Thesis defense of Janina Nicolini

Flavour-changing neutral currents, such as b-> sl+l- transitions, are forbidden at tree level in the Standard Model (SM), and can only occur at loop level. Therefore, they are sensitive to small deviations from the presence of possible New Physics (NP) effects with respect to the SM predictions. While ordinary matter is made out of baryons, very few measurements have been performed with baryonic b-> sl+l- transitions due to the production suppression of beauty baryons at collider experiments.

In this thesis, several analyses are presented to improve the knowledge of the four weakly decaying beauty baryons and respective b-> sl+l- transitions.

First of all, the current status of the angular analysis of Lambdab -> Lambdal+l- decays is performed for the first time using the full Run 1 and 2 datasets collected by the LHCb experiment. All ten angular coefficients are attempted to be measured in the dilepton invariant mass squared, q2, range from 15 to 20 GeV^2/c^4 for the muon mode. The muon mode fit procedure has been validated with pseudo-experiments. The angular observables of the Lambdab -> Lambdamu+mu- are kept blind in the thesis.

Furthermore, the charmonium decay modes, Xib- -> Xi-Jpsi and Omegab- -> Omega-Jpsi, have been used to improve the knowledge of the Omegab- baryon properties. Similarly, the previously not observed Xib0 -> Xi0Jpsi and Xib0 -> Xi0 psi(2S) decays have been studied. In addition, this thesis also presents the current status for the first search for the Xib- -> Xi-mu+mu- and the observation of the respective Xib- -> Xi-psi(2S) decay.

Beside the analysis work conducted in this thesis, the contribution to the Scintillating Fibre (SciFi) detector of the LHCb experiment are discussed.

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