Study of the coherent production on carbon of pπ+π- and nπ+ systems by 19GeV/c protons

The production reactions pC→nπ+C and pC→pπ+π-C have been studied at 19GeV/c in the CERN 'Gargamelle' bubble chamber, for low transverses momenta of the recoiling target. Both channels exhibit coherent peaks in the distributions of transferred momentum. The mass spectra of the coherently produced events show enhancements at 1.25GeV/c in the nπ+ channel and at 1.41 and 1.67GeV/c in the pπ+π- channel. The comparison of the values obtained for the branching ratios of these enhancements into nπ+ and pπ+π- with those measured in formation experiments demonstrates that the production of N* resonances does not contribute in a dominant way to these enhancements. The precision required for this analysis was obtained through a detailed study of the parameters of the bubble chamber's optics and, in particular, by taking into account the variation of these parameters from one expansion of the chamber to the other