Positron annihilation from excited states of [X-e+] systems

The relative probabilities for the radiative de-excitation 2p₊ → ls₊ versus 2γ-annihilation for the hdot; ns²np⁶2p₊, ²P state of the [X^-e⁺] system with X = F, Cl, Br, and I are presented. It is shown that a positron captured into a 2p₊ orbital undergoes annihilation with electrons of the system instead of radiative transition to the ground state of the [X^-e⁺] system.     

Something,but not much follows from the quark line rule in nucleon-antinucleon annihilations

Validity and consequences of the quark line rule (QLR) in nucleon (N)— antinucleon (¯N) annihilations into two or three mesons at LEAR energies are investigated. Recent data on proton-antiproton annihilation into anη orη′ together with additional non-strange pseudoscalar or vector meson (s) is used to successfully test the rule. We find that for present data any pseudoscalar meson mixing angle Φ_PS restricted to ?26⁰<Φ_PS0 is approximately consistent with the QLR. Since the assumptions leading to this test are valid in any present-day quark model of nucleon-antinucleon annihilation, improvement of the data will be of utmost importance. If proven valid, the QLR can be used to test if quark-antiquark annihilation dominates over quark exchange inN¯N → mesons at LEAR energies or vice versa. Previously proposed tests of the quark line diagrams (annihilation or rearrangement) describing the quark flavor flux under either of these assumptions are worked out. We investigate without a definite conclusion if dominance of annihilation over rearrangement is consistent with present data onp¯p → π⁰ π⁰,ηη, π⁰ρ⁰, π⁰ω, ηρ⁰,ηω, ρ⁰ρ⁰,ωω. As a main consequence, dominance of annihilation predicts without any ambiguity equality of the proton-antiproton annihilation cross sections σ(ωω) and σ(ρ⁰ρ⁰). Further consequences of dominance of either annihilation or rearrangement diagrams for proton-antiproton annihilation into two or three mesons are also worked out. We compare the predictions of the models we discuss to the sparse present data. It is emphasized that our predictions only exploit the quark flavor flux within the quark line diagrams that are assumed to dominate. They thus are independent of gluon contributions to these diagrams.     

Results from DASP one + e − annihilation between 3.1 and 5.2 GeV

This paper summarizes the measurements one ⁺ e ^? annihilation performed by the DASP Collaboration in the energy range between 3.1 and 5.2 GeV. The following topics are covered: total cross section, production and two body decays of the narrow resonances, radiative decays of theJ/ψ and ψ′ resonances and evidence for theX(2.82), ψ′ cascade decays, inclusive η production and evidence for theF meson, semileptonic decays of charmed mesons and properties of the heavy lepton.     

Finite corrections to quark fragmentation functions in perturbative QCD

The finite corrections of order α _s in perturbative QCD to the cross-sections for semi-inclusive hadron production from deep inelastic leptonhadron scattering and electron-positron annihilation are calculated. We define the effective quark fragmentation functions viae ⁺ e ^? → hadron +X including the finite terms in order to estimate these corrections for the reactions lepton + hadron → lepton + hadron + anything. Contrary to the leading term the next-to-leading order term does not factorize into parts depending on the target and the fragment, respectively. For the processese +p →e + π^± +X andv +p →μ ^? + π^± +X the finite corrections of order α _s turn out to be at most 20% in the range of momenta covered by present experiments.     

The B3Π(0+) → X1Σ+ emission spectrum of 79BrF and 81BrF in the range 6250–8700 Å: Rotational analysis of bands in the v′ = 0, 1, 2, 3, 4 progressions,and merged molecular constants for the X1Σ+ and B3Π(0+) states

Sixteen emission bands of the B³Π(0⁺) → X¹Σ⁺ systems of ⁷⁹BrF and ⁸¹BrF have been analyzed rotationally. Measured line frequencies are fitted by least-squares to determine the rotational constants and origin for each band. The least-squares results for 0 ≤ v′ ≤ 4 and 4 ≤ v″ ≤ 12 are merged with constants from previously reported B ← X absorption and X-state microwave data. RKR potentials for the two states and Franck-Condon factors and r-centroids for the BrF (B-X) system are reported.     

Electron impact induced fluorescence of dissociating fragments from jet-cooled methane,methanol and ethanol

Dissociation fragments, following 20 keV electron impact on supersonic jet targets of methane, methanol and ethanol, have been analysed to determine rotational temperatures. The intensities of individual rotational lines of the CH A² Δ-X²Π, CH B²∑^- -X²Π and CH⁺A¹ Π-X¹∑⁺ transitions were measured and fitted to Boltzmann distributions. The temperatures obtained were about 4000 K for the CH A-X, 2000 K for the B-X and 1650 K for the CH⁺A-X transitions. The recorded spectra showed distributions at single temperatures. The intensities were also fitted to theoretical distributions in order to obtain excess energies. Possible fragmentation mechanisms are discussed.     

Penetration depths of superconducting U6X (X = Fe,Co, Mn)

The penetration depths, λ(T), of the heavy-fermion uranium-based superconductors U₆X (X = Fe, Co, Mn) have been measured as a function of temperature at ∼ 35 MHz. It was found that the temperature dependence of λ(T) for these compounds agrees well with the BCS theory. However, the values of λ(0) are large. By comparing the Slater-Pauling curve of the X elements with λ(0)^-1 for the U₆X superconductors, we have found that λ(0)^-1 is proportional to the saturation spin moments of elemental X, suggesting that there is a correlation between the superconductivity of these U₆X superconductors and the magnetic nature of the X elements.     

Cosmic gamma-rays associated with annihilation of relativistic e+ −e− pairs

Results of electron-positron annihilation spectrum investigations are reported. The radiation spectra of an e⁺ ?e^? relativistic maxwellian plasma are presented. We consider the particular case of positron annihilation on electrons at rest. It is shown that for positrons with a suprathermal power law distribution the radiation due to annihilation exceeds bremsstrahlung up to at least ω ≈ 100 mc².     

Exciton-phonon coupling in indirect AlxGa1−xAs

Several persistent high-energy peaks in the photo-luminescence spectrum of indirect Al_xGa_1?xAs are reported. These transitions are assigned to zero-phonon and phonon-assisted bound-exciton annihilation processes. Symmetry determined selection rules indicate that the major interband recombination mechanism is due to LO phonon scattering of electrons near X(100) to the energetically adjacent Γ^CB₁ (000) intermediate state. Scattering associated with alloy disorder may also contribute to the spectrum. The change in the phonon-assisted spectra at x = 0.43 ± 0.01 provides an additional means of identification of the direct-indirect conduction band crossover.     

Electronic excitation of HgX (X = Cl,Br, I) due to electron and methyl mercury halide collisions

Electronic excitation of HgX (X = Cl, Br, I) radicals in the B-state has been observed as the result of collisions with low energy electrons and methyl mercury halide (CH₃HgX) molecules. The emission intensity has been observed to be much weaker than that observed for electron-HgX₂ collisions under similar experimental conditions. Using the strongest band head of the B-X band system, an attempt has been made to calculate the emission cross section due to electron CH₃HgX collisions at 10 eV electron kinetic energy. For HgCl, HgBr, and HgI radicals, these cross sections are 1 × 10^-18, 7 × 10^-17, and 2 × 10^-17 cm², respectively, with an estimated uncertainty of ±30%. Our measured threshold electron energy for excitation of CH₃HgX molecules and observation of the B-X emission band system and emission cross sections measured at 10 eV are greatly different from those measured by Allision and Zare [Chem. Phys. 35, 263 (1978)].     

分子XH(X=O,S, Se和 Te)中的正电子能级与正电子原子

基于全对称群的Dirac方程, 研究当存在核场时的正电子能级及其与核场的关系, 即计算在分子OH, SH, SeH和 TeH的核场下的正电子能级. 这时正电子的能量约为 e⁺=-1.022 MeV. 对于低能级, 当核场强增大时, 其能量有所升高, 而对较高能级, 核场强增大时, 其能量无明显变化. 正负电子的湮没过程为三光子湮没过程(the three-photon annihilation). 而当生成e⁺- e^-< 关键词： Dirac方程 三光子湮没过程 正态的正电子原子 电荷宇称守衡     

Solid solution formation in the systems CuMIIIX2-AgMIIIX2 where MIII=Al,Ga, In and X2=S,Se

A study of solid solution formation in the systems CuAlX₂-AgAlX₂, CuGaX₂-AgGaX₂ and CuInX₂-AgInX₂, where X=S, Se, has shown that when M^III=Al and Ga, CuM^IIIX₂ and AgM^IIIX₂ were not completely miscible. The CuInX₂-AgInX₂ system, however, showed complete solid solubility. The limits of solid solubility are explained in terms of the c/a ratio, and the internal atomic coordinate u. The lattice constant a is a linear function of composition, while c bows upwards. This behavior is also discussed in terms of trends in 2-c/a.     

Hypercharge annihilation

Aspects of the process K^?p → Λ + pions for K^? mesons of momentum 8.25 GeV/c are examined. It is shown that the hypercharge annihilation process can be effectively separated into off-shell baryon (B?B) and strangeness (K?K) annihilation. Both annihilation regions have many features in common and show strong similarities to on-shell annihilation processes; some differences are also noted.     

Production of hypothetical,light neutral particles in high-energy channeling

The rates forX ^° creation by photons and electrons channeling along a crystal axis are estimated. The process is found to depend strongly on the parameters of the crystal fields. PromisingX ^° production rates can therefore be obtained for germanium rather than for lighter elements.     

Self,nitrogen and oxygen broadening of the 115-GHz line of carbon monoxide

Self nitrogen, oxygen and air-broadened half-widths of the 115-GHz line of CO have been measured at various temperatures between 293 K (room temperature) and 220 K. The temperature dependence of the broadening parameter CCO-XW is described by a power law CCO-XW (T) = CCO-XW(293 K)(T/293)-n co-x. The values of CCOW (293 K) and nCO-X are presented for each broadening gas X, X - CO, N2 and O2. The usual relation CCO-airW (T) = 0.78CCO−N2W(T) + 0.21CCO−O2 W(T) is found to be valid in the temperature and pressure ranges of the present experiments.     

Search for a new light gauge boson in π0, η and η′ decays

Upper limits for the production of new light gauge bosons in π⁰, η and η′ decays have been obtained with the Crystal Barrel detector. The kinematically well-constrained reactions p?p → π⁰π⁰ P have been studied, where P ? π ⁰, η, η′ decays through the emission of a single photon recoiling against a missing state X. X can be a long-lived weakly interacting particle or it decays into ???. The resulting branching ratio upper limits (90 % C.L.) are: 6 × 10^?5 for masses M _X of the missing particle X lying between 65 MeV/c² and 125 MeV/c² (π⁰ decay), 6 × 10^?5 for M _X between 200 MeV/c² and 525 MeV/c² (gh decay), and 4 × 10^?5 for M _X between 50 MeV/c² and 925 MeV/c² (η′ decay). The π⁰-decay limit represents an improvement by a factor of 4 to 8 (depending on M _X) when compared to the existing limit, whereas the η and η′ decay limits have been measured for the first time, thereby extending the M _X range from 125 MeV/c² up to 925 MeV/c².     

The A3Π(1) → X1Σ+ emission spectrum of ICl in the near infrared: Rotational analysis of bands in the v′ = 0, 1, 2, 3, 4, progressions and molecular constants for the X1Σ+ and A3Π(1) states by merging with absorption data

Ten bands of the A³Π(1) → X¹Σ⁺ emission system of I³⁵Cl, lying at wavelengths of 8180 – 10000 Å, have been analyzed rotationally in the ranges 0 ≤ v′ ≤ 4 and 6 ≤ v″ ≤ 9. Constants determined from least-squares fits of frequencies of individual bands are merged with constants derived from absorption data. RKR potentials for both states are reported, and the Franck-Condon factors for ICl (A-X) have been computed for 0 ≤ v′ ≤ 35 and 0 ≤ v″ ≤ 9.     

Analysis of the B 0(+) → J/ΨD 0(+) decays

We analyze B ⁰⁽⁺⁾ → J/ΨD ⁰⁽⁺⁾ decays by considering the contributions of annihilation diagrams. For each diagram, we calculate the branching ratios for various parameters X _A , which have played a significant role in our results. These parameters have been concluded from the divergence integrals in hard-scattering kernels. Here, we have considered three effective variables, including: Λ(225, 500 MeV), ρ _A (0, 1, 1/2), and φ _A . It is found that the most of the obtained data are placed in the experimental range at Λ = 225 MeV and Λ = 500 MeV for B ⁺ → J/ΨD ⁺ and B ⁰ → J/ΨD ⁰, respectively.     

Pressure shift and/or broadening of lines in the electronic spectra of Cl2, Br2, I2, O2, HD,AlH and H2CO

Line positions and widths of the B³Π_o⁺u?X¹Σ⁺_g electronic transitions of chlorine and bromine gases are measured in absorption as functions of pressure by means of a scanning Fabry-Perot interferometer spectrometer (resolving power > 10⁶). No dependences on quantum numbers are detected. Deconvolutions of measured full-widths-at-half-maxima (FWHM) reveal collision broadening for pressures between 1 and 225 torr. The ratio of self-broadening to shift is always less than that expected for a van der Waals interaction in the impact approximation, namely -2.77. Accordingly, the Lennard-Jones potential is used to determine the effect of the electronic transitions on C₆ and C₁₂, and there are found 14 and 6% changes in C₆ for Cl₂ and Br₂, respectively. If, instead, one uses the self-broadening only, and a pure van der Waals interaction, the changes are 6 and 5%. Because the effects are in either model unexpectedly small, comparisons are made with less complete measurements (from the literature) for self-broadening in I₂, the B¹Σ⁺_g?X³Σ^-_g system of O₂ and the B^′Σ⁺_g?X¹Σ⁺_g system of HD, and for foreign-gas broadening in the A¹Π?X¹Σ system of A1H and the A&#x030B;¹A₂(π¹, n)?X&#x030B;¹A₁ system of H₂CO as well as the HD system.