Precision calculations in the Higgs sector within and beyond the Standard Model

Capozi, Matteo (2020): Precision calculations in the Higgs sector within and beyond the Standard Model. Dissertation, LMU München: Fakultät für Physik

Abstract

The discovery of a boson consistent with the Standard Model (SM) Higgs boson in 2012 at the Large Hadron Collider (LHC) finally closed the hunting for the last unob- served SM particle and experimentally confirmed the electroweak symmetry breaking mechanism. Nevertheless there are still open questions suggesting extensions of the SM. At the moment there is no evidence contradicting the SM and proving the pres- ence of New Physics. New Particles could likely show up in the TeV range, if it is the case a good choice is to parametrise the Beyond Standard Model (BSM) effects in an Effective Field Theory framework. The New Physics effects are encoded in anomalous couplings. At the moment the Higgs sector is least explored and allows deviations from SM predictions, giving hints to extend this sector. We present the study of two processes of particular interest at the LHC: Higgs boson pair production and Higgs plus one jet production. In both cases we present the next- to-leading order (NLO) QCD cross section and differential distributions with full top mass dependence within the framework of a non-linearly realised Effective Field Theory in the Higgs sector. In these calculations we explore the anomalous couplings parameter space probing the effects of these parameters on the observables. Concerning the Higgs boson pair production in the gluon fusion channel, character- ized by five anomalous couplings, we present a calculation of the NLO QCD corrections where we analyse the impact of modifications of the anomalous couplings on the distri- butions in the Higgs boson pair invariant mass and the transverse momentum of one of the Higgs bosons. We provide an analytical parametrisation for the total cross-section and the mhh distribution as a function of the anomalous Higgs couplings that includes NLO corrections. We further present our shapes classification of Higgs boson pair invariant mass dis- tributions mhh. We use two approaches: an analysis based on predefined shape types and a classification into shape clusters based on unsupervised learning. We find that our method based on unsupervised learning allows a more detailed study of the impact of anomalous couplings on the mhh shape compared to more conventional approaches to a shape analysis. Higgs jet. At last we present the calculation of NLO QCD corrections for the Higgs plus one jet production. The computation is implemented in a Monte Carlo event generator code which will be publicly available. The scattering amplitude of the process is function of two anomalous couplings. Certain configurations of the couplings produce total cross sections which are almost the same. We study two of these configurations, and we show how to disentangle them.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 530 Physik
• Fakultäten: Fakultät für Physik
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 20. März 2020
• 1. Bericht­erstatter:in: Buchalla, Gerhard