Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userImportance of isobar density distributions on the chiral magnetic effect search
122
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Under the approximate chiral symmetry restoration, quark interactions with topological gluon fields in quantum chromodynamics can induce chirality imbalance and parity violation in local domains. An electric charge separation ({sc cs}) could be generated along the direction of a strong magnetic field ({bf B}), a phenomenon called the chiral magnetic effect ({sc cme}). {sc cs} measurements by azimuthal correlators are contaminated by a major background from elliptic flow anisotropy ($v_2$). Isobaric $^{96}_{44}$Ru+$^{96}_{44}$Ru and $^{96}_{40}$Zr+$^{96}_{40}$Zr collisions have been proposed to identify the {sc cme} (expected to differ between the two systems) out of the background (expected to be almost the same). We show, by using the density-functional calculated proton and neutron distributions, that these expectations may not hold as originally anticipated, because the two systems may have sizable differences in eccentricity and $v_2$ and because their difference in {bf B} may suffer from large uncertainties.
rate research
Read More
We study chiral magnetic effect in collisions of AuAu, RuRu and ZrZr at s = 200GeV. The axial charge evolution is modeled with stochastic hydrodynamics and geometrical quantities are calculated with Monte Carlo Glauber model. By adjusting the relaxation time of magnetic field, we find our results in good agreement with background subtracted data for AuAu collisions at the same energy. We also make prediction for RuRu and ZrZr collisions. We find a weak centrality dependence of initial chiral imbalance, which implies the centrality dependence of chiral magnetic effect signal comes mainly from those of magnetic field and volume factor. Our results also show an unexpected dependence on system size: while the system of AuAu has larger chiral imbalance and magnetic field, it turns out to have smaller signal for chiral magnetic effect due to the larger volume suppression factor.
An observable sensitive to the chiral magnetic wave (CMW) is the charge asymmetry dependence of the $pi^{-}$ and $pi^{+}$ anisotropic flow difference, $Delta v_{n}(A_{rm ch})$. We show that, due to non-flow correlations, the flow measurements by the Q-cumulant method using all charged particles as reference introduce a trivial linear term to $Delta v_{n}(A_{rm ch})$. The trivial slope contribution to the triangle flow difference $Delta v_{3}(A_{rm ch})$ can be negative if the non-flow is dominated by back-to-back pairs. This can explain the observed negative $Delta v_{3}(A_{rm ch})$ slope in the preliminary STAR data. We further find that the non-flow correlations give rise to additional backgrounds to the slope of $Delta v_{2}(A_{rm ch})$ from the competition among different pion sources and from the larger multiplicity dilution to $pi^{+}$ ($pi^{-}$) at positive (negative) $A_{rm ch}$.
$textbf{Background:}$ The chiral magnetic effect (CME) is extensively studied in heavy-ion collisions at RHIC and LHC. In the commonly used reaction plane (RP) dependent, charge dependent azimuthal correlator ($Deltagamma$), both the close and back-to-back pairs are included. Many backgrounds contribute to the close pairs (e.g. resonance decays, jet correlations), whereas the back-to-back pairs are relatively free of those backgrounds. $textbf{Purpose:}$ In order to reduce those backgrounds, we propose a new observable which only focuses on the back-to-back pairs, namely, the relative back-to-back opposite-sign (OS) over same-sign (SS) pair excess ($r_{text{BB}}$) as a function of the pair azimuthal orientation with respect to the RP ($varphi_{text{BB}}$). $textbf{Methods:}$ We use analytical calculations and toy model simulations to demonstrate the sensitivity of $r_{text{BB}}(varphi_{text{BB}})$ to the CME and its insensitivity to backgrounds. $textbf{Results:}$ With finite CME, the $varphi_{text{BB}}$ distribution of $r_{text{BB}}$ shows a clear characteristic modulation. Its sensitivity to background is significantly reduced compared to the previous $Deltagamma$ observable. The simulation results are consistent with our analytical calculations. $textbf{Conclusions:}$ Our studies demonstrate that the $r_{text{BB}}(varphi_{text{BB}})$ observable is sensitive to the CME signal and rather insensitive to the resonance backgrounds.
We give a numerical simulation of the generation of the magnetic field and the charge-separation signal due to the chiral magnetic effect (CME) --- the induction of an electric current by the magnetic field in a parity-odd matter --- in the collisions of isobaric nuclei, $^{96}_{44}$Ru + $^{96}_{44}$Ru and $^{96}_{40}$Zr + $^{96}_{40}$Zr, at $sqrt{s_{rm NN}}=200$ GeV. We show that such collisions provide an ideal tool to disentangle the CME signal from the possible elliptic-flow driven background effects. We also discuss some other effects that can be tested by using the isobaric collisions.
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. ...
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
