Single top channel in association with H→bb̄ production at ATLAS : a feasible study

Master Thesis


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University of Cape Town

A degeneracy in the minima of the profile likelihood function of the Higgs boson coupling to fermions and bosons, where boson couplings are assumed to be positive, is reported by both ATLAS and CMS. Although one minimum lies in the region of positive fermionic coupling scale factors, consistent with the Standard Model, the second minimum lies in the negative region-a region which would indicate new physics. This degeneracy can potentially be resolved by studying a fermionic-bosonic interference that takes place in the single top quark production in association with a Higgs particle, in which the cross-section is significantly enhanced for anomalous coupling values. A truth level feasibility study of the tH process with H→bb̄ is conducted at 8 TeV and 21 fb-¹ of integrated luminosity. the equivalent of the 2012 run at the LHC. A sensitivity of l.7σ is found for the enhanced case of a coupling scale factor of cF = -1. This is insufficient for a detection. A projection to 14 TeV centre-of-mass energies indicates that at truth-level a 3σ significance with 15 fb-¹ of integrated luminosity can be reached for the enhanced case. However, assuming as low as 5% systematic uncertainty lowers this to below 2σ across the whole luminosity range, indicating that the upcoming run at LHC will also be insufficient to resolve the degeneracy.