Abstract
The data for the upper limit on the electric dipole moment of the neutron (nEDM) can be explained by using different mechanisms beyond the Standard Model (SM). The nEDM can be generated by a CP-violating transition of η and η′ mesons into pion pairs. We derive the upper limits for the rates of the CP-violating decays η(η′) → 2π are by orders of magnitude more stringent than those from existing experiments so far.
Highlights
The investigation of the electromagnetic moments of hadrons, in particular, of proton and neutron, and leptons is one of the promising goals in our understanding of the hadron structure
Within the strong-interaction sector, the neutron EDM is induced by the CP-violating θ-term of quantum chromodynamics (QCD)
The θ-term preserves the renormalizability and gauge invariance of QCD, but breaks the P- and T-parity invariance. It plays an important role in QCD, e.g., for the QCD vacuum, the topological charge, and the solution of the U(1)A problem of the mass of the η meson
Summary
The investigation of the electromagnetic moments of hadrons, in particular, of proton and neutron, and leptons is one of the promising goals in our understanding of the hadron structure. The existing upper experimental limits for the EDM of the electron or the neutron have values of order of 10−26 ÷ 10−27e · cm, which are more than six orders of magnitude larger than SM predictions. The θ-term preserves the renormalizability and gauge invariance of QCD, but breaks the P- and T-parity invariance It plays an important role in QCD, e.g., for the QCD vacuum, the topological charge, and the solution of the U(1)A problem of the mass of the η meson Direct measurements of rare decays can show how large the difference between the CP-violation process in the EDM and processes in rare decays are, or if they obey the same mechanism This calculation aims to show that the bound on the width of rare CP-violating decays of η and η mesons into pairs of pions is several orders of magnitude lower than the existing experimental limits of branching fractions.
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