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 ($\hat{I}{\P }_t$) dependent through the process $p{e}^{-}\to \bar{t}h\hat{I}{½}_e$ 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 $\hat{I}{\P }_t$ 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 $\hat{I}{\P }_t$ by considering significance based on fiducial cross sections at different $\ddot{I}ƒ$-levels. For electron and proton beam-energies of 60 GeV and 7 TeV respectively, at $L=100$~fb${}^{-1}$, the regions above $\ddot{I}€/5<\hat{I}{\P }_t\le \ddot{I}€$ are excluded at 2$\ddot{I}ƒ$ 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 $\hat{I}º=1.00\pm 0.17(0.08)$ at $\sqrt{s}=1.3(1.8)$ TeV for an ultimate $L=1{\mathrm{ab}}^{-1}$.

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