Results on angular distributions of thermal dileptons in nuclear collisions

The NA60 experiment at the CERN SPS has studied dimuon production in 158 AGeV In-In collisions. The strong pair excess above the known sources found in the mass region $0.2<M<2.5$ GeV has been previously interpreted as thermal radiation. In this paper results on the associated angular distributions for $M<1$ GeV, as measured in the Collins-Soper reference frame, are presented. The structure function parameters $\lambda$, $\mu$, $\nu$ are consistent with zero and the projected polar and azimuth angle distributions are uniform. The absence of any polarization is consistent with the interpretation of the excess dimuons as thermal radiation from a randomized system.