Roper Excitation in Alpha-Proton Scattering

We study the Roper excitation in the $(\alpha,\alpha')$ reaction. We consider all processes which may be relevant in the Roper excitation region, namely, Roper excitation in the target, Roper excitation in the projectile, and double $\Delta$ excitation processes. The theoretical investigation shows that the Roper excitation in the proton target mediated by an isoscalar exchange is the dominant mechanism in the process. We determine an effective isoscalar interaction by means of which the experimental cross section is well reproduced. This should be useful to make predictions in related reactions and is a first step to construct eventually a microscopic $NN \rightarrow NN^*$ transition potential, for which the present reaction does not offer enough information.