Standard Model Phenomenology

Hamilton's research concerns the development of high precision simulations of collider physics processes. These facilitate discovery and interpretation of new physics at the Large Hadron Collider (LHC). While precision simulations may not be needed to claim a discovery, e.g. if new physics appears as a clear `bump' in a smooth distribution, (as did the Higgs boson), in many new physics scenarios, signals are expected to manifest as subtle distortions in the shapes of distributions. An accurate understanding of the Standard Model background, subject to all experimental cuts, is then unavoidable for claiming a discovery, or setting exclusion limits. Precision simulations are also essential to determine what it is that has been found. The recently discovered Higgs boson is the prime example of this. Together with collaborators in Milan and Munich, Hamilton developed the world's most accurate simulation of Higgs boson production. This simulation is used, by default, by the ATLAS and CMS collaborations, appearing in dozens of publications, confronted with measurements designed to probe Higgs boson properties. Since 2016 Hamilton has collaborated with Dasgupta, Salam, and Soyez (Panscales), to clarify and significantly improve the accuracy of the core, parton shower, component of general purpose Monte Carlo event generators -- the most widely used theoretical tools in particle physics. After four challenging years, in Feb 2020, the Panscales team presented novel final-state parton shower algorithms in full agreement with a broad range of independent, dedicated, analytic calculations, at next-to-leading logarithmic accuracy; something not previously achieved in 40-years of parton showers.

Thorne's work is complementary to that of Hamilton. It involves the precise details of the initial state appearing in hadronic particle collisions. At hadron colliders, e.g. the Large Hadron Collider (LHC), the particle beam is effectively made up of the fundamental particles inside the proton - quarks and gluons, generically known as partons. Predictions for Standard Model processes, and potentially those of new physics, require the precise partonic composition of the hadrons in terms of both the energy scale of the scattering process (e.g., the mass of a particle produced) and the momentum fraction of the incoming proton carried by the parton. Thorne is the lead member of an established PDF group, MSHT, that provides one of the three sets of parton distribution functions (PDFs) used as standard by both the experimental and theoretical analyses at the LHC and other high energy particle physics experiments. The approach is continually improved, both in terms of theoretical sophistication, and by inclusion of data which become available and due to increased precision or different sensitivity to PDFs, lead to further PDF constraints. Thorne's work will lead to improved PDF determination, providing updated PDFs for universal use, and he will also investigate the implications of any changes. This will lead to a better understanding of current and upcoming measurements, and will also influence planning for future high energy particle physics experiments, e.g. the EIC. Additionally, Thorne is a core member of the PDF4LHC working group (a member of the steering committee since the inception, and one of the main drivers and organisers) which provides recommendations for use of PDF sets at the LHC and acts as a direct liason to the LHC, and wider, experimental community.

Both Hamilton and Thorne are involved in increasing precision for calculations at particle colliders, which is particularly essential in order maximise the potential of the LHC, particularly given the current situation of no very clear signals of new physics, but continual appearance of unprecedented variety and precision of Standard Model tests. Both will provide expertise in interpreting any deviations which could be the first sign of Beyond the Standard Model (BSM) Physics.