A new LHC search channel for a light Higgs boson and associated QCD calculations

Abstract : This thesis addresses various topics related to LHC studies and predictions. We were first interested in a boosted ($p_t>200$ GeV) light Higgs boson at the LHC ($M_H\simeq 120$ GeV) in the $pp\rightarrow WH$ and $pp\rightarrow ZH$ search channels with $H\rightarrow b\bb$. We showed how these challenging channels can be recovered as promising search channels using a subjet analysis procedure in two steps: a ``mass-drop'' analysis, which allows one to reduce the large QCD backgrounds, and a ``filtering'' analysis, which improves the resolution on the reconstructed Higgs jet mass. Then we focused on the filtering analysis, which allows one to suppress the diffuse background from the underlying-event and pile-up, which are mainly responsible for the bad Higgs mass resolution. We optimised its parameters using semi-analytical calculations which led us to examine the structure of the non-global logarithms that appear in this problem. Finally, we studied some processes whose perturbative series converges poorly at next-to-leading (NLO) order for some observables, a property that we had noticed in the Z+jet and W+jet processes at high-$p_t$ during our Higgs analysis. This is important because it leads to questions about the reliability of the predictions resulting from perturbative calculations. It thus becomes necessary to examine higher-order corrections. The method that we developed, called ``LoopSim'', consists in approximating these higher-order corrections by merging different orders of perturbation theory such that all infra-red and collinear divergences are cancelled.
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Contributor : Mathieu Rubin <>
Submitted on : Thursday, August 5, 2010 - 3:33:07 PM
Last modification on : Sunday, March 31, 2019 - 1:32:57 AM
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  • HAL Id : tel-00508770, version 1


Mathieu Rubin. A new LHC search channel for a light Higgs boson and associated QCD calculations. High Energy Physics - Experiment [hep-ex]. Université Pierre et Marie Curie - Paris VI, 2010. English. ⟨tel-00508770⟩



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