# Quark Matter 2018

13-19 May 2018
Venice, Italy
Europe/Zurich timezone
The organisers warmly thank all participants for such a lively QM2018! See you in China in 2019!

## Impact of magnetic field fluctuations on the CME in small systems

15 May 2018, 17:00
2h 40m
First floor and third floor (Palazzo del Casinò)

### First floor and third floor

#### Palazzo del Casinò

Poster Chirality, vorticity and polarisation effects

### Speaker

Xinli Zhao (Shanghai Institute of Applied Physics, Chinese Academy of Scien)

### 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 ($\gamma=$) 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  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 Presenter name already specified

### Primary author

Xinli Zhao (Shanghai Institute of Applied Physics, Chinese Academy of Scien)

### Co-authors

Prof. Yu-Gang Ma (Shanghai INstitute of Applied Physics (SINAP), CAS) Guo-Liang Ma (Shanghai INstitute of Applied Physics (SINAP), CAS)