New-physics searches in $C!P$-violating $eta$ muonic decays

In this work we investigate the possibility to observe $C!P$-violation in $eta$ decays containing muons at the proposed REDTOP experiment. Employing the SMEFT to parametrize the new-physics $C!P$-violating effects, we find that a single operator exists for which is possible to observe $C!P$-violation at REDTOP in $etatomu^+mu^-$ decays, while evading bounds from the neutron electric dipole moment and $D^-tomubar{ u}$