Weak radiative hyperon decays in the quark model

Weak radiative hyperon decays are considered on the basis of the quark model including one-quark transitions associated with the effective sdγ vertex and two-quark processes s + u → u + d + γ induced by W-boson exchange. The phenomenological model proposed in this study gives values that describe experimental data well and makes predictions for the asymmetry of the decays Λ → n + γ and ξ^? → Σ^? + γ.     

Comments on the symmetry relations in the hyperon radiative decays

We demonstrate that in general Hara's theorem which gives various symmetry relations for the hyperon radiative decays is not valid. The new relations we derive are different from those given by Hara. But for the Σ⁺→P_γ decay, the asymmetry parameter is still zero in the exact SU(3) limit.     

Weak radiative decays of baryons

Using recent experimental baryon weak radiative decay data for the fiveB→B′γ decays, we employ the pole model self-consistently to extract the reduced matrix elements 〈B′|H _w|B〉. The resulting pattern is compatible with weak pion decaysB→B′π and also with the quark model.     

Hara’s theorem and W—exchange in hyperon weak radiative decays

We reconsider Hara’s theorem and relate it to the well-known properties of β-decay. All assumptions necessary for the theorem to be true are explicitly formulated. Further, we study the W—exchange contribution to weak radiative decays and show that it does not violate Hara’s theorem. However, this contribution reveals the essential role of particle mixing in symmetry considerations and some peculiar features of gauge-invariant amplitudes under perturbative expansion. Together they explain an effect, which was treated as contradicting Hara’s theorem, without any violation. The properties of W—exchange we describe here may have more general importance and should be taken into account in further detailed calculations of weak processes.     

Quark model analysis of hyperon semileptonic decays

A study of hyperon semileptonic decays has been made in various quark models and compared with the standard Cabibbo analysis which is found to be in good agreement with experiments. Results obtained in a quasirelativistic constituent quark model are in reasonable agreement with the standard Cabibbo analysis and show no sizeableSU(3) symmetry breaking effects. Results in other quark models which take into account theSU(3) symmetry breaking effects in the dominant form factors are similar to the quasirelativistic constituent quark model.     

Weak hyperon nucleon interaction in a quark model

The nonmesonic decay moded of Λ in nuclear matter, ΛN → NN, and production of Λ in proton-neutron scattering, pn → Λn, are studied theoretically. The weak transition of baryon is described by the one meson exchange mechanism and the direct quark-quark interaction mechanism.     

Hidden-gauge model and radiative decays

We consider the radiative decay widths in a hidden-gauge model. For calculating the decay widths we use the anomalousVVP Lagrangian.g _VVP is a function off _P due to the symmetry breaking effects. It is shown thatf _P is consistent with that obtained by the one-loop calculation. A reasonable agreement with the experimental decay widths is achieved.     

Weak radiative decays of hyperons within theSU(6) broken quark-diquark model

In view of persisting discrepancy between experimental and theoretical results, specially in the weak radiative decays of∑ ⁺ andΞ ⁰, we analyse these decays within the framework of the QCD inspired quark-diquark model. On introducing a slightSU(6) breaking we obtainα(∑ ⁺→p+γ)≈?0.9 which is in excellent agreement with experimental value. Other decays are also improved in this scheme.     

Pole model for nonlepton and radiative hyperon decay

Nonlepton and weak radiative decays of hyperons are analyzed on the basis of the pole model. In contrast with other analyses, the contributions from both baryon and meson poles are taken into account. Experimental information on these decays is used to find the parameters of the effective weak two-baryon interaction.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 8, pp. 17–22, August, 1969.The author thanks V. A. Filimonov and G. M. Radutskii for stimulating discission of this study.