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

Final-state interactions in semi-inclusive deep inelastic scattering off the Deuteron

Semi-inclusive deep inelastic scattering off the Deuteron with production of a slow nucleon in recoil kinematics is studied in the virtual nucleon approximation, in which the final state interaction (FSI) is calculated within general eikonal approximation. The cross section is derived in a factorized approach, with a factor describing the virtual photon interaction with the off-shell nucleon and a distorted spectral function accounting for the final-state interactions. One of the main goals of the study is to understand how much the general features of the diffractive high energy soft rescattering accounts for the observed features of FSI in deep inelastic scattering(DIS). Comparison with the Jefferson Lab data shows good agreement in the covered range of kinematics. Most importantly, our calculation correctly reproduces the rise of the FSI in the forward direction of the slow nucleon production angle. By fitting our calculation to the data we extracted the $W$ and $Q^2$ dependences of the total cross section and slope factor of the interaction of DIS products, $X$, off the spectator nucleon. This analysis shows the $XN$ scattering cross section rising with $W$ and decreasing with an increase of $Q^2$. Finally, our analysis points at a largely suppressed off-shell part of the rescattering amplitude.Comment: 27 pages, 8 figures. Corrected typos, section II.E has been expanded a bit. Figures have been updated to conform to the publication guidelines. Results and conclusions haven't changed. Accepted for publication in PR

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

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

Final-state interactions in deep-inelastic scattering from a tensor polarized deuteron target

Deep-inelastic scattering (DIS) from a tensor polarized deuteron is sensitive to possible non-nucleonic components of the deuteron wave function. To accurately estimate the size of the nucleonic contribution, final-state interactions (FSIs) need to be accounted for in calculations. We outline a model that, based on the diffractive nature of the effective hadron-nucleon interaction, uses the generalized eikonal approximation to model the FSIs in the resonance region, taking into account the proton-neutron component of the deuteron. The calculation uses a factorized model with a basis of three resonances with mass $W<2$ GeV as the relevant set of effective hadron states entering the final-state interaction amplitude for inclusive DIS. We present results for the tensor asymmetry observable $A_{zz}$ for kinematics accessible in experiments at Jefferson Lab and Hermes. For inclusive DIS, sizeable effects are found when including FSIs for Bjorken $x>0.2$, but the overall size of $A_{zz}$ remains small. For tagged spectator DIS, FSIs effects are largest at spectator momenta around 300 MeV and for forward spectator angles.Comment: 7 pages, 3 figures, proceedings of the Tensor Polarized Solid Target Workshop March 10-12, 2014 (Jefferson Lab, Newport News, USA

DIS on a polarized spin-1 target with spectator tagging

We discuss the process of deep-inelastic electron scattering (DIS) on the polarized deuteron with detection of a nucleon in the nuclear fragmentation region (“spectator tagging”). We cover (a) the general structure of the semi-inclusive DIS cross section on a spin-1 target; (b) the tagged structure functions in the impulse approximation, where deuteron structure is described by the NN light-front wave function; (c) the extraction of free neutron structure through on-shell ex-trapolation in the recoil proton momentum. As an application we consider the extraction of the neutron structure function F 2n and spin structure function g 1n through electron scattering on the (un)polarized deuteron with proton tagging and on-shell extrapolation. Such measurements would be possible at an Electron-Ion Collider (EIC) with polarized deuteron beams and forward proton detectors

Mass dependence of short-range correlations in nuclei and the EMC effect

An approximate method to quantify the mass dependence of the number of two-nucleon (2N) short-range correlations (SRC) in nuclei is suggested. The proposed method relies on the concept of the "local nuclear character" of the SRC. We quantify the SRC and its mass dependence by computing the number of independent-particle model (IPM) nucleon pairs in a zero relative orbital momentum state. We find that the relative probability per nucleon for 2N SRC follows a power law as a function of the mass number $A$. The predictions are connected to measurements which provide access to the mass dependence of SRC. First, the ratio of the inclusive inelastic electron scattering cross sections of nuclei to $^{2}$H at large values of the Bjorken variable. Second, the EMC effect, for which we find a linear relationship between its magnitude and the predicted number of SRC-prone pairs.Comment: 12 pages, 4 figures, preprint proceeding Thirty First International Workshop on Nuclear Theory (IWNT31-2012), organized by the Nuclear Theory Laboratory of the Institute for Nuclear Research and Nuclear Energy of the Bulgarian Academy of Science

Exploring the limits of a hadronic picture of nuclei through pion and nucleon removal reactions

A relativistic and quantum mechanical framework to compute nuclear transparencies for pion and nucleon production reactions is presented. Final state interactions for the ejected pions and nucleons are implemented in a relativistic Glauber eikonal approach. The proposed model can account for the color transparency (CT) phenomenon and short-range correlations (SRC) in the nucleus. Results are presented for kinematics corresponding to completed experiments for A(gamma,pi -p), A(e, e’ pi+) and A(gamma, pp). The influence of CT and SRC on the nuclear transparency is studied. Both the SRC and CT mechanisms increase the nuclear transparency. The two mechanisms can be clearly separated, though, as they exhibit a completely different dependence on the hard-scale parameter. Recent A(e, e pi+) results point towards the early onset of the CT phenomenon in pion production processes. The similarities in the trends and magnitudes of the computed nuclear transparencies compared to semi-classical models indicate that they are not subject to strong model dependencies. A comparison made in the model between the density dependence of the A(e, e’p), A(p, 2p) and A(gamma, pp) reactions shows that 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

Quantifying short-range correlations in nuclei

Background: Short-range correlations (SRC) are an important ingredient of the dynamics of nuclei. Purpose: An approximate method to quantify the magnitude of the two-nucleon (2N) and three-nucleon (3N) short-range correlations and their mass dependence is proposed. Method: The proposed method relies on the concept of the "universality" or "local nuclear character" of the SRC. We quantify the SRC by computing the number of independent-particle model (IPM) nucleon pairs and triples which reveal beyond-mean-field behavior. It is argued that those can be identified by counting the number of nucleon pairs and triples in a zero relative orbital momentum state. A method to determine the quantum numbers of pairs and triples in an arbitrary mean-field basis is outlined. Results: The mass dependence of the 2N and 3N SRC is studied. The predictions are compared to measurements. This includes the ratio of the inclusive inelastic electron scattering cross sections of nuclei to H-2 and He-3 at large values of the Bjorken variable. Corrections stemming from the center-of-mass motion of the pairs are estimated. Conclusions: We find that the relative probability per nucleon for 2N and 3N SRC has a soft dependence with mass number A and that the proton-neutron 2N SRC outnumber the proton-proton (neutron-neutron) 2N SRC. A linear relationship between the magnitude of the EMC effect and the predicted number of proton-neutron SRC pairs is observed. This provides support for the role of local nuclear dynamics on the EMC effect