Observation of spin alignment of resonances produced in the 3-body reactions: $$\bar pp \to \bar pp\omega ^0 $$ and $$\bar pp \to \bar {\mathcal{N}}*^{ - - } \mathcal{N}*^{ + + } \pi ^0 $$ at 5.7 GeV/cat 5.7 GeV/c

Abstract

The reaction\(\bar pp \to \bar pp\pi ^ - \pi ^ + \pi ^0 \) has been studied at 5.7 GeV/c in the 81 cm Saclay hydrogen bubble chamber. Production of ω0 and η0 mesons has been observed. The ω0 mesons are collimated in the forward and backward directions in the c.m.s. The decay angular distribution of the ω0 indicates that it is produced with the spin aligned in the plane perpendicular to the incident\(\bar p\) (or p) momentum transformed to the ω0 rest frame, an effect which is enhanced when the four-momentum transfert is limited to |t|<0.5 (GeV/c)2. It has been found that of the observedN*++ (1238) and\(\bar {\mathcal{N}}*^{ - - } \) (1238) isobars about 80% are produced in pairs in the 3-body reaction\(\bar pp \to \bar {\mathcal{N}}*^{ - - } \mathcal{N}*^{ + + } \pi ^0 \). In this reaction theN* isobars are produced in aligned states with the spin directions of theN* and\(\bar {\mathcal{N}}*\) being strongly correlated such that there are few events in which both theN* and\(\bar {\mathcal{N}}*\) decay with the p and\(\bar p\) from the isobars making large angles relative to initial p or\(\bar p\) direction transformed into the isobar rest frame.