Anomalous Top-Higgs Couplings and Top Polarisation in Single Top and Higgs Associated Production at the LHC

TL;DR

This paper constrains anomalous CP-violating top-Higgs couplings using current Higgs data and explores their measurement prospects at future colliders, analyzing effects on top polarization and lepton angular distributions.

Contribution

It provides updated constraints on CP-violating top-Higgs couplings and investigates their observability through specific production channels and angular asymmetries at the LHC and TLEP.

Findings

Current CP-violating phase constrained to |ξ|<0.6π at 95% C.L.

Future measurements at TLEP could tighten this to |ξ|<0.07π.

Pseudoscalar interactions are most promising to observe.

Abstract

In this paper, we put constraints on anomalous $\mathcal{CP}$-violating top-Higgs couplings using the currently available Higgs data and explore the prospect of measuring these couplings at 240 GeV TLEP. We find that the $\mathcal{CP}$-violating phase $\xi$ is currently limited in the range $|\xi|< 0.6\pi$ at 95\% C.L. and may be further constrained to $|\xi| <0.07\pi$ at TLEP. Under this consideration, we further investigate the observability of the scalar ($\xi =0$), pseudoscalar ($\xi =0.5\pi$) and mixed ($\xi =0.25\pi$) top-Higgs interactions through the channel $pp \to t(\to \ell^+\nu_\ell b)h(\to b\overline{b})j$. We find that it is most promising to observe pure pseudoscalar interactions with $y_t=y_t^{SM}$, although this will be challenging due to a low signal to background ratio. We also find that the anomalous top-Higgs couplings can lead to sizeable differences in lepton forward-backward asymmetries and can be distinguished by measuring the lepton angular distributions from polarised top quarks at 14 TeV LHC.