Study of γ γ → γ ψ ( 2 S ) at Belle

Le résumé fourni par la source

Using $980\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of data at and around the $\mathrm{\ensuremath{\Upsilon}}(nS)$ ($n=1$, 2, 3, 4, 5) resonances collected with the Belle detector at the KEKB asymmetric-energy ${e}^{+}{e}^{\ensuremath{-}}$ collider, the two-photon process $\ensuremath{\gamma}\ensuremath{\gamma}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\psi}(2S)$ is studied from the threshold to 4.2 GeV for the first time. Two structures are seen in the invariant mass distribution of $\ensuremath{\gamma}\ensuremath{\psi}(2S)$: one at ${M}_{{R}_{1}}=3922.4\ifmmode\pm\else\textpm\fi{}6.5\ifmmode\pm\else\textpm\fi{}2.0\text{ }\text{ }\mathrm{MeV}/{c}^{2}$ with a width of ${\mathrm{\ensuremath{\Gamma}}}_{{R}_{1}}=22\ifmmode\pm\else\textpm\fi{}17\ifmmode\pm\else\textpm\fi{}4\text{ }\text{ }\mathrm{MeV}$, and another at ${M}_{{R}_{2}}=4014.3\ifmmode\pm\else\textpm\fi{}4.0\ifmmode\pm\else\textpm\fi{}1.5\text{ }\text{ }\mathrm{MeV}/{c}^{2}$ with a width of ${\mathrm{\ensuremath{\Gamma}}}_{{R}_{2}}=4\ifmmode\pm\else\textpm\fi{}11\ifmmode\pm\else\textpm\fi{}6\text{ }\text{ }\mathrm{MeV}$; the signals are parametrized with the incoherent sum of two Breit-Wigner functions. The first structure is consistent with the $X(3915)$ or the ${\ensuremath{\chi}}_{c2}(3930)$, and the local statistical significance is determined to be $3.1\ensuremath{\sigma}$ with the systematic uncertainties included. The second matches none of the known charmonium or charmoniumlike states, and its global significance is determined to be $2.8\ensuremath{\sigma}$ including the look-elsewhere effect. The production rates are ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\gamma}\ensuremath{\gamma}}\mathcal{B}({R}_{1}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\psi}(2S))=9.8\ifmmode\pm\else\textpm\fi{}3.6\ifmmode\pm\else\textpm\fi{}1.3\text{ }\text{ }\mathrm{eV}$ assuming $({J}^{PC},|\ensuremath{\lambda}|)=({0}^{++},0)$ or $2.0\ifmmode\pm\else\textpm\fi{}0.7\ifmmode\pm\else\textpm\fi{}0.2\text{ }\text{ }\mathrm{eV}$ with $({2}^{++},2)$ for the first structure and ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\gamma}\ensuremath{\gamma}}\mathcal{B}({R}_{2}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\psi}(2S))=6.2\ifmmode\pm\else\textpm\fi{}2.2\ifmmode\pm\else\textpm\fi{}0.8\text{ }\text{ }\mathrm{eV}$ with $({0}^{++},0)$ or $1.2\ifmmode\pm\else\textpm\fi{}0.4\ifmmode\pm\else\textpm\fi{}0.2\text{ }\text{ }\mathrm{eV}$ with $({2}^{++},2)$ for the second. Here, the first errors are statistical and the second systematic, and $\ensuremath{\lambda}$ is the helicity.

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