Nuclear rho transparencies in a relativistic Glauber model

[Background] The recent Jefferson Lab data for the nuclear transparency in $\rho^ {0}$ electroproduction have the potential to settle the scale for the onset of color transparency (CT) in vector meson production. [Purpose] To compare the data to calculations in a relativistic and quantum-mechanical Glauber model and to investigate whether they are in accordance with results including color transparency given that the computation of $\rho$-nucleus attenuations is subject to some uncertainties. [Method] We compute the nuclear transparencies in a multiple-scattering Glauber model and account for effects stemming from color transparency, from $\rho$-meson decay, and from short-range correlations (SRC) in the final-state interactions (FSI). [Results] The robustness of the model is tested by comparing the mass dependence and the hard-scale dependence of the $A(e,e'p)$ nuclear transparencies with the data. The hard-scale dependence of the $(e,e' \rho ^ {0})$ nuclear transparencies for $^ {12}$C and $^ {56}$Fe are only moderately affected by SRC and by $\rho^ {0}$-decay. [Conclusions] The RMSGA calculations confirm the onset of CT at four-momentum transfers of a few (GeV/c)$^2$ in $\rho$ meson electroproduction data. A more precise determination of the scale for the onset of CT is hampered by the lack of precise input in the FSI and $\rho$-meson decay calculations.Comment: 18 pages, 5 figures. Revised version to appear in PRC. Minor corrections, added discussion and figure about CT parameters dependence. Results and conclusions remain the sam

A(e,e'p) reactions at GeV energies

An unfactorized and relativistic framework for calculating A(e,e'p) observables at typical JLAB energies is presented. Results of (e,e'p) model calculations for the target nuclei ^{12}C and ^{16}O are presented and compared to data from SLAC and JLAB.Comment: 8 pages, 3 figures, Proceedings of the Third International Conference on Perspectives in Hadronic Physics (Trieste, 2001

Charged pion electroproduction above the resonance region

[Background] Above the nucleon resonance region, the $N(e,e'\pi^\pm)N'$ data cannot be explained by conventional hadronic models. For example, the observed magnitude of the transverse cross section is significantly underestimated in a framework with Reggeized background amplitudes. [Purpose] Develop a phenomenological framework for the $N(e,e'\pi^\pm)N'$ reaction at high invariant mass $W$ and deep photon virtuality $Q^2$. [Method] Building on the work of Kaskulov and Mosel, a gauged pion-exchange current is introduced with a running cutoff energy for the proton electromagnetic transition form factor. A new transition form factor is proposed. It respects the correct on-shell limit, has a simple physical interpretation and reduces the number of free parameters by one. [Results] A study of the $W$ dependence of the $N(e,e'\pi^\pm)N'$ lends support for the newly proposed transition form factor. In addition, an improved description of the separated and unseparated cross sections at $-t \lesssim 0.5 \;\text{GeV}^2$ is obtained. The predictions overshoot the measured unseparated cross sections for $-t > 0.5 \;\text{GeV}^2$. Introducing a strong hadronic form factor in the Reggeized background amplitudes brings the calculations considerably closer to the high $-t$ data. [Conclusions] Hadronic models corrected for resonance/parton duality describe the separated pion electroproduction cross sections above the resonance region reasonably well at low $-t$. In order to validate the applicability of these models at high $-t$, separated cross sections are needed. These are expected to provide a more profound insight into the relevant reaction mechanisms.Comment: 11 pages, 8 figure

Modeling final-state interactions with a relativistic multiple-scattering approximation

We address the issue of nuclear attenuation in nucleon and pion knockout reactions. A selection of results from a model based on a relativistic multiple-scattering approximation is presented. We show transparency calculations for pion electroproduction on several nuclei, where data are in very good agreement with calculations including color transparency. Secondly, we discuss the density dependence of reactions involving one or double proton knockout. The latter reaction succeeds in probing the high density regions in the deep interior of the nucleus.Comment: 6 pages, 4 figures, "Relativistic Description of Two- and Three-Body Systems in Nuclear Physics", ECT$^*$, October 19-13 200

On the density dependence of single-proton and two-proton knockout reactions under quasifree conditions

We consider high-energy quasifree single- and two-proton knockout reactions induced by electrons and protons and address the question what target-nucleus densities can be effectively probed after correcting for nuclear attenuation (initial- and final-state interactions). Our calculations refer to ejected proton kinetic energies of 1.5 GeV, the reactions (e,e'p), (\gamma,pp) and (p,2p) and a carbon target. It is shown that each of the three reactions is characterized by a distinctive sensitivity to the density of the target nucleus. The bulk of the (\gamma,pp) strength stems from the high-density regions in the deep nuclear interior. Despite the strong attenuation, sizable densities can be probed by (p,2p) provided that the energy resolution allows one to pick nucleons from s orbits. The effective mean densities that can be probed in high-energy (e,e'p) are of the order of 30-50% of the nuclear saturation density.Comment: 10 pages, 2 figure

Incompleteness of complete kaon photoproduction

A possible roadmap for reaching a status of complete information in $\gamma p \rightarrow K^ {+} \Lambda$ is outlined.Comment: 4 pages, 2 figures, Proceedings of the NSTAR2013 conferenc

Polarization degrees of freedom in two-nucleon knockout from finite nuclei

Polarization observables for the A(e,e'NN) and A(\gamma,NN) reactions are a powerful tool to study nucleon-nucleon correlations in the nuclear medium. In this paper, model calculations for the ^{4}He(e,e'pp), ^{16}O(\vec{e},e'\vec{p}p), ^{16}O(\vec{e},e' \vec{p}n) and ^{12}C(\vec{\gamma},\vec{p}N) reactions are presented. The sensitivity of the differential cross sections and polarization observables to central and spin-dependent nucleon-nucleon correlations is discussed.Comment: 12 pages, 10 (color) figures, Talk Presented at the the Fourth Workshop on Electromagnetically Induced Two-Hadron Emission, Granada (Spain), May 26-29, 199

Photoinduced two-proton knockout and ground-state correlations in nuclei

A factorized and analytical form for the A($\gamma$,pp) and A(e,e$'$pp) cross section is proposed. In the suggested scheme the two-proton knockout cross sections can be directly analyzed in terms of the ground-state correlation functions. Central, spin-spin and tensor correlations are considered. In the longitudinal channel, the (e,e$'$pp) cross section is predicted to exhibit a peculiar sensitivity to ground-state correlation effects.Comment: 11 pages in REVtex with embedded psfigure

Final-state interactions in two-nucleon knockout reactions

Background: Exclusive two-nucleon knockout after electroexcitation of nuclei ($A(e,e'NN)$ in brief) is considered to be a primary source of information about short-range correlations (SRC) in nuclei. For a proper interpretation of the data, final-state interactions (FSI) need to be theoretically controlled. Purpose: Our goal is to quantify the role of FSI effects in exclusive $A(e,e'pN)$ reactions for four target nuclei representative for the whole mass region. Our focus is on processes that are SRC driven. We investigate the role of FSI for two characteristic detector setups corresponding with a "small" and "large" coverage of the available phase space. Results: The transparency $T^{pN}_{A}$, defined as the ratio of exclusive $(e,e'pN)$ cross sections on nuclei to those on "free" nucleon pairs, drops from $0.2-0.3$ for $^{12}$C to $0.04-0.07$ for $^{208}$Pb. For all considered kinematics, the mass dependence of the $T^{pN}_{A}$ can be captured by the power law $T^{pN}_{A} \propto A^{- \lambda}$ with $0.4 \lesssim \lambda \lesssim 0.5$. Apart from an overall reduction factor, we find that FSI only modestly affects the distinct features of SRC-driven $A(e,e'pN)$ which are dictated by the c.m. distribution of close-proximity pairs. Conclusion: The SCX mechanisms represent a relatively small (order of a few percent) contribution of SRC-driven $A(e,e'pN)$ processes. The mass dependence of FSI effects in exclusive $A(e,e'pN)$ can be captured in a robust power law and is in agreement with the predictions obtained in a toy model