arXiv subjects

Misak M. Sargsian

Publications and source records attributed to Misak M. Sargsian.

28 records · Page 2Linked to original sources

arXiv2010

Large Q2 electrodisintegration of the deuteron

The break up of the deuteron is studied at high $Q^2$ kinematics, with main motivation to probe the deuteron at small internucleon distances. For this, two main issues are studied: electromagnetic interaction of the virtual photon with the bound nucleon and the strong interactions of the produced baryons in the final state of the reaction. Within virtual nucleon approximation we developed a new prescription to account for the bound nucleon effects in the electromagnetic interaction. The final state interaction at high $Q^2$ kinematics is calculated within generalized eikonal approximation ~ (GEA). Comparison with the first 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. Also the forward recoil nucleon angles are best suited for studies of the deuteron at small distances.

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arXiv2009

Quark Structure of the Nucleon and Angular Asymmetry of Proton-Neutron Hard Elastic Scattering

We investigate an asymmetry in the angular distribution of hard elastic proton-neutron scattering with respect to 90deg center of mass scattering angle. We demonstrate that the magnitude of the angular asymmetry is related to the helicity-isospin symmetry of the quark wave function of the nucleon. Our estimate of the asymmetry within the quark-interchange model of hard scattering demonstrates that the quark wave function of a nucleon based on the exact SU(6) symmetry predicts an angular asymmetry opposite to that of experimental observations. On the other hand the quark wave function based on the diquark picture of the nucleon produces an asymmetry consistent with the data. Comparison with the data allowed us to extract the relative sign and the magnitude of the vector and scalar diquark components of the quark wave function of the nucleon. These two quantities are essential in constraining QCD models of a nucleon. Overall, our conclusion is that the angular asymmetry of a hard elastic scattering of baryons provides a new venue in probing quark-gluon structure of baryons and should be considered as an important observable in constraining the theoretical models.

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arXiv2008

Hard Break-Up of Two-Nucleons and QCD Dynamics of NN Interaction

We discus recent developments in theory of high energy two-body break-up 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 between two outgoing nucleons. This final state hard rescattering can be expressed through the hard NN scattering amplitude. Within HRM we discuss hard break-up reactions involving D and 3He targets and demonstrate how these reactions are sensitive to the dynamics of hard pn and pp interaction. 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.

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arXiv2008

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.

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arXiv2003

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 $ϕ_5$ helicity amplitude which vanishes at $θ_{cm}=90^\circ$ due to symmetry reasons. HRM predicts also a nonzero value for $C_z$ in the helicity-conserving regime and a positive $Σ$ 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.

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arXiv2002

Probing the Short-Range Dynamics in Exclusive Scattering off Polarized Deuteron

Employing the polarization degrees of freedom in the deuteron allows to isolate smaller than average inter-nucleon distances in the deuteron. As a result one can identify set of high $Q^2$ reactions off polarized deuteron which are particularly sensitive to the short range dynamics of strong interaction. We concentrate on the studies of several aspects of the short range phenomena. These are the relativistic dynamics of electron--bound-nucleon scattering, color coherence in high $Q^2$ electro-production as well as the formation of the vector mesons in coherent electro-production from the deuteron. We address also the issue of extraction of polarized deep inelastic structure function of the neutron.

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arXiv2002

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.

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arXiv2001

Selected Topics in High Energy Semi-Exclusive Electro-Nuclear Reactions

We review the present status of the theory of high energy reactions with semi-exclusive nucleon electro-production from nuclear targets. We demonstrate how the increase of transferred energies in these reactions opens a complete new window in studying the microscopic nuclear structure at small distances. The simplifications in theoretical descriptions associated with the increase of the energies are discussed. The theoretical framework for calculation of high energy nuclear reactions based on the effective Feynman diagram rules is described in details. The result of this approach is the generalized eikonal approximation (GEA), which is reduced to Glauber approximation when nucleon recoil is neglected. The method of GEA is demonstrated in the calculation of high energy electro-disintegration of the deuteron and A=3 targets. Subsequently we generalize the obtained formulae for A>3 nuclei. The relation of GEA to the Glauber theory is analyzed. Then based on the GEA framework we discuss some of the phenomena which can be studied in exclusive reactions, these are: nuclear transparency and short-range correlations in nuclei. We illustrate how light-cone dynamics of high-energy scattering emerge naturally in high energy electro-nuclear reactions.

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arXiv2000

QCD Rescattering and High Energy Two-Body Photodisintegration of the Deuteron

Photon absorption by a quark in one nucleon followed by its high momentum transfer interaction with a quark in the other may produce two final-state nucleons with high relative momentum. We sum the relevant quark rescattering diagrams, to show that the scattering amplitude depends on a convolution between the large angle $pn$ scattering amplitude, the hard photon-quark interaction vertex and the low-momentum deuteron wave function. The computed absolute values of the cross section are in reasonable agreement with the data.

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arXiv1999

Hard Rescattering in QCD and High Energy Two-Body Photodisintegration of the Deuteron

Photon absorption by a quark in one nucleon followed by its high momentum transfer interaction with a quark in the other may produce two nucleons with high relative momentum. We sum the relevant quark rescattering diagrams, to show that the scattering amplitude depends on a convolution between the large angle $pn$ scattering amplitude, the hard photon-quark interaction vertex and the low-momentum deuteron wave function. The computed cross sections are in reasonable agreement with the data.

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