Azimuthal emission patterns ofK+and ofK−mesons in Ni + Ni collisions near the strangeness production threshold

Azimuthal emission patterns of K± mesons have been measured in Ni + Ni collisions with the FOPI spectrometer at a beam kinetic energy of 1.91 A GeV. The transverse momentum pT integrated directed and elliptic flow of K+ and K− mesons as well as the centrality dependence of pT - differential directed flow of K+ mesons are compared to the predictions of hadron string dynamics and isospin quantum molecular dynamics transport models. The data exhibits different propagation patterns of K+ and K− mesons in the compressed and heated nuclear medium and favor the existence of a kaon-nucleon in-medium potential, repulsive for K+ mesons and attractive for K− mesons.Received 8 March 2013Revised 28 April 2014DOI:https://doi.org/10.1103/PhysRevC.90.025210©2014 American Physical Society