On the derivation of the PWIA cross-section for quasi-free reactions

Abstract

0n ly recently quasi-free reactions (QFR) have become, in addit ion to quasi-free scattering (QFS) processes, a s tandard tool of investigation of the cluster structure (~-s). These reactions have been performed mostly on light nuclei, where the possible two-cluster configuration seems to be more likely to occur and the high Q-value of the process ensures high momenta, at least in the exit channel. Figure 1 shows a schematic diagram for the quasi-free reaction fV(0, 1 2)S. The target nucleus N is assumed as decomposed, in the lower vertex, in the clusters SqT, where S is considered spectator of the vir tual reaction T(0, 1)2. The analysis of QFR data, as well as for QFS, is usually performed in the framework of the impulse approximation, both in plane-wave (PWIA) and distorted-wave (DWI~) treatment . I t is well known that the models based on the impulse approximation are inadeguate, at least quanti tat ively, to give a correct description of QFR at low energies. I[owever, since even DWIA is unable to take into account the absorption of the incoming and outgoing waves and in general the dynamics of the process, in most cases PWI_~ has been used, due to its simplicity, to understand quali tat ively the results of these reactions.