Searches for exotic Higgs bosons at CMS: from Level-1 jet trigger calibration to data analyses and their interpretation

Abstract

This thesis covers several topics investigating the nature of exotic Higgs bosons, using data from the Compact Muon Solenoid (CMS) at the Large Hadron Collider (LHC).A search was performed for invisible decays of a Higgs boson, using 19.5 fb−1 of data from proton-proton collisions collected during 2012. No significant excess was observed, and an observed (expected) upper limit on the invisible branching fraction of the125 GeV Higgs boson was set at BR(h → Invis.) < 0.65 (0.49) at 95% confidence level (CL).A search for a pair of light Higgs bosons with masses 4–8 GeV, produced by the discovered Higgs boson and each decaying into a pair of tau leptons, was also performed using the collision data from 2012. No significant excess was observed in this search either, and upper limits were set on the total production cross-section for such processes as a function of the light boson mass. The observed limit at 95% CL ranges from 4.5 to 10.3 pb, with corresponding expected limits 2.9 and 10.3 pb.The results of several light Higgs boson searches carried out at the LHC are interpreted within the context of the Next-to-Minimal Supersymmetric Standard Model. The limits from these searches are compared to model predictions, and theirimpact on model parameters is discussed.The upgrade of the CMS Level-1 trigger allows for more sophisticated object identification algorithms, including removal of contributions from overlapping collisions. The derivation of calibrations for the jet algorithm in both the interim and fullupgrades is examined, along with their performance.

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ORCID for Stefano Moretti: orcid.org/0000-0002-8601-7246

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