Improved estimates of rareKdecay matrix elements fromKℓ3decays

Abstract

The estimation of rare K decay matrix-elements from K ℓ3 experimental data is extended beyond LO in Chiral Perturbation Theory. Isospin-breaking effects at NLO (and partially NNLO) in the ChPT expansion, as well as QED radiative corrections, are now accounted for. The analysis relies mainly on the cleanness of two specific ratios of form-factors, for which the theoretical control is excellent. As a result, the uncertainties on the K + → π + νν and K L → π 0 νν matrix-elements are reduced by a factor of about 7 and 4, respectively, and similarly for the direct CP-violating contributions to K L → π 0 e + e − and K L → π 0 µ + µ − . They could be reduced even further with better experimental data for the K ℓ3 slopes and the K + ℓ3 branching ratios. As a result, the non-parametric errors for B (K → πνν) and for the direct CP-violating contributions to B K L → π 0 ℓ + ℓ − are now completely dominated by those on the short-distance physics.

Probing anomalous t t ¯ Z $$ t\overline{t}Z $$ interactions with rare meson decays

“…Again, the hadronic matrix element can be extracted from the K l3 decays, parametrized here by κ L [49]. As in the B q → µ + µ − decays, we include all NP effects as additional contributions to the SM top-quark function X t = X SM t + δX NP .…”

“…The hadronic matrix element of the low-energy operator is parameterized by κ + . This parameter is extracted from K 3 data and known precisely, including long-distance QED radiative corrections (∆ EM ), and NLO and partially NNLO corrections in chiral perturbation theory [49,50].…”

Indirect determinations of the top quark mass

“…where κ L accounts for the hadronic matrix element and is given by [69] κ L = (2.223 ± 0.013) × 10 −10 λ 0.2249…”

“…The branching ratio for K + → π + νν in the SM can be written as [64] BR( 34) whereκ + accounts for the hadronic matrix element, which can be extracted from the semi-leptonic decays of K + , K L and K S mesons [69], and electromagnetic corrections κ + = (5.155 ± 0.025) × 10 −11 λ 0.2249…”

J-PARC E14 KOTO experiment for $K_L\rightarrow \pi^0\nu \bar\nu$

“…The CP-violating parameter, η, can be determined through the measurement of the branching ratio, where theoretical uncertainty is 1 − 2% [3] in the Standard Model (SM) framework. Second, it is a rare flavor-changing neutral current and highly suppressed in the SM, where the branching ration was calculated to be (2.49 ± 0.39) × 10 −11 [4]. The branching ratio is very sensitive to the new physics beyond the SM and there are plenty rooms for such new physics [7] below the current limit, 1.46 × 10 −9 [6] at 90% confidence level (CL).…”