Pion-kaon femtoscopy in 200 GeV collisions in STAR at RHIC

Correlations between non-identical particles at low relative momentum in the center of mass encode unique information on the space-time structure of the emitting system [1,2], in particular a space-time offset of one particle species (e.g. kaons) with respect to another (e.g. pions). We present new high-statistics measurements of pion-kaon correlations in 200 GeV in the spherical harmonic representation [3,4]. The analysis benefits greatly from the extended particle-identification capabilities of the recently installed STAR Time of Flight detector. In $\sqrt{s_{NN}}=200$ GeV $Au+Au$ collisions, we observe an asymmetry similar to that reported at lower energies with poorer statistics. Finally, we present a first similar analysis of $\sqrt{s}=200$ GeV $p+p$ collisions.\\[4pt] [1] Lisa, Pratt, Soltz and Wiedemann, Ann. Rev. Nucl. Part. Sci. {\bf 55}, 357 (2005) \newline [2] R. Lednicky, nucl-th/0112011 \newline [3] Z. Chajecki and M. Lisa, Phys. Rev. C {\bf 78}, 064903 (2008) \newline [4] A. Kisiel and D. Brown, Phys. Rev. C {\bf 80}, 064911 (2009)