5-11 February 2017
Hyatt Regency Chicago
America/Chicago timezone

Separate measurements of physics background and the possible chiral magnetic effect in p+Au and d+Au collisions at RHIC

Not scheduled
2h 30m
Hyatt Regency Chicago

Hyatt Regency Chicago

151 East Wacker Drive Chicago, Illinois, USA, 60601
Board: A12


Dr Jie Zhao (Purdue University)


Metastable domains of fluctuating topological charges can change the chirality of quarks and induce local parity violation
in quantum chromodynamics. This can lead to observable charge separation along the strong magnetic field produced in relativistic heavy-ion collisions, a phenomenon called the chiral magnetic effect (CME). The magnetic field is generated by spectator protons and therefore best measured by the 1st-order harmonic plane ($\Psi_{1}$) using the spectator neutrons. The 2nd-order harmonic plane ($\Psi_{2}$), on the other hand, estimates the initial participant geometry, connected to the elliptic flow anisotropy ($v_{2}$).

A major background source for CME measurements is the intrinsic particle correlation coupled with $v_{2}$. In heavy-ion collisions, the $\Psi_{1}$ and $\Psi_{2}$ are correlated, thus the CME and the $v_{2}$-induced background are entangled.
In small system p+Au and d+Au collisions, the $\Psi_{2}$ is entirely due to geometry fluctuations, and thus $\Psi_{1}$ and $\Psi_{2}$ are uncorrelated. A correlation measurement w.r.t. $\Psi_{1}$ is only sensitive to CME while the $v_{2}$-induced background is averaged to zero. Likewise, a correlation measurement w.r.t. $\Psi_{2}$ is only sensitive to $v_{2}$-induced background while any CME is averaged to zero.

In this poster, we will present the STAR measurements of three-particle correlation in p+Au and d+Au collisions
at $\sqrt{s_{\rm NN}}$ = 200 GeV with respect to $\Psi_{1}$ of spectator neutrons measured by the STAR ZDC-SMD detectors. Measurements with respect to $\Psi_{2}$ are also reported, which shed light on the background contamination in similar measurements in heavy-ion collisions.

Preferred Track QCD in small systems
Collaboration STAR

Primary author

Dr Jie Zhao (Purdue University)

Presentation Materials

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