On the role of the Δ(1232) on the transverse nuclear response in the ( e, e′) reaction

Abstract

The transverse nuclear response to an electromagnetic probe which is limited to create (or destroy) a particle-hole ( ph) or delta-hole ( Δh) pair is analyzed. Correlations of the random phase approximation (RPA) type and self-energy insertions are considered. For RPA correlations we have developed a scheme which includes explicitly the Δ and the exchange terms. Self-energy insertions over ph and Δh bubbles are studied. Several residual interactions based on a contact plus a ( π + ϱ)-meson exchange potential are used. All calculations are performed in non-relativistic nuclear matter. The main effect of the Δ is to reduce the intensity over the nuclear quasi-elastic peak. Exchange RPA terms are very important, while the terms with self-energy insertions depend strongly on the residual interaction employed. Our results are compared with data for 40Ca at momentum transfer q = 410 and q = 550 MeV/ c, where the longitudinal response is also briefly discussed.