Elliptic flow of $\eta$ and ${\pi }^0$ Mesons in Heavy-Ion Collisions at 2 AGeV

Abstract

Azimuthal distributions of $\eta$ and ${\pi }^0$ 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 $\eta$ mesons, indicating a preferred emission perpendicular to the reaction plane. In contrast, only small azimuthal anisotropies are observed for ${\pi }^0$ mesons. This may indicate that $\eta$ mesons freeze out earlier from the fire ball than pions.

34 pages, presented at V TAPS workshop, Rez, September 4-8. 1999