SEMILEPTONIC HYPERON DECAYS

Abstract

ABSTRACT:We review the status of hyperon semileptonic decays. The central issue is the Vus element of the CKM matrix, where we obtain Vus = 0.2250(27). This value is of similar precision, but higher, than the one derived from K l3 , and in better agreement with the unitarity requirement, |V ud | 2 + |Vus| 2 + |V ub | 2 = 1. We find that the Cabibbo model gives an excellent fit of the existing form factor data on baryon beta decays (χ 2 = 2.96 for 3 degrees of freedom) with F + D = 1.2670 ± 0.0030, F − D = −0.341 ± 0.016, and no indication of flavour SU (3) breaking effects. We indicate the need of more experimental and theoretical work, both on hyperon beta decays and on K l3 decays.

Semileptonic Hyperon Decays and Cabibbo-Kobayashi-Maskawa Unitarity

“…We also find [12] that the g 1 form factor of the different decays, which is subject to first order corrections, is well fitted by the F, D parameters [1], with F + D = 1.2670 ± 0.0035 and F − D = −0.341 ± 0.016 with χ 2 = 2.96/3 d.f.…”

“…The consistency of the values of V us determined from the different decays is a first confirmation of the overall consistency of the model. A more detailed version of this work will be published in the Annual Reviews of Nuclear and Particle Sciences [12].In 1964 Ademollo and Gatto proved [13] that there is no first-order correction to the vector form factor, ∆ 1 f 1 (0) = 0. This is an important result: since experiments can measure V us f 1 (0), knowing the value of f 1 (0) in ∆S = 1 decays is essential for determining V us .…”

“…The consistency of the values of V us determined from the different decays is a first confirmation of the overall consistency of the model. A more detailed version of this work will be published in the Annual Reviews of Nuclear and Particle Sciences [12].…”

Baryon vector current in the chiral and1/Ncexpansions

“…[17,18]. Of particular interest in that regard is the best possible determination of the form factors f 1 for extracting |V us | through the product |f 1 V us |, which can be determined rather precisely from observables (see for example…”

Charged lepton induced one kaon production off the nucleon

“…More specifically, the g A (= D + F ) combination, related to the neutron β decay, is very well known, but the knowledge of the D and F values is less precise [23]. Also, one may investigate the Q 2 dependence of the weak axial form factors of nucleons and hyperons.…”