Feb 5 – 11, 2017
Hyatt Regency Chicago
America/Chicago timezone

Charge Asymmetry Measurements in Au+Au collisions by STAR in Search of the Chiral Magnetic Effect

Not scheduled
2h 30m
Hyatt Regency Chicago

Hyatt Regency Chicago

151 East Wacker Drive Chicago, Illinois, USA, 60601
Board: F07


Nuggehalli Ajitanand (State University of New York at Stony Brook)


Metastable domains of topological charges in QCD can cause chirality
imbalance and, under the strong magnetic field present in heavy-ion
collisions, result in charge separation along the magnetic field, a
phenomenon called the Chiral Magnetic Effect (CME) [1]. Charge
separation can also be caused by intrinsic particle correlations coupled
with elliptic flow anisotropy, a major background for the CME search. In
this talk, we report results by two analysis methods designed to reduce
or eliminate, model-independently, background contributions.

In the first method [2], a correlator Cp is constructed as the ratio of
real-event to shuffled-event differences between positive and negative
charge distributions of a correlation variable with respect to the event
plane. A second correlator Cp_perp is similarly constructed using the
particles perpendicular to the event plane. The shape of the
double-ratio $C_p/C_{p_{perp}}$ is concave for a CME-associated charge
asymmetry and flat or convex for all non-CME associated effects. The
observation of a concave shape for $C_p/C_{p_{perp}}$ in the data confirms
the presence of a CME associated charge asymmetry. Quantification of
this signal is obtained via comparisons with data driven simulations.

In the second method [3], correlators are constructed from multiplicity
asymmetries of positive and negative particles across the event plane.
The same- and opposite-sign difference is studied as a function of the
event-by-event anisotropy of the measured particles. A linear dependence
is observed in both real and mixed-events. The intercept or the
difference between real- and mixed-events measures the charge separation
with reduced flow background.

We present the results obtained via these two methods for Au+Au
collisions at several collision centralities and beam energies at RHIC.
We discuss our results in terms of the CME search.

[1] D. Kharzeev, Phys. Lett. B633, 260 (2006).
[2] N. N. Ajitanand, R. A. Lacey, A. Taranenko, and J. M.Alexander,
Phys. Rev. C 83, 011901(R) (2011).
[3] L. Adamczyk, et al. (STAR Collaboration), Phys. Rev. C 89, 044908

Preferred Track Collective Dynamics
Collaboration STAR

Primary author

Nuggehalli Ajitanand (State University of New York at Stony Brook)

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