Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userJet-Underlying Event Separation Method for Heavy Ion Collisions at the Relativistic Heavy Ion Collider
108
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Reconstructed jets in heavy ion collisions are a crucial tool for understanding the quark-gluon plasma. The separation of jets from the underlying event is necessary particularly in central heavy ion reactions in order to quantify medium modifications of the parton shower and the response of the surrounding medium itself. There have been many methods proposed and implemented for studying the underlying event substructure in proton-proton and heavy ion collisions. In this paper, we detail a method for understanding underlying event contributions in Au+Au collisions at $sqrt{s_{NN}}$ = 200 GeV utilizing the HIJING event generator. This method, extended from previous work by the ATLAS collaboration, provides a well-defined association of truth jets from the fragmentation of hard partons with reconstructed jets using the anti-$k_T$ algorithm. Results presented here are based on an analysis of 750M minimum bias HIJING events. We find that there is a substantial range of jet energies and radius parameters where jets are well separated from the background fluctuations (often termed fake jets) that make jet measurements at RHIC a compelling physics program.
rate research
Read More
These proceedings present a brief overview of the main results on jet-modifications in heavy ion collisions at RHIC. In heavy ion collisions, jets are studied using single hadron spectra and di-hadron correlations with a high-pt{} trigger hadrons. At high pt, a suppression of the yields due to parton energy loss is observed. A quantitative confrontation of the data with various theoretical approaches to energy loss in a dense QCD medium is being pursued. First results from $gamma$-jet events, where the photon balances the initial jet energy, are also presented and compared to expectations from models based on di-hadron measurements. At intermediate pt, two striking modifications of the di-hadron correlation structure are found in heavy ion collisions: the presence of a long-range {it ridge} structure in deta{}, and a large broadening of the recoil jet. Both phenomena seem to indicate an interplay between hard and soft physics.
Isobaric $^{96}_{44}$Ru+$^{96}_{44}$Ru and $^{96}_{40}$Zr+$^{96}_{40}$Zr collisions at $sqrt{s_{_{NN}}}=200$ GeV have been conducted at the Relativistic Heavy Ion Collider to circumvent the large flow-induced background in searching for the chiral magnetic effect (CME), predicted by the topological feature of quantum chromodynamics (QCD). Considering that the background in isobar collisions is approximately twice that in Au+Au collisions (due to the smaller multiplicity) and the CME signal is approximately half (due to the weaker magnetic field), we caution that the CME may not be detectable with the collected isobar data statistics, within $sim$2$sigma$ significance, if the axial charge per entropy density ($n_5/s$) and the QCD vacuum transition probability are system independent. This expectation is generally verified by the Anomalous-Viscous Fluid Dynamics (AVFD) model. While our estimate provides an approximate experimental baseline, theoretical uncertainties on the CME remain large.
A precise measurement of the hypertriton lifetime is presented. In this letter, the mesonic decay modes $mathrm{{^3_Lambda}H rightarrow ^3He + pi^-}$ and $mathrm{{^3_Lambda}H rightarrow d + p + pi^-}$ are used to reconstruct the hypertriton from Au+Au collision data collected by the STAR collaboration at RHIC. A minimum $chi^2$ estimation is used to determine the lifetime of $tau = 142^{+24}_{-21},{rm (stat.)} {pm} 31,{rm (syst.)}$ ps. This lifetime is about 50% shorter than the lifetime $tau = 263pm2$ ps of a free $Lambda$, indicating strong hyperon-nucleon interaction in the hypernucleus system. The branching ratios of the mesonic decay channels are also determined to satisfy B.R.$_{(^3{rm He}+pi^-)}/$(B.R.$_{(^3{rm He}+pi^-)}+$B.R.$_{(d+p+pi^-)})$ = $0.32rm{pm}0.05,{rm (stat.)}pm 0.08,{rm (syst.)}$. Our ratio result favors the assignment $J(mathrm{^{3}_{Lambda}H})$ = $frac{1}{2}$ over $J(mathrm{^{3}_{Lambda}H})$ = $frac{3}{2}$. These measurements will help to constrain models of hyperon-baryon interactions.
We study charm production in ultra-relativistic heavy-ion collisions by using the Parton-Hadron-String Dynamics (PHSD) transport approach. The initial charm quarks are produced by the PYTHIA event generator tuned to fit the transverse momentum spectrum and rapidity distribution of charm quarks from Fixed-Order Next-to-Leading Logarithm (FONLL) calculations. The produced charm quarks scatter in the quark-gluon plasma (QGP) with the off-shell partons whose masses and widths are given by the Dynamical Quasi-Particle Model (DQPM), which reproduces the lattice QCD equation-of-state in thermal equilibrium. The relevant cross sections are calculated in a consistent way by employing the effective propagators and couplings from the DQPM. Close to the critical energy density of the phase transition, the charm quarks are hadronized into $D$ mesons through coalescence and/or fragmentation. The hadronized $D$ mesons then interact with the various hadrons in the hadronic phase with cross sections calculated in an effective lagrangian approach with heavy-quark spin symmetry. The nuclear modification factor $R_{AA}$ and the elliptic flow $v_2$ of $D^0$ mesons from PHSD are compared with the experimental data from the STAR Collaboration for Au+Au collisions at $sqrt{s_{NN}}$ =200 GeV and to the ALICE data for Pb+Pb collisions at $sqrt{s_{NN}}$ =2.76 TeV. We find that in the PHSD the energy loss of $D$ mesons at high $p_T$ can be dominantly attributed to partonic scattering while the actual shape of $R_{AA}$ versus $p_T$ reflects the heavy-quark hadronization scenario, i.e. coalescence versus fragmentation. Also the hadronic rescattering is important for the $R_{AA}$ at low $p_T$ and enhances the $D$-meson elliptic flow $v_2$.
This document was prepared by the community that is active in Italy, within INFN (Istituto Nazionale di Fisica Nucleare), in the field of ultra-relativistic heavy-ion collisions. The experimental study of the phase diagram of strongly-interacting matter and of the Quark-Gluon Plasma (QGP) deconfined state will proceed, in the next 10-15 years, along two directions: the high-energy regime at RHIC and at the LHC, and the low-energy regime at FAIR, NICA, SPS and RHIC. The Italian community is strongly involved in the present and future programme of the ALICE experiment, the upgrade of which will open, in the 2020s, a new phase of high-precision characterisation of the QGP properties at the LHC. As a complement of this main activity, there is a growing interest in a possible future experiment at the SPS, which would target the search for the onset of deconfinement using dimuon measurements. On a longer timescale, the community looks with interest at the ongoing studies and discussions on a possible fixed-target programme using the LHC ion beams and on the Future Circular Collider.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
