Hyperon weak radiative decays in chiral perturbation theory

Abstract

We investigate the leading-order amplitudes for weak radiative decays of hyperons in chiral perturbation theory. We consistently include contributions from the next-to-leading order weak-interaction Lagrangian. It is shown that due to these terms Hara's theorem is violated. The data for the decays of charged hyperons can be easily accounted for. However, at this order in the chiral expansion, the four amplitudes for the decays of neutral hyperons satisfy relations which are in disagreement with the data. The asymmetry parameters for all the decays can not be accounted for without higher-order terms. We shortly comment on the effect of the 27-plet part of the weak interaction.Comment: 8 pages of REVTeX and using macro-package "feynman.tex" (available at http://xxx.lanl.gov/ftp/hep-ph/papers/macros) for the 2 figure

Prospects for rare and forbidden hyperon decays at BESIII

“…In addition to the two-body radiative decays, weak hyperon dilepton decays will provide additional information on the radiative transitions [31,32]. According to PDG2016, the only observed hyperon dilepton decay is the Ξ 0 → Λe + e − decay, which is measured to be B(Ξ 0 → Λe + e − ) = (7.6 ± 0.6) × 10 −6 [33], which is consistent with an inner bremsstrahlung-like production mechanism for the e + e − pair.…”

Challenges in Hyperon Decays

“…give contribution of order O(E) to the amplitudes, were not considered [6,7]. In a series of paper [6,7,8] we consistently calculated the leading-order amplitude of weak radiative decays of hyperons in ChPT.…”

“…As a results, the theory has degenerated into models that are mostly invoked to account for particular special subsets of phenomenology. For example, it was well known that the lower order chiral perturbation theory cannot account for the data on hyperon radiative decays [4,5] even after the heavy baryon chiral perturbation theory formalism is employed [6,7,8]. In an attempt to resolve this puzzle, some additional resonances are added in the analysis recently [9].…”

“…In the heavy-baryon formulation there is an additional expansion in 1/ṁ. However, all these terms can be effectively absorbed in counterterms of the theory [6,7,8].…”

“…In a series of paper [6,7,8] we consistently calculated the leading-order amplitude of weak radiative decays of hyperons in ChPT. At this order, no loop contribution need to be considered.…”