Studying flavor-changing neutral tqZ couplings: Current constraints and future prospects

TL;DR

This paper investigates non-standard flavor-changing neutral current interactions involving top quarks and Z bosons, analyzing current experimental constraints and exploring future detection prospects at high-luminosity colliders.

Contribution

It introduces an effective-Lagrangian framework with four complex couplings to study tuZ and tcZ interactions, providing updated constraints and future measurement possibilities.

Findings

Current experimental limits constrain non-standard couplings.

Future collider experiments could improve sensitivity to these interactions.

The study offers a comprehensive framework for analyzing flavor-changing top quark decays.

Abstract

Possible non-standard tuZ and tcZ interactions, which induce flavor-changing neutral-current decays of the top quark, are studied in the effective-Lagrangian framework. The corresponding Lagrangian consists of four kinds of non-standard couplings coming from SU(3)xSU(2)xU(1) invariant dimension-6 effective operators. The four coupling constants in each interaction are treated as complex numbers independent of each other, and constraints on them are derived by using the present experimental limits of the branching fractions for t -> u Z and t -> c Z processes. Future improvements of those constraints are also discussed as well as possibilities of measurements of these couplings at the High-Luminosity Large Hadron Collider.