New physics in s → d semileptonic transitions: rare hyperon vs. kaon decays

Abstract

Abstract We investigate the potential of rare hyperon decays to probe the short distance structure in the $$ s\to dv\overline{v} $$ s → dv v ¯ and s → dℓ+ℓ− transitions. Hyperon decays into neutrinos $$ \left({B}_1\to {B}_2v\overline{v}\right) $$ B 1 → B 2 v v ¯ can be reliably predicted by using form factors determined in baryon chiral perturbation theory. Their decay rates are sensitive to different short-distance operators, as compared to their kaon counterparts, and the corresponding branching fractions are in the range of 10−14 ∼ 10−13 in the standard model. In the context of the low-energy effective theory, we find that the anticipated BESIII measurements of the $$ {B}_1\to {B}_2v\overline{v} $$ B 1 → B 2 v v ¯ decays would lead to constraints on new physics in the purely axial vector $$ \overline{d}{\gamma}_{\mu }{\gamma}_5s $$ d ¯ γ μ γ 5 s current that are stronger than the present limits from their kaon siblings $$ K\to \pi \pi v\overline{v} $$ K → ππv v ¯ . On the other hand, although hyperon decays into charged leptons are dominated by long-distance hadronic contributions, angular observable such as the leptonic forward-backward asymmetry is sensitive to the interference between long- and short-distance contributions. We discuss the sensitivity to new physics of a potential measurement of this observable in comparison with observables in the kaon decays KL→ μ+μ− and K+→ π+μ+μ−. We conclude that the current kaon bounds are a few orders of magnitude better than those that could be obtained from Σ+→ pμ+μ− except for two scenarios with new physics in the $$ \left(\overline{d}{\gamma}^{\mu }s\right)\left(\overline{\mathrm{\ell}}{\gamma}_{\mu }{\gamma}_5\mathrm{\ell}\right) $$ d ¯ γ μ s ℓ ¯ γ μ γ 5 ℓ and $$ \left(\overline{d}{\gamma}^{\mu }{\gamma}_5s\right)\left(\overline{\mathrm{\ell}}{\gamma}_{\mu}\mathrm{\ell}\right) $$ d ¯ γ μ γ 5 s ℓ ¯ γ μ ℓ currents. Finally, we point out that the loop effects from renormalization group evolution are important in this context, when relating the low-energy effective field theory to new physics models in the UV.