Search for supersymmetry in opposite sign dilepton final states including tau leptons with the CMS experiment

In this document a search for physics beyond the standard model is presented in the opposite sign dilepton final states etau_h, mutau_h, and tau_htau_h. Data collected by the CMS experiment at the LHC providing proton-proton collisions at sqrts = 7TeV in 2011 was used. In this context tau_h denotes a hadronically decaying tau lepton. The search concentrates on strongly coupling initial BSM particles (e.g. gluino, squark), leading to a large amount of hadronic activity in each event. Also the existence of a stable and only weakly interacting particle is assumed, providing a dark matter candidate. With these assumptions, four search regions are defined in the H_T > 125 GeV versus Met > 200 GeV plane, which minimize contributions from standard model processes. The dominant remaining backgrounds in those search regions are caused by dileptonic ttbar decay and tau_h misidentification. Both are estimated from data: The first, by exploiting the similarity of the p_T(nu nu) = Met and p_(l l) distributions in dileptonic ttbar events as well as lepton universality. The second, by employing an isolation side band, from which the contributions of quark or gluon jets misidentified as tau_h candidates are extrapolated. All other backgrounds are estimated using simulation. The background estimation techniques are tested using simulated events as well as background dominated control regions in data. From the first systematic uncertainties are estimated which are validated in the control regions. Ultimately no excess of events in the search regions with respect to the standard model expectations is found. Thus, exclusion contours are calculated using the modified frequentist method CLS. A dedicated simplified model and a generic cMSSM scan were used as examples for possible BSM models. For the latter a combination with the published light lepton channels is performed. The simplified model concentrates on opposite sign tautau final states via gluino pair production. It is parameterized by the gluino and the LSP masses. Using this analysis gluino masses m_gluino < 800 GeV$ and LSP masses m_LSP < 175 GeV can be excluded at 95% CL. Additionally cMSSM scenarios with tanb = 10, A_0=0 GeV, and mu>0 are considered for 100