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

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

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

Polarization Observables in Hard Rescattering Mechanism of Deuteron Photodisintegration

Polarization properties of high energy photodisintegration of the deuteron are studied within the framework of the hard rescattering mechanism~(HRM). In HRM, a quark of one nucleon knocked-out by the incoming photon rescatters with a quark of the other nucleon leading to the production of two nucleons with high relative momentum. Summation of all relevant quark rescattering amplitudes allows us to express the scattering amplitude of the reaction through the convolution of a hard photon-quark interaction vertex, the large angle p-n scattering amplitude and the low momentum deuteron wave function. Within HRM, it is demonstrated that the polarization observables in hard photodisintegration of the deuteron can be expressed through the five helicity amplitudes of NN scattering at high momentum transfer. At 90$^\circ$ CM scattering HRM predicts the dominance of the isovector channel of hard $pn$ rescattering, and it explains the observed smallness of induced, $P_y$ and transfered, $C_x$ polarizations without invoking the argument of helicity conservation. Namely, HRM predicts that $P_y$ and $C_x$ are proportional to the $\phi_5$ helicity amplitude which vanishes at $\theta_{cm}=90^\circ$ due to symmetry reasons. HRM predicts also a nonzero value for $C_z$ in the helicity-conserving regime and a positive $\Sigma$ asymmetry which is related to the dominance of the isovector channel in the hard reinteraction. We extend our calculations to the region where large polarization effects are observed in $pp$ scattering as well as give predictions for angular dependences.Comment: Seven pages and three eps figure

The EMC Effect and Short-Range Correlations

We overview the progress made in studies of EMC and short range correlation (SRC) effects with the special emphasis given to the recent observation of the correlation between the slope of the EMC ratio at Bjorken x<1 and the scale factor of the same ratio at x>1 that measures the strength of the SRCs in nuclei. This correlation may indicate the larger modification of nucleons with higher momentum thus making the nucleon virtuality as the most relevant parameter of medium modifications. To check this conjecture we study the implication of several properties of high momentum component of the nuclear wave function on the characteristics of EMC effect. We observe two main reasons for the EMC-SRC correlation: first, the decrease of the contribution from the nuclear mean field due to the increase, with A, the fraction of the high momentum component of nuclear wave function. Second, the increase of the medium modification of nucleons in SRC. Our main prediction however is the increase of the proton contribution to the EMC effect for large A asymmetric nuclei. This prediction is based on the recent observation of the strong dominance of pn SRCs in the high momentum component of nuclear wave function. Our preliminary calculation based on this prediction of the excess of energetic and modified protons in large A nuclei describes reasonably well the main features of the observed EMC-SRC correlation.Comment: 5 pages, 2 figures, presented at CIPANP 2012 - Eleventh Conference on the Intersections of Particle and Nuclear Physics, 28 May - 03 June, 201

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