Bulletin of the American Physical Society
85th Annual Meeting of the APS Southeastern Section
Volume 63, Number 19
Thursday–Saturday, November 8–10, 2018; Holiday Inn at World’s Fair Park, Knoxville, Tennessee
Session K01: Nuclear Physics III |
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Chair: Grant Riley, University of Tennessee, Knoxville Room: Holiday Inn Knoxville Downtown Summit |
Saturday, November 10, 2018 11:00AM - 11:12AM |
K01.00001: Recent Jet Results in ALICE Patrick J Steffanic In ultrarelativistic heavy ion collisions quarks and gluons undergo deconfinement forming a hot dense phase of nuclear matter, the Quark Gluon Plasma (QGP). At CERN, in the LHC, a detailed study of the QGP is performed by the ALICE, ATLAS, CMS, and LHCb experiments. At an early time in the collision, high-momentum constituents of the nuclei--partons--scatter off of each other. These initial partons traverse the dense QGP medium and lose energy before exiting and fragmenting into a shower of particles, called a jet. The measurement of in-medium parton energy loss and parton shower modification, collectively referred to as quenching, gives us insight into the structure and interactions that govern the QGP and, ultimately, Quantum Chromodynamics. This talk will report some recent jet results from the ALICE experiment. Measurements from Pb--Pb collisions, where the dense medium is formed, compared to those in p--p collisions, where no medium is formed, indicate that energy loss occurs. |
Saturday, November 10, 2018 11:12AM - 11:24AM |
K01.00002: New Heavy Ion Collision Monte Carlo Analysis Functionality in RIVET-HI James C Neuhaus, Redmer Bertens, Mariah McCreary, Christine E Nattrass, Ricardo Santos, Austin Schmier, Jerrica Wilson At the Large Hadron Collider (LHC) in Europe and the Relativistic Heavy Ion Collider (RHIC) in New York, ultrarelativistic heavy nuclei collisions are studied to investigate the properties of the hot, dense state of nuclear matter known as Quark-Gluon Plasma (QGP). The JETSCAPE collaboration incorporates, in a single software package, multiple physical model Monte Carlos which attempt to describe the properties of QGP and applies these models within the limit of each model’s applicability. To better tune each model and their respective boundaries, comparisons of JETSCAPE output against published data is needed. Beginning with the Heavy Ion branch of the RIVET Monte Carlo validation software, tools for calculating observables needed for numerous Heavy Ion / QGP analyses were encoded which enable the addition of more complex analyses to RIVET-HI and their future incorporation into the software. We discuss the additions made to RIVET-HI for these comparisons and their applicability in Heavy Ion MC validation and tuning. |
Saturday, November 10, 2018 11:24AM - 11:36AM |
K01.00003: Jet v_{2} in Heavy Ion Collisions Measured at ALICE William E Witt Under the extreme conditions present in high energy heavy ion collisions, nuclear matter undergoes a phase transition into quark gluon plasma (QGP), a hot, dense, and short-lived phase of matter composed of freely interacting quarks and gluons. Hard scatterings of partons from the colliding nuclei result in collimated sprays of particles called jets. Jets form early in the collision and lose energy as they pass through the medium, making them excellent probes of the QGP’s properties. Jet v_{2} is an observable that quantifies the azimuthal angular asymmetry of jet yields. Measurements of jet v_{2} are sensitive to the path length dependence of in-medium parton energy loss. We will present jet v_{2} results from 2.76 TeV Pb-Pb collisions obtained by ALICE at the LHC. |
Saturday, November 10, 2018 11:36AM - 11:48AM |
K01.00004: Comparison of Experimental and Theoretical Calculations of Azimuthal Anisotropy in Heavy Ion Collisions Mariah McCreary, Redmer Bertens, Christine E Nattrass, James C Neuhaus, Ricardo Santos, Austin Schmier, Jerrica Wilson Beams of heavy ions are accelerated near the speed of light and collide into each other to produce a hot, dense matter called the Quark Gluon Plasma (QGP). The particles produced in these ultra-relativistic heavy ion collisions are measured in detectors such as ALICE (A Large Ion Collider Experiment), ATLAS (A Toroidal LHC ApparatuS), and CMS (The Compact Muon Solenoid) at the Large Hadron Collider (LHC) in Geneva, Switzerland. Detectors are used to capture details about the evolution of this medium for further study since the QGP only exists for a fraction of a second. The properties of the medium can be determined by studying jets, the collimated sprays of high energy particles created by partons which have traversed through the QGP. The azimuthal dependence of jet production provides information on the path length dependence of partonic energy loss. Experimental analyses will be implemented in the RIVET framework to make systematic comparisons between data and Monte Carlo models developed by the JETSCAPE collaboration. We will present the implementation of the jet anisotropy measurements in RIVET. |
Saturday, November 10, 2018 11:48AM - 12:00PM |
K01.00005: Comparing measurements of jets to JETSCAPE predictions Austin Schmier, Redmer Bertens, Mariah McCreary, Christine E Nattrass, James C Neuhaus, Ricardo Santos, Jerrica Wilson At the Large Hadron Collider and the Relativistic Heavy Ion Collider, heavy ions are collided at ultrarelativistic speeds to create what is known as a quark-gluon plasma. At sufficiently high temperatures and energy densities, quarks and gluons become asymptotically free, and are no longer confined inside of individual nucleons. Monte Carlo simulations are used to better understand how the QGP interacts and cools. These can be compared to detector data to see how well a given predictive theory matches experiment. The JETSCAPE collaboration allows for the combination of multiple models in one software package in an attempt to create a single monte carlo that accurately predicts the event. Each JETSCAPE Monte Carlo can be analyzed in the RIVET analysis framework, which allows testing by different methods provided in its library. One example is a CMS measurement of inclusive jet cross sections in proton-proton and lead-lead collisions at center of mass energy of 2.76 TeV. This implementation of the CMS jet spectrum measurement in RIVET was tested on the PYTHIA Angantyr Monte Carlo generator. We will discuss the technical details, outstanding challenges, and future directions for this work. |
Saturday, November 10, 2018 12:00PM - 12:12PM |
K01.00006: Soft and Collective Particle Generator for a Better Understanding of Heavy Ion Background in Jet Studies Charles P Hughes, Alex L Aukerman, Redmer Bertens, Thomas Krobatsch, Adam Matyja, Christine E Nattrass, James C Neuhaus, William E Witt At the Large Hadron Collider (LHC) in Europe and the Relativistic Heavy Ion Collider in New York, nuclei are made to collide at near the speed of light. These collisions generate a new phase of nuclear matter: a Quark Gluon Plasma (QGP). The QGP differs from ordinary nuclear matter because its elementary constituents are strongly interacting quarks and gluons as opposed to hadrons. Quarks and gluons in the colliding nuclei often scatter off of each other with high momentum transfer. These scatterings produce collimated streams of hadrons called jets. Jets are modified as they pass through the QGP and these modifications can be studied to determine the properties of the medium. The main difficulty in jet measurements in heavy-ion collisions is dealing with large, uncorrelated background of hadrons. This background is the result of the expansion and cooling of the short lived QGP into a multitude of hadrons. We generate a data-driven background for jets based on measurements of soft charged hadron transverse momentum spectra and charged hadron azimuthal flow at the LHC to better understand the effects of this background. We discuss how this heavy ion background generator can be used to understand the modification of jets by the background in heavy ion collisions. |
Saturday, November 10, 2018 12:12PM - 12:24PM |
K01.00007: JETSCAPE Research for Comparison of Experimental to Monte Carlo Jet Data Jerrica Wilson, Redmer Bertens, Mariah McCreary, Christine E Nattrass, James C Neuhaus, Ricardo Santos, Austin Schmier Shortly, after the Big Bang, the universe was in a state of Quark Gluon Plasma (QGP). This QGP can be recreated in the lab via high energy collisions. The Relativistic Heavy Ion Collider at Brookhaven National Lab and the Large Hadron Collider at CERN are able to accelerate particles to nearly the speed of light, making it possible for nuclei to transition to a Quark Gluon Plasma. Sometimes, when QGP is formed, a parton at high momentum will travel through the QGP, losing energy to the medium and eventually fragment into collimated sprays of particles called a jet. The JETSCAPE collaboration attempts to interpret jet measurements into properties of the Quark Gluon Plasma. One such jet measurement is the nuclear modification factor, which measures the suppression of a final state hadrons formed from high energy partons. The nuclear modification factor can provide information about physical phenomena, like jet quenching, that go on inside the QGP. We will discuss jet spectra measurements and their implementation in the RIVET framework for comparison to JETSCAPE Monte Carlo models. |
Saturday, November 10, 2018 12:24PM - 12:36PM |
K01.00008: Relativistic Heavy Ion Physics: Transverse Energy Benjamin Smith By colliding heavy nuclei at relativistic velocities, the resulting increase in temperature and density of the collision volume can cause a phase transition of the nuclear matter to what is called a quark-gluon plasma. Several experiments to observe the behavior of this phase occur at the Relativistic Heavy Ion Collider (RHIC) in New York. As an effect of the collision, many particles are ejected transversely to the beam axis. The energy these particles carry is referred to as transverse energy. Measurements of the transverse energy can be used to estimate the density of the nuclear matter in the collision zone. I will describe calculating the transverse energy obtained from previously calculated data from the STAR detector employing a novel method using identified charged particle spectra. The results will be compared to measurements by the PHENIX experiment, which is also a detector at RHIC, using a different method for extracting the transverse energy to better understand any systematic bias between them. |
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