Searches for neutral Higgs bosons in the $\tau \tau$ final state with the CMS detector

The Compact Muon Solenoid (CMS) detector is located at the CERN Large Hadron Collider. It is a general purpose detector designed to test predictions of the standard model (SM) and search for the Higgs boson, as well as to look for signatures of new physics beyond the SM. The analyses described in this thesis use proton-proton collision data recorded by CMS during 2011 and 2012. Searches for neutral Higgs bosons decaying into tau pairs are presented. The searches are performed separately for the SM Higgs boson or the neutral Higgs bosons of the minimal supersymmetric standard model (MSSM). The MSSM searches consist of two different analyses. The first is a direct search for any one of the MSSM neutral Higgs bosons in the mass range from 90 GeV to 1 TeV decaying directly into taus. The second searches for the signature from a heavy neutral Higgs boson of the MSSM decaying into two light MSSM Higgs bosons with SM-like properties (H $\to$ hh) in the final state with two b-quarks and two taus. The SM and MSSM $\tau \tau$ analyses use 4.9 fb$^{−1}$ of data collected at 7 TeV and 19.7 fb$^{−1}$ collected at 8 TeV, while the MSSM H $\to$ hh analysis uses only the 8 TeV data. In the SM analysis, an excess of events in data above the background expectation is observed with an observed (expected) local significance of 3.2 (3.7) standard deviations at 125 GeV. This excess is found to be consistent with the 125 GeV Higgs boson of the SM in mass and coupling strengths. No significant excess is observed in either MSSM search, and so upper limits are set on cross-section times branching ratio for the Higgs production processes at the 95% confidence level. Limits are also set in m$_A\,$-\,\tan \beta$ parameter space of several interesting MSSM benchmark scenarios.