Roper excitation in $\vec{p}+α\to \vec{p}+α+X$ reactions

Abstract

We calculate differential cross sections and the spin transfer coefficient $D_{nn}$ in the $\vec{p}+α\to \vec{p}+α+π^0$ reaction for proton bombarding energies from 1 to 10 GeV and $π^0 - p$ invariant masses spanning the region of the N$^*$(1440) Roper resonance. Two processes -- $Δ$ excitation in the $α$-particle and Roper excitation in the proton -- are included in an effective reaction model which was shown previously to reproduce existing inclusive spectra. The present calculations demonstrate that these two contributions can be clearly distinguished via $D_{nn}$, even under kinematic conditions where cross sections alone exhibit no clear peak structure due to the excitation of the Roper.