Search for new physics in the tau plus missing energy final states at CMS

In this thesis the first search for a heavy charged vector boson W' in the final state with a hadronicaly decaying tau lepton and two neutrinos is described.The analysed data include 20 fb-1 of LHC proton proton collisions at sqrt(s) = 8 TeV as well as 2.3 fb-1 at sqrt(s) = 13 TeV recorded with the CMS detector.A signal would appear as an excess of events with high transverse mass where the standard model background is low.The algorithm used to reconstruct taus from the detector information was extended to provide a high efficiency and correct energy reconstruction for boosted hadronic tau decays at the TeV scale.No significant excess is observed in the recorded data. Limits are set on models in which the W' decays preferentially to fermions of the third generation. These results substantially extend previous constraints on this model.W'-boson masses below 2.0 to 3.3 TeV are excluded, depending on the model parameters. In addition, the existence of a W' boson with universal fermion couplings is excluded at 95\% credibility level for W' masses below 2.7 TeV with the sqrt(s) = 8 TeV data and for masses below 3.3 TeV with sqrt(s) = 13 TeV data.For further reinterpretation, a model-independent limit on potential signals is also presented for various transverse mass thresholds.Finally a generalized interpretation of non resonant signals in the e/mu plus missing transverse energy channel is proposed.