Tagged spectator deep-inelastic scattering off the deuteron as a tool to study neutron structure

We give an overview of a model to describe deep-inelastic scattering (DIS) off the deuteron with a spectator proton, based on the virtual nucleon approximation (VNA). The model accounts for the final-state interactions (FSI) of the DIS debris with the spectator proton. Values of the rescattering cross section are obtained by fits to high-momentum spectator data. By using the so-called "pole extrapolation method", free neutron structure functions can be obtained by extrapolating low-momentum spectator proton data to the on-shell neutron pole. We apply this method to the BONuS data set and find a surprising Bjorken $x$ dependence, indicating a possible rise of the neutron to proton structure function ratio at high $x$.Comment: 6 pages, 4 figures, proceedings of POETIC

Nuclear final-state interactions in deep inelastic scattering off the lightest nuclei

We review recent progress in studies of nuclear final-state interactions in deep inelastic scattering (DIS) off the lightest nuclei tagged by a recoil nucleon. These processes hold a lot of potential for resolving the outstanding issues related to the dynamics of hadronization in QCD. Within the minimal Fock component framework, valid at large Bjorken $x$, the main features of the theoretical approach based on the virtual nucleon approximation are elaborated. In this approach, the strong final-state interaction of the DIS products with the nuclear fragments is described by an effective eikonal amplitude, whose parameters can be extracted from the analysis of semi-inclusive DIS off the deuteron target. The extraction of the $Q^2$ and $W$ mass dependences of these parameters gives a new observable in studying the QCD structure of DIS final states. Another important feature of tagged DIS off the lightest nuclei is the possibility of performing pole extrapolation with a high degree of accuracy. Such extrapolation allows an extraction of the neutron structure function in a model independent way due to suppression of the final-state interaction in the on-shell limit of the struck nucleon propagator. We review the first application of the pole extrapolation to recent experimental data. Finally, we outline the extension of the framework to inclusive DIS, including a polarized deuteron target as well as its application to the tagged DIS reactions for future experiments at fixed target and collider energies.Comment: 36 pages, final version accepted in Int. J. Mod. Phys. E. Minor changes in the tex

Longitudinal spin asymmetries in polarized deuteron DIS with spectator tagging

Polarized electron-deuteron DIS with spectator proton tagging offers a way of measuring the neutron spin structure functions with maximal theoretical control of nuclear effects. We calculate the nuclear structure factors in the longitudinal double-spin asymmetries using methods of light-front nuclear structure. A unique feature of the spin-1 system is that spin asymmetries can be formed either relative to the cross section in all three spin states ($\lambda_d = \pm 1, 0$) or in the two maximum-spin states only ($\pm 1$, involving tensor polarization). We find that the two-state deuteron spin asymmetry at small spectator proton momenta permits accurate extraction of the neutron structure function $g_{1n}$. Such measurements could be performed at a future electron-ion collider (EIC) with polarized deuteron beams and suitable forward detectors.Comment: 7 pages, 2 figures; Proceedings of 23rd International Spin Physics Symposium (SPIN2018), 10-14 September, 2018; Ferrara, Ital

Final-state interactions in inclusive deep-inelastic scattering from the deuteron

We explore the role of final-state interactions (FSI) in inclusive deep-inelastic scattering from the deuteron. Relating the inclusive cross section to the deuteron forward virtual Compton scattering amplitude, a general formula for the FSI contribution is derived in the generalized eikonal approximation, utilizing the diffractive nature of the effective hadron-nucleon interaction. The calculation uses a factorized model with a basis of three resonances with mass $W<2$ GeV and a continuum contribution for larger $W$ as the relevant set of effective hadron states entering the final-state interaction amplitude. The results show sizeable on-shell FSI contributions for Bjorken $x \gtrsim 0.6$ and $Q^2 \lesssim 10$ GeV$^2$, increasing in magnitude for lower $Q^2$, but vanishing in the high-$Q^2$ limit due to phase space constraints. The off-shell rescattering contributes at $x \gtrsim 0.8$ and is taken as an uncertainty on the on-shell result.Comment: 29 pages, 8 figures. Version accepted for publication in PRC. Minor changes: some discussion in the introduction is slightly expanded (three typos in formulas corrected

Tagged spectator DIS on a polarized spin-1 target

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 extrapolation in the recoil proton momentum. As an application we consider the extraction of the neutron spin structure function $g_{1n}$ through polarized electron scattering on the longitudinally 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.Comment: 6 pages, 2 figures. Proceedings of XXIV International Workshop on Deep-Inelastic Scattering and Related Subjects (DIS 2016), DESY Hamburg, Germany, 11-15 April, 201

Color transparency and short-range correlations in exclusive pion photo- and electroproduction from nuclei

A relativistic and quantum mechanical framework to compute nuclear transparencies for pion photo- and electroproduction reactions is presented. Final-state interactions for the ejected pions and nucleons are implemented in a relativistic eikonal approach. At sufficiently large ejectile energies, a relativistic Glauber model can be adopted. At lower energies, the framework possesses the flexibility to use relativistic optical potentials. 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 and planned experiments at Jefferson Lab. 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. The nucleon and pion transparencies as computed in the relativistic Glauber approach are compared with optical-potential and semi-classical calculations. The similarities in the trends and magnitudes of the nuclear transparencies indicate that they are not subject to strong model dependencies.Comment: 33 pages, 14 figure

Tensor-polarized structure function b1b_1 in the standard convolution description of the deuteron

Tensor-polarized structure functions of a spin-1 hadron are additional observables which do not exist for the spin-1/2 nucleon. They could probe novel aspects of the internal hadron structure. Twist-2 tensor-polarized structure functions are $b_1$ and $b_2$, and they are related by the Callan-Gross-like relation in the Bjorken scaling limit. In this work, we theoretically calculate $b_1$ in the standard convolution description for the deuteron. Two different theoretical models, a basic convolution description and a virtual nucleon approximation, are used for calculating $b_1$ and their results are compared with the HERMES measurement. We found large differences between our theoretical results and the data. Although there is still room to improve by considering higher-twist effects and in the experimental extraction of $b_1$ from the spin asymmetry $A_{zz}$, there is a possibility that the large differences require physics beyond the standard deuteron model for their interpretation. Future $b_1$ studies could shed light on a new field of hadron physics. In particular, detailed experimental studies of $b_1$ will start soon at the Thomas Jefferson National Accelerator Facility. In addition, there are possibilities to investigate tensor-polarized parton distribution functions and $b_1$ at Fermi National Accelerator Laboratory and a future electron-ion collider. Therefore, further theoretical studies are needed for understanding the tensor structure of the spin-1 deuteron, including a new mechanism to explain the large differences between the current data and our theoretical results.Comment: 12 pages, 7 eps figures, 3 style files, typos are corrected as published in Phys. Rev. D 95, 074036 (2017

Phase-space distributions of nuclear short-range correlations

Nuclear short-range correlations (SRCs) induce high-momentum/high-energy fluctuations in the nuclear medium. In order to assess their impact on nuclear bulk properties, like nuclear radii and kinetic energies, it is instrumental to determine how SRCs are distributed in phase space as this sheds light on the connection between their appearance in coordinate and momentum space. Using the lowest-order correlation operator approximation (LCA) to include SRC, we compute two-dimensional nuclear Wigner quasiprobability distributions $w(r, k)$ to locate those $({r}, {k})$ phase-space regions that are most heavily impacted by SRCs. The SRC-induced high-momentum components find their origin in a radial range that is confined to the nuclear interior. Significant SRCs strength is generated in the full momentum range $0 \leq k \lesssim 5 ~\text{fm}^{-1}$ covered in this work, but below the Fermi momentum those are dwarfed by the mean-field contributions. As an application of $w(r, k)$, we focus on the radial dependence of the kinetic energy $T$ and the momentum dependence of the radius $r_{\text{rms}}$ for the symmetric nuclei $^{12}$C, $^{40}$Ca and the asymmetric nucleus $^{48}$Ca. The kinetic energy almost doubles after including SRCs, with the largest increase occurring in the nuclear interior $r \lesssim 2$ fm. The momentum dependence of the $r_{\text{rms}}$ teaches that the largest contributions stem from $k \lesssim 2$ fm$^{-1}$, where the SRCs induce a slight reduction of the order of a few percent. The SRCs systematically reduce the $^{48}$Ca neutron skin by an amount that can be 10\%.Comment: 10 pages, 6 figures; revised version with updated Fig.1, matches published versio

Standard convolution description of deuteron tensor spin structure

Spin-1 hadrons have additional structure functions not present for spin 1/2 hadrons. These could probe novel aspects of hadron structure and QCD dynamics. For the deuteron, the tensor structure function $b_1$ inherently mixes quark and nuclear degrees of freedom. These proceedings discuss two standard convolution models applied to calculations of the deuteron $b_1$ structure functions. We find large differences with the existing HERMES data and other convolution model calculations. This leaves room for non-standard contributions to $b_1$ in the deuteron. We also discuss the influence of higher twist nuclear effects in the model calculations and data extraction at kinematics covered in HERMES and Jefferson Lab.Comment: Proceedings of 25th International Workshop on Deep Inelastic Scattering and Related Topics, 3-7 April 2017 University of Birmingha