ηγZ anomaly from the η→γμ+μ− decay

We show that the ηγZ anomaly can be measured by analysing parity-violating effects in the η→γμ+μ− decay. In this sense, we find that the longitudinal polarization of the outgoing μ+ is an appropriate observable to be considered in future high-statistics η factories. The effect is expected to lie in the range 10−5–10−6 in the Standard Model.