Master thesis Defense by Lars Egholm Pedersen – University of Copenhagen

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Master thesis Defense by Lars Egholm Pedersen

Master Thesis defense by Lars Egholm Pedersen

The search for the Higgs Boson. Optimization of the Higgs sensitivity in the ZZ*->4l channel using the 2011 datasample, collected by the ATLAS experiment at the LHC.

Abstract: The sensitivity of the H->ZZ* search channel is limited by the irreducible Standard Model ZZ* production without an intermediate Higgs boson.
Considering the 4 lepton final state I have in my work investigated if a separation between the two could be obtained using distributions uncorrelated to the lepton system invariant mass.
While the Higgs boson is produced mainly from gluon fusion and has zero spin,the Standard Model ZZ* diboson system is for the most part produced from quark exchange, and will in general not have zero spin, resulting in differences in their respective momenta, rapidities and angular distributions.
The result of a multivariate analysis trained on Monte Carlo simulations will be presented, before examining its theoretical and systematic uncertainties.
The multivariate analysis is finally added to the signal significance estimation, usually based only on invariant mass measurements, and the results for the 4.8 fb^-1 ATLAS data sample taken in 2011 at a center of mass energy sqrt{s} = 7 TeV will be presented.