| Abstract (english) | Measurements of the elliptic flow, v2, of identified hadrons (π±, K ±, K0s, p, p¯, ϕ, Λ, Λ¯, Ξ−, Ξ¯+, Ω−, Ω¯+) in Au+Au collisions at √sNN= 7.7, 11.5, 19.6, 27, 39 and 62.4 GeV are presented. The measurements were done at mid-rapidity using the Time Projection Chamber and the Time-of-Flight detectors of the STAR experiment during the Beam Energy Scan program at RHIC. A significant difference in the v2 values for particles and the corresponding anti-particles was observed at all transverse momenta for the first time. The difference increases with decreasing center-of-mass energy, √sNN (or increasing baryon chemical potential, μB) and is larger for the baryons as compared to the mesons. This implies that particles and anti-particles are no longer consistent with the universal number-of-constituent quark (NCQ) scaling of v2 that was observed at √sNN= 200 GeV. However, for the group of particles NCQ scaling at (mT−m0)/nq> 0.4 GeV/c2 is not violated within ±10%. The v2 values for ϕ mesons at 7.7 and 11.5 GeV are approximately two standard deviations from the trend defined by the other hadrons at the highest measured pT values. |
