
  • richardmitnick 3:14 pm on December 13, 2016 Permalink | Reply
    Tags: , ATLAS releases first measurement of W mass using LHC data, , , FNAL Tevatron, , , ,   

    From CERN ATLAS: “ATLAS releases first measurement of W mass using LHC data” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    CERN

    13 Dec 2016
    Harriet Kim Jarlett

    1
    ATLAS is one of the four major experiments at the LHC. It is a general-purpose particle physics experiment run by an international collaboration (Image: Claudia Marcelloni/ CERN)

    The ATLAS collaboration today reports the first measurement of the W boson mass using Large Hadron Collider (LHC) proton–proton collision data at a centre-of-mass energy of 7 TeV.

    2
    The ATLAS measurement of the W boson mass (in red) is compared to the Standard Model prediction (in purple), and to the combined values measured at the LEP and Tevatron collider (in blue) (Image: ATLAS Collaboration/CERN)

    The W boson was discovered in 1983 at the CERN SPS collider and led to a Nobel prize in physics in 1984.

    3
    Super Proton Synchrotron (SPS)

    Although the properties of the W boson have been studied for more than 30 years, measuring its mass remains a major challenge. A precise measurement of the W boson mass is vital, as a deviation from the Standard Model’s predictions could hint at new physics.

    The latest results from ATLAS show a measured value of 80370±19 MeV, which is consistent with the Standard Model prediction. It is also consistent with the combined values measured at the LEP and Tevatron colliders, and with the world average (see graph above).

    4
    Large Electron Positron collider

    FNAL/Tevatron machine
    FNAL/Tevatron

    Measuring the W mass is particularly challenging at the LHC, compared to previous colliders, due to the large number of interactions per beam crossing. Despite this, the ATLAS result matches the best single-experiment measurement of the W mass (performed by the CDF collaboration).

    FNAL/Tevatron CDF detector
    FNAL/Tevatron CDF detector

    Read more on the ATLAS experiment’s website: http://cern.ch/go/p6sN

    See the full article here.

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    Meet CERN in a variety of places:

    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New

    ALICE
    CERN ALICE New

    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    LHC

    CERN LHC Map
    CERN LHC Grand Tunnel

    CERN LHC particles

    Quantum Diaries

     
  • richardmitnick 4:13 pm on September 13, 2016 Permalink | Reply
    Tags: , , D+ mesons, , FNAL Tevatron, Strong interaction   

    From FNAL: “CDF can’t stop being charming” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

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

    September 8, 2016
    Jeffrey Appel

    FNAL/Tevatron map
    FNAL/Tevatron map

    FNAL/Tevatron CDF detector
    FNAL/Tevatron CDF detector

    Good news: there is a theory to describe the strong interaction, the interactions that bind the constituents of protons and neutrons together and create the strong force. Bad news: Calculations using the theory can be made in only a limited selection of natural phenomena.

    Quantitative predictions for interactions beyond that subset depend on measurements. This can be either for direct use or to help guide the theory about the inputs used in calculations, such as the distributions of the quark and gluon constituents inside protons and neutrons. Using the production of particles containing heavy charm and bottom quarks helps especially with gluon distributions.

    CDF is now reporting new measurements of the rate of production at the Tevatron of D+ mesons, which contain charm quarks. Furthermore, the new measurements are made in the region where the D+ mesons have the smallest momentum transverse to the incident beams. This is the region that is the hardest to calculate using the theory of strong interactions and has never been explored in proton-antiproton collisions.

    1
    This plot shows the measures, in bins of momentum transverse to incident protons, of the average probability of producing a D+ meson at the Tevatron. Shown as bands are the averages predicted in the same bins by the latest theoretical calculations.

    To probe such small transverse momenta, CDF physicists examined all types of interactions of the incoming protons and antiprotons, not just those selected to study rare occurrences.

    The results of this new analysis appear in the figure. The measurements lie within the band of uncertainty of the theoretical predictions. Using the results here, theorists can reduce the size of the band of uncertainty. They might also be able to improve the general trend of the predictions to agree better with the trends in the measurements.

    This measurement is an example of CDF’s continuing effort to produce unique and useful results that complement and supplement those of the LHC. These help improve our understanding of the fundamental forces of nature.

    Learn more.

    See the full article here .

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    Fermilab Campus

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

     
  • richardmitnick 5:26 pm on September 29, 2015 Permalink | Reply
    Tags: , , , FNAL Tevatron, , ,   

    From SMU: “Top Quark: New precise particle measurement improves subatomic tool for probing mysteries of universe” 

    SMU

    SMU Research

    September 28, 2015
    Margaret Allen

    In post-Big Bang world, nature’s top quark — a key component of matter — is a highly sensitive probe that physicists use to evaluate competing theories about quantum interactions

    Physicists at Southern Methodist University, Dallas, have achieved a new precise measurement of a key subatomic particle, opening the door to better understanding some of the deepest mysteries of our universe.

    The researchers calculated the new measurement for a critical characteristic — mass — of the top quark.

    1
    A collision event involving top quarks

    Quarks make up the protons and neutrons that comprise almost all visible matter. Physicists have known the top quark’s mass was large, but encountered great difficulty trying to clearly determine it.

    The newly calculated measurement of the top quark will help guide physicists in formulating new theories, said Robert Kehoe, a professor in SMU’s Department of Physics. Kehoe leads the SMU group that performed the measurement.

    Top quark’s mass matters ultimately because the particle is a highly sensitive probe and key tool to evaluate competing theories about the nature of matter and the fate of the universe.

    Physicists for two decades have worked to improve measurement of the top quark’s mass and narrow its value.

    “Top” bears on newest fundamental particle, the Higgs boson

    The new value from SMU confirms the validity of recent measurements by other physicists, said Kehoe.

    But it also adds growing uncertainty about aspects of physics’ Standard Model.

    2
    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    The Standard Model is the collection of theories physicists have derived — and continually revise — to explain the universe and how the tiniest building blocks of our universe interact with one another. Problems with the Standard Model remain to be solved. For example, gravity has not yet been successfully integrated into the framework.

    The Standard Model holds that the top quark — known familiarly as “top” — is central in two of the four fundamental forces in our universe — the electroweak force, by which particles gain mass, and the strong force, which governs how quarks interact. The electroweak force governs common phenomena like light, electricity and magnetism. The strong force governs atomic nuclei and their structure, in addition to the particles that quarks comprise, like protons and neutrons in the nucleus.

    The top plays a role with the newest fundamental particle in physics, the Higgs boson, in seeing if the electroweak theory holds water.

    Some scientists think the top quark may be special because its mass can verify or jeopardize the electroweak theory. If jeopardized, that opens the door to what physicists refer to as “new physics” — theories about particles and our universe that go beyond the Standard Model.

    Other scientists theorize the top quark might also be key to the unification of the electromagnetic and weak interactions of protons, neutrons and quarks.

    In addition, as the only quark that can be observed directly, the top quark tests the Standard Model’s strong force theory.

    “So the top quark is really pushing both theories,” Kehoe said. “The top mass is particularly interesting because its measurement is getting to the point now where we are pushing even beyond the level that the theorists understand.”

    He added, “Our experimental errors, or uncertainties, are so small, that it really forces theorists to try hard to understand the impact of the quark’s mass. We need to observe the Higgs interacting with the top directly and we need to measure both particles more precisely.”

    The new measurement results were presented in August and September at the Third Annual Conference on Large Hadron Collider Physics, St. Petersburg, Russia, and at the 8th International Workshop on Top Quark Physics, Ischia, Italy.

    “The public perception, with discovery of the Higgs, is ‘Ok, it’s done,’” Kehoe said. “But it’s not done. This is really just the beginning and the top quark is a key tool for figuring out the missing pieces of the puzzle.”

    The results were made public by DZero, a collaborative experiment of more than 500 physicists from around the world. The measurement is described in Precise measurement of the top quark mass in dilepton decays with optimized neutrino weighting and is available online at arxiv.org/abs/1508.03322.

    SMU measurement achieves surprising level of precision

    To narrow the top quark measurement, SMU doctoral researcher Huanzhao Liu took a standard methodology for measuring the top quark and improved the accuracy of some parameters. He also improved calibration of an analysis of top quark data.

    “Liu achieved a surprising level of precision,” Kehoe said. “And his new method for optimizing analysis is also applicable to analyses of other particle data besides the top quark, making the methodology useful within the field of particle physics as a whole.”

    The SMU optimization could be used to more precisely understand the Higgs boson, which explains why matter has mass, said Liu.

    The Higgs was observed for the first time in 2012, and physicists keenly want to understand its nature.

    “This methodology has its advantages — including understanding Higgs interactions with other particles — and we hope that others use it,” said Liu. “With it we achieved 20-percent improvement in the measurement. Here’s how I think of it myself — everybody likes a $199 iPhone with contract. If someday Apple tells us they will reduce the price by 20 percent, how would we all feel to get the lower price?”

    Another optimization employed by Liu improved the calibration precision by four times, Kehoe said.

    Shower of Top quarks post Big Bang

    Top quarks, which rarely occur now, were much more common right after the Big Bang 13.8 billion years ago. However, top is the only quark, of six different kinds, that can be observed directly. For that reason, experimental physicists focus on the characteristics of top quarks to better understand the quarks in everyday matter.

    To study the top, physicists generate them in particle accelerators, such as the Tevatron, a powerful U.S. Department of Energy particle accelerator operated by Fermi National Laboratory in Illinois, or the Large Hadron Collider in Switzerland, a project of the European Organization for Nuclear Research, CERN.

    FNAL Tevatron
    FNAL DZero
    FNAL CDF
    Tevatron, DZero, CDF

    CERN LHC Map
    CERN LHC Grand Tunnel
    CERN LHC particles
    CERN ATLAS New
    CERN CMS Detector
    LHC, ATLAS, CMS

    SMU’s measurement draws on top quark data gathered by DZero that was produced from proton-antiproton collisions at the Tevatron, which Fermilab shut down in 2011.

    The new measurement is the most precise of its kind from the Tevatron, and is competitive with comparable measurements from the Large Hadron Collider. The top quark mass has been precisely measured more recently, but there is some divergence of the measurements. The SMU result favors the current world average value more than the current world record holder measurement, also from Fermilab. The apparent discrepancy must be addressed, Kehoe said.

    Critical question: Universe isn’t necessarily stable at all energies

    “The ability to measure the top quark mass precisely is fortuitous because it, together with the Higgs boson mass, tells us whether the universe is stable or not,” Kehoe said. “That has emerged as one of today’s most important questions.”

    A stable universe is one in a low energy state where particles and forces interact and behave according to theoretical predictions forever. That’s in contrast to metastable, or unstable, meaning a higher energy state in which things eventually change, or change suddenly and unpredictably, and that could result in the universe collapsing. The Higgs and top quark are the two most important parameters for determining an answer to that question, Kehoe said.

    Recent measurements of the Higgs and top quark indicate they describe a universe that is not necessarily stable at all energies.

    “We want a theory — Standard Model or otherwise — that can predict physical processes at all energies,” Kehoe said. “But the measurements now are such that it looks like we may be over the border of a stable universe. We’re metastable, meaning there’s a gray area, that it’s stable in some energies, but not in others.”

    Are we facing imminent doom? Will the universe collapse?

    That disparity between theory and observation indicates the Standard Model theory has been outpaced by new measurements of the Higgs and top quark.

    “It’s going to take some work for theorists to explain this,” Kehoe said, adding it’s a challenge physicists relish, as evidenced by their preoccupation with “new physics” and the possibilities the Higgs and Top quark create.

    “I attended two conferences recently,” Kehoe said, “and there’s argument about exactly what it means, so that could be interesting.”

    So are we in trouble?

    “Not immediately,” Kehoe said. “The energies at which metastability would kick in are so high that particle interactions in our universe almost never reach that level. In any case, a metastable universe would likely not change for many billions of years.”

    Top quark — a window into other quarks

    As the only quark that can be observed, the top quark pops in and out of existence fleetingly in protons, making it possible for physicists to test and define its properties directly.

    “To me it’s like fireworks,” Liu said. “They shoot into the sky and explode into smaller pieces, and those smaller pieces continue exploding. That sort of describes how the top quark decays into other particles.”

    By measuring the particles to which the top quark decays, scientists capture a measure of the top quark, Liu explained

    But study of the top is still an exotic field, Kehoe said. “For years top quarks were treated as a construct and not a real thing. Now they are real and still fairly new — and it’s really important we understand their properties fully.” — Margaret Allen

    See the full article here .

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    SMU Campus

    A nationally ranked private university with seven degree-granting schools, SMU is a distinguished center for teaching and research located near the heart of Dallas. SMU’s 11,000 students benefit from small classes, leadership opportunities, international study and innovative programs.

    SMU is celebrating the centennial of its founding in 1911 and its opening in 1915. As SMU enters a second century of achievement, it is recognized as a university of increasing national prominence.

    SMU prepares students for leadership in their professions and in their communities. The University’s location near the heart of Dallas – a thriving center of commerce and culture – offers students enriching experiences on campus and beyond. Relationships in the Dallas area provide a platform for launching careers throughout the world.

    The University offers a strong foundation in the humanities and sciences and undergraduate, graduate and professional degree programs through seven schools. The learning environment includes opportunities for research, community service, internships, mentoring and study abroad.

     
  • richardmitnick 10:25 am on July 30, 2015 Permalink | Reply
    Tags: , FNAL Tevatron, ,   

    From FNAL: “Fishing for the weak and the charmed” 

    FNAL Home

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

    July 30, 2015
    Keith Matera and Andy Beretvas

    Temp 1
    The top plot shows the observed and predicted rates of vector boson plus charmed meson production at different energies for a type of vector boson called a W boson. The bottom plot shows the ratio of the observed to predicted rates. Observation and prediction are in agreement even at low energies, providing confirmation that we understand how these events behave. A well-tested model makes it easier to pick out anomalies, such as dark matter candidates.

    You collect coins, and you’re on the trail of a legend: According to rumor, a manufacturing defect led to one in every thousand 1939 nickels replacing Thomas Jefferson with a Sasquatch (also known as Bigfoot). But all of these weathered nickels now look about the same. How can you tell that you have found your elusive quarry?

    Finding something new in particle physics is much the same. We frequently know roughly what a new particle might look like, but this “signature” is often similar to that of other particles. One of the best ways to aid our search is to paint extremely accurate pictures of known particles and then look for exceptions to that rule.

    Heavy particles like dark matter candidates, the Higgs boson or particles predicted by supersymmetry share a common signature: They may decay into particles including a “vector boson V,” (a type of particle that transmits the weak force), and a “charmed meson,” D* (a particle made of two quarks, one of which is a charm quark).

    CDF physicists performed a search for these V+D* events — the normal nickels — to make certain that our picture of them is accurate.

    FNAL CDF
    CDF

    Models of events such as these are known to be accurate at high energies; however, at lower energies, subtleties in the strong force that binds together fundamental particles become more important, and the models may break down.

    This study was the first to test V+D* production at lower energies in hadron collisions. The V particle is either the W boson or the Z boson. The full Tevatron Run II data sample was used (9.7 inverse femtobarns).

    FNALTevatron
    Tevetron

    The figure shows the data when the V particle is the W particle. The experiment measured 634 ± 39 such events. The W particle is found by looking for an energetic lepton (a muon or an electron) and missing transverse energy (neutrino). The D* particle is observed from its decay into the D0 particle and a low-energy pion. The D0 decays into a negative kaon and a positive pion.

    Several sources of systematic uncertainty cancel in calculating the ratio of the decay probabilities for these two processes. We found that V+D* production behaves just as predicted. Providing such a stringent test of these models widens the net that we can cast in future studies. This, in turn, betters our chances of fishing out something new and exciting, perhaps previously undiscovered particles or particle decays.

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Fermilab Campus

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

     
  • richardmitnick 10:25 am on March 12, 2015 Permalink | Reply
    Tags: , , FNAL Tevatron, , ,   

    From FNAL- “Frontier Science Result: CDF and DZero Joining forces to test the Higgs boson’s spin and parity” 

    FNAL Home


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

    Thursday, March 12, 2015
    Tom Junk

    1
    This plot shows the observed and expected upper limits at the 95 percent credibility level on the fraction of exotic boson production for two cases (spin zero with negative parity and spin two with positive parity). A signal scale of one corresponds to the Standard Model.

    The Higgs boson caused a lot of excitement when the ATLAS and CMS collaborations announced its discovery in 2012.

    CERN ATLAS New
    ATLAS

    CERN CMS New
    CMS

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

    Everyone was bursting with questions: How much does it weigh? How is it made? How does it decay? Does it have any spin, and if so, how much? Does it look the same in a mirror or not (the question of “parity”)?

    The Standard Model predicts the answers to all of these questions, although some depend on the Higgs boson mass, which ATLAS and CMS have measured precisely.

    2
    Standard Model of Particle Physics. The diagram shows the elementary particles of the Standard Model (the Higgs boson, the three generations of quarks and leptons, and the gauge bosons), including their names, masses, spins, charges, chiralities, and interactions with the strong, weak and electromagnetic forces. It also depicts the crucial role of the Higgs boson in electroweak symmetry breaking, and shows how the properties of the various particles differ in the (high-energy) symmetric phase (top) and the (low-energy) broken-symmetry phase (bottom).

    So far, the new particle observed at the LHC is consistent with all of the Standard Model’s predictions. In particular, ATLAS and CMS’s measurements of the spin and parity allowed them to confidently identify the new particle as a Higgs boson.

    The Tevatron experiments, CDF and DZero, also found evidence for a Higgs boson in 2012, looking at events in which two bottom-flavored jets recoiled from a vector boson — either a Z or a W.

    FNALTevatron
    Tevatron

    FNAL CDF
    CDF

    FNAL DZero
    DZero

    All the same questions come up, as some models predict that one may observe a mixture of Higgs particles at the Tevatron different from what was observed at the LHC due to the different mixtures of production and decay modes that provide the most sensitivity.

    At the Tevatron, the Higgs boson’s properties were found to be consistent with those predicted for the Standard Model Higgs boson. Theorists provided a clever way to test some models of the Higgs boson’s spin and parity using Tevatron data: Higgs bosons with exotic spin and parity would be produced with more energy than the Standard Model version. CDF and DZero looked at the energies and angles of particles produced in Higgs boson events to check. But most events at the Tevatron are non-Higgs-boson background events, so a lot of hard work went in to test the models.

    Both DZero and CDF modified their Higgs boson analyses to search for the new particles, if they are present in addition to the Standard Model Higgs boson, or if they replace it entirely. Neither experiment found evidence for the exotic states, and the data prefer the Standard Model interpretation.

    But a much stronger statement can be made when CDF and DZero join forces and combine their results, using the same techniques used in the Standard Model Higgs search combinations. The signal strength of exotic Higgs bosons in the JP=0- and 2+ states is no more than 0.36 times that predicted for the Standard Model Higgs boson. Given a choice between the Standard Model Higgs boson, which has JP=0+, and one of the two exotic models replacing it with the same signal strength, the Tevatron data disfavors the exotic models with a significance of 5.0 standard deviations for 0- and 4.9 standard deviations for 2+.

    The figure above shows limits on the fraction of exotic Higgs boson production as functions of the total signal rate, assuming that the Higgs signal is a mixture of the Standard Model Higgs boson and one of the exotic kinds. The particle for which the Tevatron experiments reported evidence in 2012 is consistent with having the spin and parity predicted by the Standard Model.

    —Tom Junk

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Fermilab Campus

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

     
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