The Standard Model cannot explain the dominance of matter over anti-matter in our universe. This imbalance indicates undiscovered physics that violates combined CP symmetry.
Many extensions to the Standard Model seek to explain the imbalance by predicting the existence of new particles. Vacuum fluctuations of the fields associated with these new particles can interact with known particles and make small modifications to their properties; for example, particles which violate CP symmetry will induce an electric dipole moment of the electron (eEDM). The size of the induced eEDM is dependent on the masses of the new particles and their coupling to the Standard Model. To date, no eEDM has been detected, but increasingly precise measurements probe new physics with higher masses and weaker couplings.
Here we present the most precise measurement yet of the eEDM using electrons confined inside molecular ions, subjected to a huge intra-molecular electric field, and evolving coherently for up to 3 seconds. Our result is consistent with zero and improves on the previous best upper bound by a factor ∼2.4. Our sensitivity to 10^−19 eV shifts in molecular ions provides constraints on broad classes of new physics above 10^13 eV, well beyond the direct reach of the LHC or any other near- or medium-term particle collider.
Tanya S. Roussy, et al., "A new bound on the electron's electric dipole moment" arXiv:2212.11841 (December 22, 2022).
there is the KTeV anomaly in π0→e+e− decay
Rare decay π0→e+e-: Theory confronts KTeV data
https://www.researchgate.net › publication › 259676552_...
Jul 5, 2022 — ... The third anomaly is related to the persistently high central value observed for the width Γðπ 0 → e þ e − Þ, whose most recent and ...
arXiv:1710.03764v3 [hep-ph] 11 Sep 2020
https://arxiv.org › pdf
by DSM Alves · 2017 · Cited by 95 — A. The KTeV anomaly. 10. V. Constraints from Charged Kaon Decays. 12. A. Experimental bounds on K+ → π+(a → e+e−).
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