CKM benchmarks for electron EDM experiments

Understand

All current experiments searching for an electron EDM d_e are performed with atoms and diatomic molecules.

• Motivated by significant recent progress in searches for an EDM-type signal in diatomic molecules with an uncompensated electron spin, we provide an estimate for the expected signal in the Standard Model due to the CKM phase.
• We find that the main contribution originates from the effective electron-nucleon operator $\bar{e} i\gamma_5 e \bar{N}N$, induced by a combination of weak and electromagnetic interactions at $O(G_F^2\alpha^2)$, and not by the CKM-induced electron EDM itself.
• When the resulting atomic P,T-odd mixing is interpreted as an {\it equivalent} electron EDM, this estimate leads to the benchmark $d_e^{equiv}(CKM) \sim 10^{-38}$ ecm.