Study of the weakly decaying charmed baryons Lambda+_c , Xi+_c and Xi0_c in the Belle II data

Abstract

Charmed baryons are an exciting field of research in which a lot of work has been done, though many quantum numbers remain to be experimentally confirmed, with future research focusing on new excited and possible exotic states.In this thesis, the ground states of the weakly decaying charmed baryons Λ+c , Ξ+c and Ξ0c are studied within the Belle II experiment at the SuperKEKB e+e−collider in Tsukuba,Japan. In particular, the mode Λ+c →p+K−π+, the signal modes Ξ+c →Σ+K−π+ and Ξ0c →Ω−K+ and the normalization modes Ξ+c →Ξ−π+π+ and Ξ0c →Ξ−π+ are investigated. An optimization of parameters and fixing of signal shape is developed onsimulated Monte Carlo data for an unbiased use of Belle II data collected at the Υ(4S) resonance at 10.58 GeV. For the Λ+c →p+K−π+ decay the signal yield is determined and additionally the scaled momentum ’xp’ distribution is compared between simulated and 16.5 fb−1 of collected data revealing significant differences. This includes an underestimation of the productionrate in simulated data and differences in shape. The analysis further showed higher signal and less background for Λ+c of production via continuum, motivating a focus on continuum Monte Carlo and a xp >0.4 selection for charmed baryons. For the signal and normalization modes of Ξ+c and Ξ0c, the signal yields are determined using 90.172 fb−1 of collected data and a relative branching fraction measurement is performed yielding Br(Ξ0c→Ω−K+)/Br(Ξ0c→Ξ−π+) = 0.277 ±0.017stat ±0.014sys and Br(Ξ+c →Σ+K−π+)/Br(Ξ+c →Ξ−π+π+)=0.771 ±0.095stat ±0.118sys. The results agree with the current averages provided bythe Particle Data Group (PDG) within 0.52σ and 0.93σ. Weighted averages combining previous measurements with the ones presented in this thesis are calculated and compared to.