Coherent photoproduction of the neutral-pion and η -meson on the deuteron at incident energies below 1.15 GeV

Le résumé fourni par la source

Coherent photoproduction of the neutral-pion and $\ensuremath{\eta}$-meson on the deuteron, $\ensuremath{\gamma}d\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}\ensuremath{\eta}d$, was experimentally studied at incident photon energies ranging from the reaction threshold to 1.15 GeV. The total cross section demonstrates a rapid rise below 1 GeV. The data are underestimated by the existing theoretical calculations based on quasifree ${\ensuremath{\pi}}^{0}\ensuremath{\eta}$ photoproduction on the nucleon followed by deuteron coalescence. At the same time, the data are rather well reproduced by the calculations taking into account the final-state interaction. We also measured for the first time the differential cross sections: the ${\ensuremath{\pi}}^{0}\ensuremath{\eta}$ invariant-mass distribution $d\ensuremath{\sigma}/d{M}_{\ensuremath{\pi}\ensuremath{\eta}}$, the ${\ensuremath{\pi}}^{0}d$ invariant-mass distribution $d\ensuremath{\sigma}/d{M}_{\ensuremath{\pi}d}$, the $\ensuremath{\eta}d$ invariant-mass distribution $d\ensuremath{\sigma}/d{M}_{\ensuremath{\eta}d}$, and the distribution over the deuteron emission angle $d\ensuremath{\sigma}/d{\mathrm{\ensuremath{\Omega}}}_{d}$ in the overall center-of-mass frame. The measured cross section $d\ensuremath{\sigma}/d{\mathrm{\ensuremath{\Omega}}}_{d}$ does not exhibit strongly backward-peaking behavior predicted by the calculations. At all incident energies, an increase in $d\ensuremath{\sigma}/d{M}_{\ensuremath{\eta}d}$ near the $\ensuremath{\eta}d$ threshold is observed, which indicates a bound or virtual $\ensuremath{\eta}d$ state resulting from a strong attraction between $\ensuremath{\eta}$ and a deuteron. The possibilities of using coherent ${\ensuremath{\pi}}^{0}\ensuremath{\eta}$ photoproduction on a nucleus to study the $\ensuremath{\eta}$-nuclear interaction are also discussed.

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