Detector and Trigger Studies Towards Discovering the Higgs Boson Produced via Vector Boson Fusion Using the CMS Detector

Detection of the Higgs boson is one of the primary goals of the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC). To achieve this goal a good understanding of both the detector and its simulation is required. In this thesis the response of the CMS calorimeters to single pions extracted from test beam data will be presented, as well as a comparison with the response from simulated data. Also, a new trigger is proposed, aiming to increase the selection efficiency of the Standard Model Higgs boson, produced via the Vector Boson Fusion (VBF) mechanism and decaying into two taus with a lepton and a 𝛕-jet in the final state. Finally, the effect of this trigger on the trigger rate, as well as on the signal and background processes is investigated. Data collected from the H2 beam line at CERN were used to calculate the average energy response and resolution of pions with momenta ranging from 2 GeV/c to 300 GeV/c. The results were then compared with data produced using the full CMS detector simulation. It was found that the average responses of the hadronic calorimeter were in good agreement, but the spread was underestimated by the simulation. Also the electromagnetic calorimeter response to pions was consistently underestimated in the detector simulation. The Higgs boson decaying into two taus is a very promising channel for the detection of a low mass Higgs boson (mₕ<150 GeV/c²). A trigger of two, separated in 𝛈, jets (VBF jets) and a lepton was developed and tuned for the 2×10³³ cm⁻²s⁻¹ instantaneous luminosity regime. The trigger efficiency for a preselected VBF produced H→𝛕𝛕→l+𝛕-jet sample was calculated to be (76.1±0.7)% with a (0.6±0.3)Hz QCD rate. The combination of the new trigger with the existing ones provided an improvement of ~33% relative to the latter. The performance of the trigger on the signal and background events passing selection criteria designed for Higgs boson detection was evaluated. The combined trigger was found to be ~47% more efficient for final signal selection than the existing ones, with only a ~9% increase in background events.