Measurement of the cross section for $e^{+}{e}^{-}\to \hat{I}{ž}^{-}\bar{\hat{I}}{ž}^{+}$ and observation of an excited $\hat{I}ž$ baryon

Abstract

Using a total of 11.0 fb${}^{-1}$ of $e^{+}{e}^{-}$ collision data with center-of-mass energies between 4.009 GeV and 4.6 GeV and collected with the BESIII detector at BEPCII, we measure fifteen exclusive cross sections and effective form factors for the process $e^{+}{e}^{-}\to \hat{I}{ž}^{-}\bar{\hat{I}}{ž}^{+}$ by means of a single baryon-tag method. After performing a fit to the dressed cross section of $e^{+}{e}^{-}\to \hat{I}{ž}^{-}\bar{\hat{I}}{ž}^{+}$, no significant $\ddot{I}ˆ(4230)$ or $\ddot{I}ˆ(4260)$ resonance is observed in the $\hat{I}{ž}^{-}\bar{\hat{I}}{ž}^{+}$ final states, and upper limits at the 90\% confidence level on $\hat{I}{“}_{ee}\mathcal{B}$ for the processes $\ddot{I}ˆ(4230)$/$\ddot{I}ˆ(4260)\to \hat{I}{ž}^{-}\bar{\hat{I}}{ž}^{+}$ are determined. In addition, an excited $\hat{I}ž$ baryon at 1820 MeV/$c^2$ is observed with a statistical significance of 6.2 $\sim$ 6.5$\ddot{I}ƒ$ by including the systematic uncertainty, and the mass and width are measured to be $M=(1825.5\pm 4.7\pm 4.7)$~MeV/$c^2$ and $\hat{I}“=(17.0\pm 15.0\pm 7.9)$~MeV, which confirms the existence of the $J^P={\frac{3}{2}}^{-}$ state $\hat{I}ž(1820)$.

8 pages, 4 figures, 1 Supplemental Material with 2 pages, consistent with paper published in Phys. Rev. Lett. 124, 032002 (2020)