Observation of an energy-dependent difference in elliptic flow between particles and antiparticles in relativistic heavy ion collisions. - Adamczyk L; Adkins JK; Agakishiev G; Aggarwal MM; Ahammed Z; Alekseev I; Alford J; Anson CD; Aparin A; Arkhipkin D; Aschenauer E; Averichev GS; et al. (Physical review letters, 2013)