Study of Lambda+ c, Xi0 c and Xi+ c Charmed Baryons using Belle II Data at the Y(4S) energy

Abstract

The spectroscopy of Charmed Baryons presents a field of study that is yet to be well understood; this is despite the great experimental and theoretical progress of the past decade. There exists a plethora of resonances that have been observed whose true compositions and quantum numbers are unknown, and in a similar token, there are states that are predicted by various models but have not been observed. In this work, we study the ground-state singly charmed baryons allocated to an SU(3) J^P = 1/2+ antisymmetric antitriplet symmetry of flavor space: Λc+(udc), Ξc0(dsc) and Ξc+ (usc). These charmed baryons decay weakly into hadrons such as protons, pions and kaons, as well as strange baryons (hyperons). Using up to 90.16 fb−1 of integrated luminosity data collected by the Belle II detector from events corresponding to e+e− collisions at or near the Υ(4S) energy, we reconstruct charmed baryons from combinations of hadrons and other final state particles, particularly of the channel modes: Λc+ → pK−π+, Ξc0 → Ξ−π+, Λ0K−π+ and Ξc+ → Ξ−π+π+, Λ0K−π+π+, with the secondary decays Ξ− → Λ0π−, and Λ0 → pπ−. The charge conjugate combinations of every mode are also included in the reconstruction. We distribute reconstructed events primarily in their invariant mass and xp value. The xp variable represents the ratio of the center-of-mass momentum of the charmed baryons to the total available momentum from the e+e− collision. By optimizing the xp distributions of the charmed baryon candidates to the true signal in Monte Carlo simulations, we gain insights into the preferred prompt mechanism and kinematic regimes for the production of optimal signal events. In this thesis, it is demonstrated that the reconstruction of charmed baryons at Belle II is optimal for events from prompt cc fragmentations. Beyond establishing an optimal selection criteria for the reconstructed charmed and strange baryons, we also provide a measurement of the ratios of branching fractions B(Ξc0 → Λ0K−π+)/B(Ξc0 → Ξ−π+), and B(Ξc+ → Λ0K−π+π+)/B(Ξc+ → Ξ−π+π+).