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 $R+N\to R+N$ with other nuclear nucleons. Two distinct mechanisms and kinematic restrictions are studied: the reaction $R+N\to N(180^{\circ })+N$ and the resonance decay $R\to N(180^{\circ })+\ddot{I}€$. 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.

16 pages, 15 figures