Production of $${\mathcal{N}}^* (1518)$$ and $${\mathcal{N}}^* (1688)$$ isobars in $$\bar pp$$ interactions at 5.7 GeV/c. Determination of their widths and decay branching ratiosinteractions at 5.7 GeV/c. Determination of their widths and decay branching ratios

Abstract

The nucleon isobars\({\mathcal{N}}^* (1518)\) and\({\mathcal{N}}^* (1688)\) are observed in inelastic interactions of 5.7 GeV/c antiprotons in hydrogen. The widths of both of them are found to be small ((55±15) MeV and (70±20) MeV respectively), in agreement with recent phase-shift data. The 2-body to 3-body branching ratios are estimated (being 1.25−0.71+0.44 in the case of the\({\mathcal{N}}^* (1518)\) and less than 1.26 with 95% confidence for the\({\mathcal{N}}^* (1688)\) and show that the inelasticities of both resonances in π−p scattering are high. A detailed study of the 3-body\({\mathcal{N}}\pi \pi \) decays provides no evidence in either case for the cascade decay into\(\mathcal{N}^* (1238) + \pi \). Deviations from uniform population of the Dalitz plots for the 3-body decays are observed and are studied in terms of the 3-body decay matrix elements. Upper limits for decay of the\({\mathcal{N}}^* (1688)\) into\({\mathcal{N}}\eta \) and ΛK final states are estimated.