First results on angular distributions of thermal dileptons in nuclear collisions

Abstract

The NA60 experiment at the CERN SPS has studied dimuon production in 158A GeV In-In collisions. The strong excess of pairs above the known sources found in the complete mass region 0.2<M<2.6 GeV has previously been interpreted as thermal radiation. We now present first results on the associated angular distributions. Using the Collins-Soper reference frame, the structure function parameters λ, μand νare measured to be zero, and the projected distributions in polar and azimuth angles are found to be uniform. The absence of any polarization is consistent with the interpretation of the excess dimuons as thermal radiation from a randomized system.

Submitted to Physical Review Letters

References in corpus (4)

• First Measurement of the rho Spectral Function in High-Energy Nuclear Collisions
• Evidence for the production of thermal muon pairs with masses above 1 GeV/c^2 in 158A GeV Indium-Indium Collisions
• Evidence for radial flow of thermal dileptons in high-energy nuclear collisions
• NA60 results on the rho spectral function in In-In collisions

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