Forward--backward asymmetry in the $H\to Z\gamma\to\overline{f}{f}\gamma $ decay

Abstract

We study the forward--backward asymmetry in the three-body decay process $H\to Z\gamma\to\overline{f}f\gamma$, induced by complex form factors in the $HZ\gamma$ vertex. To estimate its magnitude, we derive constraints on the real and imaginary parts of the $CP$-violating form factor $h_3^{Z\gamma}$ using current LHC measurements, obtaining upper limits of about $0.9$ GeV. These bounds are of the same order of magnitude as those derived from electric dipole moments (EDM). We find that the asymmetry can reach values of order $10^{-1}$ and may be accessible at the HL-LHC.