New descriptions of boson plus multiple jet production at the Large Hadron Collider in the high energy limit

The abundance of data collected by the Large Hadron Collider (LHC) and its increasing precision and centre-of-mass energy √ s have posed challenges to the theory community. In particular, such energy increase has been shown to damage the convergence of the perturbative series of the scattering matrix S, by means of appearance of large logarithms of the form log(s/|t|) in all orders of the strong coupling gs. In future years, this effect will worsen with the advent of the Future Circular Collider (FCC), where the centre-of-mass energy is meant to be significantly larger than that of the LHC. Thus, in the high-energy limit regime, defined by s/|t| ≫ 1, the ratio of the centre-of-mass energy and the t−channel momentum exchanged squared is large, and specific formalisms have to be invoked to make accurate predictions. In this thesis, we explore several processes for which these high-energy logarithms are numerically significant and worth taking care of appropriately. First, the origin of these logarithms will be explained and the HEJ formalism will be introduced. Next, some results for processes with a Higgs boson plus jets will be presented with comparisons to data from the LHC, before looking at the specifics of the processes involving vector boson production alongside jets. It becomes clear that for the sake of accuracy, obtaining Next-to-Leading Logarithmic expressions is important to improve the description of data in key regions, so some of the key steps towards reaching this accuracy will be analysed. Finally, it will be shown that the formalism extends to processes outside of the scope of proton-proton collision, such as Deep Inelastic Scattering, which gives a different viewpoint for tackling tensions between theory and data in the high-energy limit

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

High energy resummed predictions for the production of a Higgs boson with at least one jet

We present all-order predictions for Higgs boson production plus at least one jet which are accurate to leading logarithm in s^/|p⊥|2. Our calculation includes full top and bottom quark mass dependence at all orders in the logarithmic part, and to highest available order in the tree-level matching. The calculation is implemented in the framework of High Energy Jets (HEJ). This is the first cross section calculated with log(s^) resummation and matched to fixed order for a process requiring just one jet, and our results also extend the region of resummation for processes with two jets or more. This is possible because the resummation is performed explicitly in phase space. We compare the results of our new calculation to LHC data and to next-to-leading order predictions and find a numerically significant impact of the logarithmic corrections in the shape of key distributions, which remains after normalisation of the cross section