Rescattering of Vector Meson Daughters in High Energy Heavy Ion Collisions

We consider the role of hadronic rescattering of daughter kaons on the observed mass spectra from $\phi$ meson decays in ultra-relativistic heavy ion collisions. A hadronic cascade code (RQMD v2.4) shows that $\sim$26% of all $\phi$'s decaying to $K^+K^-$ in central Pb+Pb collisions at SPS energies ($E_{beam} = 158 GeV/A$) have a rescattered or absorbed daughter. This significantly affects the reconstructed invariant mass of the pair and shifts $\phi$ mesons out of the mass peak. Kaon rescattering depletes the low velocity region, hardening and broadening the observed phi $m_t$ and rapidity distributions respectively, relative to the dilepton channel. This effect produces an apparent change in the experimentally determined branching ratio not necessarily related to chiral symmetry restoration. Comparisons to recent experimental measures at CERN energies reveal a possible mechanism to account for the shape of the observed spectra, though not their absolute relative magnitude.