Direct measurement of the Higgs self-coupling in $e^{+}{e}^{-}\to ZH$

Abstract

A new method to measure the trilinear Higgs self-coupling ${\lambda }_3^{}$ in a single Higgs production process is proposed. Time-reversal-odd (T-odd) asymmetries in the process $e_{}^{+}{e}_{}^{-}\to ZH$, $Z\to f\bar{f}$ are computed from the absorptive part of the electroweak one-loop amplitude. Since the T-odd asymmetries measure the tree-level $t$-channel $ZH\to ZH$ scattering, they can be direct probes of ${\lambda }_3^{}$. The proposed method is quite challenging; a relatively large statistics and polarized $e_{}^{+}{e}_{}^{-}$ beams are demanded. However, this is probably the only approach to directly measure ${\lambda }_3^{}$ in $e_{}^{+}{e}_{}^{-}$ collisions, when a beam energy above the $ZHH$ production threshold is not available.

13 pages, 5 figures