Pion-pair production on a proton by photons in the energy region of nucleon-resonance excitation

A model is proposed for describing the production of π⁺π^? pairs by real and virtual photons on protons in the energy region of nucleon-resonance excitation. The invariant-mass distributions of the π⁺π^? and π⁺ p systems at the photon point are calculated. The results are compared with available experimental data.     

Phenomenological model for describing pion-pair production on a proton by virtual photons in the energy region of nucleon-resonance excitation

A phenomenological model is developed for describing the production of π ⁺ π ^? pairs on a proton by virtual photons in the energy region of nucleon-resonance excitation.The cross sections are calculated for the channels γp → π ^?Δ⁺⁺, γp → π ⁺Δ⁰, and γp → ρp, which make a dominant contribution to pion-pair production, and the results are compared with available experimental data.The contributions of nucleon resonances to the cross section for the reaction γp → π ^?Δ⁺⁺ are predicted within the developed approach.     

Molecular probe FET: Long-wavelength fluorescence excitation effect and proton transfer reaction

We studied the steady-state fluorescence spectra of solutions of FET (4′-(diethylamino)-3-hydroxyflavone) in acetonitrile that were excited at different temperatures by quanta with different energies located in the range of the main absorption band and in its long-wavelength wing. We found that, at room temperature, the emission intensity ratio of the bands of the normal and tautomeric forms, which are located at 505 and 570 nm, respectively, depends on the excitation wavelength. In the range of the main absorption band 300–360 nm, this ratio remains nearly the same, i.e., 1.45, while, upon excitation in the range of the long-wavelength wing 360–380 nm of the main band, it decreases to 1.33 at a wavelength of 460 nm. In this same range, a long-wavelength excitation effect that is unusual for liquid inviscid solvents at room temperature, i.e., a bathochromic shift of the entire short-wavelength emission band by 11 nm, manifests itself. We propose to explain these dependences using energy diagrams, which take into account the dependence of free energy on the orientational polarization of the polar solvent. The observed effect of the long-wavelength shift of the fluorescence spectrum with increasing excitation wavelength is explained in terms of the inhomogeneous broadening of electronic spectra of polar solutions, and it should be described using the scheme of energy states that takes into account sublevels of orientational broadening due to orientational dipole-dipole interactions of the fluorophore with nearest molecules of the polar solvent, as well as the relation between the fluorophore lifetime in the excited state and the dielectric relaxation time of solvent molecules in the field of the fluorophore dipole.     

Modulation of HTSC characteristics induced by proton irradiation

Il Nuovo Cimento D - Bulk slabs of sintered YBCO were irradiated with monoenergetic protons at different energies (3.5 and 6.5 MeV) and different fluences, ranging from 1.8·1016 to...     

Helium ionization with excitation of the atom accompanied by absorption and scattering of high-energy photons

We calculate analytically the cross sections for ionization of the helium atom with absorption and scattering of high-energy photons. The electrons are assumed to be moving in the Coulomb field of the nucleus. The electron-electron interaction is taken into account in the first order of perturbation theory. The high-frequency limits for the ratios of these cross sections to the single-electron ionization cross sections are obtained for s-excitations in absorption and for s-and p-excitations in scattering. Zh. éksp. Teor. Fiz. 111, 862–870 (March 1997)     

The effect of particle motion character upon the rate of the resonant transfer of electronic excitation

Equations are derived for describing a classical system interacting arbitrarily with a quantum two-level system. The solutions for the case of two converging electron terms are analysed and applied to the problem of electronic excitation resonant transfer or resonant charge exchange. It is supposed that the classical motion of the particles (molecules) possesses a stochastic character and may be represented by the Fokker-Plank equation, when the interaction with the quantum degrees of freedom are absent. The model allows us to trace theoretically the change of excitation transfer kinetics when passing from gas to liquid and from liquid to the solid state. The general formula for one-, two- and three-dimensional relative motions are found and the three-dimensional case is discussed in detail.     

Comparison and efficiency of materials for summation of photons assisted by energy transfer

Relative and absolute efficients of anti-Stokes phosphors doped with Yb³⁺-Er³⁺ are given, accounting for the fact that concentration of the excitation energy with respect to space, time and wavelength should be considered for such non-linear materials. A figure of merit is then defined which makes the comparison possible, whatever the excitation source is, provided that no saturation takes place.     

Measurement of the excitation transfer rate between the n = 4 levels of hydrogen and deuterium

In a hydrogen-deuterium plasma of high purity the excitation transfer rate K^DH₄ for the process $\text{H}{}^1\text{(n = 4) +}\text{D}\text{(n = 1)→}\text{H}\text{(n = 1) +}\text{D}{}^1\text{(n = 4)}$ (n is the principal quantum number) has been measured by means of dye-laser fluorescence. Using an adequate numerical model, also the corresponding cross section σ^DH₄ could be determined.     

Remarks to the theory of photoluminescence concentrational depolarization by excitation energy transfer

The fluctuations of concentration of luminescent molecules (LM) are introduced into the earlier theory of concentrational influence on emission anisotropy (EA). An expression is derived which predicts values of EA, as a function of LM concentration, close to those obtained by the Monte-Carlo method carried out by Bodunov.     

Dissociation of virtual photons in events with a leading proton at HERA

The ZEUS detector has been used to study dissociation of virtual photons in events with a leading proton, , in e ⁺ p collisions at HERA. The data cover photon virtualities in two ranges, 0.03 < Q ² < 0.60 GeV² and 2 < Q ² < 100 GeV², with M _X > 1.5 GeV, where M _X is the mass of the hadronic final state, X. Events were required to have a leading proton, detected in the ZEUS leading proton spectrometer, carrying at least 90% of the incoming proton energy. The cross section is presented as a function of t, the squared four-momentum transfer at the proton vertex, , the azimuthal angle between the positron scattering plane and the proton scattering plane, and Q ². The data are presented in terms of the diffractive structure function, . A next-to-leading-order QCD fit to the higher-Q ² data set and to previously published diffractive charm production data is presented.Received: 10 August 2004, Revised: 4 October 2004, Published online: 9 November 2004     

Rapid proton transfer mediated by a strong laser field

Kinetic energy distributions of ejected from a polyatomic molecule, anthraquinone, subjected to 60 fs, 800 nm laser pulses of intensity between 0.2 and 4.0 x 10(14) W x cm(-2), reveal field-driven restructuring of the molecule prior to Coulomb explosion. Calculations demonstrate fast intramolecular proton migration into a field-dressed metastable potential energy minimum. The proton migration occurs in the direction perpendicular to the polarization of the laser field. Rapid field-mediated isomerization is an important new phenomenon in coupling of polyatomic molecules with intense lasers.