Background study of the CME-related correlations in heavy-ion collisions within a multiphase transport mode

4 Nov 2019, 17:40
Wanda Han Show Theatre & Wanda Reign Wuhan Hotel

Wanda Han Show Theatre & Wanda Reign Wuhan Hotel

Poster Presentation Chirality, vorticity and spin polarization Poster Session


Dr Subikash Choudhury (Fudan University)Dr Wanbing He (Fudan University)


The Chiral Magnetic Effect (CME) manifests itself via a separation of electric charge along the direction of the magnetic field, produced by spectator protons in heavy-ion collisions. The experimental searches for the CME, based on the charge-dependent angular correlations [1] have, however, remained inconclusive till date, because the observed features of charge separation in data are also compatible with non-CME background sources. Recently, the CMS collaboration attempted to disambiguate the origin of charge separation by measuring charge-dependent angular correlations or $\gamma$-correlators with respect to second-order ($\Psi_{2}$) and third-order ($\Psi_{3}$) symmetry planes defined as $\gamma_{112}$ and $\gamma_{123}$ respectively, in p+Pb and Pb+Pb collisions [2]. The idea is that an equality is expected in $\frac{\Delta\gamma_{112}}{\Delta\delta \times v_{2}}$ ($\kappa_{112}$) and $\frac{\Delta\gamma_{123}}{\Delta\delta \times v_{3}}$ ($\kappa_{123}$), if the charge separations are dominated by non-CME backgrounds \cite{CMS_3p}. The CMS measurements indeed reveal such equality across light-ion and heavy-ion collision systems, suggesting the observed charge separation in data arises from non-CME background contributions to a large extent. However, the signals and backgrounds in data are so entangled that such an interpretation may be naive. Instead, non-CME background models could provide a testing ground to verify or falsify such relations. In this poster, we will present results of different harmonics of $\gamma$-correlators calculated from a charge-conserved version of a multiphase transport (AMPT) model. In contrary to the CMS expectation, the AMPT model calculations show $(\kappa_{132} \approx 1) < (\kappa_{112} \approx 1.3) < (\kappa_{123} \approx 2)$.

[1] “Parity violation in hot QCD: how to detect it”, S. Voloshin, Phys. Rev. C70, 057901 (2004).
[2]“Constraints on the chiral magnetic effect using charge-dependent azimuthal correlations in pPb and PbPb collisions at the LHC, The CMS Collaboration”, Phys. Rev. C 97, 044912 (2018).

Primary authors

Dr Subikash Choudhury (Fudan University) Dr Wanbing He (Fudan University) Prof. Huan Zhong Huang (Fudan University/ UCLA) Dr Gang Wang (UCLA)

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