Azimuthal Distributions of K + Mesons in Heavy-Ion Collisions

Strange mesons are considered to be sensitive to in-medium modifications. Theory predicts a repulsive K (+) N potential and an attractive K (-) N potential in dense matter. A repulsive K (+) N potential would repel the K (+) mesons from the bulk of the nucleons and therefore cause a preferred out-of-plane emission of K (+) mesons at midrapidity and a directed flow opposite to the nucleons at target and projectile rapidity. One of observables to probe in-medium effects is the azimuthal emission pattern of K (+) mesons in heavy ion collisions. KaoS collaboration has measured the azimuthal distributions of K (+) mesons in Au + Au reactions at 1.5 A GeV and Ni + Ni reactions at 1.93 A GeV. Data show that K (+) mesons exhibit a pronounced enhancement at , i.e. perpendicular to the reaction plane. The data have also been fitted using the first two components of a Fourier series to get the directed flow v (1) and elliptic flow v (2). We used the quantum molecular dynamics model based on the covariant kaon dynamics to simulate the Au + Au collisions at 1.5 A GeV and the Ni + Ni collisions at 1.93 A GeV, to analyze the azimuthal distributions of K (+) mesons, and to calculate v (1) and v (2) of K (+) mesons. Calculated results with a repulsive in-medium K (+) N potential can reasonably describe the features of KaoS data. This indicates that the azimuthal distribution is one of sensitive probes to extract information on in-medium properties at high densities.