Study of the hγZ coupling at the ILC

Abstract

We study the hγZ coupling, which is a loop induced coupling in the Standard Model (SM), to probe new physics. In a global fit based on the SM Effective Field Theory, measurement of the SM hγZ coupling can provide a very useful constraint, in particular for the precise determination of hZZ and hWW couplings. At the International Linear Collider (ILC), there are two direct ways to study the hγZ coupling: one is to measure the branching ratio of the h → γZ decay and the other to measure the cross section for the e+e− → hγ process. We have performed a full simulation study of the e+e− → hγ process at the 250 GeV ILC, assuming 2 ab−1 data collected by the International Large Detector (ILD). The expected 1σ bound on the effective hγZ coupling (ζAZ) combining measurements of the cross section for e+e− → hγ followed by h → b¯b and the h → γZ branching ratio is −0.0015 < ζAZ < 0.0015. The expected significance for the signal cross section in the fully hadronic h → WW∗ channel is 0.09 σ for beam polarizations of P(e−, e+) = (−80%, +30%).