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

RWTH Publications (RWTH Aachen)

Abstract

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 $\mathcal{B}_{\mathrm{excl}}(t\rightarrow Zc) = 6.4 \times 10^{-5}$ 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.

Authors 5

1. Lucas Cremer

   TU Dortmund University

   Affiliation as printed

   Technische Univ. of Dortmund (Germany)

2. J. Erdmann Aachen III. Physikalisches Institut A

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen University , III. Physikalisches Institut A , Aachen , Germany

   RWTH Aachen Univ. (Germany)

3. Roni Harnik

   Fermi National Accelerator Laboratory

   Affiliation as printed

   Fermilab Accelerator Laboratory , Batavia , IL , USA

   Fermi National Accelerator Laboratory (FNAL), Batavia, IL (United States)

4. Jan Lukas Späh Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen Univ. (Germany)

5. Emmanuel Stamou

   TU Dortmund University

   Affiliation as printed

   Fakultät für Physik , TU Dortmund , D-44221 Dortmund , Germany

   Technische Univ. of Dortmund (Germany)