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Precision tests of the Standard Model: the Drell-Yan processes by Tommaso Armadillo -
Jeudi 3 septembre 2026 à 14h00 - Aula consiglio - Dipartimento di fisica - Via Giovanni Celoria 16, 20133 Milan - Italie -
The Standard Model (SM) stands as one of the most successful and extensively tested theoretical frame- work for describing fundamental particles and their interactions. To date, experimental measurements across a vast range of energy scales have shown outstanding agreement with theoretical predictions. De- spite these experimental triumphs, the theory remains fundamentally incomplete. For example, it fails to account for established physical realities such as dark matter, the matter-antimatter asymmetry of the universe, neutrino masses, and a quantum description of gravity. New physics typically manifests itself in experimental data as resonances in differential distributions. However, the absence of such direct observations indicates that, if present, it resides at energy scales beyond the kinematic reach of current colliders. While the on-shell peaks of these resonances may not be experimentally accessible, their low- energy tails can still manifest as subtle deviations in the TeV region. For this reason, the frontier of high-energy physics has shifted towards precision tests. During the High-Luminosity phase of the LHC, these high-energy regions are projected to be measured with percent or sub-percent level accuracy. To ensure a statistically meaningful comparison between experimental data and theoretical predictions, the uncertainties on the latter must be systematically reduced to the same level.
This thesis contributes to the advancement of these theoretical predictions by calculating higher-order perturbative corrections, with a specific emphasis on the electroweak (EW) sector of the SM. To this end, we developed OCEANN, a novel computational framework that lays down the pipeline from the generation of Feynman diagrams to the numerical evaluation of ultraviolet-renormalized and infrared- subtracted two-loop amplitudes. Within OCEANN, we introduced ABISS, a MATHEMATICA package designed to compute the interference between two-loop and tree-level amplitudes. While to overcome the severe computational bottlenecks associated with evaluating complex multi-scale Feynman integrals, we developed SEASYDE, a MATHEMATICA package that implements the series expansion approach. Crucially, this newly developed computational tools natively support complex masses, allowing for the stable and precise evaluation of amplitudes in resonant processes.
We applied this framework to compute the mixed QCD-EW two-loop amplitudes for both Neutral Current (NC) and Charged Current (CC) Drell-Yan (DY) processes. Alongside this, we calculated the complete two-loop QED corrections to NC-DY, an effort motivated by the need to deeply understand the infrared structure of the full two-loop EW amplitude. These calculations represents a theoretical breakthrough for the LHC precision program, effectively opening the door towards complete two-loop EW computations.
Subsequently, we implemented the two-loop mixed amplitude for NC-DY into the Monte-Carlo inte- grator MATRIX and we conducted a detailed phenomenological study. This allowed us to provide precise differential cross-sections across both the resonant and high invariant-mass regions. We also performed a comprehensive comparison of our findings against an independent calculation available in literature.
Finally, we bridge the gap between precision phenomenology and Beyond the Standard Model physics searches by interpreting potential small deviations within the framework of the Standard Model Effective Field Theory (SMEFT). Utilizing the SMEFIT framework, we integrate precise theoretical inputs into global SMEFT analyses to rigorously constrain the current parameter space of new physics. Further- more, we extend this analytical framework to evaluate the sensitivity of future high-energy colliders. By projecting the foreseen increase in experimental precision at upcoming facilities into our global fits, we systematically quantify how future measurements will enhance our ability to isolate indirect signatures of the presence of new physics.
Jury members :
Prof. Fabio Maltoni (UCLouvain) (Supervisor)
Prof. Alessandro Vicini (UNIMI, It.) (Supervisor)
Prof. Philippe Ruelle (UCLouvain) (Chairperson)
Prof. Gauthier Durieux (UCLouvain) (Secretary)
Prof. Stefano Pozzorini (Universität Zürich, C.H.)
Prof. Jonas Lindert (Univ. of Sussex, U.K.)
Pay attention : the public defense of Tommaso Armadillo will also take place in the form of a videoconference
