Dergi makalesi Açık Erişim

First Observation of a Three-Resonance Structure in ${e}^{+}{e}^{-}\to \text{Nonopen}$ Charm Hadrons

2024    CERN İşbirliği

We report the measurement of the inclusive cross sections for ${e}^{+}{e}^{-}\to \mathrm{nOCH}$ (where nOCH denotes non-open charm hadrons) with improved precision at center-of-mass (c.m.) energies from 3.645 to 3.871 GeV. We observe three resonances: $R\left(3760\right)$, $R\left(3780\right)$, and $R\left(3810\right)$ with significances of $8.1\sigma $, $13.7\sigma $, and $8.8\sigma $, respectively. The $R\left(3810\right)$ state is observed for the first time, while the $R\left(3760\right)$ and $R\left(3780\right)$ states are observed for the first time in the nOCH cross sections. Two sets of resonance parameters describe the energy-dependent line shape of the cross sections well. In set I [set II], the $R\left(3810\right)$ state has mass ($3805.7±1.1±2.7$) $\left[\left(3805.7±1.1±2.7\right)\right]\text{}\text{}\mathrm{MeV}/{c}^{2}$, total width ($11.6±2.9±1.9$) $\left[\left(11.5±2.8±1.9\right)\right]\text{}\text{}\mathrm{MeV}$, and an electronic width multiplied by the nOCH decay branching fraction of ($10.9±3.8±2.5$) $\left[\left(11.0±3.4±2.5\right)\right]\text{}\text{}\mathrm{eV}$. In addition, we measure the branching fractions $B\left[R\left(3760\right)\to \mathrm{nOCH}\right]=\left(25.2±16.1±30.4\right)%\left[\left(6.4±4.8±7.7\right)%\right]$ and $B\left[R\left(3780\right)\to \mathrm{nOCH}\right]=\left(12.3±6.6±8.3\right)%\left[\left(10.4±4.8±7.0\right)%\right]$ for the first time. The $R\left(3760\right)$ state can be interpreted as an open-charm (OC) molecular state, but containing a simple four-quark state component. The $R\left(3810\right)$ state can be interpreted as a hadrocharmonium state.