M. Gari

Parity nonconserving nucleon--nucleon scattering (one-boson-exchange) in the Weinberg--Salam model

Abstract In the present paper we discuss the implications of the Weinberg-Salam model of weak interactions for parity non-conserving nucleon-nucleon scattering. The one-boson-exchange nucleon-nucleon potentials are determined by the use of the factorization method and current algebra. The effect of the neutral hadronic currents is to enhance both the pion contribution (Δ I =1) and the vector meson contribution (ΔI=0, (2))). The Weinberg-Salam model is consistent with the recent experiment on 19F and leads to a sizable measurable polarization effect in the transition 0-, 0(1.08 MeV) to the ground state of 18F, namely, P ∼ 5 × 10−3.

Generalized vector-meson dominance and the electromagnetic structure of the nucleon

Abstract We follow our recent model to synthesize meson-dynamics and asymptotic QCD predictions to calculate the electromagnetic structure functions of the nucleon. The requirement that the photon couples asymptotically as a single field leads to a generalization of the vector-meson dominance model. The resulting structure functions (space like region) are in quantitative agreement with experiments.

Circular polarization in 18F as a probe for neutral currents

Abstract We present a discussion of the circular polarization of the 1.08 MeV transition (0−, I = 0 1+, I = 0) in 18F as a test for neutral currents. Calculations for the Cabibbo model of weak interactions predict a value for the polarization of the 1.08 MeV photons of |δc| = 3.6 × 10−4. This value is considerably larger than previously estimated. Inclusion of neutral currents via the Weinberg-Salam model results in a considerable enhancement: |δW| = 5.7 × 10−3. The measurement of the circular polarization or asymmetry of the 1.08 MeV photons therefore is likely to be one of the most promising parity experiments, and should be done in the near future.

Electric dipole sum rule for light, even--even nuclei via Brueckner-- Hartree--Fock (BHF) wave functions

Abstract We present calculations of the enhancement factor κ in the electric dipole sum done by the use of solutions of the Brueckner-Hartree-Fock (BHF) equations. Results are given for 4 He, 12 C and 16 O for various realistic nucleon-nucleon potentials.

Neutral currents in thermal np capture

Abstract We present a calculation of the circular polarization P γ and asymmetry A γ of gamma radiation in thermal neutron-proton capture with a tested numerical accuracy of 1%. The effect of neutral currents is discussed on the example of the Weinberg-Salam model of weak interaction. It is also shown that a one percent contribution of the 3 S 1 scattering state to the regular np capture cross section destroys the favourable isospin selection rule in the polarization.

Structure functions of the meson-nucleon interaction

Abstract We investigated the structure function of the omega-nucleon interaction by the use of a mesonic picture at low and medium momentum transfer and a quantum-chromodynamical (QCD) description at high momentum transfer. The results are compared with recent calculations for π- and ϱ-nucleon interaction form factors in the same model.

Information on neutral weak currents from polarized-electron deuteron disintegration

Abstract We investigate weak neutral currents in deuteron disintegration by longitudinally polarized electrons. The right-left asymmetry is discussed in dependence on momentum and energy transfer up to the pion threshold. Measurements in different kinematical regions may yield information on different parts of the weak currents.

Discrepancy in the doubly radiative neutron-proton capture

Abstract In the present paper we reinvestigate the theoretical cross-section for the doubly radiative n-p capture at thermal energies. We find the upper limit of the ratio R of the two photon emission cross-section to the one photon emission cross-section to be R ⩽ 10 −7 . This limit is 3 orders of magnitudes larger than a previous calculation, however, still four orders of magnitudes too small compared to a recent experiment which thus remains to be explained.

Dynamical aspects of photonuclear reactions below pion threshold

The reactions ( gamma ,p), ( gamma ,n), ( gamma ,pn), ( gamma ,pp) and ( gamma ,nn) below pion threshold are studied in view of a systematic treatment of electromagnetic meson exchange currents. As a numerical example the integrated and differential cross sections for ( gamma ,p) and ( gamma ,n) on /sup 4/He are calculated. (auth)

Anti-neutrino disintegration of the deuteron

Abstract The anti-neutrino disintegration of the deuteron ( ν + D→ ν + n + p and ν e + D→e + + n + n) is calculated using realistic two-body states. Meson-exchange currents are considered in the one-boson-exchange limit. The results are discussed as corrections to the cross sections obtained in effective range approximations. It is shown that the ratio of the cross sections ( σ - σ 0 ) for reactor antineutrinos is practically independent of the nuclear physics uncertainties.