Observation of ηc(2S)→3(π+π−) and measurements of χcJ→3(π+π−) in ψ(3686) radiative transitions

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The hadronic decay ${\ensuremath{\eta}}_{c}(2S)\ensuremath{\rightarrow}3({\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}})$ is observed with a statistical significance of 9.3 standard deviations using $(448.1\ifmmode\pm\else\textpm\fi{}2.9)\ifmmode\times\else\texttimes\fi{}{10}^{6}\text{ }\text{ }\ensuremath{\psi}(3686)$ events collected by the BESIII detector at the BEPCII collider. The measured mass and width of ${\ensuremath{\eta}}_{c}(2S)$ are $(3643.4\ifmmode\pm\else\textpm\fi{}2.3\text{ }(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}4.4\text{ }(\mathrm{syst}))\text{ }\text{ }\mathrm{MeV}/{c}^{2}$ and $(19.8\ifmmode\pm\else\textpm\fi{}3.9\text{ }(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}3.1\text{ }(\mathrm{syst}))\text{ }\text{ }\mathrm{MeV}$, respectively, which are consistent with the world average values within two standard deviations. The product branching fraction $\mathcal{B}[\ensuremath{\psi}(3686)\ensuremath{\rightarrow}\ensuremath{\gamma}{\ensuremath{\eta}}_{c}(2S)]\ifmmode\times\else\texttimes\fi{}\mathcal{B}[{\ensuremath{\eta}}_{c}(2S)\ensuremath{\rightarrow}\phantom{\rule{0ex}{0ex}}3({\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}})]$ is measured to be $(9.2\ifmmode\pm\else\textpm\fi{}1.0\text{ }(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}1.2\text{ }(\mathrm{syst}))\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$. Using $\mathcal{B}[\ensuremath{\psi}(3686)\ensuremath{\rightarrow}\ensuremath{\gamma}{\ensuremath{\eta}}_{c}(2S)]=\phantom{\rule{0ex}{0ex}}(7.{0}_{\ensuremath{-}2.5}^{+3.4})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$, we obtain $\mathcal{B}[{\ensuremath{\eta}}_{c}(2S)\ensuremath{\rightarrow}3({\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}})]=(1.31\ifmmode\pm\else\textpm\fi{}0.15\text{ }(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.17\text{ }(\mathrm{syst})\text{ }(\genfrac{}{}{0}{}{+0.64}{\ensuremath{-}0.47})\text{ }(\mathrm{extr}))\ifmmode\times\else\texttimes\fi{}\phantom{\rule{0ex}{0ex}}{10}^{\ensuremath{-}2}$, where the third uncertainty is from $\mathcal{B}[\ensuremath{\psi}(3686)\ensuremath{\rightarrow}\ensuremath{\gamma}{\ensuremath{\eta}}_{c}(2S)]$. We also measure the ${\ensuremath{\chi}}_{cJ}\ensuremath{\rightarrow}3({\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}})$ ($J=0$, 1, 2) decays via ${\ensuremath{\psi}}^{\ensuremath{'}}\ensuremath{\rightarrow}\ensuremath{\gamma}{\ensuremath{\chi}}_{cJ}$ transitions. The branching fractions are $\mathcal{B}[{\ensuremath{\chi}}_{c0}\ensuremath{\rightarrow}3({\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}})]=\phantom{\rule{0ex}{0ex}}(2.080\ifmmode\pm\else\textpm\fi{}0.006\text{ }(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.068\text{ }(\mathrm{syst}))\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$, $\mathcal{B}[{\ensuremath{\chi}}_{c1}\ensuremath{\rightarrow}3({\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}})]=(1.092\ifmmode\pm\else\textpm\fi{}0.004\text{ }(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.035\text{ }(\mathrm{syst}))\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$, and $\mathcal{B}[{\ensuremath{\chi}}_{c2}\ensuremath{\rightarrow}3({\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}})]=(1.565\ifmmode\pm\else\textpm\fi{}0.005\text{ }(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.048\text{ }(\mathrm{syst}))\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$.

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