# Rare decays

Rare decays of beauty hadrons constitute an ideal laboratory for the search for physics phenomena beyond the Standard Model (SM). These decays are Flavour Changing Neutral Currents (FCNC) and are thus forbidden at tree level in the SM. Rare, loop-mediated processes allow indirect access to quantum corrections from degrees of freedom at larger scales and provide excellent complementarity to direct searches of New Physics (NP).

Our group is one of the main players in the study of *b*→*sll* processes, mainly focused on two aspects: the study of the angular distribution of *B*^{0}→*K*^{*0}*μμ* decays, and the test of lepton flavour universality in *B*^{0}→*K*^{*0}*ll* decays. The main feature of these two types of analysis is that the results so far are showing tensions with the SM predictions, providing tantalizing hints of NP phenomena: on one hand, the analysis of the angular distribution of the *B*^{0}→*K*^{*0}*μμ* with LHCb Run I data shows a deviation of 3.4σ with respect to the SM prediction, and, on the other, the study of the ratio of branching fractions of *B*^{+}→*K*^{+}*μμ* and *B*^{+}→*K*^{+}*ee*, and *B*^{0}→*K*^{*0}*μμ* and *B*^{0}→*K*^{*0}*ee* decays show deviations of 2.2-2.7σ with respect to the expected value.

Our group led the effort in measuring the angular distribution of the *B*^{0}→*K*^{*0}*μμ* with LHCb Run I and is currently working on an improved and updated version of this measurement. Additionally, work is ongoing to study lepton flavour universality in the angular distributions of *B*^{0}→*K*^{*0}*μμ* and *B*^{0}→*K*^{*0}*ee* decays, which is of key importance to confirm the anomalies observed in the ratios of branching fractions.

In addition to these activities, our group has been involved in the search for long-lived scalar particles, which provide access to many different hidden sector models, and lepton flavour violation in tau decays, using data from Run I in both cases. Moreover, we are currently involved in the study of radiative decays of beauty hadrons, which can be used to constrain NP models with large right-handed currents.