18th April 2023 – every Tuesday from 2-4 pm in room 119 – ending 30th May 2023

The absence of obvious signs of new physics at the Large Hadron Collider (LHC) at CERN implies that we must now hunt for its indirect evidence through small departures from predictions. Consequently, theoretical particle physicists must push the accuracy of their simulations ever further so as to meet that of experimental origin, which inevitably reduces over time as experimentalists find more ingenuous ways of limiting their systematic uncertainties and more data is collected.

At the heart of such simulations is the perturbative computation of scattering cross-sections, which will be the main focus of the lecture. It will start with a brief reminder of the basics of Quantum ChromoDynamics (QCD) and of the overall collider simulation pipeline currently utilized by experimentalists and phenomenologists alike. We will then discuss infrared and ultraviolet singularities with the various techniques for their regularization and cover modern methods for computing (multi)-loop virtual amplitudes, including numerical ones (incl. sector decomposition and Loop-Tree Duality).

Given the importance of such computations, the last three decades saw our community develop a wealth of computational tools streamlining the solutions identified, and we will cover them together with simple illustrative example calculations carried out by hand. Numerical Monte-Carlo integration often plays a key role in this endeavour, and we will discuss many aspects pertaining to its optimization, such as importance sampling, dedicated phase-space parameterizations and fast numerical implementations.

Learning results of the course:

The objective of this course is to offer students a detailed understanding of the main theoretical and computational aspects of predicting observables for collider experiments. A strong emphasis will be put on modern (semi-)numerical approaches to this problem, along with hands-on exercises carried out on personal computers for non-trivial examples. Thus, attendees are expected to gain deeper insights into the mechanics of perturbative QFT and its state-of-the-art, as well as expertise with computational algorithms with a broad scope of applicability.

Lecturer:

Valentin Hirschi