Elastic scattering of electrons from oxygen and ozone molecules at high energies

Elastic differential cross-sections for thee-O₂ ande-O₃ systems are obtained in the independent atom model at high energies (E _i ⩾ 300 eV). The basic atomic scattering amplitudes are obtained in the partial wave method through a sum of static exchange and polarization potentials. Oure-O₂ results agree with experiments except for small angles. No data are available for O₃, for comparison.     

Cross sections and other parameters ofe − − H2O scattering (E i⩾50 eV)

Our previous theoretical work one ⁻ − H₂O scattering has been modified and extended to intermediate and high energiesE _i. Using the Bethe plot, we compare the present inelastic cross-sections with the experimental ionization cross sections. Total cross-sections are analytically represented asQ _TOT(cm²)=a.(E _ieV) ^−b and the parameters ‘a’ and ‘b’ are discussed for molecules H₂O, NH₃ and CH₄ in the rangeE _i=100–1000eV.     

Vibrationally elastice − — H2O scattering at intermediate energies

Vibrationally elastic total cross-sections ofe ⁻—H₂O scattering are calculated at intermediate energiesE _i=10–300 eV. The interaction potentials are treated in spherical models. The dipole rotational excitation, which is significant but not dominant above 10 eV, is treated incoherently. Effects of electronic excitation-ionization, significant above 30 eV or so, are considered through a complex optical potential. A dynamically distorted charge-density is employed to calculate the imaginary part of the complex potential. Comparisons are made with recent theoretical and experimental data. The mutual agreement is better in total cross-sections than in differential cross-sections.     

Resolved photon processes

We review high-energy scattering processes that are sensitive to the hadronic structure of the photon, describing theoretical predictions as well as recent experimental results. These processes include deep-inelastic electron-photon scattering ate ⁺ e ⁻ colliders; and the production of jets, heavy quarks and isolated photons in the collision of real photons ate ⁺ e ⁻ colliders, as well as in photon-photon collisions atep colliders. We also comment on minijet based calculations of totalγp andγγ cross-sections, and discuss the possibility that future lineare ⁺ e ⁻ colliders might produce very large photon fluxes due to the beamstrahlung phenomenon; in the most extreme cases, we predict more than one hadronicγγ event to occur at every bunch crossing.     

Total and ionization cross-sections of N<Subscript>2</Subscript> and CO by positron impact: Theoretical investigations

In this paper we report our calculations on several important total cross-sections (TCSs) of positron impact on isoelectronic N₂ and CO molecules, treated in the complex spherical potential formalism. Basically the total (complete) cross-section Q _T consists of elastic and inelastic contributions. Our total inelastic cross-section (Q _inel) contains ionization and electronic excitations together with positronium formation. Our goal here is to bifurcate Q _inel further to deduce total ionization cross-section, using the ‘complex scattering potential–ionization contribution’ (CSP-ic) method of electron–atom/molecule scattering. The present range of positron energy is 15–2000 eV. All the resulting cross-sections are in a good general accord with the existing data. This work highlights the importance of various scattering channels in e⁺-N₂ and e⁺-CO interactions at intermediate and high energies.     

Positron scattering from hydrocarbons

The total cross sections for positron impact on hydrocarbons have been calculated using the additivity rule in which the total cross section for a molecule is the sum of the total cross section for the constituent atoms. The energy range considered is from a few eV to several thousand eV. The total cross sections for positron impact on an atom are calculated by employing a complex spherical potential which comprises of a static, polarization and an absorption potential. We have good agreement with the experimental results for hydrocarbons for positron energy ⩾100 eV. Our results also agree with the available calculations for CH₄ and C₂H₂ which employed full molecular wavefunctions beyond 100 eV. Our absorption cross sections also agree with molecular wave-function calculations for C₂H₂ and CH₄ beyond 100 eV. We have shown the Bethe plots fore ⁺−C ande ⁺−H scattering systems and Bethe parameters have been extracted. We have fitted the cross section for positron impact on hydrocarbons in the formσ _t(C _n H _m )=naE ⁻ b+mcE ⁻ d in the energy range 300–5000 eV wherea=195.0543,b=0.7986,c=371.1757 andd=1.1379 withE in eV andσ _t in 10⁻¹⁶ cm².     

Electron-impact excitation cross-sections for the3 S 0−,3 P 0−, and3 D 0-States of a ruthenium atom

The excitation cross-sections of transitions of a ruthenium atom from the³ S ⁰−,³ P ⁰−, and³ D ⁰-levels are measured by the method of extended crossed beams. Based on the results of measurements, the excitation cross-sections of the states are calculated (ignoring cascade contribution). Moscow Power Engineering Institute, 14, Krasnokazarmennaya St., Moscow, E-250, 111250, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 1, pp. 9–13, January–February, 1998.     

Negative ion effects in CO2 convection laser discharges

Negative ions are computed to be formed on a time scale and in quantities such that they may be a cause of plasma instability observed in low pressure electrical discharge convection CO₂ lasers. In a typical CO₂−N₂−He−H₂O laser mixture the principal ions are CO ₃ ⁻ , CO ₄ ⁻ and H⁻ with the total negative ion densityn ₋ given by 0.1n _e <n ₋<n _e , wheren _e is the electron density: but if the gases are re-cycled or if there is an air leak NO ₂ ⁻ and NO ₃ ⁻ are formed in significant amounts andn ₋ can become greater thann _e in a time considerably less than the gas dwell time in the electrical excitation discharge. CO is effective in reducingn ₋ in a system without re-cycling, but is ineffective in a re-cycled system with the oxides of nitrogen present.     

Forward hadron-hadron scattering at high energy

The high energy elastic scattering of pp, , pπ⁺, pπ⁻, pk⁺ andpk ⁻ processes is studied at forward directions. The expressions for total scattering cross-sections and the ratios of real-to-imaginary parts of the forward amplitude are derived inP+f model. For the Regge part of the scattering amplitude, the standard form is taken. For the pomeron part, the Harari-Freund conjecture is assumed. The background is assumed to get dominant contributions from the multiparticle exchanges in that channel. These contributions are obtained by parametrising the branch cuts by conformal mapping and polynomial expansion methods. The agreement with the experiment is good. The fits suggest strong exchange degeneracy forpp andkp which in turn is consistent with the Harari-Freund duality.     

Hypervirial perturbation theory for eigenenergies for two types of atomic potentials

Eigenenergies are calculated for the potentialsV ₁(r)=−(a/r)[1+(1+br)e^−2br ] andV ₂(r)=−(v/r)[1 −λr(1−Z ⁻¹)(1+λr)⁻¹], using renormalized series technique. Accurate results produced here for various eigenstates agree with those available in the literature.     

Weak neutral currents in the U3(W)-gauge theory of weak and electromagnetic interactions

A discussion is given of the implications of the recently proposed U₃(W)-gauge theory of weak and electromagnetic interactions (Pandit 1976) for some phenomena resulting from its weak neutral currents: (1) neutrino-electron scattering, (2) neutrino-nucleon elastic and inelastic scattering, (3) coherent neutrino-nucleus scattering (4) weak interaction effects ine ⁺ e ⁻→μ⁺μ⁻ and (5) parity-violation in atomic physics. The theory agrees quite well with the available experimental results on neutrino processes. We find the coherent neutrino-nucleus cross-section for Fe⁵⁶ to be about 6 times larger than that in the WS-GIM theory giving some hope of accounting for supernova explosion by the resulting neutrino-radiation pressure.     

Muonium/muonic hydrogen formation in atomic hydrogen

The muonium/muonic hydrogen atom formation in μ^±−H collisions is investigated, using a two-state approximation in a time dependent formalism. It is found that muonium cross-section results are similar to the cross-section results obtained for positronium formation in e⁺-H collision. Muonic hydrogen atom formation cross-sections in μ^--H collision are found to be significant in a narrow range of energy (5 eV–25 eV).     

High energy elastice + − O2 scattering

Theoretical differential cross-sections are obtained for the elastic scattering of fast (E _i ⩾ 200 eV) positrons by oxygen molecules. Employing the independent atom model, the atomic scattering amplitudes are calculated with the (static + polarization) model potentials, in the partial wave analysis (PWA). Comparisons made with the theory and experiments on the incident electrons, show significant differences at small angles.     

The superconducting properties of YBa2(Cu1−xMx)3O7 for M=Zn and Ni

Transverse and zero-field μSR measurements were made on YBa₂(Cu_1−xNi_x)₃O_7−y withx=0.1 and 0.2, and YBa₂(Cu_1−x Zn _x )₃O_7−y withx=0.03, 0.06, 0.1, and 0.16, wherey≈0.1. Since doping may lead to magnetic ordering this was searched for with both zero and transverse field μSR, but no evidence was found over the temperature range studied: 10–100 K. However, depolarization rates as functions of temperature were obtained, and the low temperature values of these are σ=3.2 μs⁻¹.1.6μs⁻¹, and 1 μs⁻¹ forx=0.01, and 0.2 Ni, respectively, and σ=0.8 μs⁻¹, 0.75 μs⁻¹, 0.65 μs⁻¹, and 0.4 μs⁻¹ forx=0.03, 0.06, 0.1, and 0.16 Zn, respectively. Estimates for the effect of decreasing electron concentration for Zn are made, but these alone do not account for the drop in σ. Estimates for the effect of scattering on λ and hence σ are made. The reduction in σ for Ni dopant is in surprisingly good agreement with these estimates. For Zn the order of magnitude is correct, but the relative lack of further change in σ after the effect of the first 0.03 addition seems to imply a saturation of the effect of scattering.     

Measurement of high-Q2 neutral current deep inelastic e?p?scattering cross sections with a longitudinally polarised electron?beam?at HERA

Measurements of the neutral current cross sections for deep inelastic scattering in e ⁻ p collisions at HERA with a longitudinally polarised electron beam are presented. The single-differential cross-sections d σ/dQ ², d σ/dx and d σ/dy and the double-differential cross sections in Q ² and x are measured in the kinematic region y<0.9 and Q ²>185 GeV ² for both positively and negatively polarised electron beams and for each polarisation state separately. The measurements are based on an integrated luminosity of 169.9 pb ⁻¹ taken with the ZEUS detector in 2005 and 2006 at a centre-of-mass energy of 318 GeV. The structure functions and xF ₃ ^{γ Z} are determined by combining the e ⁻ p results presented in this paper with previously measured e ⁺ p neutral current data. The asymmetry parameter A ⁻ is used to demonstrate the parity violating effects of electroweak interactions at large spacelike photon virtuality. The measurements agree well with the predictions of the Standard Model.     

Electron temperature (T e) measurements by Thomson scattering system

Thomson scattering technique based on high power laser has already proved its superoirity in measuring the electron temperature (T _e and density (n _e) in fusion plasma devices like tokamaks. The method is a direct and unambiguous one, widely used for the localised and simultaneous measurements of the above parameters. In Thomson scattering experiment, the light scattered by the plasma electrons is used for the measurements. The plasma electron temperature is measured from the Doppler shifted scattered spectrum and density from the total scattered intensity. A single point Thomson scattering system involving a Q-switched ruby laser and PMTs as the detector is deployed in ADITYA tokamak to give the plasma electron parameters. The system is capable of providing the parameters T _e from 30 eV to 1 keV and n _e from 5 × 10¹²cm⁻³−5 × 10¹³cm⁻³. The system is also able to give the parameter profile from the plasma center (Z=0 cm) to a vertical position of Z=+22 cm to Z=−14 cm, with a spatial resolution of 1 cm on shot to shot basis. This paper discusses the initial measurements of the plasma temperature from ADITYA.     

Search for solar axions produced in the p + d → <Superscript>3</Superscript>He + A reaction

A search for the axioelectric absorption of 5.5-MeV solar axions produced in the p + d → ³He + γ (5.5 MeV) reaction was performed with two BGO detectors placed inside a low-background setup. Constraints on the axion-electron coupling constant were obtained for axions with masses in the (0.1–1.0)-MeV range: g _Ae ≤ (1.8–9.0) × 10⁻⁷. The solar positron flux from A → e⁻ + e⁺ decay was determined for axions with masses m _A > 2m _e. Using the existing experimental data on the interplanetary positron flux, a new constraint on the axion-electron coupling constant for axions with masses in the (1.2–5.4)-MeV range was obtained: g _Ae ≤ (1–5) × 10⁻¹⁷.     

Rotational excitations in muonic atom scattering by molecular hydrogen

A computational scheme based on the infinite order sudden approximation (IOS) is proposed for treating molecular and screening effects in muonic atom scattering at low energies. With this scheme the differential (dσ/dΩ(ɛj← 0|θ) and the total σ_tot(ɛ) cross-sections of muonic atom scattering on molecules of hydrogen isotopes are calculated at energies ɛ_rot=ℏω_I⩽ɛ⩽ɛ_vib= ℏω_03BD;. The IOS permits a quantitative analysis of the dependence of the differential cross-sections on the scattering angle and on the rotational excitations, particularly the rotational rainbow effects. An attractive feature of this approach is also to include the energy and the angular dependencies in the “input” cross-sections describing the muonic atom scattering on each bare nucleus of the molecule. The calculated total cross-sections ω_tot(ɛ) are in agreement with the data obtained earlier with the pseudopotential approach. This revised version was published online in August 2006 with corrections to the Cover Date.     

Measuring the chargino parameters

After the supersymmetric particles have been discovered, the priority will be to determine independently the fundamental parameters to reveal the structure of the underlying supersymmetric theory. In my talk I discuss how the chargino sector can be reconstructed completely by measuring the cross-sections with polarized beams at e ⁺ e ⁻ collider experiments: e ⁺ e ⁻ → [i, j=1, 2]. The closure of the two-chargino system can be investigated by analysing sum rules for the production cross-sections.     

Elastic scattering of electrons by helium atoms in high energy higher order Born approximation

The differential cross-sections forē-helium elastic scattering are calculated by using Yateshigh-energy higher order Born approximations, through 0 (K _i ^{Emphasis>−2} ) of the incident electron momentum, and comparisons have been made with the recent theoretical and experimental results.