Electroproduction of pseudoscalar mesons on the deuteron

A general analysis of polarization phenomena for coherent meson electroproduction on deuterons, $e+ d\to e+ d +P^0$, where $P^0$ is a pseudoscalar $\pi ^0$ or $\eta$-meson, is presented. The spin structure of the electromagnetic current for $P^0$-production at threshold is parametrized in terms of specific (inelastic) threshold electromagnetic form factors which depend on the momentum transfer squared and the effective mass of the produced hadronic system. We give expressions for the structure functions of the reaction $e+\vec{d}\to e +d+ P^0$ (where the deuteron target is polarized) in terms of these threshold form factors. The spin and isospin structures of the $\gamma ^{*}+d\to d+P^0$ amplitudes (where $\gamma ^*$ is a virtual photon) is established in the framework of the impulse approximation and relationships between meson electroproduction on deuterons and on nucleons are given. The reaction of $\pi^0$ electroproduction on deuterons is investigated in detail both at threshold and in the region of $\Delta$-isobar excitation, using the effective Lagrangian approach for the calculation of the amplitudes of the elementary process $\gamma^*+N\to N+\pi$. Special attention is devoted to the analysis of all standard contributions to the exclusive cross section for $d(e,e\pi^0)d$, which are functions of the momentum transfer square, $k^2$, of the excitation energy of the produced hadrons and of the pion production angle, in a region of relatively large momentum transfer. The sensitivity of these contributions to different parametrizations of the $\gamma^*\pi\omega$ form factor as well as to the choice of $NN-$potential is discussed.Comment: 44 pages 19 figure

Coherent π0\pi^0 electroproduction on the deuteron

A general analysis of polarization phenomena for coherent pion electroproduction on deuterons is presented. The spin and isospin structures of the $\gamma ^{*}+d\to d+P^0$ amplitudes (where $\gamma ^*$ is a virtual photon) are established and relationships between meson electroproduction on deuterons and on nucleons are given in the framework of the impulse approximation. The reaction $e+d\to e+d+\pi^0$ is investigated in detail, for a relatively large value of momentum transfer, 0.5 GeV$^2\le -k^2\le$ 2 GeV$^2$, both at threshold and in the region of $\Delta$-isobar excitation. Special attention is devoted to the sensitivity of different contributions to the exclusive cross section for $d(e,e\pi^0)d$, as the $\gamma^*\pi\omega$ form factor or the $NN-$potential. The predicted $k^2$-dependence of the cross section agrees well with the available experimental data

Table ronde : les degrés de liberté non-nucléoniques en physique nucléaire

École thématiqu

Quenching of the Deuteron in Flight

We investigate the Lorentz contraction of a deuteron in flight. Our starting point is the Blankenbecler-Sugar projection of the Bethe-Salpeter equation to a 3-dimensional quasi potential equation, wqhich we apply for the deuteron bound in an harmonic oscillator potential (for an analytical result) and by the Bonn NN potential for a more realistic estimate. We find substantial quenching with increasing external momenta and a significant modification of the high momentum spectrum of the deuteron.Comment: 11 pages, 4 figure

Virtual Compton Scattering and Generalized Polarizabilities of the Proton

Threshold photon electroproduction off the proton allows one to measure new electromagnetic observables which generalise the usual polarisabilities. There are -- a priori -- ten "generalised polarisabilities", functions of the virtual photon mass. The purpose of this paper is to lay down the appropriate formalism to extract these quantities from the photon electroproduction cross sections. We also give a first estimate of the generalised polarisabilities in the non relativistic quark model.Comment: 45 page postscript file including 2 figures (length just over 1Mb); also available at http://www.physics.adelaide.edu.au/theory/papers/ADP-94-25.T165.p

Occupational asthma in maritime environment

In the maritime environment, characterized by a great biodiversity, employees can be during their work exposed to chemical and above all biological substances. Some of them are the cause of occupational asthma. This is the case for some fished products such as crustaceans and mollusks and also for some products carried as cargo like cereals or chemicals used in the maintenance of ships. This article is a review of known etiological factors of occupational asthma (OA) to which seafarers and other maritime workers are likely to be exposed

Electromagnetic radiative corrections in parity-violating electron-proton scattering

QED radiative corrections have been calculated for leptonic and hadronic variables in parity-violating elastic ep scattering. For the first time, the calculation of the asymmetry in the elastic radiative tail is performed without the peaking-approximation assumption in hadronic variables configuration. A comparison with the PV-A4 data validates our approach. This method has been also used to evaluate the radiative corrections to the parity-violating asymmetry measured in the G0 experiment. The results obtained are here presented.Comment: 12 pages, 11 figure

Recent results from the G(0) experiment

We have measured parity violating asymmetries in elastic electron-proton and quasi-elastic electron-deuteron scattering at backward electron angle. These measurements have been done at two momentum transfers : Q(2) = 0.22 and 0.63 (GeV/c)(2). Together with our previous forward angle measurement [1], we can extract strange quark contributions to the electromagnetic form factors of the nucleon, as well as nucleon axial form factor coming from the neutral weak interaction. The results indicate a strange quark magnetic contribution close to zero at these Q(2), and a possible non zero strange quark electric contribution for the high Q(2). The first Q(2) behavior measurement of the nucleon axial form factor in elastic electron scattering shows a good agreement with radiative corrections calculated at Q(2) = 0 and with a dipole form using the axial mass determined in neutrino scattering

Eta-Helium Quasi-Bound States

The cross section and tensor analysing power t_20 of the d\vec{d}->eta 4He reaction have been measured at six c.m. momenta, 10 < p(eta) < 90 MeV/c. The threshold value of t_20 is consistent with 1/\sqrt{2}, which follows from parity conservation and Bose symmetry. The much slower momentum variation observed for the reaction amplitude, as compared to that for the analogous pd->eta 3He case, suggests strongly the existence of a quasi-bound state in the eta-4He system and optical model fits indicate that this probably also the case for eta-3He.Comment: LaTeX, uses elsart.sty, 10 pages, 3 Postscript figures, Submitted to Physics Letters