A relativistic framework to determine the nuclear transparency from A(p,2p) reactions

A relativistic framework for computing the nuclear transparency extracted from A(p,2p) scattering processes is presented. The model accounts for the initial- and final-state interactions (IFSI) within the relativistic multiple-scattering Glauber approximation (RMSGA). For the description of color transparency, two existing models are used. The nuclear filtering mechanism is implemented as a possible explanation for the oscillatory energy dependence of the transparency. Results are presented for the target nuclei 7Li, 12C, 27Al, and 63Cu. An approximated, computationally less intensive version of the RMSGA framework is found to be sufficiently accurate for the calculation of the nuclear transparency. After including the nuclear filtering and color transparency mechanisms, our calculations are in acceptable agreement with the data.Comment: 17 pages, 4 figures, accepted for publication in Phys. Lett.

A relativistic Glauber approach to polarization transfer in 4He(\vec{e},e'\vec{p})

Polarization-transfer components for 4He(\vec{e},e'\vec{p})3H are computed within the relativistic multiple-scattering Glauber approximation (RMSGA). The RMSGA framework adopts relativistic single-particle wave functions and electron-nucleon couplings. The predictions with free and various parametrizations for the medium-modified electromagnetic form factors are compared to the world data.Comment: 2 pages, 1 figure Proceedings of the Int. School on Nuclear Physics, 26th Course, Erice (Sicily), September 16th- 24th, 2004; To appear in Progress in Particle and Nuclear Physic

Model discrimination in pseudoscalar-meson photoproduction

To learn about a physical system of interest, experimental results must be able to discriminate among models. We introduce a geometrical measure to quantify the distance between models for pseudoscalar-meson photoproduction in amplitude space. Experimental observables, with finite precision, map to probability distributions in amplitude space, and the characteristic width scale of such distributions needs to be smaller than the distance between models if the observable data are going to be useful. We therefore also introduce a method for evaluating probability distributions in amplitude space that arise as a result of one or more measurements, and show how one can use this to determine what further measurements are going to be necessary to be able to discriminate among models

Quasi-free (p,2p) and (p,pn) reactions with unstable nuclei

We study (p,2p) and (p,pn) reactions at proton energies in the range of 100 MeV -- 1 GeV. Our purpose is to explore the most sensitive observables in unpolarized reactions with inverse kinematics involving radioactive nuclei. We formulate a model based on the eikonal theory to describe total cross sections and momentum distributions of the recoiled residual nucleus. The model is similar to the one adopted for knockout reactions with heavy ions. We show that momentum distributions are sensitive to the angular momentum of the ejected nucleon which can be used as an spectroscopic tool. The total cross sections are sensitive to the nucleon separation energies and to multiple scattering effects. Our calculations also indicate that a beam energy around 500 MeV/nucleon has a smaller dependence on the anisotropy of the nucleon-nucleon elastic scattering.Comment: 17 pages, 12 figures, Accepted for publication in the Physical review

The exclusive (e,e′'p) reaction at high missing momenta

The reduced (e,e$'$p) cross section is calculated for kinematics that probe high missing momenta. The final-state interaction is handled within a non-relativistic many-body framework. One- and two-body nuclear currents are included. Electron distortion effects are treated in an exact distorted wave calculation. It is shown that at high missing momenta the calculated (e,e$'$p) cross sections exhibit a pronounced sensitivity to ground-state correlations of the RPA type and two-body currents. The role of these mechanisms is found to be relatively small at low missing momenta.Comment: 15 pages in REVtex with embedded psfigure

Extracting the Weinberg angle at intermediate energies

A recent experiment by the NuTeV collaboration resulted in a surprisingly high value for the weak mixing angle $\sin^2 \theta_W$. The Paschos-Wolfenstein relation, relating neutrino cross sections to the Weinberg angle, is of pivotal importance in the NuTeV analysis. In this work, we investigate the sensitivity of the Paschos-Wolfenstein relation to nuclear structure aspects at neutrino energies in the few GeV range. Neutrino-nucleus cross sections are calculated for $^{16}$O and $^{56}$Fe target nuclei within a relativistic quasi-elastic nucleon-knockout model.Comment: To appear in the proceedings of International School of Nuclear Physics: 27th Course: "Neutrinos in Cosmology, in Astro, Particle and Nuclear Physics", Erice, Sicily, Italy, 16-24 Sep 200

Identifying neutrinos and antineutrinos in neutral-current scattering reactions

We study neutrino-induced nucleon knockout from nuclei. Expressions for the induced polarization are derived within the framework of the independent-nucleon model and the non-relativistic plane-wave approximation. Large dissimilarities in the nucleon polarization asymmetries are observed between neutrino- and antineutrino-induced processes. These asymmetries represent a potential way to distinguish between neutrinos and antineutrinos in neutral-current neutrino-scattering on nuclei. We discuss astrophysical applications of these polarization asymmetries. Our findings are illustrated for neutrino scattering on $^{16}$O and $^{208}$Pb.Comment: 5 pages, 5 figures, accepted for publication in Phys. Rev. Let

Electroweak interactions in a relativistic Fermi gas

We present a relativistic model for computing the neutrino mean free path in neutron matter. Thereby, neutron matter is described as a non-interacting Fermi gas in beta-equilibrium. We present results for the neutrino mean free path for temperatures from 0 up to 50 MeV and a broad range of neutrino energies. We show that relativistic effects cause a considerable enhancement of neutrino-scattering cross-sections in neutron matter. The influence of the $Q^2$-dependence in the electroweak form factors and the inclusion of a weak magnetic term in the hadron current is discussed. The weak-magnetic term in the hadron current is at the origin of some selective spin dependence for the nucleons which are subject to neutrino interactions.Comment: 11 pages, 7 figures, accepted to Phys. Rev. C, minor changes and updates of the figures are mad

Relativistic eikonal approximation in high-energy A(e,e'p) reactions

A fully relativistic model for the description of exclusive (e,e'p) reactions off nuclear targets at high energies and momentum transfers is outlined. It is based on the eikonal approximation for the ejectile scattering wave function and a relativistic mean-field approximation to the Walecka model. Results for ^{12}C(e,e'p) and ^{16}O(e,e'p) differential cross sections and separated structure functions are presented for four-momenta in the range 0.8 \leq Q^{2} \leq 20 (GeV/c)^{2}. The regions of applicability of the eikonal approximation are studied and observed to be confined to proton knockout in a relatively small cone about the momentum transfer. A simple criterium defining the boundaries of this cone is determined. The Q^2 dependence of the effect of off-shell ambiguities on the different (e,e'p) structure functions is addressed. At sufficiently high values of Q^2 their impact on the cross sections is illustrated to become practically negligible. It is pointed out that for the whole range of Q^2 values studied here, the bulk of the relativistic effects arising from the coupling between the lower components in the wave functions, is manifesting itself in the longitudinal-transverse interference term.Comment: 13 pages,11 figure