  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.

Nuclear Experiment;High Energy Physics - Experiment