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).     

Strangeness, charm, and bottom in a chiral quark-meson model

In this paper, we investigate an SU(3) extension of the chiral quark-meson model. The spectra of baryons with strangeness, charm, and bottom are considered within a “rigid oscillator” version of this model. The similarity between the quark sector of the Lagrangian in the model and the Wess-Zumino term in the Skyrme model is noted. The binding energies of baryonic systems with baryon numbers B=2 and 3 possessing strangeness or heavy flavor are also estimated. The results are in good qualitative agreement with those obtained previously in the chiral soliton (Skyrme) model.     

Parity effects in radiative Ω−-decays

It is shown that, for values of theΩ ^? magnetic moment near that predicted bySU(6), parity effects in radiativeΩ ^?-decays are expected to be small and, contrary to the situation in hyperon decays, more pronounced in decays with heavy charged particles. They depend, however, sensitively on the magnetic moment ofΩ ^? and are insensitive to the hyperon moments. This is due to the dominance of a “contact” term which has to be introduced in the amplitude in order to ensure gauge invariance.     

Exotic hyperons: Theoretical status and search perspectives in hyperon beam facilities

The theoretical models that predict the existence of exotic hyperons made of more than three quarks are reviewed. We present the properties of exotic hyperons with strangenessS=–1 (quark contents ),S=–2 ( ) andS=–3 ( ) predicted by the sum rules for reggeon-particle scattering amplitudes. The inclusive cross sections for the production of these hyperons in hyperon-proton interactions are calculated. The cross sections turn out to be of the order of millibarns, thus opening a good perspective to encounter such exotic hyperons in the available hyperon beam facilities at CERN and FNAL.We also propose to study the Regge trajectories corresponding to the exotic hyperons, analyzing the inclusive spectra of andK mesons produced in hyperon-proton collisions.     

Spin polarizability of hyperons

We review the recent progress of the theoretical understanding of spin polarizabilities of the hyperon in the framework of SU(3) heavy baryon chiral perturbation theory (HBChPT). We present the results of a systematic leading-order calculation of hyperon Compton scattering and extract the forward spin polarizability (γ ₀) of hyperons. The results obtained for γ ₀ in the case of nucleons agree with the known results of SU(2) HBChPT when kaon loops are not considered.     

Dilatons in the topological soliton model for the hyperons

We show that the predicted hyperon masses in the topological soliton model are very sensitive to the value to the gluon condensate parameter that appears when the scale invariance and trace anomaly of QCD are taken into account by introduction of a dilaton field. This contrasts with the insensitivity of the soliton properties to the dilaton coupling. In order that the predicted strange and charmed hyperon spectra agree with the empirical ones the gluon condensate parameter has to be about (400 MeV)⁴, which agrees with the result obtained from QCD sum rules. Within the framework of the present model this implies that the bag formed by the scalar field must be very shallow.     

Static hyperon properties in a linearizedSU(3)-Chiral Bag model

We use a linearized Chiral Bag model to describe the strange octet and decuplet baryons. The approach is canonically extended to spontaneously broken chiral SU(3)_L × SU(3)_R, and the corresponding Goldstone Bosons are identified with the pseudoscalar meson octet. We include explicit symmetry breaking corrections both for baryons and mesons. The linearized quark-meson intraction is applied in a self-consistent calculation of the masses and, for Δ, Σ^* and Ξ^*, of the decay widths. Our special interest is in the influence of theK- andη-cloud (in addition to theπ) on hyperon static properties. We show results for radii, masses, decay widths and renormalization constants as obtained by a fit to the experimental hyperon spectra. The effects of theK- andη-mesons are found to be non-negligible, although supressed by symmetry breaking effects. The effective gluon coupling α is reduced in comparison to the SU(2)_L × SU(2)_R case. In addition, we discuss the dependence on the bag constantB. It turns out that the lightest hyperon states, Λ and Σ are well described and stable for B^1/4 < 130 MeV. The heavier strange baryons have stable solutions also for larger values ofB. The bag radii determined at the minimal energies are R₀?1.15 fm for the octet and R₀?1.25 fm for the decuplet baryons.     

Covariant quark model for the baryons

A family of simply solvable covariant quark models for the baryons is presented. With optimal parameter choices the models reproduce the empirical spectra of the baryons in all flavor sectors to an accuracy of a few percent. Complete spectra are obtained for all states of the strange, charm and beauty hyperons with L ⩽2. The magnetic moments and axial coupling constants of the ground state baryons correspond to those of conventional quark models. We construct current-density operators tjat are consistent with empirical nucleon form factors at low and medium momenta.     

重离子碰撞中阈能附近超子产生机制

在量子分子动力学输运模型LQMD(Lanzhou quantum molecular dynamics transport model)框架下,研究了不同重离子反应系统中同位旋和核介质效应对超子产生以及动能谱的影响.基于手征有效场理论,引入了动量和密度相关的排斥超子-核子光学势,并且考虑了该势对超子产生截面阈能的修正....     

Polarization of Λ0 hyperons as a signature for the quark-gluon plasma

The momentum distribution of Λ⁰ hyperons produced from the quark-gluon plasma (QGP) in ultra-relativistic heavy-ion collisions is calculated in dependence on their polarization. The momentum distribution of Λ⁰ hyperons is defined by matrix elements of relativistic quark Wigner operators, which are calculated within the effective quark model with chiral U(3)×U(3) symmetry and the quark-gluon transport theory. We show that the polarization of the Λ⁰ hyperon depends on the spin of the strange quark that agrees well with the DeGrand-Miettinen model. We show that Λ⁰ hyperons, produced from the QGP, are fully unpolarized. This means that a detection of unpolarized Λ⁰ hyperons, produced in ultra-relativistic heavy-ion collisions, should serve as one of the signatures for the existence of the QGP in intermediate states of ultra-relativistic heavy-ion collisions.     

Ξ * resonances inΞ −be interactions

In an experiment carried out in the CERN SPS hyperon beam, the diffractive dissociation of incidentΞ ^? hyperons into ΛK ^? andΞ ^?π⁺π^? final states has been observed. Several resonances are seen in the final states, including the well known Ξ(1820) which appears in both channels, and the Ξ(1680) which appears as a narrow state (M=1691.1±2.7 MeV/c², Γ<8 MeV/c²) in the ΛK^? channel and possibly also in the Ξππ channel.     

Gravitational waves from the axial perturbations of hyperon stars

The eigen-frequencies of the axial w-mode oscillations of hyperon stars are examined.It is shown that as the appearance of hyperons softens the equation of state of the super-density matter,the frequency of gravitational waves from the axial w-mode of hyperon star becomes smaller than that of a traditional neutron star at the same stellar mass.Moreover,the eigenfrequencies of hyperon stars also have scaling universality.It is shown that the EURO thirdgeneration gravitational-wave detector has the potential to detect the gravitational-wave signal emitted from the axial w-mode oscillations of a hyperon star.     

X-ray photoelectron spectra of iron complexes: Correlation of iron 2p satellite intensity with complex spin state

Metal and ligand core-level spectra have been obtained for 36 iron complexes which possess a variety of ligands including carbonyl, nitrosyl, triphenylphosphine,o-phenylenebis(dimethylarsine), halides and pseudohalides. Formal metal oxidation states range from ? 1 to + 3, and complex spin states represented in the series include 0, $\text{1}\text{2}$, $\text{3}\text{2}$, 2 and $\text{5}\text{2}$. A clear correlation between complex spin state and satellite intensity in the Fe 2p spectra is found. The satellite intensities observed experimentally are in approximate quantitative accord with those predicted by a “spin flipping” model. Although the present analysis does not provide a definitive choice between the “sudden approximation” and “spin flipping” models, the agreement between experimental satellite intensities and the intensities predicted by the “spin flipping” model suggests that such a mechanism can be important in the satellite process.     

Quark dynamics and the weak non-leptonic decays of K and D mesons

Quark model predictions for K → 2π and D → Kπ decays were investigated in dynamical frameworks based on the separable approximation (SA), current algebra (CA), current algebra modified for the meson moment dependence (CAC) and current algebra with final-state interactions (CAF). Relativistic and non-relativistic quark model predictions were compared. The effective weak hamiltonian was modified by changing the relative strengths of its flavour $\text{20}\text{and}\text{84}$ parts. All these approaches were also applied to hyperon and $\text{Ω}{}^{\mathrm{?}}$ non-leptonic decays. When using standard QCD enhancement, the best approximation for K → 2π (CAC) works poorly with D → Kπ. The best approximatiob for D→Kπ (CAF) fails in the case of K → 2π. Only CAC with the $\text{84}$ piece of the hamiltonian quenched might be in agreement with studied weak decays.     

Hadroproduction of hyperons in the framework of the quark-parton model

TheSU (6)×O(3) classification of baryons is applied to the hyperon production in the framework of the quark-diquark fusion model. The model predictions are compared with the data measured inpp interactions at various energies. The contribution of the decay of the high-lying hyperon resonances to the observed spectra is estimated and found essential.     

Anharmonic corrections in constant-cutoff soliton model

We suggest a quantum stabilization method for theSU(2) -model, based on the constant-cutoff limit of the cutoff quantization method developed by Balakrishnaet al., which avoids the difficulties with the usual soliton boundary conditions pointed out by Iwasaki and Ohyama. We investigate the baryon numberB=1 sector of the model and show that after the collective coordinate quantization it admits a stable soliton solution which depends on a single dimensional arbitrary constant. We then derive the results for anharmonic corrections to the hyperon energy in the bound-state approach to theSU(3)-soliton model for the hyperons, withSU(3)-symmetry breaking. Thus we show that the anharmonic corrections give, as in the case of the complete Skyrme model, negative contributions to the hyperon energies and that they are of the same order of magnitude as those obtained using the complete Skyrme model for bound heavy-flavor two-meson systems in the case of cascade hyperons.     

On a present status of the gathering model for cumulative meson production

Physical grounds of the “gathering” model are discussed. It is shown that the “gathering” of nucleons in a collective interaction is a direct consequence of the behaviour of colour forces at large distances. An analytical variant of the model is presented which allows a large simplification of the calculation procedure. The results obtained are compared with the data onπ- andK-meson cumulative production. The model applicability for relativistic nucleus-nucleus collisions is discussed.     

Tests of various models for the weak decays of heavy flavour states

It is discussed how two models which were proposed to explain the lifetime difference betweenD ⁰ andD ⁺ mesons can be subjected to further tests. These two models are the “SU (4) 20-plet dominance” model and the “gluon bremstrahlung” model forW exchange. The tests can be performed by studying inclusive decays—e.g.,F ⁺ lifetime or semi-leptonic branching ratio—or special exclusive modes in the non-leptonic and semileptonic decays. It is suggested thatF ⁺ semi-leptonic decays can lead to glueball production. The decays of bottom mesons are discussed in this context, too.