Coincidence measurements of (<i>p</i>,<i>n</i>) reactions at 1.5 GeV/<i>c</i>on C and H in the Δ excitation region

Abstract

Coincidence measurements of (p,n) reactions at 1.5 GeV/c in the \ensuremath{\Delta} excitation region have been carried out for the first time. The location of the \ensuremath{\Delta} peak in the neutron spectrum is found to be dependent on the coincident particles. The peak in coincidence with p${\mathrm{\ensuremath{\pi}}}^{+}$ is shifted to lower momenta compared to the free case, in contrast to the inclusive spectrum and the coincidence with other particles where it is shifted to higher momenta. The p${\mathrm{\ensuremath{\pi}}}^{+}$ invariant-mass distribution for C is significantly lower and broader than that for H. The coincidence data set stringent constraints on theoretical models introduced to interpret the peak shift in inclusive spectra.