CME search at STAR

Abstract

The hot and dense medium produced in relativistic heavy-ion collisions has been conjectured to be accompanied by an axial charge asymmetry that may lead to a separation of electric charges in the direction of the extremely strong magnetic field, also known as the Chiral Magnetic Effect (CME) [1–3]. The measurement of azimuthal correlator (∆γ) with respect to the spectator plane [5], gives us an opportunity to measure the possible CME fraction beyond the flow background. Preliminary results using this approach with combined Au+Au collisions at √SNN = 200 GeV and U+U at √SNN = 193 GeV$\sqrt {{S_{NN}}} = 200\,{\rm{GeV}}\,{\rm{and}}\,{\rm{U + U}}\,{\rm{at}}\,\sqrt {{S_{NN}}} = 193\,{\rm{GeV}}$SNN=200 GeV and U+U at SNN=193 GeV show fCME at (8±4±8)%. Meanwhile, the observability of CME has been conjectured to be dependent on √SNN$\sqrt {{S_{NN}}}$SNN due to changes in the lifetime of the magnetic field, the strengths of CME signal and non-CME background. At lower energies, the Event Plane Detector (EPD) installed in the year 2018 provides a unique capability for CME search. The background scenario test at Au+Au √SNN$\sqrt {{S_{NN}}}$SNN = GeV by using ∆γ with respect to TPC and the new installed EPD shows a consistency with no-CME scenario in the current statistics. The method of the ongoing isobar blind analysis, and the latest sensitivity check with the eventby- event AVFD model on the different observables between Ru+Ru and Zr+Zr are also briefly discussed.