Double Delta(1232) excitation and the ABC effect in the reaction n + p -> 2H (pi pi)

Abstract

The deuteron spectrum in n+p -> 2 H(pi pi) at k_n = 1.88 GeV/c and theta_d = 0^o is explained by considering a Delta Delta excitation as the dominant reaction mechanism for the 2 pi production. We present a new theoretical approach based on a coupled channel formalism which allows to include the residual interaction within the intermediate Delta Delta and Delta N systems. The corresponding interaction potentials V_{DeltaDelta} and V_{DeltaN} are adopted from a meson exchange model with pi, rho, omega, and sigma exchange taken into account. The influence of the residual interaction on the deuteron spectrum is studied. We also predict the angular distribution of the two pions. It is shown that this distribution is closely connected to the spin structure of the DeltaDelta excitation.