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

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 $ξ$ is currently limited in the range $|ξ|< 0.6π$ at 95\% C.L. and may be further constrained to $|ξ| <0.07π$ at TLEP. Under this consideration, we further investigate the observability of the scalar ($ξ=0$), pseudoscalar ($ξ=0.5π$) and mixed ($ξ=0.25π$) top-Higgs interactions through the channel $pp \to t(\to \ell^+ν_\ell b)h(\to b\overline{b})j$. 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.

16pp, 8 figures and 2 tables; v2; updated to match published version