Enhanced $thj$ signal at the LHC with $h\rightarrow \gamma\gamma$ decay and $\mathcal{CP}$-violating top-Higgs coupling

TL;DR

This paper investigates the potential to detect non-standard top-Higgs couplings at the 14 TeV HL-LHC through the $t ightarrow u_ au b$ and $h ightarrow \gamma ext{ extasciicircum} ext{ extasciicircum}$ decay channel, highlighting the impact of CP-violation on signal significance and top polarization.

Contribution

It introduces a novel analysis of the $pp ightarrow t h j$ channel with $h ightarrow \gamma ext{ extasciicircum} ext{ extasciicircum}$ to probe CP-violating top-Higgs interactions, demonstrating enhanced observability compared to previous modes.

Findings

Signal significance reaches 2.7σ for $\xi=0.25\pi$ and 7.7σ for $\xi=0.5\pi$.

Diphoton decay mode is more promising than $bar{b}$ channel.

Top polarization asymmetries can distinguish different CP phases.

Abstract

We study the observability of non-standard top Yukawa couplings in the $pp\rightarrow t(\rightarrow \ell \nu_\ell b ) h(\rightarrow \gamma\gamma)j$ channel at 14 TeV high-luminosity LHC (HL-LHC). The small diphoton branching ratio is enhanced when the $\mathcal{CP}$-violating phase, $\xi$, of the top-Higgs interaction is non-zero. When the modulus of the top-Higgs interaction assumes the SM value, $y_t=y_t^{SM}$, we find that the signal significance reaches $2.7\sigma$ $( 7.7\sigma)$ when $\xi= 0.25\pi$ $(0.5\pi) $. Furthermore, the different couplings modify the polarisation of the top quark, and can subsequently be distinguished via asymmetries in spin correlations with the final state leptons. The diphoton decay mode is found to be significantly more promising than the previously considered $pp\rightarrow t(\rightarrow \ell \nu_\ell b ) h(\rightarrow b\overline{b})j$ channel.