Abstract
In this study, we investigate the imprints of CP violation in certain η muonic decays that could arise within the Standard Model effective field theory. In particular, we study the sensitivities that could be reached at REDTOP, a proposed η facility. After estimating the bounds that the neutron EDM places, we find still viable to discover signals of CP violation measuring the polarization of muons in η → μ+μ− decays, with a single effective operator as its plausible source.
Highlights
The article is organized as follows: in section 2, we discuss the two CP -violating scenarios arising from the SMEFT operators and their connection from quark to hadron degrees of freedom
In this study, we investigate the imprints of CP violation in certain η muonic decays that could arise within the Standard Model effective field theory
Following the operator basis in ref. [4], we can find here CP violation in three different sectors: that involving the hadronic part only, which we include in the CPH category; that mixing quark and leptons, which we include in the CPHL one; and that affecting lepton-photon interactions (OeW,eB), which we checked to be negligible and discard1 for brevity
Summary
We assume that the CP -violating new-physics effects are heavy enough to be described through the SMEFT. [4], we can find here CP violation in three different sectors: that involving the hadronic part only, which we include in the CPH category; that mixing quark and leptons, which we include in the CPHL one; and that affecting lepton-photon interactions (OeW,eB), which we checked to be negligible and discard for brevity.. Regarding the CPH category, since we are interested in decays connecting η to muons, these will result, at low-energies, in a CP -violating shift of the ηγ∗γ∗ coupling, a scenario extensively discussed in the literature in the context of light pseudoscalar mesons [8,9,10]. Accounting for the hadronization details linking the SMEFT CPH operators to FηCγP∗1γ,∗2(q12, q22) in a quantitative manner is a formidable task; this is enough to our purposes as we shall see. Coming back to the CPHL category, the relevant operators here are.
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