Azimuthal Anisotropy of $\hat{I}\cdot$ and $\ddot{I}{€}^0$ Mesons in Heavy-Ion Collisions at 2 AGeV

Abstract

Azimuthal distributions of $\hat{I}\cdot$ and $\ddot{I}{€}^0$ mesons emitted at midrapidity in collisions of 1.9 AGeV ${}^{58}$Ni+${}^{58}$Ni and 2 AGeV ${}^{40}$Ca+${}^{nat}$Ca are studied as a function of the number of projectile-like spectator nucleons. The observed anisotropy corresponds to a negative elliptic flow signal for $\hat{I}\cdot$ mesons, indicating a preferred emission perpendicular to the reaction plane. The effect is smallest in peripheral Ni+Ni collisions. In contrast, for $\ddot{I}{€}^0$ mesons, elliptic flow is observed only in peripheral Ni+Ni collisions, changing from positive to negative sign with increasing pion transverse momentum.

4 pages, 2 figures, Submitted to Phys. Rev. Lett