First Observation of $\hat{I}›\ddot{I}{€}^{+}$ and $\hat{I}›\ddot{I}{€}^{-}$ Signals near the $\bar{K}N(I=1)$ Mass Threshold in $\hat{I}{›}_c^{+}\to \hat{I}›\ddot{I}{€}^{+}\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ Decay

Abstract

Using the data sample of 980 fb${}^{-1}$ collected with the Belle detector operating at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider, we present the results of an investigation of the $\hat{I}›\ddot{I}{€}^{+}$ and $\hat{I}›\ddot{I}{€}^{-}$ invariant mass distributions looking for substructure in the decay $\hat{I}{›}_c^{+}\to \hat{I}›\ddot{I}{€}^{+}\ddot{I}{€}^{+}\ddot{I}{€}^{-}$. We find a significant signal in each mass dis\ tribution. When interpreted as resonances, we find for the $\hat{I}›\ddot{I}{€}^{+}$ ($\hat{I}›\ddot{I}{€}^{-}$) combination a mass of $1434.3\pm 0.6(\mathrm{stat})\pm 0.9(\mathrm{syst})$ MeV/$c^2$ [$1438.5\pm 0.9(\mathrm{stat})\pm 2.5(\mathrm{syst})$ MeV/$c^2$], an intrinsic width of $11.5\pm 2.8(\mathrm{stat})\pm 5.3(\mathrm{syst})$ MeV/$c^2$ [$33.0\pm 7.5(\mathrm{stat})\pm 23.6(\mathrm{syst})$ MeV/$c^2$] with a significance of 7.5$\ddot{I}ƒ$ (6.2$\ddot{I}ƒ$). As these two signals are very close to the $\bar{K}N$ threshold, we also investigate the possibility of a $\bar{K}N$ cusp, and find that \ we cannot discriminate between these two interpretations due to the limited size of the data sample.