Regular Article - Theoretical Physics
On the sensitivity of the D parameter to new physics
Université Paris-Saclay, CNRS/IN2P3, IJCLab, 91405, Orsay, France
2 Sorbonne Université, CNRS, Laboratoire de Physique Théorique et Hautes Energies (LPTHE), 75252, Paris, France
Accepted: 29 November 2022
Published online: 15 December 2022
Measurements of angular correlations in nuclear beta decay are important tests of the Standard Model (SM). Among those, the so-called D correlation parameter occupies a particular place because it is odd under time reversal, and because the experimental sensitivity is at the level, with plans of further improvement in the near future. Using effective field theory (EFT) techniques, we reassess its potential to discover or constrain new physics beyond the SM. We provide a comprehensive classification of CP-violating EFT scenarios which generate a shift of the D parameter away from the SM prediction. We show that, in each scenario, a shift larger than is in serious tension with the existing experimental data, where bounds coming from electric dipole moments and LHC observables play a decisive role. The tension can only be avoided by fine tuning of the parameters in the UV completion of the EFT. We illustrate this using examples of leptoquark UV completions. Finally, we comment on the possibility to probe CP-conserving new physics via the D parameter.
© The Author(s) 2022
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