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  • richardmitnick 5:37 pm on January 8, 2018 Permalink | Reply
    Tags: , , , PHENIX, , RHIC,   

    From BNL: “Surprising Result Shocks Scientists Studying Spin” 

    Brookhaven Lab

    January 8, 2018
    Karen McNulty Walsh
    kmcnulty@bnl.gov
    (631) 344-8350

    Peter Genzer,
    genzer@bnl.gov
    (631) 344-3174

    Findings on how differently sized nuclei respond to spin offer new insight into mechanisms affecting particle production in proton-ion collisions at the Relativistic Heavy Ion Collider (RHIC).

    BNL RHIC Campus


    1
    The PHENIX detector at the Relativistic Heavy Ion Collider (RHIC).


    Alexander Bazilevsky discusses surprising particle spin results from the Relativistic Heavy Ion Collider at Brookhaven National Laboratory.

    Imagine playing a game of billiards, putting a bit of counter-clockwise spin on the cue ball and watching it deflect to the right as it strikes its target ball. With luck, or skill, the target ball sinks into the corner pocket while the rightward-deflected cue ball narrowly misses a side-pocket scratch. Now imagine your counter-clockwise spinning cue ball striking a bowling ball instead, and deflecting even more strongly—but to the left—when it strikes the larger mass.

    That’s similar to the shocking situation scientists found themselves in when analyzing results of spinning protons striking different sized atomic nuclei at the Relativistic Heavy Ion Collider (RHIC)—a U.S. Department of Energy (DOE) Office of Science User Facility for nuclear physics research at DOE’s Brookhaven National Laboratory. Neutrons produced when a spinning proton collides with another proton come out with a slight rightward-skew preference. But when the spinning proton collides with a much larger gold nucleus, the neutrons’ directional preference becomes larger and switches to the left.

    2
    Brookhaven Lab physicist Alexander Bazilevsky and RIKEN physicist Itaru Nakagawa use billiards and a bowling ball to demonstrate surprising results observed at the Relativistic Heavy Ion Collider’s PHENIX detector when small particles collided with larger ones.

    “What we observed was totally amazing,” said Brookhaven physicist Alexander Bazilevsky, a deputy spokesperson for the PHENIX collaboration at RHIC, which is reporting these results in a new paper just published in Physical Review Letters. “Our findings may mean that the mechanisms producing particles along the direction in which the spinning proton is traveling may be very different in proton-proton collisions compared with proton-nucleus collisions.”

    Understanding different particle production mechanisms could have big implications for interpreting other high-energy particle collisions, including the interactions of ultra-high-energy cosmic rays with particles in the Earth’s atmosphere, Bazilevsky said.

    Detecting particles’ directional preferences

    Spin physicists first observed the tendency of more neutrons to emerge slightly to the right in proton-proton interactions in 2001-2002, during RHIC’s first polarized proton experiments. RHIC, which has been operating since 2000, is the only collider in the world with the ability to precisely control the polarization, or spin direction, of colliding protons, so this was new territory at the time. It took some time for theoretical physicists to explain the result. But the theory they developed, published in 2011, gave scientists no reason to expect such a strong directional preference when protons were colliding with larger nuclei, let alone a complete flip in the direction of that preference.

    3
    Neutrons produced when a spin-aligned (polarized) proton collides with another proton come out with a slight rightward-skew preference. But when the polarized proton collides with a much larger gold nucleus, the neutrons’ directional preference becomes larger and switches to the left. These surprising results imply that the mechanisms producing particles along the beam direction may be very different in these two types of collisions.

    “We anticipated something similar to the proton-proton effect, because we couldn’t think of any reasons why the asymmetry could be different,” said Itaru Nakagawa, a physicist from Japan’s RIKEN laboratory, who served as PHENIX’s deputy run coordinator for spin measurements in 2015. “Can you imagine why a bowling ball would scatter a cue ball in the opposite direction compared with a target billiard ball?”

    2015 was the year RHIC first collided polarized protons with gold nuclei at high energy, the first such collisions anywhere in the world. Minjung Kim—a graduate student at Seoul National University and the RIKEN-BNL Research Center at Brookhaven Lab—first noticed the surprisingly dramatic skew of the neutrons—and the fact that the directional preference was opposite to that seen in proton-proton collisions. Bazilevsky worked with her on data analysis and detector simulations to confirm the effect and make sure it was not an artifact from the detector or something to do with the adjustment of the beams. Then, Nakagawa worked closely with the accelerator physicists on a series of experiments to repeat the measurements under even more precisely controlled conditions.

    “This was truly a collaborative effort between experimentalists and accelerator physicists who could tune such a huge and complicated accelerator facility on the fly to meet our experimental needs,” Bazilevsky said, expressing gratitude for those efforts and admiration for the versatility and flexibility of RHIC.

    The new measurements, which also included results from collisions of protons with intermediate-sized aluminum ions, showed the effect was real and that it changed with the size of the nucleus.

    “So we have three sets of data—colliding polarized protons with protons, aluminum, and gold,” Bazilevsky said. “The asymmetry gradually increases from negative in proton-proton—with more neutrons scattering to the right—to nearly zero asymmetry in proton-aluminum, to a large positive asymmetry in proton-gold collisions—with many more scatterings to the left.”

    Particle production mechanisms

    To understand the findings, the scientists had to look more closely at the processes and forces affecting the scattering particles.

    “In the particle world, things are much more complicated than the simple case of (spinning) billiard balls colliding,” Bazilevsky said. “There are a number of different processes involved in particle scattering, and these processes themselves can interact or interfere with one another.”

    “The measured asymmetry is the sum of these interactions or interferences of different processes,” said Kim.

    Nakagawa, who led the theoretical interpretation of the experimental data, elaborated on the different mechanisms.

    The basic idea is that, in the case of large nuclei such as gold, which have a very large positive electric charge, electromagnetic interactions play a much more important role in particle production than they do in the case when two small, equally charged protons collide.

    “In the collisions of protons with protons, the effect of electric charge is negligibly small,” Nakagawa said. In that case, the asymmetry is driven by interactions governed by the strong nuclear force—as the theory developed back in 2011 correctly described. But as the size, and therefore charge, of the nucleus increases, the electromagnetic force takes on a larger role and, at a certain point, flips the directional preference for neutron production.

    The scientists will continue to analyze the 2015 data in different ways to see how the effect depends on other variables, such as the momentum of the particles in various directions. They’ll also look at how preferences of particles other than neutrons are affected, and work with theorists to better understand their results.

    Another idea would be to execute a new series of experiments colliding polarized protons with other kinds of nuclei not yet measured.

    “If we observe exactly the asymmetry we predict based on the electromagnetic interaction, then this becomes very strong evidence to support our hypothesis,” Nakagawa said.

    In addition to providing a unique way to understand different particle production mechanisms, this new result adds to the puzzling story of what causes the transverse spin asymmetry in the first place—an open question for physicists since the 1970s. These and other results from RHIC’s polarized proton collisions will eventually contribute to solving this question.

    This work was supported by the DOE Office of Science, and by all the agencies and organizations supporting research at PHENIX.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition
    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 9:33 am on June 17, 2016 Permalink | Reply
    Tags: , , Particle colliders, RHIC,   

    From BNL: “Calorimeter Components Put to the Test” 

    Brookhaven Lab

    June 15, 2016
    Karen McNulty Walsh
    kmcnulty@bnl.gov

    Brookhaven scientists, students, and university partners help build and test key components for a possible future RHIC detector upgrade

    1
    Brookhaven Lab physicist Martin Purschke with sPHENIX calorimeter components at the Fermilab Test Beam Facility (Photo credit: Fermilab)

    Tracking particles created in subatomic smashups takes precision. So before the components that make up detectors at colliders like the Relativistic Heavy Ion Collider (RHIC) get the chance to see a single collision, physicists want to be sure they are up to the task.

    BNL RHIC CampusBNL RHIC
    BNL/RHIC map; RHIC collider

    A group of physicists and students hoping to one day build a new detector at RHIC—a DOE Office of Science User Facility for nuclear physics research at the U.S. Department of Energy’s Brookhaven National Laboratory—recently spent time at DOE’s Fermi National Accelerator Laboratory putting key particle-tracking components to the test.

    “We want to do full jet reconstruction,” said physicist Megan Connors, a member of the new sPHENIX collaboration building and testing components for a proposed upgrade to RHIC’s PHENIX detector designed to transform it into a new state-of-the-art experiment.

    BNL/RHIC PhenixBrookhaven Phenix
    BNL/RHIC Phenix

    Connors spent time tracking “jets” as a graduate student and postdoc at RHIC and the Large Hadron Collider. Now a RIKEN-BNL Research Center Fellow who will begin teaching at Georgia State University next year, Connors says a new high-energy jet detector would offer the best opportunity to see deep into the hot particle soup created in RHIC’s most energetic smashups. By adding up the energy of the sprays of particles emitted when high-energy quarks and gluons traverse the quark-gluon plasma, physicists hope to understand how its remarkable properties emerge from the individual quark and gluon interactions.

    The device that measures the energy of these jet particle sprays is called a calorimeter. To do a good job, it must completely surround the collision zone and be thick enough to catch all the particles.

    Anne Sickles, a physicist at the University of Illinois at Urbana-Champaign, has been working with her students and a company in San Diego to build electron- and light-sensing bricks for the inner layer, the “electromagnetic” calorimeter.

    They start with a tungsten powder that looks like black sand, placing fibers that look like straws into the powder. “Then we draw epoxy through it all to end up with bricks that have scintillating fibers running through them,” she explained.

    “When a photon—a particle of light—hits these bricks, it starts to interact with the tungsten, and those interactions produce more photons and more interactions, like a chain reaction. Ultimately you get a shower with lots of light that travels down the length of the scintillating fibers to a silicon photomultiplier—a photo detector that changes the light to electric signals we read out. We use all this information to measure how much energy was in the initial photon.”

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    Megan Connors, a RIKEN-BNL Research Center Fellow and member of sPHENIX, holds an electronic readout from the hadronic calorimeter the team is designing for the detector upgrade.

    Getting that measurement right is crucial, Sickles explained, because when a photon is emitted from a particle collision back-to-back with a jet, it tells you how much energy the jet started with. The next step is determining how much energy the jet loses in its interactions with the quark-gluon plasma by measuring and adding up the energy of all the jet particles moving in the opposite direction.

    Photons and electrons would deposit all of their energy in the electromagnetic calorimeter. Heavier particles made of quarks, known as hadrons, deposit some energy in the electromagnetic calorimeter. But in many cases, they continue to fly right through. To stop them and measure their full energy, you need a hadronic calorimeter—the detector component Connors has been working on.

    “The hadronic calorimeter is made of two independent parts—the inner and outer hadronic calorimeters—which will be located just inside and outside the sPHENIX magnet,” Connors said. “They consist of alternating layers of steel plates and angled scintillator tiles.

    “When particles hit the steel they lose energy and produce secondary particles, which ‘excite’ the tiles and make them emit light. A light-sensing fiber running through each tile collects the light so it can be read out by a silicon photomultiplier, just as is done for the electromagnetic calorimeter,” she explained.

    4
    sPHENIX member Anne Sickles, left, with some of her students at the University of Illinois at Urbana-Champaign who helped to build components for a prototype electromagnetic detector: postdoctoral fellow Vera Loggins, graduate student Mike Phipps, and undergraduates Simon Li and Michael Higdon (Photo credit: University of Illinois)

    The Test Beam Facility at Fermilab [FNAL] is the perfect place to put these components through their paces.

    FNAL Test Beam Facility
    FNAL Test Beam Facility

    Sickles was heavily involved in the first round of tests. She and her team built a prototype of the full electromagnetic calorimeter using 32 bricks, each made of two one-by-one-inch tungsten towers. Working with Brookhaven physicists who had connected these components to the electronic readouts, they placed an 8” by 8” grid of bricks into the path of a beam of electrons.

    Photons and electrons will both interact with the calorimeter in the same way and sPHENIX will use its capabilities to measure both kinds of particles. By tracking electrons, the sPHENIX electromagnetic calorimeter would also help physicists trace the interactions of “upsilon” particles with the quark-gluon plasma.

    “We use electron beams at various energies,” Sickles explained. “Since we know what energy goes in and we measure what comes out, and the width of the distribution in energies, we can determine how good the resolution of the detector is. We are looking for a narrow peak—a tight correlation between what we put in and what we measure.”

    5
    A closeup of the scintillating fibers traversing one of the tungsten bricks designed to track electrons and photons in the sPHENIX electromagnetic calorimeter. (Photo credit: Anne Sickles)

    They also took measurements to compare the response of bricks built by Sickles and postdoc Vera Loggins and several students at the University of Illinois with those built by Tungsten Heavy Powder, the company in San Diego. “The plan for the actual sPHENIX detector is to have 25,000 tungsten towers,” Sickles said, “so we have to be sure they all have the same level of performance.”

    Similar to the way the electromagnetic calorimeter was tested using an electron beam, the energy-resolution capabilities of the hadronic calorimeter were tested using a hadron beam of known energy. First the scientists did standalone tests to measure the hadronic calorimeters’ performance alone. Following those studies, members of the sPHENIX team placed the prototype hadronic calorimeter components directly behind the electromagnetic mockup to study how the two detector layers would ultimately work together.

    “The tests of the hadronic calorimeter with the electromagnetic calorimeter in front of it measure the performance we would expect to see in sPHENIX,” Connors said. “We also placed metal in between the inner and outer hadronic calorimeters to simulate the material of the magnet.

    6
    Additional members of the team involved in testing sPHENIX calorimeter components at the Test Beam Facility at Fermilab: Brookhaven Lab physicists Jin Huang and Martin Purschke; Ron Belmont, University of Colorado, Boulder; and Brookhaven physicists John Haggerty and Craig Woody. (Photo credit: Fermilab)

    “It’s really coming to life,” said Connors, who has been analyzing the data from the prototype testing. “It’s great to be able to access the data from these tests remotely so people all over the world can be involved if they want.

    “We will take what we learn about how well the detector will perform based on the testing at Fermilab, and then use that knowledge to finalize the design,” she said.

    The electromagnetic and hadronic calorimeter prototypes were assembled at Brookhaven Lab by technicians Carter Biggs, Sal Polizzo, Mike Lenz, and Frank Toldo under the direction of Brookhaven physicists John Haggerty, Jin Huang, Edward Kistenev, Eric Mannel, and Craig Woody, and physics associate Sean Stoll. The prototypes, designed and engineered by Richie Ruggiero, incorporated electronics designed by Steve Boose and data acquisition software provided by Martin Purschke. John Lajoie and Abhisek Sen of Iowa State University and Ron Belmont from the University of Colorado worked closely with the Brookhaven team on the hadronic calorimeter construction and analysis. Mandy Rominsky and Todd Nebel of the Fermilab Test Beam Facility were also instrumental in the success of the tests.

    sPHENIX R&D is supported by the DOE Office of Science and also by Brookhaven Lab’s Laboratory Directed Research and Development program, BNL Program Development, and in-kind contributions from collaborating universities.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition
    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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