Leptoquarks at RUN III ATLAS

Leptoquarks are particles that carry both quark and lepton quantum numbers. Leptoquarks are theoretically motivated by similarities in the lepton and quark sector. They are a feature of many models that go beyond the Standard Model, particularly models dealing with unification: SUSY (Supersymmetry), Technicolor, etc.

Leptoquarks are a possible explanation of anomalies observed in B-meson decays, given their unique ability to mediate lepton flavour universality violation. They can also contribute to the muon g-2 anomalous magnetic moment discrepancy between theory and experiment.

The PhD project aims to conduct a new leptoquark pair search that uses multi-variant techniques and focus on the multi-TeV mass regime to get the best out of the Run III dataset. The analysis will include all possible lepton-quark combinations apart from those with third generation fermions - a total of 25 possible decays will be investigated. Leptoquark decays with neutrinos will be included. Muon momentum resolution is poor at high energy, these will be included in the analysis.

The major improvement to the analysis is to use multivariant techniques. Previously, the average mass of the two leptoquarks was used as the final discriminant. This was adequate in the low mass regime where the analysis was optimised.

For the new analysis, in the high mass regime, the plan is to use multiple input observables that can better discriminate signal from background events through multivariate techniques and possible graph neural networks. The mass cannot be fully reconstructed in decays involving neutrinos or where the muon resolution is poor, instead several final state observables must be optimally combined.

ATLAS is aiming to upgrade the current RNN based algorithm for Tau ID and decay mode classification to a GNN based architecture. Currently, there are two proposed solutions: TauJetGraph and GNTau. As part of the qualification task, a study of the two GNN's will be conducted to evaluate the performance differences. The goal is to implement and deploy officially into the ATLAS framework, subsequent to this a data-based evaluation will need to be performed