Two phase simulation of ultrarelativistic nuclear collisions

A two phase cascade is presented for ultrahigh energy ion-ion collisions from $\sqrt{s}=17\mathrm{}–200\mathrm{GeV}.$ First a high-energy cascade is performed, in which original baryons and any freed hard partons collide. This stage ignores energy loss from soft processes. In this first version no hard processes, aside from Drell-Yan production, are included. The space-time history of the hard cascade is used to reconstruct the soft energy loss. Soft meson production is treated as coherent over groups of interacting nucleons. Two body data, though, are used to guide this reconstruction. A second, low-energy cascade is then carried out. The model selected to describe elementary hadron-hadron collisions in the soft cascade incorporates generic mesons and baryons as the agents for rescattering. We imagine a constituent quark model applies, with generic mesons consisting of an excited $q\overline{q}$ pair, and generic baryons constructed from three quarks. The chief result is a reconciliation of the important Drell-Yan measurements, indicating high-mass lepton pairs are produced as if no energy is lost from the nucleons, with the apparent success of a purely hadronic, soft cascade in describing nucleon stopping and meson production in heavy ion experiments at the CERN SPS. The LUCIFER II code may be downloaded under the GNU General Public License from http://bnlnth.phy.bnl.gov/.