Dimuon radiation at relativistic energies available at the CERN Super Proton Synchrotron within a (3 + 1)D hydrodynamic + cascade model

Journal Article · Fri Jul 15 00:00:00 EDT 2011 · Physical Review. C, Nuclear Physics

DOI:https://doi.org/10.1103/PHYSREVC.84.014901· OSTI ID:21596598

Santini, E; Steinheimer, J; Bleicher, M ^[1]; Schramm, S ^[2]

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1. Institut fuer Theoretische Physik, Goethe-Universitaet, Max-von-Laue-Str. 1, D-60438 Frankfurt am Main (Germany)
2. Frankfurt Institute for Advanced Studies (FIAS), Ruth-Moufang-Str. 1, D-60438 Frankfurt am Main (Germany)

We analyze dilepton emission from hot and dense matter using a hybrid approach based on the ultrarelativistic quantum molecular dynamics (UrQMD) transport model with an intermediate hydrodynamic stage for the description of heavy-ion collisions at relativistic energies. During the hydrodynamic stage, the production of lepton pairs is described by radiation rates for a strongly interacting medium in thermal equilibrium. In the low-mass region, hadronic thermal emission is evaluated by assuming vector meson dominance including in-medium modifications of the {rho} meson spectral function through scattering from nucleons and pions in the heat bath. In the intermediate-mass region, the hadronic rate is essentially determined by multipion annihilation processes. Emission from quark-antiquark annihilation in the quark gluon plasma (QGP) is taken into account as well. When the system is sufficiently dilute, the hydrodynamic description breaks down and a transition to a final cascade stage is performed. In this stage dimuon emission is evaluated as commonly done in transport models. By focusing on the enhancement with respect to the contribution from long-lived hadron decays after freezeout observed at the SPS in the low-mass region of the dilepton spectra, the relative importance of the different thermal contributions and of the two dynamical stages is investigated. We find that three separated regions can be identified in the invariant mass spectra. Whereas the very low and the intermediate-mass regions mostly receive contribution from the thermal dilepton emission, the region around the vector meson peak is dominated by the cascade emission. Above the {rho}-peak region the spectrum is driven by QGP radiation. Analysis of the dimuon transverse mass spectra reveals that the thermal hadronic emission shows an evident mass ordering not present in the emission from the QGP. A comparison of our calculation to recent acceptance-corrected NA60 data on invariant as well as transverse mass spectra is performed.

• OSTI ID: 21596598
• Journal Information: Physical Review. C, Nuclear Physics, Vol. 84, Issue 1; Other Information: DOI: 10.1103/PhysRevC.84.014901; (c) 2011 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0556-2813
• Country of Publication: United States
• Language: English

Related Subjects

73 NUCLEAR PHYSICS AND RADIATION PHYSICS
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
ANNIHILATION
CERN SPS SYNCHROTRON
COMPARATIVE EVALUATIONS
EMISSION
HEAVY ION REACTIONS
LEPTONS
MASS
MASS SPECTRA
MOLECULAR DYNAMICS METHOD
NUCLEAR DECAY
PIONS
PROTONS
QUARK MATTER
QUARK-ANTIQUARK INTERACTIONS
RELATIVISTIC RANGE
SCATTERING
SPECTRAL FUNCTIONS
THERMAL EQUILIBRIUM
TRANSPORT THEORY
VECTOR MESONS
ACCELERATORS
BARYONS
BOSONS
CALCULATION METHODS
CYCLIC ACCELERATORS
DECAY
ELEMENTARY PARTICLES
ENERGY RANGE
EQUILIBRIUM
EVALUATION
FERMIONS
FUNCTIONS
HADRONS
INTERACTIONS
MATTER
MESONS
NUCLEAR REACTIONS
NUCLEONS
PARTICLE INTERACTIONS
PSEUDOSCALAR MESONS
SPECTRA
SYNCHROTRONS