Muon pairs from In+In collision at SPS energy

TL;DR

This paper models muon pair spectra from In+In collisions at SPS energy, explaining the non-monotonic inverse slope parameters through a phase transition from partonic to hadronic matter.

Contribution

It demonstrates that the observed spectra can be explained by a partonic phase formation and a weak first order phase transition at T_c ~ 175 MeV, which previous models without partonic phases could not.

Findings

Reproduces the invariant mass and transverse momentum spectra of muon pairs.

Shows the non-monotonic behavior of inverse slope parameters is explained by a partonic phase.

Without the partonic phase, the non-monotonic behavior cannot be reproduced.

Abstract

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. It is observed that a scenario without the formation of a partonic phase does not reproduce the non-monotonic behaviour of the inverse slope parameter non typical of radial flow.