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Title: Measurements of the associated production of a Higgs boson decaying into two beauty quarks with a weak vector boson
Author: Ambroz, Luca
ISNI:       0000 0004 9356 5261
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2020
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For more than four decades, the Higgs boson has been the most sought-after particle in Particle Physics. Its observation, by the ATLAS and CMS collaborations in 2012, has confirmed the existence of the Higgs field, which is responsible for the spontaneous symmetry breaking mechanism in the electroweak sector and the mass generation of fermions through the Yukawa interaction. Since then, many measurements have been performed, with increasing accuracy, to check whether its properties matched the Standard Model predictions. The measurement of the Higgs boson decay to beauty quarks is the first test of the Yukawa coupling to bottom-type quarks. Although this decay channel has the largest branching ratio, it has been difficult to observe it at the LHC due to the presence of the large multi-jet background. In this regard, the associated production of a Higgs boson with a leptonically decaying vector boson offers an excellent leverage to reject this background. Furthermore, this production mode is particularly sensitive to Beyond Standard Model physics in the form of Effective Field Theories operators. This thesis presents inclusive and differential measurements of the associated production of a Higgs boson decaying into two beauty quarks with a weak vector boson using the full Run 2 ATLAS dataset. The inclusive measured signal strength is μbbVH = 1.02+0.18-0.17 = 1.02 +0.12-0.11 (stat.) +0.14-0.13(syst.) , which corresponds to a rejection of the background-only hypothesis with a significance of 6.7 standard deviations, when 6.7 standard deviations are also expected. The differential measurements are reported in five bins of Simplified Template Cross Sections, defined with respect to the transverse momentum of the vector boson. The total uncertainties on each bin range from 85% to 30%. These analyses represent some of the first steps towards the era of precision measurements in Higgs physics, which will characterize the future physics programme of the LHC and the high-luminosity LHC.
Supervisor: Bortoletto, Daniela Sponsor: Science and Technology Facilities Council ; Sub-Department of Particle Physics ; University College ; Clarendon Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Particle Physics