Precision measurements of the pp\to π^+pn and pp\to π^+d reactions: importance of long-range and tensor force effects

Abstract

Inclusive measurements of pion production in proton--proton collisions in the forward direction were undertaken at 400 and 600 MeV at COSY using the Big Karl spectrograph. The high resolution in the $\ddot{I}{€}^{+}$ momentum ensured that there was an unambiguous separation of the $pp\to \ddot{I}{€}^{+}d/\ddot{I}{€}^{+}pn$ channels. Using these and earlier data, the ratio of the production cross sections could be followed through the $\hat{I}”$ region and compared with the predictions of final state interaction theory. Deviations are strongly influenced by long-range terms in the production operator and the tensor force in the final $pn$ system. These have been investigated in a realistic $pp\to \ddot{I}{€}^{+}d/\ddot{I}{€}^{+}pn$ calculation that includes $S\rightleftharpoons D$ channel coupling between the final nucleons. A semi-quantitative understanding of the observed effects is achieved.

10 pages, 3 figures