اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدImpact of magnetic-field fluctuations on measurements of the chiral magnetic effect in collisions of isobaric nuclei
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We investigate the properties of electromagnetic fields in isobaric $_{44}^{96}textrm{Ru}+,_{44}^{96}textrm{Ru}$ and $_{40}^{96}textrm{Zr}+,_{40}^{96}textrm{Zr}$ collisions at $sqrt{s}$ = 200 GeV by using a multiphase transport model, with special emphasis on the correlation between magnetic field direction and participant plane angle $Psi_{2}$ (or spectator plane angle $Psi_{2}^{rm SP}$), i.e. $langle{rm cos} 2(Psi_B - Psi_{2})rangle$ [or $langle{rm cos} 2(Psi_B - Psi_{2}^{rm SP})rangle$]. We confirm that the magnetic fields of $_{44}^{96}textrm{Ru}+,_{44}^{96}textrm{Ru}$ collisions are stronger than those of $_{40}^{96}textrm{Zr}+,_{40}^{96}textrm{Zr}$ collisions due to their larger proton fraction. We find that the deformation of nuclei has a non-negligible effect on $langle{rm cos} 2(Psi_B - Psi_{2})rangle$ especially in peripheral events. Because the magnetic-field direction is more strongly correlated with $Psi_{2}^{rm SP}$ than with $Psi_{2}$, the relative difference of the chiral magnetic effect observable with respect to $Psi_{2}^{rm SP}$ is expected to be able to reflect much cleaner information about the chiral magnetic effect with less influences of deformation.
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The isobaric collision experiment at RHIC provides the unique opportunity to detect the possible signal of Chiral Magnetic Effect (CME) in heavy ion collisions. The idea is to contrast the correlation observables of the two colliding systems that sup
posedly have identical flow-driven background contributions while quite different CME signal contributions due to the 10% variation in their nuclear charge and thus magnetic field strength. With the recently developed quantitative simulation tool for computing CME signal, the Anomalous-Viscous Fluid Dynamics (AVFD), we demonstrate that a joint (multiplicity + elliptic-flow) event selection is crucial for this purpose. We further propose to use the absolute difference between RuRu and ZrZr events (after using identical event selection) for detecting CME signal and make predictions for the correlation observables.
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 collision
s 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.
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 al
ong 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 $20-60%$.
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 ma
gnetic 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.
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rated by the colliding nuclei. We then analyze recent measurements of the global polarization of $Lambda$ and $bar Lambda$ hyperons in terms of the bounds they set on the magnitude of the late time magnetic field.
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