Improvement of a Data-Driven Method for the Simulation of the ττ-Mass Shape in Z → ττ → ee + 4ν for ATLAS at the LHC

At the LHC the b-quark associated Higgs boson production channel, gb → b+h/A/H, gg → bbar+h/A/H, bbar → h/A/H, is one of the most relevant search channels for the supersymmetric Higgs bosons. In particular a large tanβ value would enhance the neutral Higgs bosons decay into a τ-lepton pair significantly. For low Higgs boson masses (mh/A/H <= 140GeV) the Z → ττ decay presents an irreducible background, due to its similar kinematics. In this thesis, a data-driven method for the simulation of the ττ-mass distribution in Z → ττ → ee + 4ν for the ATLAS detector at the LHC is refined. As no collision data is available yet simulated data was used for the study of possible improvements of this method. Z → ee data is modified such, that the reconstructed invariant ττ mass spectrum, m_ττ, simulates the one obtained from Z → ττ → ee +4ν events, this is performed by rescaling of the electron energies. The shape of an electromagnetic shower changes however depending on the energy of the incident particle. This effect is taken into account in this work. An electromagnetic shower shape parametrization was customized for the ATLAS calorimeter geometry for this task. Correction factors were determined and implemented into an algorithm. This procedure results in an invariant mass distribution which reproduces the Z → ττ → ee + 4ν distribution from Monte Carlo data within the statistical error. The mass di stribution derived this way, agrees well with the Z → ττ → ee + 4ν distribution, even after the applying the selection cuts used in h/A/H → ττ → ll + 4ν analysis.