Elliptic flow of electrons from heavy-flavor hadron decays in Au + Au collisions at s_(NN)~(1/2) = 200, 62.4, and 39 GeV

摘要

We present measurements of elliptic flow (ν_2) of electrons from the decays of heavy-flavor hadrons (e_(HF)) by the STAR experiment. For Au+Au collisions at s_(NN)~(1/2) = 200 GeV we report ν_2, for transverse momentum (p_T) between 0.2 and 7 GeV/c, using three methods: the event plane method (ν_2{EP}), two-particle correlations (ν_2{2}), and four-particle correlations (ν_2{4}). For Au+Au collisions at s_(NN)~(1/2) = 62.4 and 39 GeV we report ν_2{2} for p_T ＜ 2 GeV/c. ν_2{2} and ν_2{4} are nonzero at low and intermediate p_T at 200 GeV, and ν_2{2} is consistent with zero at low p_T at other energies. The ν_2{2} at the two lower beam energies is systematically lower than at s_(NN)~(1/2) = 200 GeV for p_T ＜ 1 GeV/c. This difference may suggest that charm quarks interact less strongly with the surrounding nuclear matter at those two lower energies compared to s_(NN)~(1/2) = 200 GeV.