Multistrange Hyperon Production in Pb+Pb collisions at 30, 40, 80 and 158 A$\cdot$GeV

Abstract

A non-monotonic energy dependence of the $K^{+} / π^{+}$ ratio with a sharp maximum close to 30 A$\cdot$GeV is observed in central Pb+Pb collisions. Within a statistical model of the early stage, this is interpreted as a sign of the phase transition to a QGP, which causes a sharp change in the energy dependence of the strangeness to entropy ratio. This observation naturally motivates us to study the production of multistrange hyperons ($Ξ$, $Ω$) as a function of the beam energy. Furthermore it was suggested that the kinematic freeze-out of $Ω$ takes place directly at QGP hadronization. If this is indeed the case, the transverse momentum spectra of the $Ω$ directly reflect the transverse expansion velocity of a hadronizing QGP. In this report we show preliminary NA49 results on $Ω^{-}$ and $\barΩ^{+}$ production in central Pb+Pb collisions at 40 and 158 A$\cdot$GeV and compare them to measurements of $Ξ^{-}$ and $\barΞ^{+}$ production in central Pb+Pb collisions at 30, 40, 80 and 158 A$\cdot$GeV.