UCLA

Measurements of the elliptic flow, v2, of identified hadrons (π±, K±, Ks0, p, p̄, φ, Λ, Λ̄, Ξ-, Ξ̄+, Ω-, Ω̄+) 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 midrapidity using the time-projection chamber and the time-of-flight detectors of the Solenoidal Tracker at RHIC experiment during the beam-energy scan program at Relativistic Heavy Ion Collider. A significant difference in the v2 values for particles and the corresponding antiparticles was observed at all transverse momenta for the first time. The difference increases with decreasing center-of-mass energy, √s NN (or increasing baryon chemical potential, μB), and is larger for the baryons as compared to the mesons. This implies that particles and antiparticles 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 selected group of particles (π+, K+, Ks0, p, Λ, Ξ-, Ω-) NCQ scaling at (mT-m0)/n q>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. © 2013 American Physical Society.