Sideward Peak of Intermediate Mass Fragments in High Energy Proton Induced Reactions?

Intermediate mass fragment (IMF) formation in the 12 GeV proton induced reaction on Au target is analyzed by using a combined framework of a transport model (JAM/MF) and a newly developed non-equilibrium percolation (NEP) model. In this model, we can well reproduce the mass distribution of fragments. In addition, the sideward peaked angular distribution would emerge under the condition that the fragment formation time is very short, around 20 fm=c. Within this short time period, the un-heated part of the residual nucleus is kept to have doughnut shape, then the Coulomb repulsion from this shape strengthens the sideward peak of IMF. Key words: intermediate mass fragment, sideward angular distribution