Thermal dileptons at SPS energies

Abstract

Clear signs of excess dileptons above the known sources were found at the SPS since long. However, a real clarification of these observations was only recently achieved by NA60, measuring dimuons with unprecedented precision in 158A GeV, In-In collisions. The excess mass spectrum in the region M<1 GeV is consistent with a dominant contribution from pi+pi- -> rho -> mu+mu- annihilation. The associated rho spectral function shows a strong broadening, but essentially no shift in mass. In the region M>1 GeV, the excess is found to be prompt, not due to enhanced charm production. The inverse slope parameter Teff associated with the transverse momentum spectra rises with mass up to the rho, followed by a sudden decline above. While the initial rise, coupled to a hierarchy in hadron freeze-out, points to radial flow of a hadronic decay source, the decline above signals a transition to a low-flow source, presumably of partonic origin. The mass spectra show at low transverse momenta the steep rise towards low masses characteristic for Planck-like radiation. The polarization of the excess referred to the Collins Soper frame is found to be isotropic. All observations are consistent with the interpretation of the excess as thermal radiation.

Prepared for 20th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions: Quark Matter 2008 (QM2008), Jaipur, India, 4-10 Feb. 2008

References in corpus (12)

• Dilepton Radiation at the CERN Super Proton Synchrotron
• Comprehensive Interpretation of Thermal Dileptons at the SPS
• Evidence for radial flow of thermal dileptons in high-energy nuclear collisions
• NA60 results on the rho spectral function in In-In collisions
• Low Mass Dimuons Produced in Relativistic Nuclear Collisions
• Thermal Dimuon Yields at NA60
• Dimuon transverse momentum spectra as a tool to characterize the emission region in heavy-ion collisions
• First measurement of the rho spectral function in nuclear collisions
• Lepton-pair production in nuclear collisions - past, present, future
• The dilepton probe in heavy-ion collisions
• $\varphi$ Meson Production in In-In Collisions and the $\varphi$ Puzzle
• Thermal Dilepton Production from Dropping rho in the Vector Manifestation

Cited by in corpus (24)

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• Exploring the influence of bulk viscosity of QCD on dilepton tomography
• Dilepton Radiation from Strongly Interacting Systems
• $\varphi$ Production in In-In Collisions at 158 AGeV
• Investigating the temperature dependence of the specific shear viscosity of QCD matter with dilepton radiation
• Observing many body effects on lepton pair production from low mass enhancement and flow at RHIC and LHC energies
• e+e- Pairs: a clock and a thermometer of heavy ion collisions
• Transport responses from rate of decay and scattering processes in the Nambu--Jona-Lasinio model
• Muon pairs from In+In collision at SPS energy
• In-medium vector mesons and low mass lepton pairs from heavy ion collisions
• Dimuon production from in-medium rho decays from QCD sum rules
• Measuring radial flow of partonic and hadronic phases in relativistic heavy ion collision
• Electromagnetic signals from Au+Au collisions at RHIC energy, $\sqrt{s_{NN}}$=200 GeV and Pb+Pb collisions at LHC energy, $\sqrt{s_{NN}}$=2.76 TeV
• Weinberg sum rules at finite temperature
• Search and study of Quark Gluon Plasma at the CERN-LHC
• Low mass enhanced probability of pion in hadronic matter due to its Landau cut contributions
• Summary of Experimental Results: Photons, Leptons and Heavy Quarks
• Dilepton creation based on an analytic hydrodynamic solution
• Velocity dependence of the mass modifications of $\rho$ and $\omega$ mesons in 12 GeV $p+A$ reactions
• Dileptons and Direct Photons at SPS