Muon pairs from In+In collision at SPS energy

Understand

NA60 collaboration has extracted the inverse slope parameters, T_{eff} of the dimuon spectra originating from the In+In collisions at root(s_NN)=17.3 GeV for various invariant mass region.

• They have observed that the inverse slope parameter as a function of invariant mass of the lepton pair drops beyond the rho-peak.
• In the present work, first we reproduce the observed invariant mass and transverse momentum spectra of the muon pairs.
• Then show that the slope parameters extracted from the transverse momentum distributions for various invariant mass region windows can be explained by assuming formation of a partonic phase initially which reverts to hadronic phase through a weak first order phase transition at a temperature T_c ~ 175 MeV.