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!

Response studies of the CME-sensitive sine observable to heavy ion backgrounds

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 Poster Session

Speaker

Yicheng Feng (Purdue University)

Description

A new sine observable, $R(\Delta s)$, has been proposed [1] to measure the Chiral Magnetic Effect (CME) in heavy ion collisions, where $\Delta s$ is the $\langle\sin\phi\rangle$ difference between positive and negative charges ($\phi$ is the particle azimuth) and $R(\Delta s)$ is the ratio of the out-of-plane to in-plane $\Delta s$ distributions. Studies with A Multi-Phase Transport (AMPT) and Anomalous Viscous Fluid Dynamics (AVFD) models show concave R($\Delta s$) distributions for CME signals and convex ones for typical resonance backgrounds [1]. A recent hydrodynamic study, however, indicates concave shapes for backgrounds as well [2]. Preliminary STAR data, on the other hand, reveal concave $R(\Delta s)$ distributions in 200 GeV Au+Au collisions.

To better understand these results, we present a systematic study of the $v_{2}$ and $p_{T}$ dependences of resonance backgrounds by toy-model simulations, based on the toy model used in our previous study [3]. The resonance $v_{2}$ introduces different numbers of decay $\pi^+\pi^-$ pairs in the in-plane and out-of-plane directions. The resonance $p_{T}$ affects the opening angle of the decay $\pi^+\pi^-$ pair. Low $p_{T}$ resonances decay into large opening-angle pairs, and result in more ``back-to-back'' pairs out-of-plane because of the more in-plane resonances, mimicking a CME charge separation signal perpendicular to the reaction plane, or a concave $R(\Delta s)$. High $p_{T}$ resonances, on the other hand, decay into small opening-angle pairs, and result in a background behavior of convex $R(\Delta s)$. With this toy-model insight, we further investigate the responses of the $R(\Delta s)$ observable to AMPT backgrounds and AVFD CME signals,and the possible implications of the preliminary STAR data.

[1] N. Magdy, S. Shi, J. Liao, N. Ajitanand and R. A. Lacey, arXiv:1710.01717

[2] P. Bozek, arXiv:1711.02563

[3] F. Wang, J. Zhao, Phys. Rev. C95, 051901 (R) (2017)

Centralised submission by Collaboration Presenter name already specified
Content type Theory

Primary authors

Yicheng Feng (Purdue University) Jie Zhao (Purdue University) Fuqiang Wang (Purdue University)

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