Observation of different azimuthal emission patterns for K+ and of K-   mesons in Heavy Ion Collisions at 1-2 AGeV
  Azimuthal distributions of pi+, K+ and K- mesons have been measured in Au+Au reactions at 1.5 AGeV and Ni+Ni reactions at 1.93 AGeV. In semi-central collisions at midrapidity, pi+ and K+ mesons are emitted preferentially perpendicular to the reaction plane in both collision systems. In contrast for K- mesons in Ni+Ni reactions an in-plane elliptic flow was observed for the first time at these incident energies. 
F. Uhlig, A. Foerster, I. Boettcher, M. Debowski, F. Dohrmann, E.   Grosse, P. Koczon, B. Kohlmeyer, F. Laue, M. Menzel, L. ...