Nonleptonic Hyperon Decays Research Articles

Possibility of CP violation in the cascade non-leptonic decays

There is more than one parameter expressing CP violation in the non-leptonic hyperon decays. The recent experimental results provide us with indications that CP conservation may not be valid for the Ξ decays. Especially for the Ξ dacays this is not due to the deviations from the exact ΔI=1/2 rule.

Partial rate differences from CP violation in hyperon nonleptonic decays

The partial rate differences between particle and antiparticle into their corresponding CP conjugate states, e.g., λ, Σ, Ξ→ πB, and λ, Σ, Ξ→π B , are estimated in the framework of the three left-handed-doublet model of Kobayashi and Maskawa using the current algebra methods. The CP- odd effects in general are very small.

P-wave non-leptonic hyperon decay amplitudes and the positive-parity excited baryons

It is shown that 1 2 + resonance poles contribute significantly to the p-wave hyperon non-leptonic decay amplitudes. The calculation was carried out by using the QCD-corrected WS GIM weak hamiltonian and the Isgur-Karl description of the positive-parity baryons. The agreement with experiment is very much improved. This is achieved by using parameters either straight from experiment or from the Isgur-Karl harmonic oscillator model. That means that the expected accuracy of our calculations is of about 20% at best and that it should be smaller for the amplitudes found by subtracting large numbers.

Quark-quark interaction and Ω-non-leptonic decays

The one-gluon-exchange phenomenological potentials of Bhaduri et al. (1980), observed to reproduce the experimentally fitted values of the ratio D/F and F for hyperon non-leptonic decays reasonably well, are used to study the weak non-leptonic decays of Omega -. The calculated partial decay rates are in fair agreement with the experimental data.

A “unified” phenomenological approach to the non-leptonic decays of hyperons

In analogy with the pole model for the non-leptonic hyperon decays, a new model is proposed, and which gives satisfactory results for all the non-leptonic decays of the hyperons (B→B′π,B→B′γ andB→B′πγ).

Quark-quark interaction and non-leptonic hyperon decays

Shows that an effective phenomenological Hamiltonian, in which the relativistic corrections are small and the spin-dependent force is essentially of long range, is successful in reproducing the experimentally fitted values of D/F and F for non-leptonic hyperon decays.

Exclusive modes of proton decay in SU(5)

We compute two-body branching ratios in proton decay in the SU(5) Grand Unification scheme. Using spin-flavor symmetries, we obtain algebraic relations between the matrix elements. The absolute magnitude is fixed from non-leptonic decays of hyperons. Pion modes are very important due to phase space, and ωe + is quite sizeable due to its large matrix element. We find also an important K 0μ + fraction. Bound state effects are quite crucial since we get a lifetime at the edge of the experimental limits, τ, (p) ≈ 10 31 yr for M X = 6 × 10 14 GeV.

Hyperon decays revisited

We examine the standard quantum-chromodynamics-inspired description of nonleptonic hyperon decays. We point out that the discrepancy between s- and p-wave amplitudes which emerged from a PCAC (partial conservation of axial-vector current) analysis cannot be cured by the inclusion of factorizable diagrams. We include anomalous contributions to the axial-vector current divergence which appear in the presence of the effective local Fermi interaction. Like factorizable diagrams, these preserve the successful results of PCAC for s-wave amplitudes, but are insufficient to give a quantitatively satisfactory description. We estimate the decay rates for ..cap omega../sup -/ ..-->.. ..xi..*..pi.. and ..xi../sup 0/l/sup -/..nu../sub l/ in view of further tests of the standard model.

QCD effects in a model of non-leptonic hyperon decays

Inclusion of QCD corrections is shown to result in substantial changes in the quark model predictions for non-leptonic hyperon decays.

Calculations of nonleptonic [formula omitted] decay branching ratios

Nonleptonic Ω − decay branching ratios have been calculated using the Weinberg-Salam model with QCD corrections and the MIT bag model. The whole scheme is equivalent to that which works well for nonleptonic hyperon decays. The calculated values are in qualitative and even rough quantitative with experimental data.

Non-leptonic hyperon decays and harmonic oscillator quark model for baryons

Non-leptonic hyperon decay amplitudes have been calculated using the Weinberg-Salam model with QCD corrections. Baryon states have been described using the harmonic oscillator (Isgur-Karl) model. The results agree with experiments and with the results obtained previously using the MIT bag model for baryons. It seems that the theoretical predictions are practically quark-model independent.

Calculation of non-leptonic hyperon decay amplitudes without arbitrary parameters

Non-leptonic hyperon decay amplitudes are calculated starting from the Weinberg-Salam model and employing the QCD renormalized effective weak Hamiltonian which includes the effects of SU(4) symmetry breaking. The amplitudes are described through the commutator approximation (s-wave), the ground-state pole approximation (p-wave) and separable contributions. Values of all parameters are taken from either experiments or theoretical estimates. Such a no-parameter approach works well for s-wave amplitudes, reproducing their relative signs and absolute magnitudes. For p-wave amplitudes the relative signs are correctly reproduced, while some magnitudes are too small. The importance of separable contributions and of the so-called “penguin” terms is explicitly shown.

Violation of theΔI=12rule and the Melosh transformation

The Miura-Minamikawa-Pati-Woo theorem is reexamined incorporating the idea of the Melosh transformation, which relates the current quarks to the consituent ones. It is shown that the small component induced by the internal motion of quarks in a hadron introduces the violation of $\ensuremath{\Delta}I=\frac{1}{2}$ rule in hyperon nonleptonic decays, and it is of the order of charge-symmetry breaking.

Comprehensive sum rules for s-wave amplitudes of nonleptonic hyperon decays

Sum rules for the S-wave amplitudes of the nonleptonic hyperon decays are discussed. A new sum rule √12( Λ 0 0 + Ξ 0 0) = (∑ − − − ∑ + +) is proposed as one of the comprehensive sum rules in the SU(4) symmetry theory.

Nonleptonic Hyperon Decays and Lightlike Chiral Structure of Hadrons. III: The Roles of H(8, 1) and H(8, 8) Hamiltonians for the P-Wave Decays

Nonleptonic Hyperon Decays and Lightlike Chiral Structure of Hadrons. III: The Roles of H(8, 1) and H(8, 8) Hamiltonians for the P-Wave Decays

CP violation and the deviations from the ΔI=1/2 rule in the nonleptonic hyperon decays

In this paper we investigate the problem of CP violation in the nonleptonic decays of hyperons. Three parameters are proposed which express the extent of CP violation in these decays. The problem of CP violation in the nonleptonic hyperon decays is not only different from that in the K decays, but it is seen to be related very closely with the deviations from the exact ΔI=1/2 rule. Furthermore, model-dependent calculations give also similar results and some additional relations.

Nonleptonic Hyperon Decays in the Constituent Rearrangement Model and Universality of d/f Ratios

Nonleptonic decays of hyperons are investigated in terms of the constituent rearrange­ ment (CR) model by assuming i) dominance of 15 and 20 components of the weak Hamil­ tonian in SU (4), ii) universality of d/ f ratios and iii) spin non-flip along spectator constituent lines. vVe analyze the CP invariant CR amplitudes and obtain ..St=O as well as the Lee­ Sugawara relation for s-wave decays. It is shown that the contribution of 15 is much larger than that of 20 in the s-wave decays, while the 20 component is important for describing the p-wave amplitudes.

Absolute magnitude of non-leptonic hyperon decays and electromagnetic hyperfine splittings

In the quark model with current-current interaction, non-leptonic hyperon decays are controlled by the baryon wave function at small distances. An independent estimate of this quantify is provided by a related phenomenon: the baryon electromagnetic hyperfine splittings, given by the Fermi contact interaction. A good estimate is obtained with the standard Cabibbo-suppressed interaction. Important remaining problems for S-waves are emphasized.

Non-Leptonic decays of hyperons in the quartet model

The non-leptonic hyperon decays are investigated in the framework of the colored quartet model with GIM current. We take two octet components of the weak Hamiltonian which belong to 15 and 20″ representations of SU(4) symmetry. The 15 Hamiltonian arising from the symmetry breaking is assumed to have the universal spurion coupling. We obtain remarkable fits to s- and p-wave amplitudes both in the current algebra approach and the dispersion theory. It is shown that the standard arguments for s-wave decays based on the K ∗ pole dominance, on the duality arguments and on the current algebra lead to different physical consequences with one another.

Extended partially conserved axial-vector current hypothesis and soft-meson theorems

General expressions are derived for soft-meson theorems in the framework of the recently proposed extended partially conserved axial-vector current hypothesis (EPCAC). Applications are made to ${K}_{l3}$, $K\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\pi}\ensuremath{\pi}$, $K\ensuremath{\rightarrow}2\ensuremath{\pi}$, nonleptonic hyperon decays, pseudoscalar-meson photoproduction, and meson-nucleon scattering. In all cases it is found that the EPCAC predictions improve the agreement between soft-meson results and experiment. Moreover, the EPCAC approach allows a unified treatment of several chiral-symmetry-breaking problems. Finally, an extension to SU(4) \ifmmode\times\else\texttimes\fi{} SU(4) is briefly discussed.