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

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

Large Q2 Electrodisintegration of the Deuteron in Virtual Nucleon Approximation

The two-body break up of the deuteron is studied at high $Q^2$ kinematics, with main motivation to probe the deuteron at small internucleon distances. Such studies are associated with the probing of high momentum component of the deuteron wave function. For this, two main theoretical issues have been addressed such as electromagnetic interaction of the virtual photon with the bound nucleon and the strong interaction of produced baryons in the final state of the break-up reaction. Within virtual nucleon approximation we developed a new prescription to account for the bound nucleon effects in electromagnetic interaction. The final state interaction at high $Q^2$ kinematics is calculated within generalized eikonal approximation (GEA). We studied the uncertainties involved in the calculation and performed comparisons with the first experimental data on deuteron electrodisintegration at large $Q^2$. We demonstrate that the experimental data confirm GEA's early prediction that the rescattering is maximal at $\sim 70^0$ of recoil nucleon production relative to the momentum of the virtual photon. Comparisons also show that the forward recoil nucleon angles are best suited for studies of the electromagnetic interaction of bound nucleons and the high momentum structure of the deuteron. Backward recoil angle kinematics show sizable effects due to the $\Delta$-isobar contribution. The latter indicates the importance of further development of GEA to account for the inelastic transitions in the intermediate state of the electrodisintegration reactions.Comment: 22 pages, 9 figure

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