Backward nucleon production by heavy baryonic resonances in proton-nucleus collisions

Abstract

The production of backward nucleons, $N(180^\circ)$, at $180^\circ$ in the nuclear target rest frame in proton-nucleus ($\mathrm{p}+A$) collisions is studied. The backward nucleons appearing outside of the kinematically allowed range of proton-nucleon ($\mathrm{p}+N$) reactions are shown to be due to secondary reactions of heavy baryonic resonances produced inside the nucleus. Baryonic resonances $R$ created in primary $\mathrm{p}+N$ reactions can change their masses and momenta due to successive collisions $R+N\rightarrow R +N $ with other nuclear nucleons. Two distinct mechanisms and kinematic restrictions are studied: the reaction $R+N\rightarrow N(180^\circ)+N$ and the resonance decay $R\rightarrow N(180^\circ)+\pi$. Simulations of $\mathrm{p}+A$ collisions using the Ultra-relativistic Quantum Molecular Dynamics model support these mechanisms and are consistent with available data on proton backward production.