Observation of di-structures in $e^{+}{e}^{-}\to J/\ddot{I}ˆ\mathrm{X}$ at center-of-mass energies around 3.773 GeV

Abstract

We report a measurement of the observed cross sections of the inclusive $J/\ddot{I}ˆ$ production in $e^{+}{e}^{-}\to J/\ddot{I}ˆ\mathrm{X}$ based on 3.21 fb${}^{-1}$ of data accumulated at energies from 3.645 to 3.891 GeV with the BESIII detector operated at the BEPCII collider. The energy-dependent lineshape obtained from the measured cross sections cannot be well described by two Breit-Wigner (BW) amplitudes of the expected decays $\ddot{I}ˆ(3686)\to J/\ddot{I}ˆ\mathrm{X}$ and $\ddot{I}ˆ(3770)\to J/\ddot{I}ˆ\mathrm{X}$. Instead it can be better described with three BW amplitudes of the decays $\ddot{I}ˆ(3686)\to J/\ddot{I}ˆ\mathrm{X}$, $R(3760)\to J/\ddot{I}ˆ\mathrm{X}$ and $R(3790)\to J/\ddot{I}ˆ\mathrm{X}$ with two distinct structures referred to as $R(3760)$ and $R(3790)$. Under this assumption, we extracted their masses, total widths, and the product of the leptonic width and decay branching fractions to be $M_{R(3760)}=3761.7\pm 2.2\pm 1.2$ MeV/$c^2$, $\hat{I}{“}_{R(3760)}^{\mathrm{tot}}=6.7\pm 11.1\pm 1.1$ MeV, $\hat{I}{“}_{R(3760)}^{ee}\mathcal{B}[R(3760)\to J/\ddot{I}ˆ\mathrm{X}]=(4.0\pm 4.3\pm 1.2)$ eV, $M_{R(3790)}=3784.7\pm 5.7\pm 1.6$ MeV/$c^2$, $\hat{I}{“}_{R(3790)}^{\mathrm{tot}}=31.6\pm 11.9\pm 3.2$ MeV, $\hat{I}{“}_{R(3790)}^{ee}\mathcal{B}[R(3790)\to J/\ddot{I}ˆ\mathrm{X}]=(18.1\pm 10.3\pm 4.7)$ eV, where the first uncertainties are statistical and second systematic.

8 pages, 3 figures