Protons in High Density Neutron Matter

We discuss the possible implication of the recent predictions of two new properties of high momentum distribution of nucleons in asymmetric nuclei for neutron star dynamics. The first property is about the approximate scaling relation between proton and neutron high momentum distributions weighted by their relative fractions ($x_p$ and $x_n$) in the nucleus. The second is the existence of inverse proportionality of the high momentum distribution strength of protons and neutrons to $x_{p/n}$. Based on these predictions we model the high momentum distribution functions for asymmetric nuclei and demonstrate that it describes reasonably well the high momentum characteristics of light nuclei. We also extrapolate our results to heavy nuclei as well as infinite nuclear matter and calculate the relative fractions of protons and neutrons with momenta above $k_{F}$. Our results indicate that for neutron stars starting at {\em three} nuclear saturation densities the protons with $x_p = {1\over 9}$ will populate mostly the high momentum tail of the momentum distribution while only $2\%$ of the neutrons will do so. Such a situation may have many implications for different observations of neutron stars which we discuss.Comment: 6 pages, 2 eps figures, For the proceedings of International Conference on "The Modern Physics of Compact Stars and Relativistic Gravity", 18-21 September 2013, Yerevan, Armeni

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

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

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 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

High Energy Break-Up of Few-Nucleon Systems

We discus recent developments in theory of high energy two-body break-up reactions of few-nucleon systems. The characteristics of these reactions are such that the hard two-body quasielastic subprocess can be clearly separated from the accompanying soft subprocesses. We discuss in details the hard rescattering model (HRM) in which hard photodisintegration develops in two stages. At first, photon knocks-out an energetic quark which rescatters subsequently with a quark of the other nucleon. The latter provides a mechanism of sharing the initial high momentum of the photon by the outgoing two nucleons. Within HRM we discuss hard break-up reactions involving $^2D$ and $^3He$ targets. Another development of HRM is the prediction of new helicity selection mechanism for hard two-body reactions, which was apparently confirmed in the recent JLab experiment.Comment: To appear in the proceedings of Workshop on Exclusive Reactions at High Momentum Transfer, Newport News, Virgina, 21-24 May 200

Hard Rescattering Mechanism in High Energy Photodisintegration of the Light Nuclei

We discuss the high energy photodisintegrataion of light nuclei in which the energy of the absorbed photon is equally shared between two nucleons in the target. For these reactions we investigate the model in which photon absorption by a quark in one nucleon followed by its high momentum transfer interaction with a quark of the other nucleon leads to the production of two nucleons with high relative momentum. We sum the relevant quark rescattering diagrams, and demonstrate that the scattering amplitude can be expressed as a convolution of the large angle NN scattering amplitude, the hard photon-quark interaction vertex and the low-momentum nuclear wave function. Within this model we calculate the cross sections and polarization observables of high energy gamma + d --> pn and gamma + ^3He --> pp + n reactions.Comment: 8 pages Latex, 2 eps figures. Contribution to the conference "Exclusive Processes at High Momentum Transfer", held at Jefferson Laboratory May 15-18, 200