Measurement of the $\mathit{H Z\gamma}$ coupling at the future linear e ⁺ e ^- collider

Abstract.

We examine the prospects for measuring the $H Z \gamma$ coupling of a standard model-like Higgs boson with a mass between 120 and 160 GeV at the future TESLA linear e ⁺ e ^- collider, assuming an integrated luminosity of 1 ab^-1 and a center-of-mass energy of 500 GeV. We consider the Higgs boson produced in association with $\nu_e \bar{\nu_e}$ via the W W fusion reaction $e^+e^- \rightarrow \nu_e \bar{\nu_e} H$, followed by the rare decay into a Z boson and a photon, $H \rightarrow Z \gamma$. Accounting for all main background contributions, a precision of 27% can be achieved in unpolarized e ⁺ e ^- collisions for M _H = 140 GeV. With appropriate initial state polarisations $\Delta$BF( $H \rightarrow Z \gamma$)/BF( $H \rightarrow Z \gamma$), or the precisions on the $H \rightarrow Z \gamma$ partial width, can be improved to 17% and provide valuable information on the $H Z \gamma$ coupling. For M _H = 120 and 160 GeV, the small significance of the signals in unpolarized collisions sets upper limits of 79% respectively 72% at 90% confidence level on the $H \rightarrow Z \gamma$ branching fraction.