Upper bound on all products of R-parity violating couplings λ′ and λ″ from proton decay

We prove that any product of R-parity violating couplings λ′ (L-violating) and λ″ (B-violating) can be strongly restricted by proton decay data. For any pair λ′ and λ″ the decay exists at least at one loop level. For squark masses below 1 TeV we find the conservative bounds |λ′ · λ″| < 10⁻⁹ in absence of squark flavor mixing, and |λ′ · λ″| < 10⁻¹¹ when this mixing is taken into account. We study the dependence of the bounds on the flavor basis in which R-parity breaking couplings are determined.     

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.     

Rigorous pion-pion scattering lengths from threshold πN → ππN data

A new evaluation of the universal ππ scattering length relation is used to extract the ππ s-wave scattering lengths from threshold pion production data. Previous work has shown that the chiral perturbation series relating threshold pion production to ππ scattering lengths appears to converge well only for the isospin-2 case, giving a₂ = −0.031 ± 0.007m_π⁻¹. A model-independent and data-insensitive universal curve then implies a₀ = 0.235 ± 0.03m_π⁻¹ for the isospin-0 scattering length.     

Symmetry breaking and the decays ψ′ → J/ψπ(η) and J/ψ → η(η′) γ

The theoretical mechanisms for the decays ψ′ → ψπ⁰ and ψ′ → ψη, which violate SU₂ and SU₃, respectively discussed. It is argued that symmetry breaking in the decay amplitudes may be as important as π⁰ −η −η′ mixing. The π⁰ −η mechanism ψ′ → ψν → ψπ⁰ leads to Γ(ψ′ → ψπ⁰) = (3.3±1.0) × 10⁻³ Γ(ψ′ → ψν), but this number may be enhanced by a factor as large as 12 by π⁰−η′ mixing and isospin violation in the decay amplitude. The related decays ψ → ηγ and ψ → η′γ are also discussed.     

Compton scattering by the proton through θcms = 75° and 90° in the Δ-resonance region

Differential cross sections for Compton scattering by the proton have been measured in the energy interval between 200 and 500 MeV at scattering angles of θcms = 75° and θcms = 90° using the CATS, the CATS/TRAJAN, and the COPP setups with the Glasgow Tagger at MAMI (Mainz). The data are compared with predictions from dispersion theory using photo-meson amplitudes from the recent VPI solution SM95. The experiment and the theoretical procedure are described in detail. It is found that the experiment and predictions are in agreement as far as the energy dependence of the differential cross sections in the Δ-range is concerned. However, there is evidence that a scaling down of the resonance part of the M1+3/2 photo-meson amplitude by (2.8 ± 0.9)% is required in comparison with the VPI analysis. The deduced value of the M1+3/2-photoproduction amplitude at the resonance energy of 320 MeV is: |M1+3/2| = (39.6 ± 0.4) × 10−3 mπ+−1.     

X → 2γ from π p → neutral meson + neuron at 3.8 GeV/c

We report on a measurement for the branching-ratio X⁰ → 2γ/X⁰ ar all. Our result is X⁰ → 2γ/X⁰ → all = (2.9 ± 0.9)%.     

A measurement of the η radiative width Γη→γγ

The radiative width of the η meson has been measured at PETRA in photon-photon collisions. The resulting value is Γ_η→γγ = 0.53±0.04±0.04 keV.     

Supersymmetric contributions to direct CP violation in K→ππγ decays

We analyze the supersymmetric contributions to direct–CP–violating observables in K→ππγ decays induced by gluino–mediated magnetic–penguin operators. We find that ε′_+−γ and the differential width asymmetry of K^±→π^±π⁰γ decays could be substantially enhanced with respect to their Standard Model values, especially in the scenario where ε′/ε is dominated by supersymmetric contributions. These observables could therefore provide a useful tool to search for New Physics effects in |ΔS|=1 transitions, complementary to ε′/ε and rare decays.     

βγ(CP) correlation measurements and anti-analogue structure in the decay of Ca

β-γ(CP) correlation measurements have been carried out on the sequence in the decay of the ground state of ⁴⁹Ca to the (presumed) anti-analogue state at 3.105 MeV excitation in ⁴⁹Sc. An asymmetry parameter of A = −0.132 ± 0.017 was obtained, making any spin-parity assignment other than very unlikely for the 3.105 MeV state. The deduced Fermi matrix element for the decay is |M_{v| = |1.4 ± 9.7| × 10⁻³}, which leads to an isospin impurity ( ) corresponding to the mixing of the analogue state (at 11.6 MeV) and the 3.105 MeV state of ||² 1.6 × 10⁻⁵. This leads in turn to an effective Coulomb matrix element of |H_c| = |3.9 ± 27.4| keV, a low value compared to the value of 100 keV obtained from a theoretical estimate based on simple shell-model wave functions for the single-particle states involved.     

Surface structures of S/Ni(111) in (√3 × √3 )R30° and (5√3 × 2) phases studied by surface extended X-ray absorption fine structure spectroscopy

The local surface structures of S/Ni(111) in the ( √3 × √3) R30° and (5√3 × 2) phases have been investigated by means of polarization-dependent sulfur K-edge surface EXAFS. In the (√3 × √3 ) R30° phase, sulfur adatoms are found to occupy threefold hollow sites with a S---Ni distance of 2.13 Å and an inclination angle ω of the Sz.sbnd;Ni bonds at 44° from the surface plane. In contrast, in the (5√3 × 2) phase, it is determined that the Sz.sbnd;Ni bond is longer, 2.18 Å, more inclined, ω = 31°, and that the coordination number is not 3 but 4. These results strongly support a picture involving reconstruction of the top nickel layer to form a rectangular structure. Consideration of several models proposed for the (5√3 × 2) phase leads to one which is compatible with both the present results and results recently reported using STM.     

nn Scattering parameters ann and rnn from the photon spectrum of the reaction πd → γnn

A high-statistics measurement of the photon spectrum of the reaction π⁻d → γnn has been performed. The comparison of this spectrum with theoretical spectra folded with the response curve of the spectrometer (measured by the reaction π⁻p → γn) has provided precise values of the neutron-neutron scattering length, a_nn = −18.5 ± 0.4 fm, and of the effective range, r_nn = 2.80 ± 0.11 fm. Theoretical uncertainties of 0.20 fm and 0.11 fm, respectively, have been evaluated.     

Experimental study of the time-dependent rate of K → πππ

The time-dependence of the decay rate of initially pure K⁰ into the final state (π⁺π⁻π⁰) has been studied in search for the decay k_S⁰→π⁺π⁻π⁰. No evidence is found in a sample of 384 observed events. The ratio of the CP -violating K_S⁰ amplitude and the K_L⁰ amplitude is η₊₋₀ = (0.13_−0.20^+0.17) + i(0.17_−0.26^+0.27); the ratio of the CP-conserving K_S⁰ amplitude and the K_L⁰ amplitude is < 0.4. The energy dependence of the K⁰→π⁺π⁻π⁰ matrix element is found to be a₊₋₀ = −0.31 ± 0.03.     

The asymmetry in π−He scattering

We show that the π⁺−³He asymmetry data obtained in a recent TRIUMF experiment at T_π = 100 MeV can be understood in terms of the elementary πN amplitudes. Through a comparison to a full optical-potential calculation that employs realistic Faddeev wave functions for the trinucleon we show that all nuclear-structure dependence cancels for at lower energies. At higher pion energies around the Δ-resonance region the sign flip of offers the possibility of extracting information about the smaller partial waves.     

Dilatometry of the high-temperature proton conductor Ba3Ca1.18Nb1.82O9 − δ

Firstly, the production of solid bulk specimens of the proton conductor Ba₃Ca_1.18Nb_1.82O_{9 − gd} (BCN18) of known water content up to [H^.] = n_H/n_Ba = 0.16 is described. Secondly, measuring the length change of such samples versus water content [H^.] demonstrated that the sample lengths increased linearly with a slope of (Δl/l)/[H^.] = (2.13 ±0.07) × 10⁻². Thirdly, the density of bulk samples was found to decrease linearly with water content [H^.]. This decrease was in good agreement with the above values derived from the length change. Fourthly, high temperature dilatometry showed that samples reach the thermodynamic solubility values in water vapor atmospheres only at temperatures above 700 °C. Two time scales were observed for the time-dependence of the elongation upon exposure to water vapor. A fast process occurred within minutes above 700 °C, a slow one took several hours. The fast one was identified as the chemical diffusion of the diffusion pair H^. and V_o^. which is required for the water uptake and loss of BCN18. The chemical diffusivity of water is described by the parameters D₀ = (0.022 ± 0.002) cm²/s and ΔH* = (0.79 ± 0.05) eV.     

Solid-state synthesis of potassium β- and β″-gallates

Direct synthesis of K-β- and β″-gallates by Ga₂O₃–K₂O solid-state reaction is described. The formation of K-β- or β″-gallates depends on the initial Ga₂O₃ phase. -Ga₂O₃ leads to K-β-gallate; β-Ga₂O₃ leads to K-β″-gallate. K-β″-Gallate is stable <1200°C. The high temperature stability of K-β″-gallate can be enhanced by doping with aliovalent ions.     

Transport properties of SrCe0.95Y0.05O3−δ and its application for hydrogen separation

Transport properties of SrCe_0.95Y_0.05O_3−δ were studied by impedance spectroscopy and by measuring open-cell voltage (OCV) and gas permeation. Ionic transference numbers were determined by measuring the OCV of concentration cells and water vapor evolution of an O₂/H₂ fuel cell. We observed interfacial polarization on the basis of the I–V curves obtained by discharging a hydrogen concentration cell or an O₂/H₂ fuel cell. The observed high protonic conductivity (high proton and low oxide ion transference numbers) makes SrCe_0.95Y_0.05O_3−δ a potential material for hydrogen separation. From proton conductivity measurements, under a given hydrogen partial pressure difference of 4%/0.488%, the hydrogen permeation rate (of a dense membrane with 0.11 cm in thickness) was calculated to be ≈0.072 cm³ (STP) cm⁻² min⁻¹ at 800°C, whereas the permeation rate calculated from short-circuit current measurements was ≈0.023 cm³ (STP) cm⁻² min⁻¹ at 800°C. The difference between calculated and observed permeation rates is probably due to interfacial polarization.     

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.     

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.     

Measurement of the slope parameter for the neutral pion spectrum in KL → πππ decay

The π⁰ spectrum in the K_L⁰ → 3π decay was measured using a wire chambers magnetic spectrometer. In the usual approximation, the matrix element can be expressed as: M² ≈ 1 + 2a₀(M_K/M_π²)(2T_π⁰−T_π⁰max) + a₁(M_K²/M_π⁴)(2T_π⁰−T_π⁰max)². We obtained a₀ = −0.282 ± 0.011 and a₁ consistent with zero.