$\phi$ production in Pb-Pb collisions at 158 GeV/c per nucleon incident momentum

The production of vector mesons $\phi$ , $\rho$ and $\omega$ has been measured in Pb-Pb collisions at 158 GeV/c per nucleon incident momentum at the CERN/SPS. The muon spectrometer of experiment NA50 detects $\phi$ , $\rho$ and $\omega$ mesons via their $\mu^{+} \mu^{-}$ decay channel in the collision center of mass rapidity range 0$\leqslant$ $\gamma_{CM}$ $\leqslant$ 1. The results reported here show that the relative production of the $\phi$ compared to the ($\rho$ + $\omega$) and the $\phi$ multiplicity per participant nucleon ($N_{part}$) increase with the centrality of the collision. On the other hand, the ($\rho$ + $\omega$) multiplicity per participant does not exhibit any $N_{part}$ dependence within our errors. The inverse slope parameter as deduced from an exponential fit to the $\phi$ transverse mass distribution is 228 $\pm$ 10 MeV. Our results are compared with those obtained by experiment NA49 and with theoretical calculations. (26 refs).