23,106 research outputs found
Chiral magnetic effect search in p+Au, d+Au and Au+Au collisions at RHIC
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
direction of the strong magnetic field produced by spectator protons in
relativistic heavy-ion collisions, a phenomenon called the chiral magnetic
effect (CME). A major background source for CME measurements using the
charge-dependent azimuthal correlator () is the intrinsic
particle correlations (such as resonance decays) coupled with the azimuthal
elliptical anisotropy (). In heavy-ion collisions, the magnetic field
direction and event plane angle are correlated, thus the CME and the
-induced background are entangled. In this report, we present two
studies from STAR to shed further lights on the background issue. (1) The
should be all background in small system p+Au and d+Au
collisions, because the event plane angles are dominated by geometry
fluctuations uncorrelated to the magnetic field direction. However, significant
is observed, comparable to the peripheral Au+Au data, suggesting
a background dominance in the latter, and likely also in the mid-central Au+Au
collisions where the multiplicity and scaled correlator is similar. (2)
A new approach is devised to study as a function of the particle
pair invariant mass () to identify the resonance backgrounds and hence
to extract the possible CME signal. Signal is consistent with zero within
uncertainties at high . Signal at low , extracted from a
two-component model assuming smooth mass dependence, is consistent with zero
within uncertainties.Comment: ISMD 2017 conference proceeding contributio
Continuous Cluster Expansion for Field Theories
A new version of the cluster expansion is proposed without breaking the
translation and rotation invariance. As an application of this technique, we
construct the connected Schwinger functions of the regularized theory
in a continuous way
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