Resonances production from the NA60 experiment

Abstract

Abstract. The NA60 experiment at the CERN SPS has studied light vector meson production in In-In collisions at 158A GeV. The φ meson was detected via both the K + K − and the μ + μ − decay channels. The yields and inverse slope parameters of the m T spectra observed in the two channels are compatible within errors, different from the large discrepancies seen in Pb-Pb collisions between the hadronic (NA49) and dimuon (NA50) decay channels. In the invariant mass region 0.2 < M μμ < 2.6 GeV, a strong excess of pairs above the sources that describe the mass spectrum in p-A collisions is observed. The mass spectrum for M μμ < 1 GeV is consistent with a dominant contribution from the pion annihilation process π + π → ρ → μ + μ − . For M μμ > 1 GeV, the excess is found to be prompt, with remarkable differences with respect to the Drell-Yan process. The T eff slope parameter, extracted from the transverse mass spectra, shows a rise with mass up to the ρ, followed by a sudden decline for higher masses. The former is consistent with radial ow of a hadronic source, while the latter suggests a dominantly partonic emission source.