Pair invariant mass to isolate background in the search for the chiral magnetic effect in Au + Au collisions at sNN =200 GeV

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3 Scopus citations


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 (Δγ) is contaminated by background arising, in part, from resonance decays coupled with elliptic anisotropy (v2). We report here differential measurements of the correlator as a function of the pair invariant mass (minv) in 20-50% centrality Au+Au collisions at sNN=200 GeV by the STAR experiment at the BNL Relativistic Heavy Ion Collider. Strong resonance background contributions to Δγ are observed. At large minv where this background is significantly reduced, the Δγ value is found to be significantly smaller. An event-shape-engineering technique is deployed to determine the v2 background shape as a function of minv. We extract a v2-independent and minv-averaged signal Δγsig=(0.03±0.06±0.08)×10-4, or (2±4±5)% of the inclusive Δγ(minv>0.4 GeV/c2)=(1.58±0.02±0.02)×10-4, within pion pT=0.2-0.8 GeV/c and averaged over pseudorapidity ranges of -1<η<-0.05 and 0.05<η<1. This represents an upper limit of 0.23×10-4, or 15% of the inclusive result, at 95% confidence level for the minv-integrated CME contribution.

Original languageEnglish
Article number034908
JournalPhysical Review C
Issue number3
StatePublished - Sep 2022

Bibliographical note

Funding Information:
We thank the RHIC Operations Group and RCF at BNL, the NERSC Center at LBNL, and the Open Science Grid consortium for providing resources and support. This work was supported in part by the Office of Nuclear Physics within the U.S. DOE, Office of Science; the U.S. National Science Foundation; the National Natural Science Foundation of China; the Chinese Academy of Science; the Ministry of Science and Technology of China and the Chinese Ministry of Education; the Higher Education Sprout Project by the Ministry of Education at NCKU; the National Research Foundation of Korea; the Czech Science Foundation and Ministry of Education, Youth and Sports of the Czech Republic; the Hungarian National Research, Development and Innovation Office; the New National Excellency Programme of the Hungarian Ministry of Human Capacities; the Department of Atomic Energy and the Department of Science and Technology of the Government of India; the National Science Centre of Poland; the Ministry of Science, Education and Sports of the Republic of Croatia; the German Bundesministerium für Bildung, Wissenschaft, Forschung and Technologie (BMBF); the Helmholtz Association; the Ministry of Education, Culture, Sports, Science, and Technology (MEXT); and the Japan Society for the Promotion of Science (JSPS).

Publisher Copyright:
© 2022 American Physical Society.

ASJC Scopus subject areas

  • Nuclear and High Energy Physics


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