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L. P. Kaptari

Publications and source records attributed to L. P. Kaptari.

At least 55 records · Page 3Linked to original sources
arXiv2008

Non-factorized calculation of the process 3He(e,e'p)2H at medium energies

The exclusive process 3He(e,e'p)2H has been analyzed by a non-factorized and parameter-free approach based upon realistic few-body wave functions corresponding to the $AV18$ interaction and treating the rescattering of the struck nucleon within a generalized eikonal approximation. The results of our calculations, compared with recent JLab experimental data, show that the left-right asymmetry exhibits a clear dependence upon the final state interaction demonstrating the breaking down of the factorization approximation at "negative" and large (> 300 MeV/c) values of the missing momentum.

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arXiv2008

Lepton Scattering off Few-Nucleon Systems at Medium and High Energies

The interpretation of recent Jlab experimental data on the exclusive process A(e,e'p)B off few-nucleon systems are analyzed in terms of realistic nuclear wave functions and Glauber multiple scattering theory, both in its original form and within a generalized eikonal approximation. The relevance of the exclusive process 4He(e,e'p)^3H for possible investigations of QCD effects is illustrated.

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arXiv2007

Interpretation of recent JLab results on quasi elastic (e,e'p) reactions off few-nucleon systems

Recent JLab experimental data on quasi elastic 3He(e,e'p)2H(pn) and 4He(e,e'p)3H processes are interpreted using an approach based upon realistic wave functions and Glauber multiple scattering theory within a generalized eikonal approximation (GEA). The results of a non factorized calculation of the left-right asymmetry A_{TL} of the process 3He(e,e'p)2H, obtained using the full covariant form of the electromagnetic operator, are also presented.

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arXiv2007

Two-Fermion Bound States within the Bethe-Salpeter Approach

To solve the spinor-spinor Bethe-Salpeter equation in Euclidean space we propose a novel method related to the use of hyperspherical harmonics. We suggest an appropriate extension to form a new basis of spin-angular harmonics that is suitable for a representation of the vertex functions. We present a numerical algorithm to solve the Bethe-Salpeter equation and investigate in detail the properties of the solution for the scalar, pseudoscalar and vector meson exchange kernels including the stability of bound states. We also compare our results to the non relativistic ones and to the results given by light front dynamics.

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arXiv2007

On the dependence of the wave function of a bound nucleon on its momentum and the EMC effect

It is widely discussed in the literature that the wave function of the nucleon bound in a nucleus is modified due to the interaction with the surrounding medium. We argue that the modification should strongly depend on the momentum of the nucleon. We study such an effect in the case of the point-like configuration component of the wave function of a nucleon bound in a nucleus A, considering the case of arbitrary final state of the spectator A-1 system. We show that for non relativistic values of the nucleon momentum, the momentum dependence of the nucleon deformation appears to follow from rather general considerations and discuss the implications of our theoretical observation for two different phenomena: i) the search for medium induced modifications of the nucleon radius of a bound nucleon through the measurement of the electromagnetic nucleon form factors via the A(e,e'p)X process, and ii) the A-dependence of the EMC effect; in this latter case we also present a new method of estimating the fraction of the nucleus light-cone momentum carried by the photons and find that in a heavy nuclei protons loose about 2% of their momentum.

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arXiv2007

Final State Interaction Effects in Semi-inclusive Deep Inelastic processes A(e,e'p)X off the deuteron and complex nuclei

The effects of the final state interaction (FSI) in semi inclusive deep inelastic electron scattering processes $A(e,e'p)X$ off nuclei are investigated in details. Proton production is described within the spectator and the target fragmentation mechanisms whose relevance to the experimental study of the deep inelastic structure functions of bound nucleons and the non perturbative hadronization process is analyzed. Particular attention is paid to the deuteron target within kinematical conditions corresponding to the available and forthcoming experimental data at Jlab. We argue that there are kinematical regions where FSI effects are minimized, allowing for a reliable investigation of the DIS structure functions, and regions where the interaction of the quark-gluon debris with nucleons is maximized, which makes it possible to study hadronization mechanisms. Nuclear structure has been described by means of realistic wave functions and spectral functions and the final state interaction has been treated within an eikonal approximation approach which takes into account the rescattering of the quark-gluon debris with the residual nucleus and, in the case of complex nuclei, within an optical potential approach to account for the FSI of the struck proton.

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arXiv2007

A non factorized calculation of the process ^3He(e,e'p)^2H at medium energies

The exclusive process ^3He(e,e^\prime p)^2H has been analyzed using realistic few-body wave functions corresponding to the AV18 interaction and treating the final state interaction (FSI) within the Eikonal Approximation to describe the multiple rescattering of the struck nucleon with the nucleons of the spectator two-nucleon system. Calculations have been performed in momentum space so that the nucleon electromagnetic current could be left in the fully covariant form avoiding by this way non relativistic reductions and the factorization approximation. The results of calculations, which are compared with recent JLab experimental data, show that the left-right asymmetry exhibit a clear dependence upon the multiple scattering in the final state and demonstrate the breaking down of the factorization approximation at ϕ=0 i.e. for "negative" and large \geq 300MeV/c values of the missing momentum.

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arXiv2007

Di-electrons from $η$ meson Dalitz decay in proton-proton collisions

The reaction $ pp \to pp η\to pp γe^+ e^-$ is discussed within a covariant effective meson-nucleon theory. The model is adjusted to data of the subreaction $pp \to pp η$. Our focus is on di-electrons from Dalitz decays of $η$ mesons, $η\to γγ^* \toγe^+e^-$, and the role of the corresponding transition form factor $F_{ηγγ^*}$. Numerical results are presented for the intermediate energy kinematics of HADES experiments.

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arXiv2006

Peculiarities in the Structure of Two-Particle States within the Bethe-Salpeter Approach

The two-fermion bound system is an attractive subject of atomic and sub-atomic physics. Despite these systems are rather simple the study of two-particle bound states is challenging and still remains a source of progress in quantum theory. Here we present a new method of solving the Bethe Salpeter equations for the bound states of spinor particles by using the expansion of the vertex functions over the complete set of four-dimensional hyperspherical harmonics. Within this method the BS equation is treated in a ladder approximation for the cases of scalar, pseudoscalar and vector meson exchanges with corresponding form factors. This method is shown to be effective and stable.

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arXiv2006

$ω- πγ^*$ transition form factor in proton-proton collisions

Dalitz decays of $ω$ and $ρ$ mesons, $ω\to π^0γ^*\toπ^0 e^+e^-$ and $ρ^0\to π^0γ^*\toπ^0 e^+e^-$, produced in $pp$ collisions are calculated within a covariant effective meson-nucleon theory. We argue that the $ω$ transition form factor $F_{ω\to π^0γ^*}$ is experimentally accessible in a fairly model independent way in the reaction $pp \to pp π^0 e^+ e^-$ for invariant masses of the $π^0 e^+ e^-$ subsystem near the $ω$ pole. Numerical results are presented for the intermediate energy kinematics of envisaged HADES experiments.

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arXiv2006

Hadron Propagation in Medium: the Exclusive Process A(e,e'p)B in Few-Nucleon Systems

The mechanism of propagation of hadronic states in the medium is a key point for understanding particle-nucleus and nucleus-nucleus scattering at high energies. We have investigated the propagation of a baryon in the exclusive process A(e,e'p)B in few-nucleon systems using realistic nuclear wave functions and Glauber multiple scattering theory both in its original form and within a generalized eikonal approximation. New results for the processes 3He(e,e'p)2H and 4He(e,e'p)3H are compared with data recently obtained at the Thomas Jefferson Laboratory (JLAB).

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arXiv2005

Di-Electron Bremsstrahlung in Intermediate-Energy pn and Dp Collisions

Invariant mass spectra of di-electrons stemming from bremsstrahlung processes are calculated in a covariant diagrammatical approach for the exclusive reaction D p \to p_{\rm sp} n p e^+ e^- with detection of a forward spectator proton, p_{sp}. We employ an effective nucleon-meson theory for parameterizing the sub-reaction n p \to n p e^+ e^- and, within the Bethe-Salpeter formalism, derive a factorization of the cross section in the form {dσ_{D p \to p_{\rm sp} n p e^+ e^-}}/{dM}= {dσ_{n p \to n p e^+ e^-}}/{dM} \times kinematical factor related solely to the deuteron (M is the e^+ e^- invariant mass). The effective nucleon-meson interactions, including the exchange mesons π, σ, ωand ρas well as excitation and radiative decay of Δ(1232), have been adjusted to the process pp \to pp e^+ e^- at energies below the vector meson production threshold. At higher energies, contributions from ωand ρmeson excitations are analyzed in both, NN and Dp collisions. A relation to two-step models is discussed. Subthreshold di-electron production in Dp collisions at low spectator momenta is investigated as well. Calculations have been performed for kinematical conditions envisaged for forthcoming experiments at HADES.

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arXiv2005

On the Interpretation of the Processes 3He(e,e'p)2H and 3He(e,e'p)(pn) at High Missing Momenta

It is shown that the effects of the Final State Interaction (FSI) in the exclusive processes 3He(e,e'p)2H and 3He(e,e'p)(pn), can be successfully treated in terms of a Generalized Eikonal Approximation (GEA), based upon the direct calculation of the Feynman diagrams describing the rescattering of the struck nucleon. As a matter of fact, using realistic three-body wave functions corresponding to the AV18 interaction, the results of our parameter free calculation exhibits a very satisfactory agreement with recent experimental data from Jlab covering the region of missing momentum and energy with p_m < 1.0 GeV/c and E_m < 100 MeV. It is demonstrated that the missing momentum dependence of the experimental cross section of the process 3He(e,e'p)2H is mainly governed at p_m < 0.2 GeV/c by the Plane Wave Impulse Approximation (PWIA), at 0.2 < p_m < 0.6 GeV/c by the single rescattering FSI, and at 0.6 GeV/c < p_m by the double rescattering FSI.

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arXiv2005

Calculations of the Exclusive Processes 2H(e,e'p)n, 3He(e,e'p)2H and 3He(e,e'p)(pn) within a Generalized Glauber Approach

The exclusive processes 2H(e,e'p)n, 3He(e,e'p)2H and 3He(e,e'p)(pn), have been analyzed using realistic few-body wave functions and treating the final state interaction (FSI) within a Generalized Eikonal Approximation (GEA), based upon the direct calculation of the Feynman diagrams describing the rescattering of the struck nucleon with the nucleons of the A-1 system. The approach represents an improvement of the conventional Glauber approach (GA), in that it allows one to take into account the effects of the nuclear excitation of the $A-1$ system on the rescattering of the struck nucleon. Using realistic three-body wave functions corresponding to the AV18 interaction, the results of our parameter free calculations are compared with available experimental data. It is found that in some kinematical conditions FSI effects represent small corrections, whereas in other kinematics conditions they are very large and absolutely necessary to provide a satisfactory agreement between theoretical calculations and experimental data. It is shown that in the kinematics of the experimental data which have been considered, covering the region of missing momentum and energy with p_m < 0.6 GeV/c and E_m < 100 MeV in the perpendicular kinematics, the GA and GEA predictions differ only by less than 3-4 %.

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arXiv2004

Solving the inhomogeneous Bethe-Salpeter equation

We develop an advanced method of solving homogeneous and inhomogeneous Bethe-Salpeter equations by using the expansion over the complete set of 4-dimensional spherical harmonics. We solve Bethe-Salpeter equations for bound and scattering states of scalar and spinor particles for the case of one meson exchange kernels. Phase shifts calculated for the scalar model are in agreement with the previously published results. We discuss possible manifestations of separability for one meson exchange interaction kernels.

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arXiv2004

Combined Analysis of Near-Threshold Production of omega and phi Mesons in Nucleon-Nucleon Collisions within an Effective Meson-Nucleon Model

Vector meson ($V = ω, ϕ$) production in near-threshold elementary nucleon-nucleon collisions $pp\to ppV$, $pn\to pnV$ and $pn\to dV$ is studied within an effective meson-nucleon theory. It is shown that a set of effective parameters can be established to describe fairly well the available experimental data of angular distributions and the energy dependence of the total cross sections without explicit implementation of the Okubo-Zweig-Iisuka rule violation. Isospin effects are considered in detail and compared with experimental data whenever available.

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arXiv2003

Realistic Calculations of One- and Two-Hadron Emission Processes off Few- and Many-Body Nuclei

The exclusive electro-disintegration processes 2H(e,e'p)n, 3He(e,e'p)2H, 3He(e,e'p)pn, 3He(e,e'pp)n and 4He(e,e'p)3H have been calculated using realistic few-body wave functions and treating final state interaction (FSI) effects within a generalized eikonal approach. The semi-inclusive scattering A(e,e'p)X off complex nuclei has been analyzed using many-body wave functions for 16O and 40Ca, obtained within the framework of a linked cluster expansion and taking FSI into account by a Glauber-type approach. The effect of color transparency has also been included by considering the Finite Formation Time (FFT) that the hit hadron needs to reach its asymptotic physical state.

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