Advances in Precision Calculations of Higgs Boson and Single Top Quark Production at the Large Hadron Collider

Since the discovery of the Higgs boson in 2012, particle physics has entered an era of precision. With the upcoming increase in luminosity of the Large Hadron Collider (LHC), we will gain access to deep and detailed insights into the behaviour of fundamental particles. On the theoretical side, the description of partonic cross sections with next-to-next-to-leading order (NNLO) accuracy in Quantum Chromodynamics (QCD) is becoming a standard. Despite the astonishing agreement between the experiments and theoretical predictions, it is clear that the Standard Model (SM) of particle physics is incomplete. One way to search for New Physics is to push the accuracy of the theoretical predictions and experimental measurements further. In this thesis, we study three problems related to precision description of Higgs boson and top quark production at the LHC. In the first part, we investigate the interference contribution between two Higgs production mechanisms in the pp → H + jetc process. This process can be used to study the Yukawa coupling of the charm quark. The interference studied in this thesis requires a helicity flip on the charm-quark line, forcing us to treat the charm quarks as massive. This requirement leads to unconventional QCD phenomena, such as the importance of soft quarks and unusual collinear factorisation. In the second part, we calculate the so-called non-factorisable corrections to t-channel single top production. These corrections arise from the crosstalk between the two fermion lines present in this process. Until now, the non-factorisable contributions to single top production have been neglected because they do not appear at next-to-leading order (NLO) and they are colour-suppressed compared to the factorisable ones. However, recent studies indicate that the factorisable corrections are relatively small at NNLO and that the non-factorisable ones can be dynamically enhanced. We compute the non-factorisable corrections and discuss their numerical impact on t-channel single top production at the LHC and the Future Circular Collider (FCC). In the third part, we consider the same type of corrections to Higgs production in weak boson fusion (WBF). Contrary to the case of t-channel single top production, an exact computation of these corrections is currently impossible. We construct an expansion of the double-virtual contribution around the forward limit of the tagging jets. It turns out that the expression of the double-virtual contribution at the next-to-leading order in the eikonal approximation can be expressed in a quite compact form

On the interference of ggHggH and ccˉHc\bar{c}H Higgs production mechanisms and the determination of charm Yukawa coupling at the LHC

Higgs boson production in association with a charm-quark jet proceeds through two different mechanisms - one that involves the charm Yukawa coupling and the other that involves direct Higgs coupling to gluons. The interference of the two contributions requires a helicity flip and, therefore, cannot be computed with massless charm quarks. In this paper, we consider QCD corrections to the interference contribution starting from charm-gluon collisions with massive charm quarks and taking the massless limit, $m_c \to 0$. The behavior of QCD cross sections in that limit differs from expectations based on the canonical QCD factorization. This implies that QCD corrections to the interference term necessarily involve logarithms of the ratio $M_H/m_c$ whose resummation is currently unknown. Although the explicit next-to-leading order QCD computation does confirm the presence of up to two powers of $\ln(M_H/m_c)$ in the interference contribution, their overall impact on the magnitude of QCD corrections to the interference turns out to be moderate due to a cancellation between double and single logarithmic terms.Comment: 28 pages, 4 figure

Non-factorizable virtual corrections to Higgs boson production in weak boson fusion beyond the eikonal approximation

Non-factorizable virtual corrections to Higgs boson production in weak boson fusion at next-to-next-to-leading order in QCD were estimated in the eikonal approximation [1]. This approximation corresponds to the expansion of relevant amplitudes around the forward limit. In this paper we compute the leading power correction to the eikonal limit and show that it is proportional to first power of the Higgs boson transverse momentum or the Higgs boson mass over partonic center-of-mass energy. Moreover, this correction can be significantly enhanced by the rapidity of the Higgs boson. For realistic weak boson fusion cuts, the next-to-eikonal correction reduces the estimate of non-factorizable contributions to fiducial cross section by (20) percent

On non-factorisable contributions to t-channel single-top production

We compute the non-factorisable contribution to the two-loop helicity amplitude for t-channel single-top production, the last missing piece of the two-loop virtual corrections to this process. Our calculation employs analytic reduction to master integrals and the auxiliary mass flow method for their fast numerical evaluation. We study the impact of these corrections on basic observables that are measured experimentally in the single-top production process

On non-factorisable contributions to t-channel single-top production

We compute the non-factorisable contribution to the two-loop helicity amplitude for t-channel single-top production, the last missing piece of the two-loop virtual corrections to this process. Our calculation employs analytic reduction to master integrals and the auxiliary mass flow method for their fast numerical evaluation. We study the impact of these corrections on basic observables that are measured experimentally in the single-top production process

Non-factorisable contribution to t-channel single-top production

We compute the non-factorisable $Ο(α^{2}_{s})$ corrections to t-channel single-top quark production at the LHC. These peculiar corrections arise because of interactions between the heavy- and the light-quark lines and appear for the very first time at next-to-next-to-leading order in perturbative QCD. We find that the non-factorisable corrections change the single-top production cross section and the relevant kinematic distributions in this process by about half a percent

Non-factorizable virtual corrections to Higgs boson production in weak boson fusion beyond the eikonal approximation

Abstract Non-factorizable virtual corrections to Higgs boson production in weak boson fusion at next-to-next-to-leading order in QCD were estimated in the eikonal approximation [1]. This approximation corresponds to the expansion of relevant amplitudes around the forward limit. In this paper we compute the leading power correction to the eikonal limit and show that it is proportional to first power of the Higgs boson transverse momentum or the Higgs boson mass over partonic center-of-mass energy. Moreover, this correction can be significantly enhanced by the rapidity of the Higgs boson. For realistic weak boson fusion cuts, the next-to-eikonal correction reduces the estimate of non-factorizable contributions to fiducial cross section by (20) percent