Measurement of masses of the Ξc(2645)Ξc(2645) and Ξc(2815)Ξc(2815) baryons and observation of Ξc(2980)→Ξc(2645)πΞc(2980)→Ξc(2645)π

We report a precise measurement of the masses of the Ξc(2645)Ξc(2645) and Ξc(2815)Ξc(2815) baryons using a data sample of 414 fb−1 collected by the Belle Collaboration at the KEKB e+e−e+e− collider. The states Ξc(2645)0,+Ξc(2645)0,+ are observed in the Ξc+,0π−,+ decay modes, while the Ξc(2815)0,+Ξc(2815)0,+ are reconstructed in the Ξc(2645)+,0π−,+Ξc(2645)+,0π−,+ decay modes. The following mass splittings are determined: mΞc(2645)+−mΞc(2645)0=(−0.1±0.3(stat)±0.6(syst)) MeV/c2mΞc(2645)+−mΞc(2645)0=(−0.1±0.3(stat)±0.6(syst)) MeV/c2 and mΞc(2815)+−mΞc(2815)0=(−3.4±1.9(stat)±0.9(syst)) MeV/c2mΞc(2815)+−mΞc(2815)0=(−3.4±1.9(stat)±0.9(syst)) MeV/c2 with a much better precision than the current world averages. We also observe a new decay mode, Ξc(2980)0,+→Ξc(2645)+,0π−,+Ξc(2980)0,+→Ξc(2645)+,0π−,+.