Observation of thed*Effect in thep¯d→pp¯π+π−nReaction at 5.55GeVc

Abstract

This experiment is based on 150 000 photographs, taken at the Zero Gradient Synchrotron with the 30-in. bubble chamber. We present results on a subsample of ${p}_{s}\overline{p}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}n$ events in which the protons stopping in the chamber do not show the characteristic nucleon-spectator behavior. The selection procedure for this sample is discussed. A strong low-mass ${p}_{s}n{\ensuremath{\pi}}^{+}$ enhancement at 2.2 $\frac{\mathrm{GeV}}{{c}^{2}}$ is observed. This bump is not considered as a real resonance and is interpreted as having the same origin as the 2.2-$\frac{\mathrm{GeV}}{{c}^{2}}$ $d\ensuremath{\pi}$ enhancement observed, for instance, in the $\overline{p}d\ensuremath{\rightarrow}\overline{p}d{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ reaction at the same energy.