85 research outputs found
Pair invariant mass to isolate background in the search for the chiral magnetic effect in Au+Au collisions at = 200 GeV
Quark interactions with topological gluon configurations can induce local
chirality imbalance and parity violation in quantum chromodynamics, which can
lead to the chiral magnetic effect (CME) -- an electric charge separation along
the strong magnetic field in relativistic heavy-ion collisions. The
CME-sensitive azimuthal correlator observable () is contaminated
by background arising, in part, from resonance decays coupled with elliptic
anisotropy (). We report here the first differential measurements of the
correlator as a function of the pair invariant mass () in 20-50\%
centrality Au+Au collisions at = 200 GeV by the STAR
experiment at RHIC. Strong resonance background contributions to
are observed. At large where this background is significantly
reduced, the value is found to be also significantly smaller. An
event shape engineering technique is deployed to determine the
background shape as a function of . A -independent signal,
possibly indicating a -integrated CME contribution, is extracted
to be = (0.03 0.06 0.08)
, or of the inclusive GeV/). This presents an
upper limit of , or of the inclusive result at
confidence level.Comment: 7 pages, 4 figure
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