First Observation of An Excited Charm Baryon Decaying to Omega Charm Baryon at the BaBar Experiment

Book excerpt: We have carried out a search for a charmed baryon [Omega]$*\atop{c}$ decaying to [Omega]$0\atop{c}$ and a [gamma] where [Omega] c candidates are reconstructed using decay modes [Omega]-[pi]+(c1), [Omega]-[pi]+[pi]0(c2), [Omega]-[pi]+[pi]-[pi]+(c3) and [Xi]-K-[pi]+[pi]+(c4). This search is performed by analyzing integrated luminosity of 230.7 fb-1 data collected by the BABAR detector at the Stanford Linear Accelerator Center. In decay channel [Omega]$*\atop{c}$ → [Omega]$0\atop{c}$([Omega]-[pi]+)[gamma] (C1), we observe a signal yield of 39.2$+9.8\atop{-9.1}$ (stat)±6.0(syst) events with a significance of 4.2 standard deviations. In decay channels [Omega]$*\atop{c}$ → [Omega]$0\atop{c}$([Omega]-[pi]+[pi]0)[gamma] (C2) and [Omega]$*\atop{c}$ →} [Omega]$0\atop{c}$([Xi]-K-[pi]+[pi]+)[gamma] (C4), we observe signal yields of 55.2$+16.1\atop{-15.2}$ ± 5.6 and 20.2$+9.3\atop{-8.5}$ ± 3.1 with significances of 3.4 and 2.0 [sigma], respectively. As for the [Omega]$*\atop{c}$ → [Omega]$0\atop{c}$([Omega]-[pi]+[pi]-[pi]+)[gamma] (C3) decay channel, we observe signal yields of -5.1$+5.3.8\atop{-4.7}$±1.0 without a positive significance. We assume the same production mechanism for the four decay channels of [Omega]$*\atop{c}$ studied. By combining these four channels, the fit results in a signal yield of 105.3$+21.2\atop{-20.5}$± 6.0 events with a significance of 5.2 [sigma]. We report the mass difference [Omega]$*\atop{c}$ - [Omega]$0\atop{c}$([delta]m) of the singly charmed baryon [Omega]$*\atop{c}$ to be 70.8$+1.0\atop{-1.0}$±1.1 MeV. Finally, the ratios of production cross sections are calculated: [sigma](e+e-→C1)/[sigma](e+e-→c1) = 0.71$+0.19\atop{-0.18}$±0.11, [sigma](e+e-→C2)/[sigma](e+e-→c2) = 1.76$+0.71\atop{-0.69}$±0.19, [sigma](e+e-→C3)/[sigma](e+e-→c3) = -0.66$+0.74\atop{-0.66}$±0.13, [sigma](e+e-→C4)/[sigma](e+e-→c4) = 1.70{sup +1.0}{sub -1.0}±0.27 and [sigma](e+e-→[Omega]$*\atop{c}$ (combined))/[sigma](e+e-→[Omega]$0\atop{c}$) = 1.0$+0.23\atop{-0.22}$±0.11.