Search for Gaugino Mediation Non-Universal Higgs Masses Model with ν˜τ NLSP with the ATLAS Detector in Final States with Jets and Missing Transverse Momentum and 20.3 fb−1 of √ s = 8 TeV Proton-Proton Collision Data

Supersymmetry (SUSY) is one of the best motivated extensions of the Standard Model, and its searches at the LHC represent an important result in the Physics Beyond the Standard Model. The subject of this thesis is the analysis of two SUSY scenarios using 20.3 fb−1 of ATLAS data at 8 TeV center of mass energy. The main topic of the thesis is a study of the Non-Universal Higgs Masses model with gaugino mediation and ν˜τ NLSP (NUHMG). This is a R-parity conserving realistic SUSY model, where ν˜τ decays into ντ and G˜ LSP. The model is distinguished from other SUSY models by allowed ˜lL decays, threebody decays of τ˜1, where the dominant decay is into a pair of fermions and missing transverse energy, and a mass spectrum where χ˜ 0 1 has visible decays. It is characterized by long decay chains with lots of soft leptons and jets. The produced missing transverse energy from neutrinos can cancel out with the missing transverse energy from the NLSP, which brings to relatively low missing transverse energy. A study showed that NUHMG can be found using q˜ and g˜ production, using final states with zero leptons of transverse momenta higher than 10 GeV, multiple jets and missing transverse energy. This is the most inclusive selection, which in fact includes soft objects, but does not depend on the b-jet tagging or τ reconstruction. Therefore, an analysis using 2-6 jets and missing transverse energy has been set in place for the NUHMG model. The NUHMG model viable parameter space for the 8 TeV data and 20.3 fb−1 of integrated luminosity has been determined using a simultaneous scan using multiple criteria. The selected parameter space points were selected to have the ν˜τ NLSP, that are not excluded by LEP, have Higgs mass close to 125 GeV, are not excluded by previous LHC searches, and have a viable cross-section for the analysis. A dedicated optimization for the NUHMG model has been performed in three steps. First, the optimal sensitive variable and jet multiplicity has been determined, using a newly developed fast cut-flow optimization method. It relies on the Rectangular Cuts method with Genetic Algorithm in TMVA, where purely Monte Carlo input has been used for signal and background modeling. Second, the optimal variable combination and jet multiplicity have been further optimized using a setup which uses data in the control regions, and performs a likelihood fit to obtain Standard Model and potential SUSY signal estimates, accounting systematic uncertainties. Third, the obtained cut flow is further refined and integrated into a more general analysis with 2-6 jets and missing transverse energy as a signal region labeled 6jt+, within ATLAS inclusive searches for q˜ and g˜ with zero leptons. A data analysis has been performed using the log likelihood fit, and a statistical analysis has been set up to interpret the data. For expected 4.9±1.4 Standard Model events, 6 have been observed, which is within 1 sigma uncertainty of the expectation. As no significant excess of data has been seen, the 95% CL exclusion limits on the NUHMG model have been set, where q˜ and g˜ masses are excluded up to 1250 and 1400 GeV respectively. In addition, the 6jt+ signal region improves the exclusion limits by about 100 GeV for the g˜ inv the compact mass region, for the simplified model of gluino production, with one step decay via χ˜±1 . A search for the NUHMG using 1 lepton, multiple jets and missing transverse energy has shown to give compatible results. Second SUSY model studied in this thesis is the Non-universal Higgs Masses model with χ˜ 0 1 LSP (NUHM). It is well motivated in the framework of Radiatively Driven Natural SUSY (RNS), where Higgs of mass around 125 GeV, q˜ and g˜ masses at the TeV scale are accommodated with low level of electroweak fine tuning. A study of RNS NUHM model final states, mass spectrum and production cross-sections showed that the search for this model is viable using the direct gaugino production, using multiple leptons and missing transverse energy. A data analysis using a statistical combination of 2, 3 and 4 leptons has been performed. As no significant excess of data has been observed, 95% CL exclusion limits have been set on the RNS NUHM model. The statistical combination is driven by the analysis with 3 leptons, and it reaches m1/2 up to 300 GeV, and extends up to the highest tested value of µ = 500 GeV. In addition to physics analyses, a program developed for online monitoring of the ATLAS trigger, called Trigger Presenter (TriP), is described in this thesis. It is aimed for a shifter and expert user in the control room. It receives the information from Level 1, Level 2 and Event Filter trigger rates and HLT computer farm status. Using various methods for reading out relevant information, and developed naming conventions, the information is received, calculated, and presented in a graphical user friendly interface. TriP was used in the ATLAS control room for trigger monitoring at the first LHC startup.