Low Mass Dimuons Produced in Relativistic Nuclear Collisions

TL;DR

This paper reports precise measurements of low-mass dimuon production in relativistic nuclear collisions, demonstrating consistency with in-medium vector meson modifications and a dynamical model scaled from hadronic data.

Contribution

It provides the first detailed comparison of low-mass dimuon data with a dynamical model incorporating in-medium vector meson properties at finite temperature and density.

Findings

Data aligns with in-medium $ ho$ and $ ho$-meson modifications.

Including vacuum decay after freeze-out explains low-mass dimuon spectra.

Model reproduces transverse mass spectra and correlations.

Abstract

The NA60 experiment has measured low-mass muon pair production in In-In collisions at 158 A GeV with unprecedented precision. We show that this data is reproduced very well by a dynamical model with parameters scaled from fits to measurements of hadronic transverse mass spectra and Hanbury-Brown and Twiss correlations in Pb-Pb and Pb-Au collisions at the same energy. The data is consistent with in-medium properties of $\rho$ and $\omega$-mesons at finite temperature and density as deduced from empirical forward-scattering amplitudes. Inclusion of the vacuum decay of the $\rho$-meson after freeze-out is necessary for an understanding of the mass and transverse momentum spectrum of dimuons with $M \apprle 0.9 {\rm GeV}/c^2$.