On the pp → ppη(η′) reactions near threshold

The production rate for η′ in pp → ppη′ at rest is calculated in a covariant one boson exchange model, previously applied to study π⁰ and η production in NN collisions. The transition amplitudes for the elementary BN → η′N processes with B being the meson exchanged (B = π, σ, η, , ω and a₀) are taken to be the sum of s- and u-channels with a nucleon in the intermediate states, and an a₀ meson pole in a t-channel. The couplings of the η′ to hadrons are a factor 0.4 weaker than the respective η-hadron couplings, as suggested by a quark model and a singlet-octet mixing angle θ = −23°. The model reproduces near threshold cross sections for the quasielastic processes π⁻p → nη(η′) and pp → ppη(η′) reactions.     

Relativistic field-theoretical equations for the three-body multichannel πN and γN scattering reactions and propagator of the Δ-resonance

A new form of the relativistic three-body equations for the coupled πN and γN scattering reactions with three particle final states ππN and γπN is suggested. These equations are derived in the framework of the time-ordered three dimensional field theory. The solutions of the considered equations satisfy the unitarity condition and are exactly gauge invariant. The form of these three-body equations is does not depend on the choice of the model of Lagrangian and is also the same for the formulations with and without quark degrees of freedom.

The effective potentials of the suggested equations are defined by the vertex functions with two on-mass shell particles. It is emphasized that these input vertex functions can be constructed from experimental data. Special attention is given to the construction of the propagator of the Δ-resonance in the framework of the separable πN potential model. The strong dependence of the multichannel πN and γN cross sections on the form of the Δ-resonance propagator[2] is discussed.

The used formulation of the relativistic three-dimensional and three-body equations allows us to overcome a number of approximations which are usually used by practical calculations of the πN and γN scattering reactions.     

Four-body calculation of ΛH and ΛHe with realistic YN and NN interactions

We carried out four-body calculations of _Λ⁴H and _Λ⁴He taking both the 3N + Λ and 3N + Σ channels explicity with the use of realistic NN and YN interactions. The Σ-channel component plays an important role in binding energies of the A = 4 hypernuclei though the admixture is approximately 1%. The ΛN - ΣN coupling is found to be of central-force type in the Nijmegen model D and of tensor-force type in the model F.     

Interpolating between Ising, XY-, and non-linear σ-models

The β-functions of O(N)-symmetric non-linear σ-models on the lattice were recently discovered to be non-monotonic for N 3. We explain the non-monotonic behaviour as a non-perturbative lattice effect by relating it to the Kosterlitz-Thouless transition of the XY-model. We also relate the latter transition to the phase transition of the Ising model. These relationships are established by interpolating between the O(N)- and the O(N − 1)-symmetric non-linear σ-models by suppression of the Nth component of the N-vector field with a mass term. A critical line in the coupling-mass plane connects the critical point of the Ising model (N = 1) with the critical point of the XY-model (N = 2). This line extends towards the region of non-monotonic behaviour of the β-function of the O(3)-symmetric model. The nature of the transition lines is also investigated.     

η in the nuclear medium within a chiral unitary approach

The s-wave η self-energy in the nuclear medium is calculated in a chiral unitary approach. A coupled channel Bethe–Salpeter equation is solved to obtain the effective ηN interaction in the medium. The base model reproduces well the free space πN elastic and inelastic scattering at the ηN threshold or N^*(1535) region. The Pauli blocking on the nucleons, binding potentials for the baryons and self-energies of the mesons are incorporated, including the η self-energy in a self-consistent way. Our calculation predicts about −54−i29 MeV for the optical potential at normal nuclear matter for an η at threshold but also shows a strong energy dependence of the potential.     

The NN → NNη reaction close to threshold

The pp → ppη and np → npη reactions at energies near the η production threshold are studied in a non-relativistic one boson exchange model, where the N^* (1535 MeV) S11 resonance is excited through the exchange of π, η, and ω mesons and subsequently decays into an ηN pair. Energy integrated cross sections and energy spectra of the out going η's are reported. Providing NN and ηN final state interactions are taken into account coherently, the model reproduces both the scale and energy dependence of the cross section for the pp → ppη reactions up to 100 MeV. Final state interaction corrections due to the nucleon-nucleon and meson-nucleon forces influence strongly the scale and shape of the cross sections. The shape of the energy spectra of the outgoing η's provides a clear signature of the ηN force.     

The Λc and its inclusive nonleptonic decay

The inclusive nonleptonic decay of the Λ_c⁺ is reanalyzed using a nonrelativistic quark model representation of the Λ_c⁺- wavefunction. It is shown that the same approximation which leads to the familiar spectator and annihilation type contributions naturally also gives interference terms as a direct consequence of Fermi statistics. Numerical estimates which include these novel contributions, are presented for the Λ_c⁺ lifetime and semileptonic branching ratio.     

πN scattering and electromagnetic corrections in the perturbative chiral quark model

We apply the perturbative chiral quark model to give predictions for the electromagnetic O(p²) low-energy couplings of the ChPT effective Lagrangian that define the electromagnetic mass shifts of nucleons and first-order (e²) radiative corrections to the πN scattering amplitude. We estimate the leading isospin-breaking correction to the strong energy shift of the π⁻p atom in the 1s state, which is relevant for the experiment “Pionic Hydrogen” at PSI.     

Upper limit on the decay Σ(1385)→Σγ and cross section for γΣ→Λπ

Coherent Λπ⁻ production on Pb of 600 GeV Σ⁻ hyperons has been studied with the SELEX facility at Fermilab. Using the Primakoff formalism, we set a 90% CL upper limit on the radiative decay width Γ[Σ(1385)⁻→Σ⁻γ]<9.5 keV, and estimate the cross section for γΣ⁻→Λπ⁻ at  GeV to be 56±16 μb.     

High-resolution gamma-ray spectroscopy of ΛLi

We report on the first observation of hypernuclear γ transitions using germanium detectors. Using a large-acceptance Ge detector system, we observed two γ transitions in _Λ⁷Li, the spin-flip transition at 689±4keV and the transition at 2050±2 keV (preliminary). The strength of the ΛN spin-spin interaction is derived from the energy of the former transition. As for the latter transition, B(E2) was measured to be 3.9±0.6±0.4 e²fm⁴ (preliminary), which indicates a shrinkage of the nuclear size of _Λ⁷Li from ⁶Li and confirms “glue-like role” of Λ.     

CP test in J/ψ→γφφ decay

We propose to test CP symmetry in the decay J/ψ→γφφ, for which large data sample exists at BESII, and a data sample of 10¹⁰ J/ψ's will be collected with BESIII and CLEO-C program. We suggest some CP asymmetries in this decay mode for CP test. Assuming that CP violation is introduced by the electric- and chromo-dipole moment of charm quark, these CP asymmetries can be predicted by using valence quark models. Our work shows a possible way to get information about the electric- and chromo-dipole moment of charm quark, which is little known. Our results show that with the current data sample of J/ψ, electric- and chromo-dipole moment can be probed at order of 10⁻¹³ e cm. In the near future with a 10¹⁰ data sample, these moments can be probed at order of 10⁻¹⁴ e cm.     

Photoproduction of Θ and other pentaquark states

We present constraints on the relative photoproduction cross sections of positive parity pentaquark states, Σ₅, Λ₅, and N₅, based on a minimum phenomenology gained in and their baryon–meson couplings as in the work of Close and Dudek. The possibility of anomalous signals in γp→K⁰_S(Θ⁺;Σ_d⁺) is discussed. We emphasize the importance of comparing with “conventional” states such as γN→KΣ(1660).     

η → 3π to one loop

We calculate the amplitude of the decays η → π⁰π⁺π⁻ and η → π⁰π⁰π⁰ to first non-leading order in the low-energy expansion. It is shown that the infrared singularities of chiral perturbation theory strongly enhance the perturbation generated by the quark mass term. The corrections of order m_s increase the current algebra prediction for the rate by more than a factor of two and remove the well-known discrepancy between the low-energy theorems of current algebra and experiment.     

Isomerism in Ag and non-yrast levels in Pd and Rh, studied in β decay

The β decay of ⁹⁶Ag (Z=47,N=49) was investigated by measuring positrons, X rays as well as β-delayed protons and γ rays. The γ radiation was studied by means of germanium detectors and a NaI total-absorption spectrometer. Two β-decaying isomers in ⁹⁶Ag were established with half-lives of 4.40(6) and 6.9(6) s and tentative spin–parity assignments of (8⁺) and (2⁺), respectively. For both isomers, the intensities of β transitions to low-lying levels of ⁹⁶Pd (Z=46,N=50) and β-delayed proton decays to levels in ⁹⁵Rh (Z=45,N=50) were measured. Several new ⁹⁶Pd levels were firmly established. The level energies, their γ decays and the Gamow–Teller decay of ⁹⁶Ag are compared to shell-model predictions. A new low-lying level in ⁹⁵Rh was found at 680 keV excitation energy. Through a comparison with low-lying states of N=50 isotones, this level is interpreted as the first excited 7/2⁺ state built on the proton 9/2⁺ ground state. The assignments of further excited states in ⁹⁵Rh are discussed.     

Determination of Z/β for strange quark matter candidates with CR-39 track detector

In order to confirm the existence of strange quark matter (SQM) in cosmic rays, a series of international balloon flights with a hybrid system combining active counters and passive detectors was conducted under the collaboration between Japan and Italy. In this report, the methodology of how to detect SQM with the hybrid system and how to determine Z/β with CR-39 track detectors are presented.     

Λ-hyperon superfluidity in neutron star cores

Superfluidity of Λ hyperons in neutron star cores is investigated by a realistic approach to use reliable ΛΛ interactions and the effective mass of Λ based on the G-matrix calculations. It is found that Λ superfluid can exist at - (_{t d}) with _t - 2₀(₀ being the nuclear density) and _d - (3 – 4.5)₀, depending on hyperon core models.     

Continuum limit of finite temperature λφ3 from lattice Monte Carlo

The φ₃⁴ model at finite temperature is simulated on the lattice. For fixed N_t we compute the transition line for N_s → ∞ by means of finite size scaling techniques. The crossings of a renormalization group trajectory with the transition lines of increasing N_t give a well-defined limit for the critical temperature in the continuum. By considering different RG trajectories, we compute T^c/g as a function of the renormalized parameters.     

The radiative decay of the Λ(1405)

A recent result for the branching ratio for the decay of the kaonic hydrogen atom to Λγ is used to derive a value for the transition moment for the decay Λ(1405) → Λγ. Two solutions are found, −0.29 < κ < −0.07 and 0.60 < κ < 0.81 proton magnetons, giving decay widths of Γ(Λ(1405) → Λγ) = 6 ± 6 and 74 ± 22 keV, respectively.