Vortex field structures in a laser with multiply connected aperture

The scheme and operating principle of a new polarizing optical microscope for observing physical fields on object surfaces are described for the first time. New functions of the microscope are achieved because its optical scheme includes a liquid-crystal space-time light modulator, which achieves the contact of the surface under study with a layer of nematic liquid crystal. Examples and prospects of application of this microscope in photonics are considered.     

Resonant alteration of propagation in guiding structures with complex Robin parameter and its magnetic-field-induced restoration

Solutions of the scalar Helmholtz wave equation are derived for the analysis of the transport and thermodynamic properties of the two-dimensional disk and three-dimensional infinitely long straight wire in the external uniform longitudinal magnetic field B under the assumption that the Robin boundary condition contains extrapolation length Λ with nonzero imaginary part Λ_i. As a result of this complexity, the self-adjointness of the Hamiltonian is lost, its eigenvalues E become complex too and the discrete bound states of the disk characteristic for the real Λ turn into the corresponding quasibound states with their lifetime defined by the eigenenergies imaginary parts E_i. Accordingly, the longitudinal flux undergoes an alteration as it flows along the wire with its attenuation/amplification being E_i-dependent too. It is shown that, for zero magnetic field, the component E_i as a function of the Robin imaginary part exhibits a pronounced sharp extremum with its magnitude being the largest for the zero real part Λ_r of the extrapolation length. Increasing magnitude of Λ_r quenches the E_i − Λ_i resonance and at very large Λ_r the eigenenergies E approach the asymptotic real values independent of Λ_i. The extremum is also wiped out by the magnetic field when, for the large B, the energies tend to the Landau levels. Mathematical and physical interpretations of the obtained results are provided; in particular, it is shown that the finite lifetime of the disk quasibound states stems from the Λ_i-induced currents flowing through the sample boundary. Possible experimental tests of the calculated effect are discussed; namely, it is argued that it can be observed in superconductors by applying to them the external electric field E normal to the surface.     

Calculation of parameters of plane-transverse inhomogeneities in waveguides with complex cross sections in the multimode regime

We present a method for studying plane-transverse inhomogeneities in waveguides with complex cross sections in the regime of incidence of several propagating and nonpropagating waves on an inhomogeneity. Vector eigenfunctions and critical wave numbers of waveguides with complex cross section have been determined using the method of partial regions allowing for a singularity on the edge. State University, Rostov-on-Don, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 10, pp. 1286–1301, October, 1997.     

Production cross sections of multiply charged fragments in heavy ion interactions at 150–200 MeV/nucleon

A total of 1720 ¹⁶O-emulsion nucleus interactions at 150–200 MeV/nucleon have been investigated. Production cross sections of multiply charged projectile fragments are given. It is found that the cross section for the production of N, C, B and Be projectile fragments in ¹⁶O-nucleus interactions is similar at 0.2 and 2 GeV/nucleon. The fragmentation cross sections for Li and He are larger at 0.2 than at 2 GeV/nucleon.     

Analysis of propagation of ionization waves in nonuniform channels with noncircular cross sections

We investigate the propagation of ionization waves in nonuniform channels of a dc glow discharge. The dependences of the distances between adjacent strata on the cross-sectional area of the channel are measured using the method of image visualization and processing. It is found that the form of the dependences is determined to a considerable extent by the channel geometry: for a specific channel, the dependence can be increasing, decreasing, or nonmonotonic with a local peak.     

Scaling properties of target excitation cross sections in collisions between atoms and multiply charged ions

The scaling properties of one-electron target excitation cross sections in collisions between atoms and multiply charged ions are investigated. For the example of bare-ion (Z)-hydrogen collisions with various charge numbers Z it is shown that, in many-state calculations for Z ≥ 2 and energies E/Z ≈ 15–100 keV/amu, calculated 2p excitation cross sections lie approximately on a universal curve. This curve deviates from the one which has been derived earlier by Janev and Presnyakov for all Z on the basis of a simplified three-state model, and in fact results from a consistent three-state treatment show no scaling. The scaling properties of the excitation cross sections are easily understood in a purely classical model of distant collisions.     

Measurement of dijet cross sections in photoproduction at HERA

Dijet cross sections as functions of several jet observables are measured in photoproduction using the H1 detector at HERA. The data sample comprises data with an integrated luminosity of 34.9 pb. Jets are selected using the inclusive algorithm with a minimum transverse energy of 25 GeV for the leading jet. The phase space covers longitudinal proton momentum fraction and photon longitudinal momentum fraction in the ranges and . The predictions of next-to-leading order perturbative QCD, including recent photon and proton parton densities, are found to be compatible with the data in a wide kinematical range. Received: 4 January 2002 / Published online: 12 July 2002     

Measurements of cross sections and forward-backward asymmetries at the Z resonance and determination of electroweak parameters

Abstract. We report on measurements of hadronic and leptonic cross sections and leptonic forward-backward asymmetries performed with the L3 detector in the years 1993–95. A total luminosity of was collected at centre-of-mass energies and which corresponds to 2.5 million hadronic and 245 thousand leptonic events selected. These data lead to a significantly improved determination of Z parameters. From the total cross sections, combined with our measurements in 1990–92, we obtain the final results: An invisible width of is derived which in the Standard Model yields for the number of light neutrino species . Adding our results on the leptonic forward-backward asymmetries and the tau polarisation, the effective vector and axial-vector coupling constants of the neutral weak current to charged leptons are determined to be and . Including our measurements of the forward-backward and quark charge asymmetries a value for the effective electroweak mixing angle of is derived. All these measurements are in good agreement with the Standard Model of electroweak interactions. Using all our measurements of electroweak observables an upper limit on the mass of the Standard Model Higgs boson of GeV is set at 95% confidence level. Received: 4 February 2000 / Published online: 18 May 2000     

Anomalous bumpy structures in the capture cross sections of antiprotons by helium

We investigate the state-specified capture process of antiprotons by helium. Freezing one of the two electrons, we reduce this four-body rearrangement problem into a three-body problem. The capture cross sections are calculated by solving the Chew-Goldberger-type integral equation. Differing from the capture of antiprotons by hydrogen atoms, the bumpy structures are revealed in the total angular momentum dependent capture cross sections. Further analysis shows that the bumps arise from the partial channel closing due to the removal of the energy degeneracy in the antiprotonic helium.     

Measurement of inclusive jet cross sections in photoproduction at HERA

Inclusive jet cross sections are measured in photoproduction at HERA using the H1 detector. The data sample of events in the kinematic range of photon virtualities and photon-proton centre-of-mass energies represents an integrated luminosity of . Jets are defined using the inclusive algorithm. Single- and multi-differential cross sections are measured as functions of jet transverse energy E_T ^jet and pseudorapidity in the domain and . The cross sections are found to be in good agreement with next-to-leading order perturbative QCD calculations corrected for fragmentation and underlying event effects. The cross section differential in E_T ^jet, which varies by six orders of magnitude over the measured range, is compared with similar distributions from colliders at equal and higher energies.Received: 24 February 2003, Revised: 26 May 2003, Published online: 11 July 2003     

Measurement of prompt photon cross sections in photoproduction at HERA

Results are presented on the photoproduction of isolated prompt photons, inclusively and associated with jets, in the center of mass energy range 142 < W < 266 GeV. The cross sections are measured for the transverse momentum range of the photons GeV and for associated jets with E _T ^jet > 4.5 GeV. They are measured differentially as a function of , the pseudorapidities and and estimators of the momentum fractions and x _p of the incident photon and proton carried by the constituents participating in the hard process. In order to further investigate the underlying dynamics, the angular correlation between the prompt photon and the jet in the transverse plane is studied. Predictions by perturbative QCD calculations in next to leading order are about below the inclusive prompt photon data after corrections for hadronisation and multiple interactions, but are in reasonable agreement with the results for prompt photons associated with jets. Comparisons with the predictions of the event generators PYTHIA and HERWIG are also presented.Received: 13 July 2004, Revised: 15 November 2004, Published online: 17 December 2004     

Measurement of neutral current cross sections at high Bjorken-x with the ZEUS detector at HERA

A new method is employed to measure the neutral current cross section up to Bjorken-x values of one with the ZEUS detector at HERA using an integrated luminosity of 65.1 pb^-1 for e⁺p collisions and 16.7 pb^-1 for e^-p collisions at and 38.6 pb^-1 for e⁺p collisions at . Cross sections have been extracted for Q²≥648 GeV² and are compared to predictions using different parton density functions. For the highest x bins, the data have a tendency to lie above the expectations using recent parton density function parametrizations.     

Multichannel excitation cross sections of sodium atoms at slow collisions with hydrogen atoms

Excitation cross sections at slow collisions of hydrogen and sodium atoms are calculated based on two sets of quantum-chemical data. The results of calculations permit one to conclude that, upon the excitation of the sodium atom from the ground state in the region of near-threshold energies, the cross sections are highly sensitive to matrix nonadiabaticity elements. In addition, the matrix nonadiabaticity element was varied for the transition 3s → 3p of the sodium atom at fixed collision energy near the reaction threshold. It was found that the variation leads to a significant change in the excitation cross section 3s → 3p, and the range of the energetic dependence of this cross section was determined.     

Dynamics of pp collisions at small impact parameters,universality of cross sections of hadron-hadron collisions and critical phenomena at superhigh energies

Studies of the small x dynamics at HERA energies allow one to quantify the range of momentum transfers and energies for which strength of the interaction approaches the maximum strength allowed by the unitarity in the gluon channel (black disk limit-BDL). Implications for the proton-proton interactions at collider energies (Tevatron, LHC) include a dominance of BDL up to transverse momenta of hadrons (jets) in the final state of a few GeV for collisions at small impact parameters, and explanation of proximity of the profile function of pp interaction to one at small impact parameters, leading to the universality of cross sections at superhigh energies. We discuss briey theoretical challenges in the applications of pQCD to small x phenomena, the onset of BDL for hard processes at large energies and universal limiting behavior: F ₂, xG ∝ ln³(x _o/x), σ(γ T) ∝ ln³(s/s _o). We explain that the onset of BDL should be accompanied by generic nonlinear phenomena for the produced states such as kinks, different symmetry of final states, etc and related tunneling transitions. Characteristic features of QCD physics of central collisions at ultrahigh energies correspond to a new regime: (i) interaction is dominated by hard interactions of quarks and gluons leading to disappearance of the soft physics and hadronic degrees of freedom, (ii) change with energy of the space-time evolution of produced quark-gluon states, (iii) change of the avor composition of the produced system, (iv) formation of a color network, etc. Hence, such collisions are likely to result in the production of new forms of the QCD matter. We also comment on the implications of the discussed physics for cosmic ray interactions at ultrahigh energies and on the methods to get information necessary for modeling cosmic rays at energies much higher than LHC using planned experiments at LHC.     

Inclusive dijet production at HERA: direct photon cross sections in next-to-leading order QCD

We have calculated inclusive two-jet cross sections in next-to-leading order QCD for direct photo-production in lowQ ² ep collisions at HERA. Infrared and collinear singularities in real and virtual contributions are cancelled with the phase space slicing method. Analytical formulas for the different contributions giving the dependence on the slicing parameter are presented. Various one and two-jet distributions have been computed demonstrating the flexibility of the method.     

Measurement of D*+- diffractive cross sections in photoproduction at HERA

The first measurement of the cross sections for D*^±-meson diffractive photoproduction was performed with the ZEUS detector at the HERA ep collider by using an integrated luminosity of 38 pb^?1. The measurement was performed for photon-proton c.m. energies in the range 130<W<280 GeV and photon virtualities in the region Q ²<1 GeV². The product D*^± mesons were reconstructed for p _T ^D* >2 GeV and ?1.5<η ^D*<1.5 from the decay channel D*⁺ → D ⁰ π _s ⁺ with D ⁰ → K ^? π ⁺ (+ c.c.). The diffractive component was selected for 0.001 <x _P<0.018. The measured cross section in this kinematical range is $\sigma _{ep \to e'D^ * X_{p'} }^{diff} = 0.74 \pm 0.21(stat.)_{ - 0.18}^{ + 0.27} (syst.) \pm 0.16(p.diss.)$ nb (ZEUS preliminary). The measured integrated and differential cross sections are compared with theoretical expectations.     

Inclusive two-jet production at HERA: direct and resolved cross sections in next-to-leading order QCD

We have calculated inclusive two-jet cross sections in next-to-leading order QCD for low Q ² ep collisions superimposing direct and resolved contributions. Infrared and collinear singularities in the virtual and real contributions are cancelled with the phase space slicing method. Various inclusive two-jet distributions have been computed. The results are compared with recent data from the ZEUS collaboration at HERA.     

Elastic cross sections of 1s-muonic atoms at low energies in non-adiabatic approach

The low-energy elastic cross-section in collisions of a muonic atom with the hydrogen isotope is investigated, employing a new wave function (trial) and using the coordinate-space Faddeev–Hahn model. The wave function includes non-adiabatic terms. Our results of s–wave cross-sections are given, at the tμ(1s) + d scattering. Calculated cross-sections are in good accord with the results published by Chiccoli et al., while having no good agreement with other recent reports.