NA60 results on $p_T$ spectra and the $\rho$ spectral function in In-In collisions

J. Seixas , R. Arnaldi , R. Averbeck , K. Banicz , J. Castor (1) , B. Chaurand (2) , C. Cicalo , A. Colla , P. Cortese , S. Damjanovic , A. David , A. de Falco , A. Devaux (1) , A. Drees , L. Ducroux (3) , H. Enyo , A. Ferretti , M. Floris , A. Forster , P. Force (1) , N. Guettet (1) , A. Guichard (3) , H. Gulkanian , M. Keil , L. Kluberg (2) , C. Lourenco , J. Lozano , F. Manso (1) , A. Masoni , P. Martins , A. Neves , H. Ohnishi , C. Oppedisano , P. Parracho , Philippe Pillot (3) , G. Puddu , E. Radermacher , P. Ramalhete , P. Rosinsky , E. Scomparin , S. Serci , R. Shahoyan , P. Sonderegger , H.J. Specht , R. Tieulent (3) , G. Usai , R. Veenhof , H.K. Wohri

1 LPC - Laboratoire de Physique Corpusculaire - Clermont-Ferrand
2 LLR - Laboratoire Leprince-Ringuet
3 IPNL - Institut de Physique Nucléaire de Lyon

The NA60 experiment at the CERN SPS has studied low-mass muon pairs in 158 AGeV In-In collisions. A strong excess of pairs is observed above the yield expected from neutral meson decays. The unprecedented sample size of close to 400K events and the good mass resolution of about 2% have made it possible to isolate the excess by subtraction of the decay sources (keeping the $\rho$). The shape of the resulting mass spectrum exhibits considerable broadening, but essentially no shift in mass. The acceptance-corrected transverse-momentum spectra have a shape atypical for radial flow and show a significant mass dependence, pointing to different sources in different mass regions.

Domaines: Physique Nucléaire Expérimentale [nucl-ex]

J. Seixas, R. Arnaldi, R. Averbeck, K. Banicz, J. Castor, et al.. NA60 results on $p_T$ spectra and the $\rho$ spectral function in In-In collisions. 19th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions: Quark Matter 2006 (QM2006), Nov 2006, Shanghai, China. pp.S1023-S1027, ⟨10.1088/0954-3899/34/8/S148⟩. ⟨in2p3-00148802⟩