Charged particle cross sections in photoproduction and extraction of the gluon density in the photon

Photoproduction data collected with the H1 detector at HERA in 1994 are used to study the cross-sections for inclusive charged particle production and the structure of the photon. The differential cross-sections , for in the HERA laboratory frame, and for GeV/c and GeV/c have been measured. Model calculations of these cross-sections, based on perturbative QCD, indicate that the results are sensitive to the parton densities of the photon as well as to higher order effects, which are phenomenologically treated by multiple interactions. This sensitivity is exploited to determine the leading order distribution of partons in the photon using a new method based on high charged particles. The gluon content of the photon is extracted and found to rise with decreasing . Received: 8 October 1998 / Published online: 8 September 1999     

Photoionisation using Kohn-Sham wave functions

The determination of photoionisation cross-sections using the Kohn-Sham wave functions from accurate density functional theory (DFT) calculations is considered. The continuum electrons wave function is specified by its momentum measurable in the detector rather than fixed angular momentum and energy. The method is applied to the test case of a water molecule, where the DFT calculations show excellent agreement to experiment in the ionisation energies if a vertical transition is considered. The continuum electron is described by an analytical wave function and the matrix elements are calculated in both in length and velocity form of the dipole operator. The cross-sections agree well with the experiment in particular for the velocity form.     

What do electron and neutrino experiments tell us about nuclear effects in the deuteron?

We have performed an analysis of data from electron, neutrino and antineutrino scattering experiments on hydrogen and deuterium within the framework of the quark-parton model. The data indicate that the distortion of the structure functions of the neutrons and protons in the deuteron are small. This is in contrast with the observed distortion of the structure functions of nucleons bound in a heavy nucleus such as iron. These results support the hypothesis that the “EMC Effect” is related to the density of nucleons in a nucleus.     

Incoherent scattering of 59.5 keV gamma-rays by light,medium and heavy elements

Summary Total atomic incoherent-scattering differential cross-sections were determined experimentally for 59.5 keV gamma-rays in Ti, Ni, Zn, Se, Mo, Ru, Cd, Sn, Te, Yt, W and Pb at 120° scattering angle using Ge(Li) detector. The background correction and detection efficiency are also included in the study. The experimental values have been compared with those estimated on the basis of the non-relativistic Hartree-Fock wave functions. Good agreement is observed between theory and experiment.     

Studies of the EMC effect in the QCD framework with the EMC iron and hydrogen structure functions

The QCD evolution of the measured structure functions F₂ in iron and hydrogen have been analysed to show that the momentum distribution of the valence quarks is lower in iron than in hydrogen and that the opposite is true for the gluon and sea quark distributions in the region of 0.1<x<0.65.     

Deceleration of muonic hydrogen atoms in solid hydrogens

Results of recent calculations of cross-sections for muonic hydrogen atom scattering in solid hydrogen isotope targets are presented. The coherent parts of these cross-sections, namely, the elastic Bragg scattering and phonon coherent scattering, are calculated accurately for the first time. A fine structure of Bragg peaks is obtained in the case of Bravais fcc structure of hydrogen targets frozen rapidly at 3 K. The one-phonon coherent cross-section is estimated using the Debye approximation. The calculated differential cross-sections are used for Monte Carlo simulations of muonic atom diffusion and slowing down in solid hydrogens. Also is calculated the energy-dependent rate of resonant ddμ molecule formation in 3 K solid deuterium quantum crystal, using the Debye model and Van Hove's formalism of the response function. This rate is very different from that obtained for the 3 K gas model. The influence of dμ atom slowing down on the average ddμ formation rate is considered. It is shown that very slow dμ deceleration below 10 meV is important for explanation of experimental results. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of Polarization Potential on Proton–Sodium Inelastic Scattering

Inelastic collisions of protons with sodium atoms are treated for the first time within the framework of the coupled static and frozen core approximations. The method is used for calculating partial and total cross-sections with the assumption that only two channels (elastic and hydrogen formation in 2s-state) are open. The calculations are carried out, in each case, for seven values of the total angular momentum ?(0?≤???≤?6). In the second channel, the effect of “switching on” the polarization potential of hydrogen (in 2s-state) on the coupled static cross-sections is investigated. Although the resulting hydrogen (in 2s-state) formation cross-sections are smaller than the elastic ones, their large values should draw the attention of experimental and theoretical physicists to the field of proton–alkali atom collisions. Our results for the total hydrogen (2s-state) formation cross-sections and those determined by previous authors are in reasonable agreement.     

Inclusive interactions of high-energy neutrinos and antineutrinos in iron

We present results on charged current inclusive neutrino and antineutrino scattering in the neutrino energy range 30–200 GeV. The results include a) total cross-sections; b)y distributions; c) structure functions; and d) scaling violations observed in the structure functions. The results, as well as their comparison with the results of electron and muon inclusive scattering, are in agreement with the expectations of the quark parton model and QCD.     

Nuclear structure functions and heavy flavour leptoproduction off the nucleus at small x in perturbative QCD

Nuclear structure functions and cross-sections for heavy flavour production in lepton–nucleus collisions are investigated in the low x region accessible now or in the near future. The scattering on a heavy nucleus is described by the sum of fan diagrams of BFKL pomerons, which is exact in the high-colour limit. The initial condition for the evolution at x=0.01 is taken from a saturation model, which reproduces the experimental data on the proton. The dependence of the structure functions is well described by a power factor , with reaching values as low as 1/2 at extremely low x. The total cross-sections for heavy flavour production reach values of the order of mb, and the corresponding transverse momentum distributions are sizable up to transverse momenta larger than the initial large scale . Received: 10 July 2001 / Revised version: 23 September 2001 / Published online: 5 November 2001     

Light cone constraints and two asymptotic domains in lepton-nucleon and meson-nucleon scattering

Effective bare masses of the “current-quarks” are estimated from some testable inequalities, linking deep inelastic lepton-nucleon structure functions and high energy meson-nucleon total cross-sections, derived on the basis of the light-cone commutators of the pseudoscalar densities of quark-field theory.     

Problems of Deep Inelastic Lepton-Nucleus Interaction

The deep inelastic scattering of electrons (muons) and neutrinos on the nuclei and the process of lepton pair production in hadron-nucleus collisions are considered. The expressions for the corresponding differential cross-sections are derived provided the final lepton and the spectator fragment of the initial nucleus are detected in coincidence. The structure functions of the processes under consideration are analysed by the principle of automodelity. Some scale-invariant regularities are established for them. In the framework of “light front” formalism for many-body systems the relations of these structure functions to the usual structure functions of the deep inelastic lepton hadron interaction are obtained. A hypothesis is put forward on the scale invariance of structure functions with respect to the ξ-variable which is some complicated dimensionless combination of kinematic invariants.     

Measurement of the <Emphasis Type="Italic">Z</Emphasis>/A dependence of neutrino charged-current total cross-sections

A relative measurement of total cross-sections is reported for polyethylene, marble, iron, and lead targets for the inclusive charged-current reaction . The targets, passive blocks of kg each, were exposed simultaneously to the CERN SPS wide-band muon-neutrino beam over a period of 18 weeks. Systematic effects due to differences in the neutrino flux and detector efficiency for the different target locations were minimised by changing the position of the four targets on their support about every two weeks. The relative neutrino fluxes on the targets were monitored within the same experiment using charged-current interactions in the calorimeter positioned directly downstream of the four targets. From a fit to the Z/A dependence of the total cross-sections a value is deduced for the effective neutron-to-proton cross-section ratio.Received: 9 December 2002, Revised: 1 July 2003, Published online: 11 August 2003     

Elastic scattering of 1.17 and 1.33 MeV gamma rays by molybdenum,tantalum and lead

Elastic scattering cross-sections of lead, tantalum and molybdenum were determined with the help of a Ge (Li) detector for 1.17 and 1.33 MeV rays between 30° and 115°. Theoretical evaluations of the cross-sections are based on a coherent addition of the well-known nuclear Thomson scattering amplitudes, the Rayleigh amplitudes calculated by Kissel and Pratt and the Delbrück amplitudes given by Papatzacos and Mork. The fairly good agreement between experiment and theory reveals the importance of the real Delbrück amplitudes. However, the experimental results in the 30–60° range tend to lie slightly but systematically below the calculated cross-sections. Work supported in part by a grant from the National Bureau of Standards, Washington, DC under the SFCP programme.     

A measurement of differential cross-sections and nucleon structure functions in charged-current neutrino interactions on iron

A high-statistics measurement of the differential cross-sections for neutrino-iron scattering in the wide-band neutrino beam at the CERN SPS is presented. Nucleon structure functions are extracted and theirQ ² evolution is compared with the predictions of quantum chromodynamics.     

Beauty and charm physics at CDF Run II

The European Physical Journal C - Using the data samples collected with the CDF Run II detector during the year 2002 and early 2003, new measurements of the production cross-sections and the...     

Quark momentum distributions fromep collisions: strategies and prospects

We present the results of a comprehensive investigation of possibilities to extract structure functions and momentum distributions of individual quark flavours from cross-section measurements atep colliders. Approximate determinations based on single cross-sections are examined and compared with an exact unfolding procedure which, however, requires the combination of neutral and charged current data for both electron and positron beams. Using Monte Carlo methods we evaluate the precision that can be expected from the forthcoming HERA experiments in measuring the shape in Bjorken-x of structure functions and quark distributions.     

The coadsorption of hydrogen and potassium on Ir(111)

The adsorption of gas-phase atomic hydrogen on potassium-precovered Ir(111) surfaces was investigated. Even very low coverages of potassium adatoms strongly inhibit the dissociative adsorption of molecular hydrogen. However, using gas-phase atomic hydrogen allows us to overcome the activation barrier for dissociative hydrogen adsorption. In addition, abstraction of hydrogen adatoms by impinging atomic hydrogen occurs. The probabilities and cross-sections for both reactions and the maximum number of hydrogen adsorption sites are derived and compared to data obtained on other surfaces. Furthermore, a kinetic isotope effect in the desorption of hydrogen and deuterium was observed. Implications of these results with respect to the potassium-hydrogen interaction are discussed.     

Excited states of muonium in atomic hydrogen

Muonium formation in excited states in muon-hydrogen charge-exchange collision is investigated using a method developed in a previous paper. Differential cross-section results are found to resemble positronium formation cross-section results of positron—hydrogen charge-exchange problem. Forward differential and integrated cross-sections are computed for muon energy of 2 keV and higher. Total muonium formation cross-sections are computed using Jackson and Schiff scaling rules. Muonium formation cross-section results obtained from proton—hydrogen charge-exchange cross-section results, using velocity scaling are compared with the results of the present calculation     

Positivity bounds on total neutrino cross-sections as means to restrict the mass of thr intermediate boson

Positivity restrictions on the structure functions for deep inelastic lepton scattering are used to derive upper and lower bounds for total neutrino cross-sections. Comparison with experiment leads to a lower limit for the mass of the (charged) intermediate vector boson.     

Laser-Assisted particle-atom inelastic collisions. Role of the field polarization

Summary A theoretical treatment, of first order in the collision dynamics, is presented to analyse the role of electric polarization in offresonance laser-assisted atomic collisions. General expressions are presented for evaluating the modified spectrum and wave functions for anyn level of hydrogenic atoms in the presence of a laser, taken to be linearly and circularly polarized. Specific calculations are carried out for excitation of hydrogen atoms to the leveln=2 by electron impact. The two polarizations are found to yield large differences i) in the atomic-spectrum modifications, ii) in the structure of the cross-sections and iii) in the numerical results. In particular, only for linear polarization, the distribution in energy of the scattered electrons at a fixed scattering angle has the structure of a series of equally spaced lines of different height (the spacing being equal to the laser photon energy ℏw and the height of the line accounting for the number of final electrons with a given energy). For circular polarization no such a regular pattern is predicted. Since, among laser-assisted particle-atom collisions, at present energy gain-loss spectra of scattered electrons are most easily observed, it is hoped that the reported results may serve as a stimulus for new observations in this new class of atomic collisions. The theory to treat the multiphoton resonance case is outlined too. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.