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First measurement of the $\rho$ spectral function in nuclear collisions

Abstract : 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 close to 400K events and the good mass resolution of about 2% made it possible to isolate the excess by subtraction of the decay sources. The shape of the resulting mass spectrum shows some non-trivial centrality dependence, but is largely consistent with a dominant contribution from pi+pi- ->rho ->mu+mu- annihilation. The associated rho spectral function exhibits considerable broadening, but essentially no shift in mass. The pT-differential mass spectra show the excess to be much stronger at low pT than at high pT. The results are compared to theoretical model predictions; they tend to rule out models linking hadron masses directly to the chiral condensate.
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http://hal.in2p3.fr/in2p3-00131869
Contributor : Sylvie Flores <>
Submitted on : Tuesday, February 20, 2007 - 8:45:46 AM
Last modification on : Thursday, June 17, 2021 - 3:18:40 PM

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R. Arnaldi, R. Averbeck, K. Banicz, J. Castor, B. Chaurand, et al.. First measurement of the $\rho$ spectral function in nuclear collisions. Hot Quarks 2006: Workshop for Young Scientists on the Physics of Ultrarelativistic Nucleus-Nucleus Collisions, May 2006, Villasimius, Italy. pp.235-241, ⟨10.1140/epjc/s10052-006-0060-2⟩. ⟨in2p3-00131869⟩

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