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  • richardmitnick 6:44 pm on November 4, 2014 Permalink | Reply
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    From BNL: “Physicists Narrow Search for Solution to Proton Spin Puzzle” 

    Brookhaven Lab

    November 4, 2014
    Karen McNulty Walsh

    New RHIC results reveal that gluons make a significant contribution to spin, an important intrinsic particle property; transient sea quarks also play a role.

    Results from experiments at the Relativistic Heavy Ion Collider (RHIC), a particle collider located at the U.S. Department of Energy’s Brookhaven National Laboratory, reveal new insights about how quarks and gluons, the subatomic building blocks of protons, contribute to the proton’s intrinsic angular momentum, a property more commonly known as “spin.” Specifically, the findings show for the first time that gluons make a significant contribution to proton spin, and that transient “sea quarks”—which form primarily when gluons split—also play a role.

    The new precision measurements will help solve a mystery that has puzzled physicists since the 1980s, when findings from early spin experiments in Europe and elsewhere simply didn’t add up. Those experiments showed that the spins of quarks—including the three valence quarks that determine most of the basic properties of the proton—plus antiquarks could account for, at most, a third of the proton’s total spin.

    thing
    How the spins of the building blocks of matter add up: Measurements from RHIC’s STAR and PHENIX experiments reveal that gluons (yellow corkscrews) contribute about as much as quarks (red, green, and blue) to the overall spin of a proton. But there is still a mystery to explain what accounts for the rest of the “missing” spin.

    “RHIC has conclusively, for the first time ever in the world, taken measurements to tell us that the gluon contribution to spin is about equal to the contribution of the quarks.”
    — RHIC physicist Renee Fatemi, University of Kentucky

    “Those results made it apparent that it was naïve to assume that the spin of the proton was carried by its three valence quarks, and this triggered a search for the source of the ‘missing’ spin,” said Brookhaven physicist Elke Aschenauer, a leader in the spin program at RHIC, a DOE Office of Science User Facility for nuclear physics research that was built in part to address this question. “RHIC is the only facility in the world capable of colliding spin-polarized protons,” Aschenauer said, explaining how colliding beams of protons with their spins aligned in a particular direction, and the ability to flip the polarization, gives physicists an elegant way to directly probe the spin contributions of gluons as well as quarks.

    Solving the proton spin puzzle is more than a matter of accounting. Tracking down the sources of proton spin is offering new insight into these particles’ internal structure—including quarks and the gluons that bind them, which are numerous and often split to form transient sea quarks. Spin can also have influence on a wide range of more familiar physical characteristics, including optical, electrical, and magnetic properties—some of which are used in everyday applications such as magnetic resonance imaging (MRI). Pinpointing where spin comes from could yield new information about the mechanisms of the complex subatomic particle interactions within protons, the effects of spin on other properties, and perhaps even ways to control those properties for future, unforeseen applications.

    Narrowing the focus

    mags
    Specialized accelerator magnets known as Siberian snakes have a corkscrew design that helps maintain the polarization of proton beams for RHIC experiments. Keeping all the proton spins aligned in a given direction within at least one of RHIC’s colliding beams helps scientists tease out the spin contributions of the proton’s internal components.

    The latest results on possible sources of spin, some published and some undergoing final analysis, come from the STAR and PHENIX collaborations, two groups each with 500+ scientists poring over data from millions of proton collisions at RHIC.

    BNL Star
    STAR

    BNL Phenix
    PHENIX

    BNL RHIC
    RHIC

    “After the early spin experiments found such a small contribution to spin from a proton’s quarks, people started making big predictions for gluons, the particles that hold quarks together within protons,” said Kieran Boyle, a fellow of the Riken-BNL Research Collaboration (RBRC) who conducts research at PHENIX.

    To gauge the gluon contribution, STAR measures jets of particles coming out of the proton-proton collisions when the spins of the protons in one beam align directly with the spins in the other beam, and repeating the experiment with the spins in one beam flipped, or antialigned relative to the other. PHENIX does the same thing, but measures the number of pions, the most abundant particles produced in jets. Any difference observed in jet or pion production rates when one proton beam’s polarization is flipped is an indication of how much the gluons’ spins are aligned with, and therefore contribute to, the spin of the proton.

    Early spin results from RHIC appeared to deepen the spin mystery, showing gluons didn’t make the huge contribution to spin that everyone had expected. In fact, the measurements came out close to zero, but with a lot of uncertainty.

    “The problem is that these measurements need a lot of data,” said Renee Fatemi, a University of Kentucky physicist who is a deputy spokesperson for the STAR experiment. “All we had was the ability to say the contribution [of gluons] wasn’t very huge. But with very little data we had very large error bars. All we could tell was the difference between huge and not huge.”

    More data reveal significant role of gluons

    RHIC has since collided many more polarized protons thanks to additional running time and accelerator advances that have vastly increased collision rates within each run and improved the degree of polarization in RHIC’s colliding proton beams. In addition, the detectors, particularly STAR, have new capabilities that allow them to capture more collision events. With these expanded data sets, the error bars have shrunk and both STAR and PHENIX now have definitive results.

    “RHIC has conclusively, for the first time ever in the world, taken measurements to tell us that the gluon contribution to spin is about equal to the contribution of the quarks,” about 20-30 percent of the total proton spin, Fatemi said.

    The fact that STAR and PHENIX got similar results gives the scientists great confidence in their findings.

    “These experiments were designed to be complementary,” said PHENIX deputy spokesperson John Lajoie of Iowa State University. “Measuring the same physics with different experiments gives us a way to cross-check our findings and also increases the validity of the comparisons of experimental results with predictions derived from nuclear physics theory.”

    There’s still a caveat to the claim, however, because RHIC is designed to measure particles streaming out of collisions in a particular “kinematic range”—tracking only the particles that emerge at particular angles. PHENIX mainly looks at particles streaming out perpendicular to the paths of the colliding protons. STAR captures that same range plus particles knocked a bit farther forward or backward from the collision zone—produced by more “lopsided” collisions between a high-momentum quark in one beam with a lower-momentum gluon in the other.

    “Our measurement makes assumptions about places we can’t even look yet,” Fatemi said. She emphasized that the new results build on the experiments that came before, thus showcasing the importance of extending the range of measurements. They also set the stage for possible future explorations, such as those that could be done at an electron ion collider (EIC), a facility nuclear physicists hope to build to help solve the spin mystery and other scientific challenges.

    “An EIC would allow us to make numerous, extremely precise measurements across a much wider range of momentum fractions,” Aschenauer said. “It would be the only facility in the world that could measure the distribution of polarized gluons as a function of their momentum and also their spatial distribution in the proton—like a microscope that resolves even the smallest features very precisely. ”

    Splitting fractions, gluons, sea quarks and spin

    But that doesn’t mean physicists have given up the quest to measure gluons’ role in spin even more precisely and over a greater range of momentum fractions at RHIC.

    For example, PHENIX is working on measuring the gluon contribution to the proton spin at more forward angles. These measurements will extend to a different kinematic region, giving results for the gluons carrying a smaller fraction of the overall momentum of the proton, which may offer further insight into the spin puzzle.

    The physicists are also searching for other possible sources of spin. In 2011, they reported the first measurements at RHIC of so-called sea quarks, virtual quark-antiquark pairs that form when gluons achieving a certain energy—say, when protons are accelerated to near the speed of light at RHIC—split and then reform. Though these transient sea quarks flit in and out of existence, they may contribute to spin—and possibly in a way that depends on their flavor.

    col
    Collisions of polarized protons (beam entering from left) and unpolarized protons (right) result in the production of W bosons (in this case, W-). RHIC’s detectors identify the particles emitted as the W bosons decay (in this case, electrons, e-) and the angles at which they emerge. The colored arrows represent different possible directions, which probe how different quark flavors (e.g., “anti-up,” u and “down,” d) contribute to the proton spin.

    To track the sea quarks’ contributions to spin, physicists again compare what happens when the polarization of one of RHIC’s beams is flipped, but this time colliding it with an unpolarized proton beam and tracking the production of particles called W bosons.

    “W’s are produced when a quark inside a proton in one beam collides with an antiquark in the other beam. So W’s are more selective than jets, which can come from quark-quark, gluon-gluon, or quark-gluon interactions,” said Ernst Sichtermann, a physicist at DOE’s Lawrence Berkeley National Laboratory and another deputy spokesperson for STAR. “The Ws pick out the quark-antiquark signal.”

    Even better, the electric charge of the W can precisely identify the type, or flavor, of the antiquark involved in the collision. W- particles decay into electrons, giving information about “anti-up” quarks, while W+ particles decay into positrons, revealing information about “anti-down” quarks.

    So far the results from PHENIX and STAR indicate these sea quarks make a fairly minor contribution to spin. More specifically, the measurements of W+ particles at RHIC indicate that the anti-down quarks’ contribution to spin is in agreement with earlier experiments that looked at sea quark contributions in a less direct way.

    “Our result is more precise and was done in a different way, which provides strong confirmation of what’s been seen before,” STAR’s Fatemi said.

    The results for W-, on the other hand, give the first glimpse that there is an unexpected difference in the polarizations of the anti-up and anti-down sea quarks.

    “While our uncertainties are still significant, the RHIC data hint that the contribution from W-, or anti-up quarks, may be a bit larger than had been expected,” Sichtermann said.

    Aside from suggesting a difference in the spin contribution depending on the flavor of the antiquark, this result could offer interesting insight into the mechanism by which gluons split to form sea quarks in the first place, Sichtermann said.

    “Gluons can split into up/anti-down or down/anti-up,” he explained. “If that’s the only mechanism, and gluons don’t care about flavor, you should get equal numbers and equal polarization. So if there is a preference [for anti-up quarks to be more polarized than anti-down], there must be some other mechanism for generating these sea quarks.”

    STAR will continue to analyze data to increase precision. “With the 2013 data, we have every expectation that the uncertainties could be reduced and we may have evidence in the end,” Sichtermann said.

    Again, the measurement from STAR comes from the most central region of the collision, not a wide range of momentum fractions. “More forward measurements using similar methods to measure muons will be able to better tease out the antiquark contributions,” PHENIX’s Boyle said. Recent upgrades to enhance the detection of forward muons were in place for the 2013 run, the data has been fully reconstructed, and the PHENIX collaboration is currently finalizing the results for publication.

    “Together, these results show that RHIC lays the ground work for starting to understand the complexity of the spin of the proton—one of the fundamental quantum numbers of every single particle in the universe,” Aschenauer said. “But the ultimate answer to unravel its mystery would come from an EIC.”

    Research at RHIC is funded primarily by the DOE Office of Science (NP), and also by these agencies and organizations.

    See the full article here.

    BNL Campus

    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
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  • richardmitnick 8:21 pm on October 2, 2014 Permalink | Reply
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    From LBL: “A Closer Look at the Perfect Fluid” 

    Berkeley Logo

    Berkeley Lab

    October 2, 2014
    Kate Greene 510-486-4404

    Researchers at Berkeley Lab and their collaborators have honed a way to probe the quark-gluon plasma, the kind of matter that dominated the universe immediately after the big bang.

    gp
    A simulated collision of lead ions, courtesy the ALICE experiment at CERN. – See more at: http://newscenter.lbl.gov/2014/10/02/a-closer-look-at-the-perfect-fluid/#sthash.LuD3V5BH.dpuf

    By combining data from two high-energy accelerators, nuclear scientists have refined the measurement of a remarkable property of exotic matter known as quark-gluon plasma. The findings reveal new aspects of the ultra-hot, “perfect fluid” that give clues to the state of the young universe just microseconds after the big bang.

    The multi-institutional team known as the JET Collaboration, led by researchers at the U.S. Department of Energy’s Lawrence Berkeley National Lab (Berkeley Lab), published their results in a recent issue of Physical Review C. The JET Collaboration is one of the Topical Collaborations in nuclear theory established by the DOE Office of Science in 2010. JET, which stands for Quantitative Jet and Electromagnetic Tomography, aims to study the probes used to investigate high-energy, heavy-ion collisions. The Collaboration currently has 12 participating institutions with Berkeley Lab as the leading institute.

    “We have made, by far, the most precise extraction to date of a key property of the quark-gluon plasma, which reveals the microscopic structure of this almost perfect liquid,” says Xin-Nian Wang, physicist in the Nuclear Science Division at Berkeley Lab and managing principal investigator of the JET Collaboration. Perfect liquids, Wang explains, have the lowest viscosity-to-density ratio allowed by quantum mechanics, which means they essentially flow without friction.

    Hot Plasma Soup

    To create and study the quark-gluon plasma, nuclear scientists used particle accelerators called the Relativistic Heavy-ion Collider (RHIC) at the Brookhaven National Laboratory in New York and the Large Hadron Collider (LHC) at CERN in Switzerland. By accelerating heavy atomic nuclei to high energies and blasting them into each other, scientists are able to recreate the hot temperature conditions of the early universe.

    BNL RHIC Campus
    BNL RHIC
    BNL RHIC schematic
    RHIC at BNL

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

    Inside protons and neutrons that make up the colliding atomic nuclei are elementary particles called quarks, which are bound together tightly by other elementary particles called gluons. Only under extreme conditions, such as collisions in which temperatures exceed by a million times those at the center of the sun, do quarks and gluons pull apart to become the ultra-hot, frictionless perfect fluid known as quark-gluon plasma.

    “The temperature is so high that the boundaries between different nuclei disappear so everything becomes a hot-plasma soup of quarks and gluons,” says Wang. This ultra-hot soup is contained within a chamber in the particle accelerator, but it is short-lived—quickly cooling and expanding—making it a challenge to measure. Experimentalists have developed sophisticated tools to overcome the challenge, but translating experimental observations into precise quantitative understanding of the quark-gluon plasma has been difficult to achieve until now, he says.

    Looking Inside

    In this new work, Wang’s team refined a probe that makes use of a phenomenon researchers at Berkeley Lab first theoretically outlined 20 years ago: energy loss of a high-energy particle, called a jet, inside the quark gluon plasma.

    “When a hot quark-gluon plasma is generated, sometimes you also produce these very energetic particles with an energy a thousand times larger than that of the rest of the matter,” says Wang. This jet propagates through the plasma, scatters, and loses energy on its way out.

    Since the researchers know the energy of the jet when it is produced, and can measure its energy coming out, they can calculate its energy loss, which provides clues to the density of the plasma and the strength of its interaction with the jet. “It’s like an x-ray going through a body so you can see inside,” says Wang.

    we
    Xin Nian Wang, physicist in the Nuclear Science Division at Berkeley Lab and managing principal investigator of the JET Collaboration.

    One difficulty in using a jet as an x-ray of the quark-gluon plasma is the fact that a quark-gluon plasma is a rapidly expanding ball of fire—it doesn’t sit still. “You create this hot fireball that expands very fast as it cools down quickly to ordinary matter,” Wang says. So it’s important to develop a model to accurately describe the expansion of plasma, he says. The model must rely on a branch of theory called relativistic hydrodynamics in which the motion of fluids is described by equations from Einstein’s theory of special relativity.

    Over the past few years, researchers from the JET Collaboration have developed such a model that can describe the process of expansion and the observed phenomena of an ultra-hot perfect fluid. “This allows us to understand how a jet propagates through this dynamic fireball,” says Wang

    Employing this model for the quark-gluon plasma expansion and jet propagation, the researchers analyzed combined data from the PHENIX and STAR experiments at RHIC and the ALICE and CMS experiments at LHC since each accelerator created quark-gluon plasma at different initial temperatures. The team determined one particular property of the quark-gluon plasma, called the jet transport coefficient, which characterizes the strength of interaction between the jet and the ultra-hot matter. “The determined values of the jet transport coefficient can help to shed light on why the ultra-hot matter is the most ideal liquid the universe has ever seen,” Wang says.

    BNL Phenix
    PHENIX at BNL

    BNL Star
    STAR at BNL

    CERN ALICE New
    ALICE at CERN

    CERN CMS New
    CMS at CERN

    Peter Jacobs, head of the experimental group at Berkeley Lab that carried out the first jet and flow measurements with the STAR Collaboration at RHIC, says the new result is “very valuable as a window into the precise nature of the quark gluon plasma. The approach taken by the JET Collaboration to achieve it, by combining efforts of several groups of theorists and experimentalists, shows how to make other precise measurements of properties of the quark gluon plasma in the future.”

    The team’s next steps are to analyze future data at lower RHIC energies and higher LHC energies to see how these temperatures might affect the plasma’s behavior, especially near the phase transition between ordinary matter and the exotic matter of the quark-gluon plasma.

    This work was supported by the DOE Office of Science, Office of Nuclear Physics and used the facilities of the National Energy Research Scientific Computing Center (NERSC) located at Berkeley Lab.

    See the full article here.

    A U.S. Department of Energy National Laboratory Operated by the University of California

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  • richardmitnick 7:09 pm on August 26, 2014 Permalink | Reply
    Tags: , , Brookhaven RHIC, , ,   

    From Live Science 

    ls

    August 22, 2014
    Tia Ghose

    Hints of a mysterious particle that has been long suspected to exist but has never been spotted are being revealed in a new experiment.

    So far, the elusive particles, called extra-heavy strange baryons, haven’t been seen directly, but they are leaving tantalizing hints of their existence.

    These extra-heavy strange baryons may be freezing out other subatomic particles in a plasma soup of subatomic particles that mimics conditions in the universe a few moments after the Big Bang, nearly 14 billion years ago.

    Primordial soup

    The particles were created during an experiment conducted inside the Relativistic Heavy Ion Collider (RHIC), an atom smasher at Brookhaven National Laboratory in Upton, New York. There, scientists created a soupy concoction of unbound quarks — the subatomic particles that make up protons and neutrons — and gluons, the tiny particles that bind quarks together and carry the strong nuclear force. Physicists think this quark-gluon plasma is similar to the primordial soup that emerged milliseconds after the universe was born.

    Using the RHIC, physicists are trying to understand how quarks and gluons initially came together to form protons, neutrons and other particles that are categorized as hadrons.

    Brookhaven RHIC
    RHIC at Brookhaven

    “Baryons, which are hadrons made of three quarks, make up almost all the matter we see in the universe today,” study co-author and Brookhaven theoretical physicist Swagato Mukherjee, said in a statement.

    Elusive matter

    But while ordinary baryons are ubiquitous throughout the universe, the Standard Model — the physics theory that explains the bizarre world of subatomic particles — predicts the existence of a separate class of baryons made up of heavy or ”strange” quarks. These heavy baryons would exist only fleetingly, making them hard to spot.

    sm
    The Standard Model of elementary particles, with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.

    If extra-heavy baryons did exist, they should leave some trace behind, scientists say.

    Enter the RHIC experiment, which accelerates gold nuclei, or the protons and neutrons in a gold atom, to nearly the speed of light, and then crashes these gold ions into one another. The resulting collisions can raise the temperature inside the collider to a mind-boggling 7.2 trillion degrees Fahrenheit (4 trillion degrees Celsius), or 250,000 times as hot as the heart of the sun. The huge burst of energy released during the collision melts the protons and neutrons in the nuclei into their smaller components, quarks and gluons.

    In this soupy plasma of quarks and gluons, Mukherjee and his colleagues noticed that other, more common, strange baryons were freezing out of the plasma at a lower temperature than would ordinarily be predicted. (There are several types of strange baryons.) The scientists hypothesized that this freezing-out occurred because the plasma contained as-yet-undiscovered hidden particles, such as hadrons composed of extra-heavy strange baryons.

    “It’s similar to the way table salt lowers the freezing point of liquid water,” Mukherjee said in the statement. “These ‘invisible’ hadrons are like salt molecules floating around in the hot gas of hadrons, making other particles freeze out at a lower temperature than they would if the ‘salt’ wasn’t there.”

    By combining their measurements with a mathematical model of quarks and gluons interacting in a 3D lattice, the team was able to show that extra-heavy strange baryons were the most plausible explanation for the RHIC’s experimental results.

    Now, the team is hoping to create a map of how different types of matter, such as quark-gluon plasma, change phases at different temperatures. Just as the chemical symbol H20 represents water in the form of a liquid, ice or steam depending on the temperature and pressure, the subatomic particles in an atom’s nucleus take different forms at different temperatures. So, the team is hoping the new results could help them to create a map of how nuclear matter behaves at different temperatures.

    The findings were reported Aug. 11 in the journal Physical Review Letters.

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  • richardmitnick 4:33 pm on August 25, 2014 Permalink | Reply
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    From Livermore Lab: “Calculating conditions at the birth of the universe” 


    Lawrence Livermore National Laboratory

    08/25/2014
    Anne M Stark, LLNL, (925) 422-9799, stark8@llnl.gov

    Using a calculation originally proposed seven years ago to be performed on a petaflop computer, Lawrence Livermore researchers computed conditions that simulate the birth of the universe.

    When the universe was less than one microsecond old and more than one trillion degrees, it transformed from a plasma of quarks and gluons into bound states of quarks – also known as protons and neutrons, the fundamental building blocks of ordinary matter that make up most of the visible universe.

    The theory of quantum chromodynamics (QCD) governs the interactions of the strong nuclear force and predicts it should happen when such conditions occur.

    In a paper appearing in the Aug. 18 edition of Physical Review Letters, Lawrence Livermore scientists Chris Schroeder, Ron Soltz and Pavlos Vranas calculated the properties of the QCD phase transition using LLNL’s Vulcan, a five-petaflop machine. This work was done within the LLNL-led HotQCD Collaboration, involving Los Alamos National Laboratory, Institute for Nuclear Theory, Columbia University, Central China Normal University, Brookhaven National Laboratory and Universität Bielefed in Germany.

    vulcan
    A five Petaflop IBM Blue Gene/Q supercomputer named Vulcan

    This is the first time that this calculation has been performed in a way that preserves a certain fundamental symmetry of the QCD, in which the right and left-handed quarks (scientists call this chirality) can be interchanged without altering the equations. These important symmetries are easy to describe, but they are computationally very challenging to implement.

    “But with the invention of petaflop computing, we were able to calculate the properties with a theory proposed years ago when petaflop-scale computers weren’t even around yet,” Soltz said.

    The research has implications for our understanding of the evolution of the universe during the first microsecond after the Big Bang, when the universe expanded and cooled to a temperature below 10 trillion degrees.

    Below this temperature, quarks and gluons are confined, existing only in hadronic bound states such as the familiar proton and neutron. Above this temperature, these bound states cease to exist and quarks and gluons instead form plasma, which is strongly coupled near the transition and coupled more and more weakly as the temperature increases.

    “The result provides an important validation of our understanding of the strong interaction at high temperatures, and aids us in our interpretation of data collected at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory and the Large Hadron Collider at CERN.” Soltz said.

    Brookhaven RHIC
    RHIC at Brookhaven

    CERN LHC Grand Tunnel
    LHC at CERN

    Soltz and Pavlos Vranas, along with former colleague Thomas Luu, wrote an essay predicting that if there were powerful enough computers, the QCD phase transition could be calculated. The essay was published in Computing in Science & Engineering in 2007, “back when a petaflop really did seem like a lot of computing,” Soltz said. “With the invention of petaflop computers, the calculation took us several months to complete, but the 2007 estimate turned out to be pretty close.”

    The extremely computationally intensive calculation was made possible through a Grand Challenge allocation of time on the Vulcan Blue Gene/Q Supercomputer at Lawrence Livermore National Laboratory.

    See the full article here.

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  • richardmitnick 10:31 am on August 19, 2014 Permalink | Reply
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    From Brookhaven Lab: “First Indirect Evidence of So-Far Undetected Strange Baryons” 

    Brookhaven Lab

    August 19, 2014
    Karen McNulty Walsh, (631) 344-8350 or Peter Genzer, (631) 344-3174

    “Invisible” particles containing at least one strange quark lower the temperature at which other particles “freeze out” from quark-gluon plasma

    New supercomputing calculations provide the first evidence that particles predicted by the theory of quark-gluon interactions but never before observed are being produced in heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC), a facility that is dedicated to studying nuclear physics. These heavy strange baryons, containing at least one strange quark, still cannot be observed directly, but instead make their presence known by lowering the temperature at which other strange baryons “freeze out” from the quark-gluon plasma (QGP) discovered and created at RHIC, a U.S. Department of Energy (DOE) Office of Science user facility located at DOE’s Brookhaven National Laboratory.

    Brookhaven RHIC
    RHIC at Brookhaven

    RHIC is one of just two places in the world where scientists can create and study a primordial soup of unbound quarks and gluons—akin to what existed in the early universe some 14 billion years ago. The research is helping to unravel how these building blocks of matter became bound into hadrons, particles composed of two or three quarks held together by gluons, the carriers of nature’s strongest force.

    man
    “These ‘invisible’ hadrons are like salt molecules floating around in the hot gas of hadrons, making other particles freeze out at a lower temperature than they would if the ‘salt’ wasn’t there.”
    — Brookhaven theoretical physicist Swagato Mukherjee

    “Baryons, which are hadrons made of three quarks, make up almost all the matter we see in the universe today,” said Brookhaven theoretical physicist Swagato Mukherjee, a co-author on a paper describing the new results in Physical Review Letters. “The theory that tells us how this matter forms—including the protons and neutrons that make up the nuclei of atoms—also predicts the existence of many different baryons, including some that are very heavy and short-lived, containing one or more heavy ‘strange’ quarks. Now we have indirect evidence from our calculations and comparisons with experimental data at RHIC that these predicted higher mass states of strange baryons do exist,” he said.

    Added Berndt Mueller, Associate Laboratory Director for Nuclear and Particle Physics at Brookhaven, “This finding is particularly remarkable because strange quarks were one of the early signatures of the formation of the primordial quark-gluon plasma. Now we’re using this QGP signature as a tool to discover previously unknown baryons that emerge from the QGP and could not be produced otherwise.”

    Freezing point depression and supercomputing calculations

    The evidence comes from an effect on the thermodynamic properties of the matter nuclear physicists can detect coming out of collisions at RHIC. Specifically, the scientists observe certain more-common strange baryons (omega baryons, cascade baryons, lambda baryons) “freezing out” of RHIC’s quark-gluon plasma at a lower temperature than would be expected if the predicted extra-heavy strange baryons didn’t exist.

    “It’s similar to the way table salt lowers the freezing point of liquid water,” said Mukherjee. “These ‘invisible’ hadrons are like salt molecules floating around in the hot gas of hadrons, making other particles freeze out at a lower temperature than they would if the ‘salt’ wasn’t there.”

    To see the evidence, the scientists performed calculations using lattice QCD, a technique that uses points on an imaginary four-dimensional lattice (three spatial dimensions plus time) to represent the positions of quarks and gluons, and complex mathematical equations to calculate interactions among them, as described by the theory of quantum chromodynamics (QCD).

    “The calculations tell you where you have bound or unbound quarks, depending on the temperature,” Mukherjee said.

    The scientists were specifically looking for fluctuations of conserved baryon number and strangeness and exploring how the calculations fit with the observed RHIC measurements at a wide range of energies.

    The calculations show that inclusion of the predicted but “experimentally uncharted” strange baryons fit better with the data, providing the first evidence that these so-far unobserved particles exist and exert their effect on the freeze-out temperature of the observable particles.

    These findings are helping physicists quantitatively plot the points on the phase diagram that maps out the different phases of nuclear matter, including hadrons and quark-gluon plasma, and the transitions between them under various conditions of temperature and density.

    “To accurately plot points on the phase diagram, you have to know what the contents are on the bound-state, hadron side of the transition line—even if you haven’t seen them,” Mukherjee said. “We’ve found that the higher mass states of strange baryons affect the production of ground states that we can observe. And the line where we see the ordinary matter moves to a lower temperature because of the multitude of higher states that we can’t see.”

    The research was carried out by the Brookhaven Lab’s Lattice Gauge Theory group, led by Frithjof Karsch, in collaboration with scientists from Bielefeld University, Germany, and Central China Normal University. The supercomputing calculations were performed using GPU-clusters at DOE’s Thomas Jefferson National Accelerator Facility (Jefferson Lab), Bielefeld University, Paderborn University, and Indiana University with funding from the Scientific Discovery through Advanced Computing (SciDAC) program of the DOE Office of Science (Nuclear Physics and Advanced Scientific Computing Research), the Federal Ministry of Education and Research of Germany, the German Research Foundation, the European Commission Directorate-General for Research & Innovation and the GSI BILAER grant. The experimental program at RHIC is funded primarily by the DOE Office of Science.

    See the full article here.

    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
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  • richardmitnick 10:51 am on August 8, 2014 Permalink | Reply
    Tags: , Brookhaven RHIC, , ,   

    From Brookhaven Lab: “A New Look for RHIC & Sharper View of QCD: Looking Back at the 2014 RHIC-AGS Users’ Meeting” 

    Brookhaven Lab

    August 8, 2014
    Joe Gettler

    Scientists use the Relativistic Heavy Ion Collider (RHIC) at Brookhaven Lab to re-create the conditions microseconds after the Big Bang, before the “strong” force confined quarks and gluons into the protons and neutrons that make up what’s seen in the universe today, nearly 14 billion years later. RHIC and the theory of those strong interactions between quarks and gluons, called quantum chromodynamics (QCD), were the main topics of discussion among nearly 200 scientists from the RHIC and Alternating Gradient Synchrotron (AGS) user communities who trekked to the Lab in late June—some from institutions as far as Europe and Asia—for four days of workshops and sessions during the 2014 users’ meeting, titled “A New Look for RHIC: Sharpening the View of QCD.”

    Brookhaven RHIC
    RHIC

    Brookhaven Phenix
    PHENIX at RHIC

    Brookhaven Star
    STAR at RHIC

    “This meeting is happening at a very opportune time,” said Deputy Associate Laboratory Director for Nuclear and Particle Physics David Lissauer, as he welcomed attendees to the first plenary session. “The RHIC experiments added new capabilities to the detectors in the past year, the RHIC luminosity is breaking records and with more gold-gold collisions in this run than the combined total of all previous runs, the experiments have performed remarkably well collecting these record amounts of data, and plans for eRHIC are progressing well.”

    people
    A sampling of the nearly 200 people who attended the 2014 RHIC-AGS Users’ Meeting

    Highlights From RHIC Run 14

    Christoph Montag and Guillaume Robert-Demolaize, both of the Lab’s Collider-Accelerator Department, spoke next, giving overviews of Run 14, which began in February and continued until early July. Run 14 included three weeks of gold-gold collisions at 15 billion electron volts (GeV), 14 weeks of gold-gold collisions at 200 GeV, and two weeks colliding gold with the isotope helium-3 at 100 (GeV).

    “Nuclear science is going to continue to be an important part of the U.S. science investment strategy for new knowledge, new technology, and supporting U.S. security and competiveness.”
    — Timothy Hallman, U.S. Department of Energy Office of Science Associate Director for Nuclear Physics

    Robert-Demolaize noted that C-AD delivered record-breaking bunch intensities and luminosity—collision rates—to both the PHENIX and STAR experiments during the 200 GeV gold-gold portion of Run 14. Luminosity exceeded the initial design goals for Run 14 by nearly 50 percent, largely due to the high performance of injectors and RHIC’s stochastic cooling system, as well as two electron lenses and a 56-megahertz superconducting radio-frequency cavity that prevent the ions in each collision-bound bunch from spreading out. These upgrades continued increasing achievable luminosities and optics, and were part of a series of upgrades leading to the current “RHIC-II era.”

    During the STAR report for RUN 14, Flemming Videbaek of the Lab’s Physics Department and STAR collaboration discussed two recent detector upgrades: the heavy flavor tracker, a 460-megapixel silicon detector which scientists used to track two different quark “flavors”—charm and beauty—with microns precision, as well as a muon telescope detector, for studies of particles called Charmonium and Bottomonium mesons in gold-gold collisions. Videbaek also noted that STAR collected significant amounts of data, thanks to both the accelerator and detector’s solid performances.

    Klaus Dehmelt of Stony Brook University and RHIC’s PHENIX collaboration reported that the PHENIX detector also performed well, particularly while collecting its first dataset with the forward silicon vertex tracker, which tracks particles that originate microns away from gold-gold collisions—particles likely to have come from the decay of the particles that contain charm or beauty quarks. Ultimately, PHENIX achieved about 150 percent of its data goal for gold-gold collisions at 200 GeV.
    ‘Where Are We Now? Where Do We Need to Go?’

    bm
    Associate Lab Director for Nuclear and Particle Physics Berndt Mueller

    “RHIC is the premier facility to explore the phases of QCD matter and with the RHIC-II upgrades complete, RHIC is in its prime,” Associate Lab Director for Nuclear and Particle Physics Berndt Mueller told attendees during his presentation. “Stochastic cooling, the electron beam ion source, 56-megahertz cavity, and electron lenses have contributed to unprecedented luminosity for unprecedented statistics at RHIC.”

    Compared to the Large Hadron Collider (LHC) in Europe as well as other accelerators and colliders being developed in Europe and Russia, Mueller explained, RHIC is the only machine that can cover the entire accessible region along the QCD phase boundary. This means RHIC is the right tool for pinpointing the critical value at which quarks and gluons are freed from or bound by the strong force that confines them in protons and neutrons.

    Mueller then discussed seven questions scientists will work to address at RHIC, thanks to the unprecedented luminosity achievements. He also provided year-by-year plans leading to 2024 and a proposed electron-ion collider upgrade, called eRHIC. If built, eRHIC would probe the gluon structure of the proton, determine how particles like protons and neutrons emerge from isolated quarks, and study the high-density phase of cold gluon matter.

    “If completed, eRHIC would be the most advanced, energy-efficient accelerator in the world,” Mueller added.
    Comments From DOE, NSF
    yth
    Timothy Hallman

    After Mueller’s presentation, officials from the U.S. Department of Energy (DOE) and the National Science Foundation (NSF) discussed their organizations’ objectives, achievements, and challenges.

    DOE Office of Science Associate Director for Nuclear Physics Timothy Hallman discussed the 2015 presidential budget request for the Office of Science, noting a total request of nearly $593.6 million for nuclear physics in fiscal year (FY) 2015—a $24.4 million increase over the appropriation for FY2014—and an overall upward trend.

    “No other facility worldwide, existing or planned, can rival RHIC in range and versatility,” Hallman said. “RHIC is in its prime, it’s performing better than ever, and it’s continuing to carry out a compelling science program. When scientists decide that something needs further study that they didn’t plan on a year ago, they have the flexibility with RHIC to turn on a dime, study that property, and follow their nose as far as where the most compelling science is.”

    gd
    National Science Foundation Nuclear Experiment Program Officer Gail Dodge

    Hallman then highlighted other DOE Office of Science facilities for nuclear physics research before concluding, “Nuclear science is going to continue to be an important part of the U.S. science investment strategy for new knowledge, new technology, and supporting U.S. security and competiveness.”

    NSF Nuclear Experiment Program Officer Gail Dodge spoke next, explaining that the President’s FY15 request included an overall 1.2 percent increase for NSF funding compared with estimates for FY14, but the FY15 allotment for physics would be down one percent with a request for $263.7 million.

    “We took a big cut in FY13 and in FY14 it was up a little bit, but we expect next year to be difficult,” Dodge said before highlighting NSF’s contributions to physics research, as well as proposal and award opportunities for researchers.

    Thesis Awards

    ta
    From left, Deputy Associate Laboratory Director for Nuclear and Particle Physics David Lissauer with two thesis awardees, Ariel Nause of Tel-Aviv University and Dennis Perepelitsa of Brookhaven Lab and Columbia University, and John Harris of Yale University and the STAR collaboration, who accepted Alice Ohlsen’s honorable mention on her behalf. Each honoree received a certificate and a check for $3,000, and both gave presentations on their research.

    Nause’s thesis is titled Beating the Shot-Noise Limit: Collective Interaction Optical Noise Suppression in Charged Particle Beam, and he performed an experiment at the Lab’s Accelerator Test Facility. The selection committee recognized Nause for demonstrating, “for the first time, suppression of current noise at optical frequencies. This result has important applications for Free Electron Laser technology and may lead to the achievement of temporally coherent outputs.”

    Perepelitsa’s thesis is titled, Inclusive Jet Production in Ultrarelativistic Proton-Nucleus Collisions. The selection committee honored him for focusing “on jet measurements in deuteron-gold collisions at PHENIX as well as proton-lead collisions as part of the ATLAS experiment at the LHC. The unexpected and remarkable centrality dependence of jet production he discovered at RHIC and subsequently confirmed at the LHC has challenged our previous understandings of geometric effects on hard scattering rates, and it has pointed the community toward new directions for future study.”

    Alice Ohlsen of Yale University received honorable mention for her thesis, titled Investigating Parton Energy Loss in the Quark-Gluon Plasma with Jet Hadron Correlations and Jet Azimuthal Anisotropy at STAR.

    User Executive Committee Election Results

    Before the four-day meeting ended, Paul Sorensen of the Lab’s Physics Department and now-Outgoing Chair of the RHIC-AGS UEC announced the UEC election results. The UEC provides an organized avenue for discussion among Lab administration and those who use the Lab’s nuclear, high-energy, heavy-ion, radiobiological, and accelerator testing facilities. Joining Sorenson and chair Daniel Cebra of the University of California at Davis, Justin Frantz of Ohio University was voted chair-elect, along with new members Ágnes Mócsy of Pratt Institute, Christine Nattrass of the University of Tennessee, and Christina Swinson of Brookhaven Lab. Daniel McDonald of the University of Houston and Mustafa Mustafa of Lawrence Berkeley National Laboratory were elected student/postdoc representatives.

    Outgoing UEC members now include past chair Mei Bai of the Lab’s Collider-Accelerator Department and former members Sarah Campbell of Iowa State University; Martin Codrington of the University of Texas at Austin; Cesar Luiz da Silva of Los Alamos National Laboratory; James Rosenzweig of the University of California at Los Angeles; Murad Sarsour of Georgia State University; Anne Sickles, formerly of Brookhaven, now of the University of Illinois at Urbana-Champaign; Jim Thomas of Lawrence Berkeley National Laboratory; and Zhangbu Xu of Brookhaven’s Physics Department.

    gg
    Artist Sarah Szabo (right) with pieces from her “Glamorous Gluons” collection and mentor Ágnes Mócsy, a theoretical physicist at RHIC and professor at Pratt Institute.

    While members of the RHIC and AGS users communities discussed a sharper view of QCD, they were also treated to a different view of RHIC science during the debut of an art exhibit, called “Glamorous Gluons,” the night before the end of the annual users’ meeting. Artist Sarah Szabo, who graduated from Pratt Institute, created the exhibit to visualize RHIC science after learning about physics at Brookhaven from her astronomy professor, Ágnes Mócsy.

    See the full article here.

    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
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  • richardmitnick 8:54 am on August 7, 2014 Permalink | Reply
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    From Brookhaven Lab: “RHIC Run 14: a Flawless ‘Run of Firsts'” 

    Brookhaven Lab

    August 6, 2014
    Rebecca Harrington

    Brookhaven’s atom smasher produced more gold collisions than all previous runs combined, and collided Helium-3 and Gold for the first time

    team
    Physicists from Brookhaven’s Collider-Accelerator Department gather in RHIC’s main control room. In the front row from left are Brian Martin, Shawn Perez, Michiko Minty, Haixin Huang, Steven Tepikian, Angelika Drees, Low Energy Run Coordinator Christoph Montag, Run Coordinator Guillaume Robert-Demolaize, Lee Hammons, Keith Zeno, Nicholas Kling, and Kiel Hock. In the back row from left are Ian Blackler, William Jackson, associate chair for Accelerators of Brookhaven’s Collider-Accelerator Department Wolfram Fischer, Henry Lovelace III, Chuyu Liu, and Xiaozhe Shen.

    The familiar lighter-than-air gas filling birthday balloons has a rare isotope: a nucleus consisting of two protons and a single neutron called helium-3. But instead of using this gas for fanciful decorations, scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory made use of its interesting triangular shape in a new series of collisions in the Relativistic Heavy Ion Collider (RHIC)—an atom smasher probing the structure and properties of the building blocks of matter.

    Brookhaven RHIC
    RHIC at Brookhaven

    Over the last 14 years, scientists have used the RHIC accelerator to collide many types of nuclei, both large and small, and to create and study quark-gluon plasma (QGP), a trillion-degree substance that mimics what existed at the dawn of the universe. This year, in RHIC Run 14, scientists spent months colliding gold nuclei, initially at low energy and then at RHIC’s top energy. Everything went so well — Run 14 produced more collisions than all of the previous RHIC runs combined — that RHIC scientists seized the opportunity to capitalize on RHIC’s legendary versatility to try something they had never done before: collisions of the rare triangular He-3 nucleus with gold.

    “We already knew that RHIC is the most versatile collider in the world,” said Associate Laboratory Director for Nuclear and Particle Physics Berndt Mueller, “but the fact that it exceeded even the most optimistic expectations in the helium-3 on gold run is truly a feat for the record books. I congratulate the RHIC operations staff for this outstanding achievement.”

    New technologies for focusing beams, collecting data

    two
    Christoph Montag (left) and Guillaume Robert-Demolaize

    Click on the image to download a high-resolution version. RHIC Run 14 Coordinators Christoph Montag (left) and Guillaume Robert-Demolaize in RHIC’S main control room.

    RHIC accelerator scientists use many techniques and a wide array of devices to keep the beams circulating inside tightly controlled and focused in order to produce more effective collisions. This run, RHIC scientists were commissioning a number of new features on both the detectors’ side and on the collider-accelerator side, including a new Laser Ion Source to feed particle beams into the machine.

    “Every single thing that could be pushed to its limit was pushed to its limit,” said Run Coordinator Guillaume Robert-Demolaize. “We really maximized the contribution of everybody involved to dredge every bit of physics that we could get out of the machine.”

    The team also installed a new superconducting radiofrequency (RF) cavity, helping further reduce the ion beam size using a technique of longitudinal focusing.

    “With the new RF cavity,” Low Energy Run Coordinator Christoph Montag said, “we demonstrated that we have expertise in building, installing, commissioning, and operating superconducting cavities here at Brookhaven.”
    ‘An enormous fire hose of high quality data’

    graph
    The sharp increase this year in integrated luminosity — a measure of machine performance directly tied to the number of collisions for study — was almost 800 times higher than the integrated luminosity reached during the first full-energy RHIC run in 2001.

    These improvements, many of which were part of the RHIC II upgrade, enabled the machine to achieve an integrated luminosity — a measure of machine performance directly tied to the number of collisions for research — almost 800 times higher than the integrated luminosity reached during the first full-energy RHIC run in 2001. Back then, RHIC produced about 600 million collisions over the entire 16-week run. This year, RHIC produced that many collisions every three hours.

    Zhangbu Xu, spokesperson for the STAR detector collaboration, said this incredible improvement was because both the complicated system of accelerators feeding into RHIC can now produce such high collision rates, and because the detectors can now record data at such a high rate to observe more collisions. For example, this year the STAR detector observed the number of collisions produced in the entire 2001 run every five minutes. This also means that the cost of a single nuclear collision at RHIC has been reduced by almost a factor of 1000 over the past 13 years.

    star
    STAR at Brookhaven RHIC

    “The Collider-Accelerator Department can deliver a lot of luminosity,” Xu said, “and STAR and PHENIX have improved their capability to detect the luminosity.”

    phenox
    PHENIX at Brookhaven RHIC

    More collisions mean more RHIC science. Some particles that give RHIC scientists new ways to investigate the physics of the QGP are produced very rarely (for example, the very heavy B meson). So physicists need to collect massive amounts of data to have enough of these rare events to study. More collisions also allow scientists to analyze the highest quality data with the fewest uncertainties—the events recorded when all parts of the complex detectors were performing optimally, and where the ions collided just right.

    “The high luminosity of Run 14 succeeded in providing more collisions than even the most optimistic forecasts had anticipated,” said PHENIX detector collaboration co-spokesperson Dave Morrison.
    Smashing helium-3 into gold: a nuclear cookie cutter

    he
    A helium-3 ion stripped of its electrons. Leveraging the starting triangular shape of helium-3 when colliding it with gold is a powerful tool for investigating the physics of quantum chromodynamics (QCD), the theory that describes the interactions of subatomic quarks and gluons.

    quark
    A proton, composed of two up quarks and one down quark. (The color assignment of individual quarks is not important, only that all three colors be present.)

    gluon
    In Feynman diagrams, emitted gluons are represented as helices. This diagram depicts the annihilation of an electron and positron.

    When two gold nuclei smash into each other in a RHIC collision, the “shape” of the QGP that results depends on how the two nuclei collide. A head-on collision produces a round blob of QGP, while a glancing collision makes a more elongated shape.

    Whatever shape it starts out with, the blob cools down and vaporizes into particles in the blink of an eye. As such, different starting shapes can produce different subatomic particle emission patterns. When a spherical proton collides with a gold nucleus, for example, it smashes straight through, producing a circular pattern of subatomic particles flowing around the impact point.

    Scientists at RHIC use this connection between starting shapes and ending patterns to investigate the physics of quantum chromodynamics (QCD), the theory that describes the interactions of subatomic quarks and gluons. Being able to control the starting shape precisely is a powerful tool in this investigation.

    The best way to test our understanding of how QGP behaves, Morrison said, is to subject it to different conditions, to “poke it” to see how it responds, like you would to find out more about any material. Since helium-3 is shaped a bit like a triangular cookie cutter, he said, its collision with a gold nucleus provides a fantastic new tool for controlling the starting shape of the collision.

    Morrison said they proposed colliding helium-3 and gold after the high- and low-energy gold-gold collisions went so well that both the STAR and PHENIX detectors had collected the data they needed for this year’s experiments.

    “This was really an opportunity to flexibly address physics that is very current, and has a lot of potential to answer a lot of questions,” Morrison said. “And RHIC is versatile enough to be able to accelerate pretty much anything you can put in the beam pipe.”
    A good year to be ‘luminosity hungry’

    diag
    The STAR collaboration’s exploration of the “nuclear phase diagram” shows signs of a sharp border—a first-order phase transition—between the hadrons that make up ordinary atomic nuclei and the quark-gluon plasma (QGP) of the early universe when the QGP is produced at relatively low energies/temperatures. The data may also suggest a possible critical point, where the type of transition changes from the abrupt, first-order kind to a continuous crossover at higher energies.

    To study the QGP in a different way, physicists with the STAR detector have been working on a “beam energy scan” to determine at what collision energy matter turns into the hot primordial soup. Analysis of existing data offered tantalizing hints that a possible “critical point” of the phase transition into QGP might take place at a low energy. So for the first three weeks of Run 14, RHIC ran at 7.3 GeV per nucleon, an energy lower than the nominal injection energy of the machine.

    Xu said the team is now analyzing the 5.8 petabytes (PB) of data STAR collected from the high and low energy gold collisions this run, an amount of data that would be like watching HD TV streaming for 100 years.

    This run also marked the first appearance of the STAR Heavy Flavor Tracker (HFT), a device that can detect the decay products of particles like “charm” and “beauty” quarks, which are much heavier than the “up” and “down” quarks that make up ordinary matter. Xu said the team is excited to analyze the wealth of data that the HFT provided.

    STAR’s Muon Telescope Detector, which measures the heavier counterparts of electrons, was also new this year. It was an opportune time, Xu said, since this detector component is “luminosity hungry,” requiring a lot of collisions produced under very stable conditions—a difficult combination achieved during this run.

    “Almost any condition we ask for, the Collider-Accelerator Department can actually make it happen,” Xu said, “making the experiments we want to carry out possible.”

    Looking ahead to Run 15

    Before Run 14 ended, RHIC scientists were already preparing for next year’s run when, for the first time at RHIC, physicists will collide gold ions with protons. Since gold has a ratio of mass to electrical charge that’s very different from that of protons, the superconducting magnets that steer the ion beams inside RHIC have to be physically moved two inches in order to aim these different beams into collision. While the scientists who designed RHIC had the foresight to make the magnets movable, Montag said, they have never actually had to move them.

    Physicists will also collide polarized protons next run, which they first did in 2001, to further probe where protons get their spin.

    “What can we do to keep pushing? What can we do to deliver even more physics?” Robert-Demolaize said they must always ask themselves. “Ultimately, the success of a run depends on the team.”

    Research at RHIC is funded primarily by the DOE Office of Science, and also by these agencies and organizations. RHIC is an Office of Science User Facility.

    DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

    See the full article here.

    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
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  • richardmitnick 8:01 pm on July 22, 2014 Permalink | Reply
    Tags: , , Brookhaven RHIC, , , ,   

    From Brookhaven Lab via Scientific American: “Proton Spin Mystery Gains a New Clue” 

    Brookhaven Lab

    sa
    Jul 21, 2014
    Clara Moskowitz

    Physicists long assumed a proton’s spin came from its three constituent quarks. New measurements suggest particles called gluons make a significant contribution

    Protons have a constant spin that is an intrinsic particle property like mass or charge. Yet where this spin comes from is such a mystery it’s dubbed the “proton spin crisis.” Initially physicists thought a proton’s spin was the sum of the spins of its three constituent quarks. But a 1987 experiment showed that quarks can account for only a small portion of a proton’s spin, raising the question of where the rest arises. The quarks inside a proton are held together by gluons, so scientists suggested perhaps they contribute spin. That idea now has support from a pair of studies analyzing the results of proton collisions inside the Relativistic Heavy-Ion Collider (RHIC) at Brookhaven National Laboratory in Upton, N.Y.

    Brookhaven RHIC Campus
    RHIC Campus

    Physicists often explain spin as a particle’s rotation, but that description is more metaphorical than literal. In fact, spin is a quantum quantity that cannot be described in classical terms. Just as a proton is not really a tiny marble but rather a jumble of phantom particles appearing and disappearing continuously, its spin is a complex probabilistic property. Yet it is always equal to one half.

    Quarks also have a spin of one half. Physicists originally assumed that two of the proton’s three quarks were always spinning in opposite directions, canceling one another out, leaving the remaining one half as the proton’s total spin. “That was the naïve idea 25 years ago,” says Daniel de Florian of the University of Buenos Aires, leader of one of the new papers, which was published July 2 in Physical Review Letters. “By the end of the ‘80s it was possible to measure the contribution of the spin of the quarks to the spin of the proton, and the first measurement showed it was 0 percent. That was a very big surprise.” Later measurements actually suggested quarks can contribute up to 25 percent of the proton’s total spin, but that still leaves the lion’s share unaccounted for.

    Gluons are also present inside protons as the representatives of the strong nuclear force, a fundamental interaction that binds the quarks together. Gluons each have a spin of 1, and depending on which direction it is they could add up to make most of rest of the proton’s spin. Measuring their contribution is a tricky task. RHIC is the only experiment that can address the question, because it is the only particle accelerator built to collide “spin-polarized” protons, meaning that the particles are all spinning in a certain direction when they crash. (At the more powerful Large Hadron Collider in Switzerland, the particles’ spins are not aligned.)

    When two protons slam together, their interaction is controlled by the strong force, so gluons are intimately involved. If gluon spin is an important ingredient of proton spin, then the orientation of the colliding protons’ spins should affect the outcome. Scientists would expect collisions between two protons whose spins were aligned would happen at a different frequency than collisions between those spinning in opposite directions. And according to recent data from RHIC, there is a difference. “If there is no preferred position, the difference will be exactly zero,” says University of Oxford physicist Juan Rojo, a member of the so-called NNPDF Collaboration that wrote the second paper, which was submitted to Nuclear Physics B. “Since the asymmetry is not zero, this tells us the distribution of the spin is not trivial.” Rojo’s team calculated that gluons probably contribute about half the spin that quarks do to the proton. De Florian and his colleagues analyzed the same data from RHIC, but used a different mathematical analysis to calculate the gluon contribution. They also found that gluon spin must be significantly involved. “This data for the first time shows the gluon polarization is actually nonzero; we see the gluons are polarized,” de Florian says. “Basically they could be responsible for the rest of the proton spin, but the uncertainty is very large.”

    Both teams say their work is just the beginning of the quest to understand how gluons affect proton spin. To be certain, a larger experiment is needed. The best candidate, they say, is a proposed electron–ion collider that could be built at Brookhaven. This machine would collide polarized protons at higher energies than RHIC does and could probe the contribution of higher-energy gluons to proton spin, rather than the relatively lower-energy range the current data do.

    If gluon spin does not provide the balance of the missing proton spin, the rest might arise from the orbital angular momentum of the quarks and gluons swarming around inside the proton. Just as Earth rotates on its own axis as well as orbits the sun, quarks and gluons have their own internal spin, along with angular momentum that comes from their movement around the center of the proton. The question, says physicist Robert Jaffe of Massachusetts Institute of Technology, who was not involved in the research, is what portion of the total spin each of these elements contributes. He adds: “Measuring the gluon contribution to the proton spin is one step—an important one—to answer this question.”

    Resolving the proton spin crisis is vital not just for understanding spin, but to learn where protons and many other particles get their masses. The recently discovered Higgs boson is often said to be responsible for bestowing mass on all other particles. This is true, but is not the whole truth, Rojo says. In addition to the Higgs mechanism, another process is at work to give protons mass. This process is related to confinement—the reason quarks and gluons are always found confined within other particles, such as protons, and never alone. The dynamics of confinement also affect the spin polarization of quarks and gluons. “One of the most outstanding problems in modern theoretical physics is to understand confinement,” Rojo says. “The better we understand the polarization distribution of quarks and gluons, the closer we get to an understanding of confinement. With our data we have the underlying mechanism for confinement and ultimately for where the mass of the protons comes from.”

    See the full article here.

    One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. The Laboratory’s almost 3,000 scientists, engineers, and support staff are joined each year by more than 5,000 visiting researchers from around the world.Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.
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  • richardmitnick 9:06 am on July 16, 2014 Permalink | Reply
    Tags: , , Brookhaven RHIC, , ,   

    From isgtw: “Planning for an electron-ion collider at Brookhaven” 

    isgtw

    July 16, 2014
    Greg Moore

    In a paper detailing the scientific goals for a new high-energy electron-ion collider (EIC) at Brookhaven National Laboratory in Upton, New York, US, the authors use the phrase, “understanding the glue that binds us all.” One of the co-authors, Liang Zheng, a PhD exchange student from Central China Normal University in Wuhan, explains it like this:

    “The EIC is a project to help us understand the origin and structure of the core of the atom, the nucleus and nucleons within it, which account for essentially all the mass of the visible universe. Even though the strong nuclear force, the force that joins the nucleons together to make the atom’s nucleus, makes up 95% of the visible mass of the universe, and indeed us, it is the least understood of the forces in the standard model.”

    Quantum chromodynamics (QCD), a theory of strong interactions, has led nuclear scientists to develop new tools that reveal the interactions of quarks and gluons inside protons and neutrons. For researchers at Brookhaven, these new tools could be further enhanced by the EIC.

    By adding an electron ring and other accelerator components to the existing Relativistic Heavy Ion Collider (RHIC) at Brookhaven, the EIC could help explain what makes matter stick together. The EIC would be unique among such facilities worldwide, due to the 5- to 10-billion-electron-volt (GeV) electron ring inside the existing RHIC tunnel.

    Brookhaven RHIC
    RHIC

    Brookhaven RHIC Campus
    RHIC Campus

    Zheng’s job is to help make the physics case for the EIC. To do that, he runs large Monte Carlo simulation programs on the Open Science Grid (OSG). Since the physical EIC facility doesn’t yet exist, Zheng and colleagues need to predict what will happen in experiments and modify the collider environment accordingly. Simulations run on Sartre, an event generator developed at Brookhaven specifically to study electron-ion collisions, using random sampling techniques based on the researchers’ numerical calculations.

    eic
    A schematic of the world’s first electron-ion collider (EIC). Adding an electron ring (red) to the Relativistic Heavy Ion Collider (RHIC) at Brookhaven would create the eRHIC. Image courtesy Brookhaven National Laboratory-CAD eRHIC group.

    “We have to know what kind of signal we are going to observe in the real experiment,” Zheng says. “Before then, we have to rely on the Monte Carlo predictions. They will tell us what kind of detector we need, and we will design it based on those predictions.”

    “The difficulty in the simulations,” explains Zheng, “is that to achieve a prediction with reasonable precision, we have to provide a refined pre-calculated table for the end users of Sartre. The generation of such a pre-calculated table has to deal with an intensive numerical calculation with a sizable data configuration, which needs a powerful computing system. If we didn’t have more powerful computing resources, it would take years to get any reasonable analysis.”

    Because the OSG offers freely accessible high-performance computing resources, Zheng can run his large data simulations within an acceptable timeframe. “We can distribute our program to a wide range of computing nodes that are physically located at many different sites. With the seemingly unlimited computing power of OSG, we are able to solve all the computing challenges we confront in our simulation work.”

    Occasionally Zheng runs into issues with job scripts. “At these moments, the OSG support group is always very helpful, especially our local technical support [from] Alexandr Zaystev. And Chander Sehgal, Marko Slyz, and Tanya Levshina at Fermilab are very professional and can help me solve all sorts of problems. During this process, I have learned a lot of useful tricks.”

    “I really wish to recommend the OSG to other scientists who need to deal with large-scale data or intensive computing jobs,” Zheng adds. “It is easy to get started, and you can always get help from the people in this great community.”

    “Our research is going to open a new window for us to gaze into the universe around us and the matter inside us,” Zheng says. “It will shed light on our understanding of the fundamental building blocks of the visible universe. It will provide a cost-effective way for us to get a new source of knowledge and a platform to test some of our newest technologies. By exploring a region which is largely unknown to us in the strong force, it is research exploring the interactions that bind us all.”

    See the full article here.

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    “We report on all aspects of distributed computing technology, such as grids and clouds. We also regularly feature articles on distributed computing-enabled research in a large variety of disciplines, including physics, biology, sociology, earth sciences, archaeology, medicine, disaster management, crime, and art. (Note that we do not cover stories that are purely about commercial technology.)

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  • richardmitnick 9:32 pm on July 11, 2014 Permalink | Reply
    Tags: , , Brookhaven RHIC, ,   

    From physicsworld.com: “Gluons get in on proton spin” 

    physicsworld
    physicsworld.com

    Jul 11, 2014
    Edwin Cartlidge

    For a quarter of a century, physicists have faced a paradox regarding the net spin of protons and neutrons – the spin of their constituent quarks accounts for only a small fraction of their overall spin. Now, new research carried out by physicists in Argentina and Germany who have analysed data produced by the Relativistic Heavy Ion Collider (RHIC), suggests that the missing spin might come from gluons that hold quarks together.

    phenix
    Gluon gun: RHIC’s PHENIX detector

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

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

    Misplaced spins?

    Spin, an intrinsic angular momentum, is a property of both protons and neutrons (collectively known as nucleons). Until the 1980s, physicists had assumed that the spin-1/2 of both the neutron and the proton was simply the sum of the spin-1/2 of their three constituent quarks – with two quarks spinning in the opposite direction to the third. But a series of experiments found that the quark spins contributed only a small fraction to the nucleon spins, leading to what was known as the “spin crisis“. Those experiments involved firing spin-polarized beams of electrons or muons at targets containing spin-polarized nucleons. The idea was to compare the deflection of the particles in the beam when their spin axis was pointed in the same direction as the beam with those in the opposite direction. The results of these scattering experiments showed that no more than about 25% of nucleon spin comes from the constituent quarks, meaning that physicists could not determine where protons and neutrons get their net spin.

    One possibility lay with gluons that hold quarks together and are exchanged by quarks in strong-force interactions. As the experiments studying quark spin cannot measure the properties of gluons, which do not interact electromagnetically, researchers turned to RHIC. Situated at the Brookhaven National Laboratory near New York, it collides two beams of protons – the gluon from one proton can interact with the quark in another via the strong force.

    Brookhaven RHIC
    RHIC Tunnel

    Brookhaven RHIC Campus
    RHIC campus

    Gyrating gluons

    In the latest work, a group of theorists – Daniel de Florian, from the Aires University in Argentina, and colleagues – analysed several years’ worth of collision data from RHIC’s STAR and PHENIX experiments. De Florian and colleagues have now studied data collected up until 2009, and have compared those data with a theoretical model they have developed that predicts the likely spin direction of gluons carrying a certain fraction of the momentum involved in the proton collisions.

    Brookhaven RHIC
    Brookhaven Star

    Brookhaven Phenix
    Brookhaven Phenix

    The researchers discovered, in contrast to a null result they obtained using fewer data five years ago, that gluon spin does tend to line up with that of the protons, rather than against it. In fact, they estimate that gluons could supply as much as half of a proton’s spin. “This is the first evidence that suggests gluons could make a significant contribution to proton spin,” says team member Werner Vogelsang of Tübingen University in Germany, who adds that, on theoretical grounds, gluons ought to supply the same amount of spin to neutrons.

    Dizzy orbits

    Vogelsang cautions that he and his colleagues cannot be sure of their result because they have not yet analysed the possible spin contribution of gluons with low momenta. Doing so, he says, will require data from higher-energy collisions at RHIC, where proton energies have recently been increased from 100 to 250 GeV, and potentially from a new generation of very-high-energy electron–proton colliders. These advanced machines might also allow physicists to study another possible source of nucleon spin – the orbital, as opposed to spin, angular momentum of quarks and gluons – an analysis that requires the measurement of extremely rare collision outcomes.

    Robert Jaffe of the Massachusetts Institute of Technology in the US praises De Florian and co-workers for their “fine work”, saying that their research is an “important step” in understanding what makes up a proton’s spin. He adds that it makes it even more important for physicists to understand why the three-quark model of the proton works so well in describing properties such as the magnetic moment and yet falls so far short in the case of spin.

    The research is published in Physical Review Letters.

    See the full article here.

    PhysicsWorld is a publication of the Institute of Physics. The Institute of Physics is a leading scientific society. We are a charitable organisation with a worldwide membership of more than 50,000, working together to advance physics education, research and application.

    We engage with policymakers and the general public to develop awareness and understanding of the value of physics and, through IOP Publishing, we are world leaders in professional scientific communications.
    IOP Institute of Physics


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