Towards improved logarithmic descriptions of high energy processes involving jets in hadron colliders

The total cross section for QCD processes at the LHC can be expanded perturbatively in the QCD coupling, αs, and then approximated by performing calculations in quantum field theory to a fixed order. However, in the presence of a large separation of energy scales, the convergence of this perturbative expansion is known to be damaged as higher order corrections in αs become more significant. High Energy Jets (HEJ) is a resummation framework designed to include contributions from high energy logarithms in the ratio of centre of mass energy to the transverse scale of particle produced to all orders in perturbation theory. These logs can become significant at the LHC and future colliders, and are significantly enhanced by the requirement of a large dijet invariant mass or large rapidity separation common in vector boson fusion/scattering (VBF/VBS) selection cuts. The work collected together in this thesis was done to extend the HEJ description of high energy collisions; both adding support for new, experimentally relevant processes at leading-log (LL) accuracy and improving the understanding of the currently supported processes. We present the first calculation of the leading log description of same-sign W W boson production plus jets at the LHC, which is important as a necessary background processes for vector boson scattering and which has high energy logarithms which are directly enhanced by VBS cuts. We compare the HEJ LL result to that of pure next-to-leading order and with next-to-leading order matched parton shower using the setup of a recent CMS experimental analysis. We then present results from studies looking at the impact of higher order corrections for two ongoing ATLAS experimental analyses. The setup of these analyses have directly lead to improvements in the HEJ description of both pure QCD jets and W plus jets which we describe in detail. Finally, we present a look ahead to the impact on the perturbative expansion of QCD at future colliders with a higher centre of mass energy, where we expect the impact of higher energy logarithms to be increasingly significant

HEJ 2.2: W boson pairs and Higgs boson plus jet production at high energies

We present version 2.2 of the High Energy Jets (HEJ) Monte Carlo event generator for hadronic scattering processes at high energies. The new version adds support for two further processes of central phenomenological interest, namely the production of a W boson pair with equal charge together with two or more jets and the production of a Higgs boson with at least one jet. Furthermore, a new prediction for charged lepton pair production with high jet multiplicities is provided in the high-energy limit. The accuracy of HEJ 2.2 can be increased further through an enhanced interface to standard predictions based on conventional perturbation theory. We describe all improvements and provide extensive usage examples. HEJ 2.2 can be obtained from https://hej.hepforge.org.Comment: 29 pages, 2 figures and many code listing

Logarithmic corrections to the QCD component of same-sign W-pair production for vector boson scattering studies

We present the results of the first calculation of the logarithmic corrections to the QCD contribution to same-sign $W$-pair production, $pp\to e^\pm \nu_e \mu^\pm \nu_\mu jj$, for same-sign charged leptons. This includes all leading logarithmic contributions which scale as $\alpha_W^4 \alpha_s^{2+k}\log^k(\hat s/p_\perp^2)$. This process is important for the study of electroweak couplings and hence the QCD contributions are usually suppressed through a choice of Vector Boson Scattering (VBS) cuts. These select regions of phase space where logarithms in $\hat s/p_\perp^2$ are enhanced. While the logarithmic corrections lead to a small change for the cross sections, several distributions relevant for experimental studies are affected more significantly.Comment: 20 pages, 10 figures v2: Matches published version (Dec 2021

Logarithmic corrections to the QCD component of same-sign W-pair production for VBS studies

We present the results of the first calculation of the logarithmic corrections to the QCD contribution to same-sign $W$-pair production, $pp\to e^\pm \nu_e \mu^\pm \nu_\mu jj$, for same-sign charged leptons. This includes all leading logarithmic contributions which scale as $\alpha_W^4 \alpha_s^{2+k}\log^k(\hat s/p_\perp^2)$. This process is important for the study of electroweak couplings and hence the QCD contributions are usually suppressed through a choice of Vector Boson Scattering (VBS) cuts. These select regions of phase space where logarithms in $\hat s/p_\perp^2$ are enhanced. While the logarithmic corrections lead to a small change for the cross sections, several distributions relevant for experimental studies are affected more significantly