Speaker
Description
Many great efforts have been made to investigate the Chiral Magnetic Effect (CME), which replies on the existence of extremely large electromagnetic fields in relativistic heavy-ion collisions. However, the recent CMS measurements in small systems challenge the traditional CME interpretation, indicating that the dominant contribution to the CME observable of charge azimuthal correlation ($\gamma=<cos(\phi_{\alpha}+\phi_{\beta} - 2\Psi_{RP})>$) may not be related to the CME in p+Pb and Pb+Pb collisions.
In this work, we investigate the properties of the electromagnetic fields in small systems by using a multiphase transport (AMPT) model [1]. We find that compared to A+A collisions, the magnitudes of absolute electric and magnetic fields in small systems are comparable. We show that the correlation of $<cos2(\Psi_B - \Psi_{2})>$ between the magnetic field direction and the particant plane angle is strongly suppressed in high-multiplicity events, but strongly correlated in parallel in low-multiplicity events. It indicates that the traditional CME observable $\gamma$ is not valid to study the CME in high-multiplicity events. However, the strong correlation in low-multiplicity events can reduce or even change sign of the traditional CME observable, which is qualitatively consistent with the recent event-shape engineering measurement from the CMS [2]. Therefore, we suggest searching for a possible CME signal in small systems with low multiplicities.
[1] X. L. Zhao, Y. G. Ma and G. L. Ma, [arXiv:1709.05962 [hep-ph]].
[2] A. M. Sirunyan et al. [CMS Collaboration], [arXiv:1708.01602 [nucl-ex]].
| Content type | Theory |
|---|---|
| Centralised submission by Collaboration | Presenter name already specified |
