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T: Fachverband Teilchenphysik

T 60: Top Quarks: Decay and CP Violation and Mixing Angles

T 60.2: Vortrag

Mittwoch, 23. März 2022, 16:30–16:45, T-H19

Studies for the search for t→ Z c transitions via interference effects — •Lucas Cremer, Johannes Erdmann, Roni Harnik, Jan Lukas Späh, and Emmanuel Stamou — TU Dortmund University, Department of Physics

Exclusion limits for anomalous flavour-changing neutral currents (FCNC) are typically set by searching for two-body decays of the top quark, which are quadratic in the new physics (NP) coupling. The limits are constantly improved by new data, but the sensitivity to small couplings could be enhanced by an alternative approach. This approach takes advantage of the interference between the FCNC and the Standard Model (SM) contributions. The focus of this work is to access the experimental feasibility of this idea.

Concretely we investigate the three-body decay t→ bb c in the presence of an anomalous t−Z−c coupling. In the SM, this process proceeds through the emission of a W boson, while the FCNC diagram contains an intermediate Z boson. The two contributions interfere. The dominant contribution of the interference is in the restricted kinematic region in which both intermediate bosons are onshell. In this region, both the SM and the pure FCNC contribution are suppressed by the small width of the gauge bosons, which enhances the impact of the interference contribution. Because the interference scales linearly with the NP coupling constant, while the pure FCNC contribution scales with the coupling constant squared, an analysis of events in this region can potentially improve the sensitivity to small coupling constants.