Observation of new Ξ꜀⁰ states decaying to Λ꜀⁺K⁻, and development of the TORCH time-of-flight detector

Abstract

Using a data sample of proton-proton collisions at center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 5.6 fb-1 collected by the LHCb experiment, the Λc+K- mass spectrum is studied. Three new, excited Ξc0 states are observed and their masses and natural widths are measured to be

m(Ξc(2923)0) = 2923.04 ± 0.25 ± 0.18 ± 0.14 MeV, Γ(Ξc(2923)0) = 7.09 ± 0.79 ± 1.39 MeV, m(Ξc(2939)0) = 2938.55 ± 0.21 ± 0.17 ± 0.14 MeV, Γ(Ξc(2939)0) = 10.22 ± 0.77 ± 1.04 MeV, m(Ξc(2965)0) = 2964.88 ± 0.26 ± 0.14 ± 0.14 MeV, Γ(Ξc(2965)0) = 14.07 ± 0.91 ± 1.34 MeV,

where the uncertainties are statistical, systematic and the third one is due to the knowledge of the Λc+ mass. All peaks have significances greatly exceeding 5σ. Though the mass of Ξc(2965)0 is close to the known Ξc(2970)0 its natural width differs significantly and therefore it is interpreted as a different baryon.

Furthermore, this thesis summarises the status of the TORCH time-of-flight detector by describing the characterisation of Micro-Channel Plate Photomultiplier tubes (MCP-PMTs), outlining the recent beam test campaigns as well as an analysis comparing the photon yield in simulation and data.