Use of Z polarization in e+e− → ZH to measure the triple-Higgs coupling

Abstract

It is shown that a certain angular asymmetry of charged leptons produced in the decay of Z in the process e+e−→ZH, related to a tensor polarization component of the Z, can be used to constrain the anomalous triple-Higgs coupling, independent of the other anomalous couplings like the ZZH coupling which dominate at tree level. This is because the angular asymmetry is odd under naïve time reversal, and hence dependent on loop-level contributions. At a future e+e− collider like the International Linear Collider (ILC), for example, a limit of about 3.4 might be placed on the ratio of the actual triple Higgs coupling to that predicted in the standard model for a centre-of-mass energy of 500 GeV and an integrated luminosity of 30 fb−1 with electron and positron beams having longitudinal polarization of −80% and +30%, respectively.