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Electromagnetic Probes of High-Energy Nuclear Collisions, Hard Probes 2008, Illa da toxa : Espagne (2008)
NA60 results on thermal dimuons
R. Arnaldi, K. Banicz, K. Borer, J. Castor1, B. Chaurand2, W. M. Chen, C. Cicalo, A. Colla, P. Cortese, S. Damjanovic, A. David, A. De Falco, A. Devaux1, L. Ducroux3, H. En'yo, J. Fargeix1, A. Ferretti, M. Floris, A. Foerster, P. Force1, N. Guettet1, A. Guichard3, H. Gulkanian, J. M. Heuser, M. Keil, L. Kluberg2, Z. Li, C. Lourenco, J. Lozano, F. Manso1, P. Martins, A. Masoni, A. Neves, H. Ohnishi, C. Oppedisano, P. Parracho, P. Pillot3, T. Poghosyan, G. Puddu, E. Radermacher, P. Ramalhete, P. Rosinsky, E. Scomparin, J. Seixas, S. Serci, R. Shahoyan, P. Sonderegger, H. J. Specht, R. Tieulent3, G. Usai, R. Veenhof, H. K. Woehri
NA60 Collaboration(s)

The NA60 experiment at the CERN SPS has measured muon pairs with unprecedented precision in 158A GeV In-In collisions. A strong excess of pairs above the known sources is observed in the whole mass region 0.2 rho -> mu+mu- annihilation. The associated rho spectral function shows a strong broadening, but essentially no shift in mass. For M>1 GeV, the excess is found to be prompt, not due to enhanced charm production, with pronounced differences to Drell-Yan pairs. The slope parameter Teff associated with the transverse momentum spectra rises with mass up to the rho, followed by a sudden decline above. The rise for M<1 GeV is consistent with radial flow of a hadronic emission source. The seeming absence of significant flow for M>1 GeV and its relation to parton-hadron duality is discussed in detail, suggesting a dominantly partonic emission source in this region. A comparison of the data to the present status of theoretical modeling is also contained. The accumulated empirical evidence, including also a Planck-like shape of the mass spectra at low pT and the lack of polarization, is consistent with a global interpretation of the excess dimuons as thermal radiation. We conclude with first results on omega in-medium effects.
1 :  LPC - Laboratoire de Physique Corpusculaire [Clermont-Ferrand]
2 :  LLR - Laboratoire Leprince-Ringuet
3 :  IPNL - Institut de Physique Nucléaire de Lyon
Physique/Physique Nucléaire Expérimentale
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