Search for the rare B⁰ → K*⁰τ⁺τ^- decay at the LHCb experiment

A search for the rare B⁰ → K*0τ⁺τ^- decay is performed using 9 fb^-1 of proton-proton (pp) collision data collected at the LHCb experiment at CERN. The decay is reconstructed using two final states: the fully hadronic one, in which both τ leptons decay in the τ^- → π^-π⁺π^-(π⁰)ν_τ channel, and the mixed hadronic-leptonic, in which one τ decays in the aforementioned channel and the other in the τ^- → μ^-ν_τν-bar_μ channel. The measure of the branching ratio is performed relatively to that of the normalization mode B⁰ → D^-(→ π^-K⁺π^-)D⁺_s(→ K⁺K^-π⁺). The full event selection makes use of Boosted Decision Trees (BDT) based on kinematic and isolation variables in order to reduce the amount of background. A binned maximum likelihood fit on the output of a BDT classifier is performed to extract the number of signal events in the data. The data distribution is still blind, however an expected upper limit in the case where no signal is observed is computed to be 3.2. 10^-4 at 95% CL. (author)