Leveraging on-shell interference to search for FCNCs of the top quark and the Z boson

• Published in: The European physical journal. C, Particles and fields Particles and fields, 2023-09, Vol.83 (9), p.871-16, Article 871
• Main Authors: Cremer, Lucas, Erdmann, Johannes, Harnik, Roni, Späh, Jan Lukas, Stamou, Emmanuel
• Format: Article
• Language: English
• Subjects: Analysis; Artificial neural networks; Astronomy; Astrophysics and Cosmology; Business competition; Computer simulation; Couplings; Elementary Particles; Flavor (particle physics); Hadrons; Heavy Ions; Interference; Large Hadron Collider; Leptons; Luminosity; Measurement Science and Instrumentation; Monte Carlo method; Monte Carlo simulation; Neutral currents; Nuclear Energy; Nuclear Physics; Physics; Physics and Astronomy; PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; Quantum Field Theories; Quantum Field Theory; Quarks; Regular Article - Theoretical Physics; Search methods; Standard model (particle physics); String Theory
• ISSN: 1434-6052; 1434-6044; 1434-6052
• DOI: 10.1140/epjc/s10052-023-11982-1

Flavour-changing-neutral currents (FCNCs) involving the top quark are highly suppressed within the Standard Model (SM). Hence, any signal in current or planned future collider experiments would constitute a clear manifestation of physics beyond the SM. We propose a novel, interference-based strategy to search for top-quark FCNCs involving the Z boson that has the potential to complement traditional search strategies due to a more favourable luminosity scaling. The strategy leverages on-shell interference between the FCNC and SM decay of the top quark into hadronic final states. We estimate the feasibility of the most promising case of anomalous tZc couplings using Monte Carlo simulations and a simplified detector simulation. We consider the main background processes and discriminate the signal from the background with a deep neural network that is parametrised in the value of the anomalous tZc coupling. We present sensitivity projections for the HL-LHC and the FCC-hh. We find an expected 95% CL upper limit of B excl ( t → Z c ) = 6.4 × 10 - 5 for the HL-LHC. In general, we conclude that the interference-based approach has the potential to provide both competitive and complementary constraints to traditional multi-lepton searches and other strategies that have been proposed to search for tZc FCNCs.