The momentous discovery of the Higgs boson in 2012 marked the start of a new era in particle physics. The energy of collisions at the Large Hadron Collider (LHC) has since increased allowing us to probe fundamental physics at an energy scale which has been out of reach until now. This presents a challenge to particle theory to keep pace with these developments, and respond to the fact that Standard Model interactions will have different features in this new energy range. We must understand these differences in order to extract as much information as possible from LHC data, and in particular to identify any signs of new physics. My framework, High Energy Jets, is the only tool of its kind to include the dominant high-energy corrections to all orders in the strong coupling within a flexible tool which can be adapted to a wide range of experimental analyses.
The high-energy corrections I have been able to describe had already been shown to be necessary to describe data at lower collisions energies. The priority of the project was to build on this proof-of-concept to develop more accurate and more widely-applicable predictions for the LHC. This work was structured in two programmes: the first of these was based on the construction of a publicly available fully-flexible event generator while the second programme concentrated on developing theoretical understanding of scattering amplitudes in the high energy limit. There has been natural interplay between these two with new theory calculations being incorporated into the event generator and numerical results suggesting new theoretical calculations to perform.
A particular priority during the project has been providing predictions for collisions which create a Higgs boson alongside colour-charged particles, which is an important process for determining its properties. Due to the behaviour of the scattering amplitudes (which give the probabilities for these to occur), in addition to high-energy corrections my framework can include finite quark mass and loop propagator effects for higher numbers of colour-charged particles than any other method.
Highlights on the side of increased accuracy are the inclusion of a class of next-to-leading log processes and the construction of a mechanism to increase fixed-order accuracy to next-to-leading order for distributions. Both are included in the latest release of the public code, HEJ v2.2 available at
https://hej.hepforge.org(opens in new window). Throughout the grant, there has been an overhaul of this code and several version releases with accompanying documentation.
We were asked to provide predictions for two forthcoming LHC analyses by the ATLAS collaboration. The final publications have yet to appear, but they should teach us about the behaviour of QCD in the new energy regime which is now being tested.
