Dissertation at the Institute of Kernphysik on Higher Order Corrections to Processes in the Standard Model

July 20, 2022

We congratulate Dr. Matthias Heller on completing his dissertation titled

"Radiative corrections to Compton processes on the proton and to the Drell-Yan process"

In this thesis, Matthias Heller calculated radiative corrections to two fundamental processes of the Standard Model: the Compton process on the proton and the Drell-Yan process. Experimentally, the Compton process is the most important tool to study structure functions and other intrinsic properties of the proton. The Drell-Yan process, on the other hand, is one of the most basic processes measured at the LHC at CERN and has a long history of probing the theory of strong interactions.

Short summary for scientists:

For a solid interpretation of experimental data and comparison with predictions from the Standard Model of Particle Physics, one needs a precise theoretical understanding of the underlying scattering processes and one needs to incorporate higher-order corrections into theoretical predictions. However, the calculation of these corrections is in general very cumbersome and time-consuming and new techniques need to be developed that facilitate the computation. In this thesis, we study radiative corrections to two different processes at very different energy scales. Despite the fact that the underlying theories are quite different, the techniques and tools to calculate higher-order effects in both situations are the same.

In the first project, we calculate the leading-order corrections in quantum electrodynamics to the Compton process on the proton in different experimental setups. The Compton process is one of the most important processes to study the internal structure of nucleons using scattering data at different energies and from different experiments to access the Compton amplitude phenomenologically. To extract structure functions from the data, it is important to know the size of radiative corrections on the level of the theoretically predicted cross section when comparing with experimental data. We study these corrections in various experimental situations at Jefferson Lab and at the MAMI accelerator and for different models, describing the Compton amplitude in two different energy regimes.

In the second project, we study the mixed electroweak-strong radiative corrections to the Drell-Yan process. Although this type of correction received a significant amount of attention in the particle physics community during the last decades, the calculation of the full set of contributions without any approximation remained a challenge for a long time. The main technical issue was the calculation of the master integrals with two masses using differential equations. They fall into a class of integrals whose differential equations contain non-rationalizable algebraic functions such that the standard algorithm to integrate the differential equation does not work. We develop new techniques to tackle this class of differential equations and successfully calculate all master integrals for the mixed electroweak-strong two-loop corrections to the Drell-Yan process. Using these integrals, we furthermore calculate the virtual two-loop mixed electroweak-strong helicity amplitudes for the first time.