Abstract:
The yields of strange particles are
calculated with the
UrQMD model for p,Pb(158 AGeV)Pb collisions
and compared to
experimental data. The yields are enhanced in
central
collisions if compared to proton induced or
peripheral Pb+Pb
collisions. The enhancement is due to secondary
interactions. Nevertheless, only a reduction
of the quark
masses or equivalently an increase of the
string tension
provides an adequate description of the large
observed
enhancement factors (WA97 and NA49).
Furthermore, the yields
of unstable strange resonances as the
Lambda_star(1520)
resonance or the phi meson are considerably
affected by
hadronic rescattering of the decay products.