This thesis presents the search for a charged-lepton flavour violation via a model-independent Higgs-like boson decaying to a muon and a tau lepton, . The validation of high- tau lepton identification is performed with the measurement of production cross-section, using 2; of integrated luminosity from collisions at TeV collected by the LHCb experiment at the LHC in 2012. The tau leptons are reconstructed in both leptonic and hadronic decay channels. The cross-section, restricted to events with both tau leptons having a transverse momentum greater than 20 GeV/c and a pseudorapidity between 2 and 4.5, and with a tau pair invariant mass between 60 and 120 GeV/, is measured to be \sigma_{Z\rightarrow\tau^+\tau^-}} = 95.20 \pm 2.13 \pm 4.79 \pm 0.17 \pm 1.10 \pb. The uncertainties are statistical, systematic, from the LHC beam energy, and from the integrated luminosity. The results are compatible with the lepton universality hypothesis in decays, and are in agreement with NNLO Standard Model predictions. Using the validated tau-lepton identification and detection efficiencies, the search for covering 99% of tau decay modes found no statistically significant excess. The upper limit on the cross-section times branching fraction, \sigma_{gg\rightarrow H\rightarrow\mu\tau, at 95% confidence level is set, ranging from about 22 pb for GeV/ to 4 pb at 195 GeV/. Assuming the Standard Model Higgs, the limit on the braching fraction is , corresponding to a Yukawa coupling of .
Matthias Finger, Konstantin Androsov, Jan Steggemann, Qian Wang, Anna Mascellani, Yiming Li, Varun Sharma, Xin Chen, Rakesh Chawla, Matteo Galli
Matthias Finger, Konstantin Androsov, Jan Steggemann, Qian Wang, Anna Mascellani, Yiming Li, Varun Sharma, Xin Chen, Rakesh Chawla, Matteo Galli