Determination of Z -> tau tau -> e+ e− + 4nu Background Shapes From Data in Context of the b−Quark Associated Higgs Boson Production with ATLAS at the LHC

One of the most promising Higgs boson production channels in the Minimal Supersymmetric Standard Model is the production in association with a $b-$quark, $b\bar{b}\rightarrow h/A/H$. Assuming a large $\tan {\beta}$ value the Higgs boson's decay to a $\tau$ lepton pair is enhanced. For low Higgs boson masses, $m_A< \unit[130]{GeV}$, the $Z \to\tau^+\tau^-$ background is irreducible and dominant. This thesis describes a method to estimate this background from data for the Higgs boson decay of $h/A/H\to\tau^+\tau^-\to e^+e^-+4\nu$ for the ATLAS detector at the LHC. The method determines the distribution of the $Z\rightarrow \tau^+\tau^-\rightarrow e^+e^- +4\nu$ background using $Z\rightarrow e^+e^-$ events. For that purpose, $Z\rightarrow e^+e^-$ events are selected from data. Their energy deposits in the electromagnetic calorimeter are reweighted using a reference histogram from $Z\rightarrow \tau^+\tau^-\rightarrow e^+e^- +4\nu$ from Monte Carlo simulated events. The resulting invariant mass distribution mimics the \mbox{$Z\to\tau^+\tau^-\to e^+4^-+4\nu$} background and obtains a good agreement.