Measurement of the cross section for $e^{+}e^{-}\rightarrow\Xi^{-}\bar\Xi^{+}$ and observation of an excited $\Xi$ baryon

TL;DR

This study measures the cross section of the process $e^{+}e^{-} ightarrow ext{Xi}^{-} ext{Xi}^{+}$, searches for resonances, and reports the observation of an excited $ ext{Xi}$ baryon at 1820 MeV/$c^{2}$ with detailed properties.

Contribution

First measurement of the cross sections for $e^{+}e^{-} ightarrow ext{Xi}^{-} ext{Xi}^{+}$ and observation of an excited $ ext{Xi}$ baryon at 1820 MeV/$c^{2}$.

Findings

No significant $ ext{psi}(4230)$ or $ ext{psi}(4260)$ resonance observed.

Upper limits set on $ ext{Gamma}_{ee} ext{B}$ for $ ext{psi}(4230)$/$ ext{psi}(4260)$ decays.

Excited $ ext{Xi}$ baryon at 1820 MeV/$c^{2}$ observed with 6.2-6.5$\sigma$ significance.

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 $e^{+}e^{-}\rightarrow\Xi^{-}\bar\Xi^{+}$ by means of a single baryon-tag method. After performing a fit to the dressed cross section of $e^{+}e^{-}\rightarrow\Xi^{-}\bar\Xi^{+}$, no significant $\psi(4230)$ or $\psi(4260)$ resonance is observed in the $\Xi^{-}\bar\Xi^{+}$ final states, and upper limits at the 90\% confidence level on $\Gamma_{ee}\mathcal{B}$ for the processes $\psi(4230)$/$\psi(4260)\rightarrow\Xi^{-}\bar\Xi^{+}$ are determined. In addition, an excited $\Xi$ baryon at 1820 MeV/$c^{2}$ is observed with a statistical significance of 6.2 $\sim$ 6.5$\sigma$ 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 $\Gamma = (17.0 \pm 15.0 \pm 7.9)$~MeV, which confirms the existence of the $J^{P}=\frac{3}{2}^{-}$ state $\Xi(1820)$.