Helium-3 production from Pb+Pb collisions at SPS energies with the UrQMD model and the traditional coalescence afterburner

A potential version of the UrQMD（UrQMD/M） transport model and a traditional coalescence model are combined to calculate the production of;He fragments in central Pb+Pb collisions at SPS energies 20-80 Ge V/nucleon. It is found that the Lorentz transformation in the afterburner influences visibly the;He yield and should be considered in calculations. The rapidity distribution of;He multiplicities（including the concave shape） can be described well with Ur QMD/M when it stops during t;ut=（100±25） fm/c and the coalescence afterburner with one parameter set of（R;,P;）=（3.8 fm, 0.3 Ge V/c） is taken into use afterwards.