摘要
Rapidity distributions of both E895 proton data at AGS energies and NA49 net proton data at SPS energies can be described reasonably well with a potential version of the Ur QMD in which mean-field potentials for both pre-formed hadrons and confined baryons are considered, with the help of a traditional coalescence afterburner in which one parameter set for both relative distance R_0 and relative momentum P_0,(3.8 fm, 0.3 Ge V/c), is used. Because of the large cancellation between the expansion in R_0 and the shrinkage in P_0 through the Lorentz transformation, the relativistic effect in clusters has little effect on the rapidity distribution of free(net) protons. Using a Woods-Saxon-like function instead of a pure logarithmic function as seen by FOPI collaboration at SIS energies, one can fit well both the data at SIS energies and the Ur QMD calculation results at AGS and SPS energies. Further, it is found that for central Au+Au or Pb+Pb collisions at top SIS, SPS and RHIC energies, the proton fractions in clusters are about33%, 10%, and 0.7%, respectively.
Rapidity distributions of both E895 proton data at AGS energies and NA49 net proton data at SPS energies can be described reasonably well with a potential version of the UrQMD in which mean-field potentials for both pre-formed hadrons and confined baryons are considered, with the help of a traditional coalescence afterburner in which one parameter set for both relative distance R0 and relative momentum P0, （3.8 fm, 0.3 GeV/c）, is used. Because of the large cancellation between the expansion in R0 and the shrinkage in P0 through the Lorentz transformation, the relativistic effect in clusters has little effect on the rapidity distribution of free （net） protons. Using a Woods-Saxon-like function instead of a pure logarithmic function as seen by FOPI collaboration at SIS energies, one can fit well both the data at SIS energies and the UrQMD calculation results at AGS and SPS energies. Further, it is found that for central Au＋Au or Pb＋Pb collisions at top SIS, SPS and RHIC energies, the proton fractions in clusters are about 33%, 10%, and 0.7%, respectively.
基金
the National Natural Science Foundation of China(Grant Nos.11375062
11547312 and 11275068)
the project sponsored by SRF for ROCS
SEM
and the Doctoral Scientific Research Foundation(Grant No.11447109)
