Measurements of the Mass and Width of the ηc Using the Decay ψ(3686)→γηc

Le résumé fourni par la source

The mass and width of the lowest-lying $S$-wave spin singlet charmonium state, the ${\ensuremath{\eta}}_{c}$, are measured using a data sample of $1.06\ifmmode\times\else\texttimes\fi{}{10}^{8}$ $\ensuremath{\psi}(3686)$ decays collected with the BESIII detector at the BEPCII storage ring. We use a model that incorporates full interference between the signal reaction, $\ensuremath{\psi}(3686)\ensuremath{\rightarrow}\ensuremath{\gamma}{\ensuremath{\eta}}_{c}$, and a nonresonant radiative background to describe the line shape of the ${\ensuremath{\eta}}_{c}$ successfully. We measure the ${\ensuremath{\eta}}_{c}$ mass to be $2984.3\ifmmode\pm\else\textpm\fi{}0.6\ifmmode\pm\else\textpm\fi{}0.6\text{ }\text{ }\mathrm{MeV}/{c}^{2}$ and the total width to be $32.0\ifmmode\pm\else\textpm\fi{}1.2\ifmmode\pm\else\textpm\fi{}1.0\text{ }\text{ }\mathrm{MeV}$, where the first errors are statistical and the second are systematic.

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