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.     

Correlation between structural and optical properties of ion beam synthesized β-FeSi2 precipitates in Si

The structural and optical properties of β-FeSi₂ precipitates produced by ion beam synthesis have been investigated by transmission electron microscopy, photoluminescence (PL) analysis and near infrared transmission measurements. The PL spectrum of β-FeSi₂ precipitates in a dislocation free sample has been observed to consist of a sharp line at 1.54 μm and a weak peak at 1.46 μm. Optical transmission measurements showed a direct band gap about 0.8 eV smaller than in continuous β-FeSi₂ film. Calculation of the electronic bands of β-FeSi₂ for different values of the lattice parameters indicates that this reduction can be ascribed to band distortion provided by the lattice strain.     

η,η′→ππγ with coupled channels

The decays η,η′→π⁺π⁻γ are investigated within an approach that combines one-loop chiral perturbation theory with a coupled channel Bethe–Salpeter equation which satisfies unitarity constraints and generates vector mesons dynamically from composite states of two pseudoscalar mesons. It is furthermore shown that the inclusion of the η′ as a dynamical degree of freedom does not renormalize the Wess–Zumino–Witten term.     

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.     

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.     

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.     

Implications of a Higgs interpretation of the ζ(8.3)

We consider the implications if the new state seen by the Crystal Ball collaboration in radiative -decay, the ζ(8.3), is interpreted as a Higgs boson. We show that BR(ζ→gg)<0.06 or ζ(8.3) would already have been observed at FNAL. As a consequence, there would be very significant constraints on models which go beyond the standard model (supersymmetry, composite models, technicolor, …). In particular, the minimal two-higgs doublet low-energy supersymmetric models would be ruled out. We give a sum rule restricting the number of heavy colored states which couple to ζ(8.3); remarkably, only one further generation of heavy quarks could exist. It is crucial to detect the prompt semileptonic decays from charm to confirm a Higgs interpretation.     

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.     

Oscillator strengths from line absorption in a high-temperature furnace—I. The (0,0) and (1,0) bands of the A2Σ+ - X2Πi transition in OH and OD

Quantitative high-resolution spectroscopy was applied to the (0,0) and (1,0) U.V. absorption bands of OH and OD. Known concentrations of OH and OD were prepared in a high-temperature furnace containing a 2:1 mixture of water vapor and oxygen. Band oscillator strengths at 1425 K for the OH (0,0), OH(1,0), OD (0,0) and OD (1,0) bands were 9.6 × 10^-4, 2.4 × 10^-4, 9.5 × 10^-4 and 2.6 × 10^-4 with a statistical and systematic uncertainty of about 20 per cent. The use of the OH or OD rotational intensity distribution with vibration-rotation correction factors to determine gas temperature was verified. The collision width of OH or OD lines in the furnace at a total pressure of 580 torr is about 0.14 cm^-1 at low J″ and appears to decrease at higher J″.     

The Bi(d,γ)Po reaction

The yield of the ²⁰⁹Bi(d, γ)^211g.s.Po and ^211mPo (T_1/2 = 25.2s) reaction was measured for deuteron energies E_d = 8–11.5 MeV. The reaction was identified by the -activities of the Po isotope. At E_d = 10.43 MeV, the (d, γ) cross section for the population of the ground state of ²¹¹Po is σ_g.s. = 16 ± 3 μb, the ratio relative to the cross section for the metastable state is σ_g.s./σ_m = 25.4 ± 0.9. These values and the yield curves were compared with calculations using a simple model for the population of the two states. In the excitation region E* = 15–19 MeV, the branching ratio of γ- to particle emission is nearly constant and has a value of about 0.4 × 10⁻⁴.     

Development of a 4–15 μm infrared GaAs hyperspectral QWIP imager

In the on-going evolution of GaAs quantum well infrared photodetectors (QWIPs) we have developed a four band, 640 × 512, 23 μm × 23 μm pixel array which we have subsequently integrated with a linear variable etalon (LVE) filter providing over 200 spectral bands across the 4–15.4 μm wavelength region. This effort was a collaboration between NASA’s Goddard Space Flight Center (GSFC), the Jet Propulsion Laboratory (JPL) and the Army Research Laboratory (ARL) sponsored by the Earth Science Technology Office of NASA. The QWIP array was fabricated by graded molecular beam epitaxial (MBE) growth that was specifically tailored to yield four distinct bands (FWHM): Band 1; 4.5–5.7 μm, Band 2; 8.5–10 μm, Band 3; 10–12 μm and Band 4; 13.3–14.8 μm. Each band occupies a swath that comprises 128 × 640 elements. The addition of the LVE (which is placed directly over the array) further divides the four “broad” bands into 209 separate spectral bands ranging in width from 0.02 μm at 5 μm to 0.05 μm at 15 μm. The detector is cooled by a mechanical cryocooler to 46 K. The camera system is a fully reflective, f/4.2, 3-mirror system with a 21° × 25° field of view. The project goals were: (1) develop the 4 band GaAs QWIP array; (2) develop the LVE and; (3) implement a mechanical cryocooler. This paper will describe the efforts and results of this undertaking with emphasis on the overall system characteristics.     

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.     

The contribution of 2N photon absorption in C(γ,2N) reactions for Eγ = 150–400 MeV

The ¹²C(γ,pn) and ¹²C(γ,pp) reactions have been studied using tagged photons of energy E_γ = 150–400 MeV. Recoil momentum distributions are compared to the results of Monte Carlo calculations based on a two-nucleon photon absorption model and two different phase space models. The ¹²C(γ,pn) data at low missing energy are consistent with absorption on 1p² and 1s1p nucleon pairs.     

Anharmonic V–V pumping and asymmetric electron-elementary excitation interaction in emission and absorption of O2(Δg) in the crystalline phases of oxygen

Three luminescence bands in the yellow and red spectral region, which are related to the ¹Δ_g¹Δ_g→³Σ_g^{− 3}Σ_g⁻ double electronic transition of O₂, have been investigated in the , β, and γ phase of solid oxygen. The temperature dependence of the intensity of the yellow band is strongly influenced by emission from higher vibrational levels of O₂(¹Δ_g), which are populated by anharmonic V–V pumping. The broken mirror symmetry of the luminescence and absorption bands in the phase of solid O₂ points to an interaction between the electrons and the elementary excitations of the crystal, which is different in the ground and excited electronic states, e.g., a quadratic electron–phonon interaction.     

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.     

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.     

Regge-pole description of γN→πN backward-scattering data

Baryon Regge-pole contributions to u-channel helicity amplitudes for the γN→πN processes are derived, with attention to kinematic singularities and threshold conditions. An N, Nγ and Δδ Regge-exchange model is proposed that describes the backward scattering data on γp→π^op and γp→π⁺n at high energy. The N and Nγ trajectories are found to be nearly degenerate, with residues in the ratio β(Nγ)/β(N)≈0.6. Structure in the differential cross sections is explained as dominance at small u giving way to dominance at large u. An isoscaar-isovector admixture for the γ-coupling to is required by the fits. The solution extrapolates through the mean γp→π^op 180^o differential cross section at intermediate energies, as required by duality.     

The Fermi matrix elements inferred from β-γ(CP) correlation measurements in Fe decay

Measurements have been made of the β-γ circular-polarization correlation paramter A for the 273 keV β-branch in the decay of ⁵⁹Fe. It has recently been established that each of the principal β-branches of ⁵⁹Fe involves ΔJ=0 and thus has a possible non-zero Fermi matrix element M_F which can be determined from the ƒt value and A. Previous β-γ (_CP) measurements on this nucleide have all employed the usual γ-ray scattering technique. This method is suitable for the 475 keV β-branch but does not produce an accurate measurement of the lower energy branch because of energy discrimination difficulties. A transmission polarimeter with γ-discrimination has been used in the present work to obtain clean data on the 273 keV β-1.29 MeV γ-cascade. Calibration with ⁶⁰Co (1.33 MeV) and ²⁸Al (1.79 MeV) yielded A = −0.154±0.023. This gives for the isospin impurity coefficient and the effective Coulomb matrix element of the 1.29 MeV state (1.1±1.4) × 10⁻³ and 9±11 keV, respectively.     

The Ultraviolet Spectrum of the FeF Radical: A Study of the (6)Pi-X(6)Delta and (6)Phi-X(6)Delta Band Systems at 330 and 323 nm Respectively

Two band systems of FeF have been recorded at Doppler-limited linewidths by laser-induced fluorescence. The 330-nm system provided data for three subbands of the (0,0) band of the (6)Pi-X(6)Delta system and showed that levels of the (6)Pi(5/2) and (6)Pi(3/2) components are significantly perturbed. In the 323-nm system, the (0,0) band of the (6)Phi-X(6)Delta system was found to be overlapped by the (1,0) band of the (6)Pi-X(6)Delta system. Data were obtained for three subbands of the (1,0) (6)Pi-X(6)Delta system and for five subbands of the (0, 0) (6)Phi-X(6)Delta system. This work considerably extends the previous study by Pouilly et al. (B. Pouilly, J. Schamps, D. J. W. Lumley, and R. F. Barrow, J. Phys. B 11, 2281-2287 (1978)) because it is a higher resolution study with a lower temperature production of FeF by a continuous flow discharge method. The data recorded were combined with millimeter-wave data for FeF in the X(6)Delta state and fitted with an effective Hamiltonian to determine the major parameters for FeF in the X(6)Delta, (6)Pi, and (6)Phi electronic levels. Copyright 2001 Academic Press.     

QCD corrections to γγ→ZZ at small scattering angles

QCD corrections to the electroweak cross section of γγ→ZZ at high energies and small scattering angles have been calculated. The dominant contributions are due to t-channel gluon exchange, i.e., photons dissociate into quark–antiquark pairs giving rise to two colour dipoles which interact through gluons. Corrections resulting from the leading log BFKL amplitude are of the order of a few percent close to the forward region already at the 1 TeV energy range and are rising with the scattering energy. We also considered the helicity non-conserving cases in which the QCD corrections in comparison to the electroweak part of the amplitude strongly grow with energy. The helicity non-conserving scattering process is of particular interest since it is sensitive to the Higgs sector.