Measuring CP nature of top-Higgs couplings at the future Large Hadron electron collider

Abstract

We investigate the sensitivity of top-Higgs coupling by considering the associated vertex as CP phase ($ζ_t$) dependent through the process $p\, e^- \to \bar t \,h \,ν_e$ in the future Large Hadron electron collider. In particular the decay modes are taken to be $h \to b\bar b$ and $\bar t \to$ leptonic mode. Several distinct $ζ_t$ dependent features are demonstrated by considering observables like cross sections, top-quark polarisation, rapidity difference between $h$ and $\bar t$ and different angular asymmetries. Luminosity ($L$) dependent exclusion limits are obtained for $ζ_t$ by considering significance based on fiducial cross sections at different $σ$-levels. For electron and proton beam-energies of 60 GeV and 7 TeV respectively, at $L = 100$~fb$^{-1}$, the regions above $π/5 < ζ_t \leq π$ are excluded at 2$σ$ confidence level, which reflects better sensitivity expected at the Large Hadron Collider. With appropriate error fitting methodology we find that the accuracy of SM top-Higgs coupling could be measured to be $κ= 1.00 \pm 0.17 (0.08)$ at $\sqrt{s} = 1.3 (1.8)$ TeV for an ultimate $L = 1 \,\rm{ab}^{-1}$.

8 pages, 8 figures, 1 table, text modified, accepted for publication in Physics Letters B