Probing $tt\gamma$ and $ttZ$ couplings at the LHeC

TL;DR

This paper investigates how the proposed LHeC collider can probe the electromagnetic and weak dipole moments of the top quark through deep inelastic scattering and photo-production modes, potentially surpassing current indirect limits.

Contribution

It introduces a framework of gauge-invariant dimension-six operators to analyze top quark couplings at the LHeC, focusing on the top quark's MDM and EDM and their experimental constraints.

Findings

LHeC can set stronger constraints on top quark dipole moments than current indirect limits.

Photo-production mode is an excellent probe for top quark MDM and EDM.

Potential to improve limits beyond LHC capabilities.

Abstract

We study the deep inelastic scattering and photo-production modes of $t\overline{t}$ pairs at the proposed LHeC and its potential to probe the electromagnetic and weak dipole moments (MDM and EDM for $tt\gamma$) of the top quark. A framework of eight independent gauge-invariant dimension-six operators involving the top quark and the electroweak gauge bosons is used. Four of these operators modify the charged $tbW$ coupling which can be probed through the single (anti) top production mode as reported in the literature. One generates $tt\gamma (Z)$ as well as $tbW$ couplings, while the other two do not generate $tbW$ but only $tt\gamma (Z)$. Our focus is on the MDM and EDM of the top quark for which the photo-production mode of $t\overline{t}$ can be an excellent probe. At the proposed electron energies of $E_e =60$ and $140$ GeV the LHeC could set constraints stronger than the indirect limits from $b\to s \gamma$ and the potential limits of the LHC through $t\overline{t} \gamma$ production.