Thesis defense of Luca Toscano

Rare semi-leptonic charm decays such as D+ -> pi+ mu+ mu- are mediated by flavour-changing neutral current c->ull transitions. In the vicinity of intermediate hadronic resonances, the measurements of observables such as angular and CP asymmetries offer unique probes of beyond-the-standard-model effects via null-tests of the theory. In this thesis, the first measurements of CP and forward--backward asymmetries, Acp and AFB, in D+ -> pi+ mu+ mu- decays is presented. The analysis uses data collected by the LHCb experiment between 2016 and 2018 at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb-1 . At the time of writing, the analysis is under review and the central values of the asymmetries therefore remain blinded. Nevertheless, the expected sensitivities to the observables range from the order of 10^{-2} to the order of 10^{-3}, depending on the region of dimuon-mass.

The analysis procedure is validated using the control channel Ds+ -> pi+ mu+ mu-, which is not sensitive to beyond-the-standard-model physics. The measured values of Acp and AFB are found to be consistent with zero. This agreement is consistent with the Standard Model expectation for the control channel and validates the analysis procedure.