Dimuon transverse momentum spectra as a tool to characterize the emission region in heavy-ion collisions

Abstract

Previous dilepton measurements in heavy-ion collisions have mainly focused on invariant mass spectra to clarify in-medium changes of vector meson properties. However, a dimuon is characterized by two scales -- invariant mass $M$ and transverse momentum $p_T$. Like transverse momentum spectra of hadrons, $p_T$ spectra of dileptons arise from an interplay between emission temperature and collective transverse flow, whereas the invariant mass is insensitive to flow. Having two control parameters of which only one is sensitive to flow allows at given $M$ to characterize the emission region in terms of average temperature and flow. Thus, one is able to study what phases of the fireball evolution radiate into a given mass window. We demonstrate this technique using the dimuon transverse momentum spectra measured by the NA60 collaboration and present strong arguments that a thermalized evolution phase with $T>170$ MeV leaves an imprint in the spectra.

References in corpus (7)

• Space-time evolution of bulk QCD matter
• Comprehensive Interpretation of Thermal Dileptons at the SPS
• NA60 results on the rho spectral function in In-In collisions
• Thermal Dimuon Yields at NA60
• First measurement of the rho spectral function in nuclear collisions
• Elliptic flow of thermal photons and dileptons
• What does the rho-meson do? In-medium mass shift scenarios versus hadronic model calculations

Cited by in corpus (9)

• Evidence for the production of thermal muon pairs with masses above 1 GeV/c^2 in 158A GeV Indium-Indium Collisions
• NA60 results on thermal dimuons
• NA60 results on the rho spectral function in In-In collisions
• Low Mass Dimuons Produced in Relativistic Nuclear Collisions
• Dimuon radiation at the CERN SPS within a (3+1)d hydrodynamic+cascade model
• Transverse momentum spectra of dileptons at NA60
• The low and intermediate mass dilepton and photon results
• Thermal photon to dilepton ratio in ultra-relativistic heavy ion collisions
• Letter of Intent: the NA60+ experiment