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

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 $p_s\overline{p}{\pi }^{+}{\pi }^{-}n$ 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 $p_{s}n{\pi }^{+}$ 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-$\frac{\mathrm{GeV}}{c^2}$ $d\pi$ enhancement observed, for instance, in the $\overline{p}d\to \overline{p}d{\pi }^{+}{\pi }^{-}$ reaction at the same energy.