Observation of Diffractive W and Z Boson Production and Standard Model Higgs Boson Search in the $H \to W W \to \ell \nu \ell \nu$ Channel in $\sqrt{s}$ = 7 TeV pp Collisions at CMS

In this thesis, two analyses using proton-proton (pp) collision data at a center of mass energy of $\sqrt{s}$ = 7 TeV, recorded with the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC), are presented: The first analysis, using an integrated luminosity of 36 pb$^{=1}$ of low pile-up data recorded in 2010, uses the forward energy flow and the central charged particle multiplicity in events with leptonically decaying W and Z bosons to study the effects of the underlying event model. None of the studied Monte Carlo simulations describes the observed distributions from data sufficiently. Weak boson events with no significant energy deposits in one of the forward calorimeters are observed. This corresponds to a large pseudorapidity gap (LRG) of at least 1.9 units. The fraction of W(Z) events having a LRG is found to be 1.46 $\pm$ 0.09(stat.) $\pm$ 0.38(syst.)% (1.57 $\pm$ 0.25(stat.) $\pm$ 0.42(syst.)%). The majority of the charged leptons from these W/Z decays are found in the hemisphere opposite to the gap. This gives a strong indication of a diffractive component in the weak boson production, and the fraction of diffractively produced W bosons is found to be 0.73 $\pm$ 0.34% which is in agreement with observations from the Tevatron. The second analysis presents the search for the SM Higgs boson decaying to a pair of W bosons in the fully leptonic final state. The pp collision data corresponding to a luminosity of 4.9 fb$^{-1}$ recorded in 2011 are used. The $W^+ W^−$ event candidates are selected by requiring exactly two oppositely charged leptons and large missing transverse momentum from the escaping neutrinos. The shapes of the distributions of a multivariate discriminator are used to calculate upper limits on the SM Higgs production cross section. Different systematic uncertainties are studied in detail and included in the limit setting procedure using the 2011 dataset. The SM Higgs boson is excluded in the mass range of 134–211 GeV at the 95% confidence level. This is a slightly smaller range than the expected exclusion range of 125–230 GeV. An excess of about 2$\sigma$ significance is observed in the low mass region below 140 GeV, consistent with a SM Higgs boson with a mass around 125 GeV.