engleski

Study of the Higgs Discovery Potential in the Process pp-> H -> 4 muons

In this thesis we study the potential for the discovery of the Standard Model Higgs boson in the ATLAS detector in the decay channel H -> ZZ^* -> mu^+ mu^- mu^+ mu^-. The ATLAS experiment at the Large Hadron Collider at CERN is designed to study the physics phenomena appearing in the proton-proton collisions at the 14 TeV center-of-mass energy. In the study of the physics processes involving muons in the final state an important role is played by the ATLAS muon spectrometer. The spectrometer allows for a precision muon momentum measurement independently of other ATLAS subdetectors. The performance of the spectrometer is greatly influenced by the performance of the muon tracking detectors, the Monitored Drift Tube Chambers (MDT). We perform the tests of the mechanical chamber accuracy, as well as the tests of the chamber response to muons. The mechanical accuracy of the chamber construction is shown to be well within the required 20 mu m. The tests of the chamber response to muons show a spatial resolution of 100 mu m in an individual drift tube of the chamber. This resolution can be improved to 80 mu m using the final readout electronics. The efficiency of the muon detection in a drift tube is 93%, which allows for an efficient muon track reconstruction in the spectrometer. The spatial resolution and the detection efficiency stay within the specifications even atthe high photon background rates expected to appear in the spectrometer during the high luminosity running period. In addition to the chamber tests, we develope a precise method for the determination of the spatial resolution of the drift tube which is required for an efficient muon track reconstruction. The measured chamber properties are taken into account for the simulation of the H -> ZZ^* -> mu^+ mu^- mu^+ mu^- process and of the corresponding background processes in the detector. We perform the optimization of the cuts for the background rejection in order to achieve the maximum signal significance. The obtained signal significance for the studied decay channel after three years of ATLAS operation at the low luminosity is between s=2 (for Higgs masses of 130 and 180 GeV/c^2) and s=4 (for a Higgs mass of about 150 GeV/c^2).

Higgs boson; ATLAS; CERN; LHC; muon spectrometer; MDT

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