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Register a new userInvestigating the quark flavor dependence of the chiral magnetic effect with a multiphase transport model
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Because the properties of the QCD phase transition and the chiral magnetic effect (CME) depend on the number of quark flavors ($N_{f}$) and quark mass, relativistic heavy-ion collisions provide a natural environment to investigate the flavor features if quark deconfinement occurs. We introduce an initial two-flavor or three-flavor dipole charge separation into a multiphase transport (AMPT) model to investigate the flavor dependence of the CME. By taking advantage of the recent ALICE data of charge azimuthal correlations with identified hadrons, we attempt to disentangle two-flavor and three-flavor CME scenarios in Pb+Pb collisions at 2.76 TeV. We find that the experimental data show a certain potential to distinguish the two scenarios, therefore we further suggest to collect more data to clarify the possible flavor dependence in future experiments.
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Because the traditional observable of charge-dependent azimuthal correlator $gamma$ contains both contributions from the chiral magnetic effect (CME) and its background, a new observable of $R_{Psi_{m}}$ has been recently proposed which is expected to be able to distinguish the CME from the background. In this study, we apply two methods to calculate $R_{Psi_{m}}$ using a multiphase transport model without or with introducing a percentage of CME-induced charge separation. We demonstrate that the shape of final $R_{Psi_{2}}$ distribution is flat for the case without the CME, but concave for that with an amount of the CME, because the initial CME signal survives from strong final state interactions. By comparing the responses of $R_{Psi_{2}}$ and $gamma$ to the strength of the initial CME, we observe that two observables show different nonlinear sensitivities to the CME. We find that the shape of $R_{Psi_{2}}$ has an advantage in measuring a small amount of the CME, although it requires large event statistics.
The chiral magnetic effect (CME) induces an electric charge separation in a chiral medium along the magnetic field that is mostly produced by spectator protons in heavy-ion collisions. The experimental searches for the CME, based on the charge-dependent angular correlations ($gamma$), however, have remained inconclusive, because the non-CME background contributions are not well understood. Experimentally, the $gamma$ correlators have been measured with respect to the second-order ($Psi_{2}$) and the third-order ($Psi_{3}$) symmetry planes, defined as $gamma_{112}$ and $gamma_{123}$, respectively. The expectation was that with a proper normalization, $gamma_{123}$ would provide a data-driven estimate for the background contributions in $gamma_{112}$. In this work, we calculate different harmonics of the $gamma$ correlators using a charge-conserving version of a multiphase transport (AMPT) model to examine the validity of the said assumption. We find that the pure-background AMPT simulations do not yield an equality in the normalized $gamma_{112}$ and $gamma_{123}$, quantified by $kappa_{112}$ and $kappa_{123}$, respectively. Furthermore, we test another correlator, $gamma_{132}$, within AMPT, and discuss the relation between different $gamma$ correlators.
The quark-gluon matter produced in relativistic heavy-ion collisions may contain local domains in which P and CP symmetries are not preserved. When coupled with an external magnetic field, such P- and CP-odd domains will generate electric currents along the magnetic field --- a phenomenon called the chiral magnetic effect (CME). Recently, the STAR Collaboration at RHIC and the ALICE Collaboration at the LHC released data of charge-dependent azimuthal-angle correlators with features consistent with the CME expectation. However, the experimental observable is contaminated with significant background contributions from elliptic-flow-driven effects, which makes the interpretation of the data ambiguous. In this Letter, we show that the collisions of isobaric nuclei, $^{96}_{44}$Ru + $^{96}_{44}$Ru and $^{96}_{40}$Zr + $^{96}_{40}$Zr, provide an ideal tool to disentangle the CME signal from the background effects. Our simulation demonstrates that the two collision types at $sqrt{s_{rm NN}}=200$ GeV have more than $10%$ difference in the CME signal and less than $2%$ difference in the elliptic-flow-driven backgrounds for the centrality range of $20-60%$.
A quark interaction with topologically nontrivial gluonic fields, instantons and sphalerons, violates P~ and CP~ symmetry. In the strong magnetic field of a noncentral nuclear collision such interactions lead to the charge separation along the magnetic field, the so-called chiral magnetic effect (CME). Recent results from the STAR collaboration on charge dependent correlations are consistent with theoretical expectations for CME but may have contributions from other effects, which prevents definitive interpretation of the data. Here I propose to use central body-body $U+U$ collisions to disentangle correlations due to CME from possible background correlations due to elliptic flow. Further more quantitative studies can be performed with collision of isobaric beams.
Using the string melting version of a multiphase transport (AMPT) model, we focus on the evolution of thermodynamic properties of the central cell of parton matter produced in Au+Au collisions ranging from 200 GeV down to 2.7 GeV. The temperature and baryon chemical potential are calculated for Au+Au collisions at different energies to locate their evolution trajectories in the QCD phase diagram. The evolution of pressure anisotropy indicates that only partial thermalization can be achieved, especially at lower energies. Through event-by-event temperature fluctuations, we present the specific heat of the partonic matter as a function of temperature and baryon chemical potential that is related to the partonic matters approach to equilibrium.
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