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T: Fachverband Teilchenphysik
T 10: Axions/ALPS I
T 10.5: Vortrag
Montag, 16. März 2026, 17:15–17:30, KH 01.013
Search for Axion-Like Particles via Top Quark Decays with ATLAS: Statistical Methods — •Martin Christiansen, Frederic Fischer, Annika Stein, Jessica Höfner, Hendrik Smitmanns, and Lucia Masetti — Johannes Gutenberg-Universität Mainz, Institut für Physik
A search for long-lived Axion-like particles (ALPs) originating from exotic top quark decays is performed using the ATLAS detector at a center-of-mass energy of √s = 13.6 TeV. ALPs can be investigated by parameterizing their couplings to Standard Model (SM) particles. This analysis targets top-antitop events characterized by one top quark decaying leptonically and one decaying via a flavour-changing neutral current t → a + u/c, where a denotes the ALP. Portions of the viable parameter space predict ALP lifetimes sufficiently long for macroscopic displacement prior to decay. Focusing on ALPs decaying within the ATLAS hadronic calorimeter, the ratio of energy deposits in the electromagnetic and hadronic calorimeters is utilized to mitigate SM backgrounds. Statistical methods play an important role in this context. The event topology is reconstructed based on χ2 minimization combined with b-tagging information, and the resulting loglikelihood score becomes relevant also for cutflow optimization. In addition, a Boosted Decision Tree is trained on the background and signal model. With the help of this multivariate analysis technique, variables are identified that are highly discriminative yet statistically independent and that can be used for data-driven methods, further improving the sensitivity of the analysis.
Keywords: Axion-Like Particles; Top Quarks; BSM Physics; Boosted Decision Tree; ATLAS Experiment