Measurement of the $HZ\gamma$ Coupling at the Future Linear \ee 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 \ee 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 $e^+e^- \to \nu_e \bar{\nu_e} H$, followed by the rare decay into a $Z$ boson and a photon, $H \to Z \gamma$. Accounting for all main background contributions, different selection procedures are discussed. Uncertainties on the \hZg branching fraction of approximately 48% (27%, 44%) can be achieved in unpolarised \ee collisions for $M_H$ = 120 (140, 160) GeV. With appropriate initial state polarisations $\Delta$BF(\hZg)/BF(\hZg), or the precisions on the \hZg partial width, can be improved to 29% (17%, 27%) and provide valuable information on the $HZ\gamma$ coupling. We regard our results as a convincing confirmation of the great potential of a linear collider to access and reliably measure important parameters of the Higgs boson despite initially overwhelming background with final state signature similar to the signal events.