Constraints on top quark flavor changing neutral currents using diphoton events at the LHC

TL;DR

This paper demonstrates that the diphoton mass spectrum and angular distribution at the LHC can effectively constrain top quark flavor changing neutral currents, providing new limits and insights into rare top decays and neutron EDM contributions.

Contribution

It introduces a novel method using diphoton spectra and angular distributions at the LHC to set limits on top quark FCNC couplings and explores their impact on neutron EDM constraints.

Findings

Diphoton spectrum constrains FCNC couplings to the order of 10^{-4}.

Angular distribution is sensitive to anomalous FCNC couplings.

Neutron EDM bounds provide additional constraints on $tu\gamma$ FCNC coupling.

Abstract

In this paper we show that the diphoton mass spectrum in proton-proton collisions at the LHC is sensitive to the top quark flavor changing neutral current in the vertices of $tu\gamma$ and $tc\gamma$. The diphoton mass spectrum measured by the CMS experiment at the LHC at a center-of-mass energy of 8 TeV and an integrated luminosity of 19.5 fb$^{-1}$ is used as an example to set limits on these FCNC couplings. It is also shown that the angular distribution of the diphotons is sensitive to anomalous $tu\gamma$ and $tc\gamma$ couplings and it is a powerful tool to probe any value of the branching fraction of top quark rare decay to an up-type quark plus a photon down to the order of $10^{-4}$. We also show that the $tu\gamma$ FCNC coupling has a significant contribution to the neutron electric dipole moment (EDM) and the upper bound on neutron EDM can be used to constrain the $tu\gamma$ FCNC coupling.