Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userInvestigation of Experimental Observables in Search of the Chiral Magnetic Effect in Heavy-ion Collisions in the STAR experiment
185
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The chiral magnetic effect (CME) is a novel transport phenomenon, arising from the interplay between quantum anomalies and strong magnetic fields in chiral systems. In high-energy nuclear collisions, the CME may survive the expansion of the quark-gluon plasma fireball and be detected in experiments. Over the past decade, the experimental searches for the CME have aroused extensive interest at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC). The main goal of this article is to investigate three pertinent experimental approaches: the $gamma$ correlator, the $R$ correlator and the signed balance functions. We will exploit both simple Monte Carlo simulations and a realistic event generator (EBE-AVFD) to verify the equivalence in the kernel-component observables among these methods and to ascertain their sensitivities to the CME signal for the isobaric collisions at RHIC.
rate research
Read More
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.
The Chiral Magnetic Effect (CME) is a remarkable phenomenon that stems from highly nontrivial interplay of QCD chiral symmetry, axial anomaly, and gluonic topology. It is of fundamental importance to search for the CME in experiments. The heavy ion collisions provide a unique environment where a hot chiral-symmetric quark-gluon plasma is created, gluonic topological fluctuations generate chirality imbalance, and very strong magnetic fields $|vec{bf B}|sim m_pi^2$ are present during the early stage of such collisions. Significant efforts have been made to look for CME signals in heavy ion collision experiments. In this contribution we give a brief overview on the status of such efforts.
Background: The chiral magnetic effect (CME) is extensively studied in heavy-ion collisions at RHIC and the LHC. An azimuthal correlator called $R_{Psi_{m}}$ was proposed to measure the CME. By observing the same $R_{Psi_{2}}$ and $R_{Psi_{3}}$ (convex) distributions from A Multi-Phase Transport (AMPT) model, by contrasting data and model as well as large and small systems and by event shape engineering (ESE), a recent preprint (arXiv:2006.04251v1) from STAR suggests that the $R_{Psi_{m}}$ observable is sensitive to the CME signal and relatively insensitive to backgrounds, and their Au+Au data are inconsistent with known background contributions. Purpose: We examine those claims by studying the robustness of the $R_{Psi_{m}}$ observable using AMPT as well as toy model simulations. We compare $R_{Psi_{m}}$ to the more widely used $Deltagamma$ azimuthal correlator to identify their commonalities and differences. Methods: We use AMPT to simulate Au+Au, p+Au, and d+Au collisions at $sqrt{s_{NN}} = 200 text{ GeV}$, and study the responses of $R_{Psi_{m}}$ to anisotropic flow backgrounds in the model. We also use a toy model to simulate resonance flow background and input CME signal to investigate their effects in $R_{Psi_{2}}$. Additionally we use the toy model to perform an ESE analysis to compare to STAR data as well as predict the degree of sensitivity of $R_{Psi_{2}}$ to isobar collisions with the event statistics taken at RHIC. ...
We present measurements of $pi^-$ and $pi^+$ elliptic flow, $v_2$, at midrapidity in Au+Au collisions at $sqrt{s_{_{rm NN}}} =$ 200, 62.4, 39, 27, 19.6, 11.5 and 7.7 GeV, as a function of event-by-event charge asymmetry, $A_{ch}$, based on data from the STAR experiment at RHIC. We find that $pi^-$ ($pi^+$) elliptic flow linearly increases (decreases) with charge asymmetry for most centrality bins at $sqrt{s_{_{rm NN}}} = text{27 GeV}$ and higher. At $sqrt{s_{_{rm NN}}} = text{200 GeV}$, the slope of the difference of $v_2$ between $pi^-$ and $pi^+$ as a function of $A_{ch}$ exhibits a centrality dependence, which is qualitatively similar to calculations that incorporate a chiral magnetic wave effect. Similar centrality dependence is also observed at lower energies.
Correlation measurements with respect to the spectator and participant planes in relativistic heavy ion collisions were proposed to extract the chiral magnetic effect (CME) from background dominated azimuthal correlators. This paper investigates the effects of two- and three-particle nonflow correlations on the extracted CME signal fraction, $f_{text{CME}}$. It is found, guided by a multiphase transport (AMPT) model and the heavy ion jet interaction generator (HIJING) together with experimental data, that the nonflow effects amount to approximately $(4pm5)$% and $(-5pm3)$% without and with pseudorapidity gaps, respectively, in 20-50% centrality Au+Au collisions at $sqrt{s_{text{NN}}}= 200 text{ GeV}$.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
