Measurement of the Cross Section for e+e- → Ξ-Ξ+and Observation of an Excited Ξ Baryon

Using a total of 11.0 fb(-1) of e(+)e(-) collision data with center-of-mass energies between 4.009 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(-) -> Xi(-)Xi(+) by means of a single baryon-tag method. After performing a fit to the dressed cross section of e(+)e(-)-> Xi(-)Xi(+) no significant psi(4230) or psi(4260) resonance is observed in the Xi(-)Xi(+) final states, and upper limits at the 90% confidence level on T B-ee for the processes psi(4230)psi/(4260) -> Xi(-)Xi(+) are determined. In addition, an excited Xi baryon at 1820 MeV/c(2) is observed with a statistical significance of 6.2-6.5 sigma by including the systematic uncertainty, and the mass and width are measured to be M = (1825.5 +/- 4.7 +/- 4.7) MeV/c(2) and Gamma = (17.0 +/- 15.0 +/- 7.9) MeV, which confirms the existence of the J(P) =3-/2 state Xi (1820).