Measuring $CP$ nature of $h\tau \bar{\tau }$ coupling at $e^{-}p$ collider

Abstract

The proposed future $e^{-}p$ collider provides sufficient energies to produce the Standard Model Higgs Boson ($h$) through $W^{\pm }$ and $Z$-Boson fusion in charged and neutral current modes, respectively and to measure its properties. We take this opportunity to investigate the prospect of measuring the $CP$ properties of $h$ through $h\to {\tau }^{+}{\tau }^{-}$, where ${\tau }^{-}\left({\tau }^{+}\right)$ decays to a charged pion ${\pi }^{-}\left({\pi }^{+}\right)$ and a neutral pion ${\pi }^0$ in association with neutrino (anti-neutrino). An interesting $CP$ sensitive angular observable ${\alpha }_{\mathrm{CP}}$ between the two $\tau$-leptons decay plane in the ${\pi }^{+}{\pi }^{-}$ centre of mass frame is proposed and investigated in this work. For fixed electron energy of 150 GeV along with 7 (50) TeV of proton energy, the $CP$ phase can be measured approximately to $25^{\circ }$ ($14^{\circ }$) at integrated luminosity of 1~ab${}^{-1}$ for $-$80\% polarised electron at 95\% confidence level.

Comments: 12 pages, 10 figures, 2 tables, Version accepted for publication in EPJC