Local parity-odd domains are theorized to form inside a quark-gluon plasma which has been produced in high-energy heavy-ion collisions. The local parity-odd domains manifest themselves as charge separation along the magnetic field axis via the chiral magnetic effect. The experimental observation of charge separation has previously been reported for heavy-ion collisions at the top RHIC energies. In this Letter, we present the results of the beam-energy dependence of the charge correlations in Au+Au collisions at midrapidity for center-of-mass energies of 7.7, 11.5, 19.6, 27, 39, and 62.4 GeV from the STAR experiment. After background subtraction, the signal gradually reduces with decreased beam energy and tends to vanish by 7.7 GeV. This implies the dominance of hadronic interactions over partonic ones at lower collision energies.
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We thank the RHIC Operations Group and RCF at BNL, the NERSC Center at LBNL, the KISTI Center in Korea, and the Open Science Grid consortium for providing resources and support. This work was supported in part by the Offices of NP and HEP within the U.S. DOE, Office of Science; the U.S. NSF; CNRS/IN2P3; FAPESP CNPq of Brazil; the Ministry of Education and Science of the Russian Federation; NNSFC, CAS, MoST, and MoE of China; the Korean Research Foundation; GA and MSMT of the Czech Republic; FIAS of Germany; DAE, DST, and CSIR of India; the National Science Centre of Poland; the National Research Foundation (NRF-2012004024); the Ministry of Science, Education and Sports of the Republic of Croatia; and RosAtom of Russia.
Adkins, J. Kevin; Fatemi, Renee; Ramachandran, Suvarna; Webb, G.; Adamczyk, L.; Agakishiev, G.; Aggarwal, M. M.; Ahammed, Z.; Alekseev, I.; Alford, J.; Anson, C. D.; Aparin, A.; Arkhipkin, D.; and Aschenauer, E. C., "Beam-Energy Dependence of Charge Separation Along the Magnetic Field in Au+Au Collisions at RHIC" (2014). Physics and Astronomy Faculty Publications. 317.