Search for η -mesic 4 He with the WASA-at-COSY detector

Le résumé fourni par la source

An exclusive measurement of the excitation function for the $dd\ensuremath{\rightarrow}{}^{3}\mathrm{He}p{\ensuremath{\pi}}^{\ensuremath{-}}$ reaction was performed at the Cooler Synchrotron COSY-J\"ulich with the WASA-at-COSY detection system. The data were taken during a slow acceleration of the beam from 2.185 to 2.400 GeV/$c$ crossing the kinematic threshold for the $\ensuremath{\eta}$-meson production in the $dd\ensuremath{\rightarrow}{}^{4}\mathrm{He}\ensuremath{\eta}$ reaction at 2.336 GeV/$c$. The corresponding excess energy with respect to the ${}^{4}$He-$\ensuremath{\eta}$ system varied from $\ensuremath{-}$51.4 to 22 MeV. The integrated luminosity in the experiment was determined using the $dd\ensuremath{\rightarrow}{}^{3}\mathrm{He}n$ reaction. The shape of the excitation function for the $dd\ensuremath{\rightarrow}{}^{3}\mathrm{He}p{\ensuremath{\pi}}^{\ensuremath{-}}$ reaction was examined. No signal of the ${}^{4}$He-$\ensuremath{\eta}$ bound state was observed. An upper limit for the cross section for the bound state formation and decay in the process $dd\ensuremath{\rightarrow}{({}^{4}\mathrm{He}\ensuremath{-}\ensuremath{\eta})}_{\mathrm{bound}}\ensuremath{\rightarrow}{}^{3}\mathrm{He}p{\ensuremath{\pi}}^{\ensuremath{-}}$ was determined on the 90$%$ confidence level and it varies from 20 to 27 nb for the bound state width ranging from 5 to 35 MeV, respectively.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.