Searcharxiv⌕ Search

arXiv subjects

V. N. Pomerantsev

Publications and source records attributed to V. N. Pomerantsev.

35 records · Page 2Linked to original sources

Scattering Processes of Excited Exotic Atoms: Close-Coupling Approach

The scattering processes of exotic atoms in excited states from hydrogen such as elastic scattering, Stark transitions and Coulomb de-excitation are studied within a close coupling approach. The vacuum polarization and the strong interaction shifts of $ns$-states (in case of hadronic atoms) are taken into account. The differential and integral cross sections of the above processes are calculated to use them as the input in cascade calculations. The effect of closed channels on the scattering processes is investigated.

nucl-th↗

Atomic Cascade in Muonic and Hadronic Hydrogen Atoms

The atomic cascade in $μ^- p$ and $π^- p$ atoms has been studied with the improved version of the extended cascade model in which new quantum mechanical calculations of the differential and integral cross sections of the elastic scattering, Stark transitions and Coulomb de-excitation have been included for the principal quantum number values $n\le 8$ and the relative energies $E \ge 0.01$ eV. The $X$-ray yields and kinetic energy distributions are compared with the experimental data.

nucl-th↗

Scattering processes in antiprotonic hydrogen - hydrogen atom collisions

The elastic scattering, Stark transitions and Coulomb deexcitation of excited antiprotonic hydrogen atom in collisions with hydrogenic atom have been studied in the framework of the fully quantum-mechanical close-coupling method for the first time. The total cross sections $σ_{nl \to n'l'}(E)$ and averaged on the initial angular momentum $l$ cross sections $σ_{n\to n'}(E)$ have been calculated for the initial states of $(\bar{p}p)_{n}$ atoms with the principal quantum number $n=3 - 14 $ and at the relative energies $E=0.05 - 50$ eV. The energy shifts of the $ns$ states due to the strong interaction and relativistic effects are taken into account. Some of our results are compared with the semiclassical calculations.

nucl-th↗

Angular distributions of scattered excited muonic hydrogen atoms

Differential cross sections of the Coulomb deexcitation in the collisions of excited muonic hydrogen with the hydrogen atom have been studied for the first time. In the framework of the fully quantum-mechanical close-coupling approach both the differential cross sections for the $nl \to n'l'$ transitions and $l$-averaged differential cross sections have been calculated for exotic atom in the initial states with the principle quantum number $n=2 - 6$ at relative motion energies $E_{\rm {cm}}=0.01 - 15$ eV and at scattering angles $θ_{\rm {cm}}=0 - 180^{\circ}$. The vacuum polarization shifts of the $ns$-states are taken into account. The calculated in the same approach differential cross sections of the elastic and Stark scattering are also presented. The main features of the calculated differential cross sections are discussed and a strong anisotropy of cross sections for the Coulomb deexcitation is predicted.

nucl-th↗

Coulomb deexcitation of pionic hydrogen within close-coupling method

The Coulomb deexcitation of $(πp)$ atom in collisions with the hydrogen atom has been studied in the fully quantum mechanical close-coupling approach for the first time. The total Coulomb deexcitation cross-sections of $nl\to n'l'$ transitions and $l$-averaged cross-sections are calculated for $n=3 - 8$ and at the relative energies $E=0.01 - 100$ eV. The strong interaction and vacuum polarization shifts of $ns$-states are taken into account. It is shown that the $Δn > 1$ transitions are very important and make up a substantial fraction of the Coulomb deexcitation cross-section (up to $\sim 47%$).

nucl-th↗

Dibaryons as carriers of strong internucleon interactions and a basis for nuclear physics based on QCD

New concept of intermediate- and short-range nuclear force proposed by the authors a few years ago is discussed briefly. The general concept is based on an assumption on generation of the dressed dibaryon in intermediate state in $NN$ interaction. This new mechanism has been shown to lead not only to numerous new predictions in hadronic physics but also should be responsible for a large portion of nuclear binding energy and properties of nuclear wavefunctions at high momenta.

nucl-th↗

Non-reactive scattering of excited exotic hydrogen atoms

The Coulomb deexcitation of light exotic atoms in collisions with hydrogen atoms has been studied in the framework of the fully quantum-mechanical close-coupling method for the first time. The calculations of the $l$-averaged cross sections have been performed for $(μp)_n$ and $(μd)_n$ atoms in the states with the principal quantum number $n=3 ÷8$ and relative energies region $E=0.01 ÷100$ eV. The obtained results reveal the new $n$ and $E$ dependences of the Coulomb deexcitation cross sections. The large fraction (up to $\sim$ 36%) of the transition with $Δn > 1$ is also predicted.

nucl-th↗

Dibaryon model for nuclear force and the properties of the $3N$ system

The dibaryon model for $NN$ interaction, which implies the formation of an intermediate six-quark bag dressed by a $σ$-field, is applied to the $3N$ system, where it results in a new three-body force of scalar nature between the six-quark bag and a third nucleon. A new multicomponent formalism is developed to describe three-body systems with nonstatic pairwise interactions and non-nucleonic degrees of freedom. Precise variational calculations of $3N$ bound states are carried out in the dressed-bag model including the new scalar three-body force. The unified coupling constants and form factors for $2N$ and $3N$ force operators are used in the present approach, in a sharp contrast to conventional meson-exchange models. It is shown that this three-body force gives at least half the $3N$ total binding energy, while the weight of non-nucleonic components in the $^3$H and $^3$He wavefunctions can exceed 10%. The new force model provides a very good description of $3N$ bound states with a reasonable magnitude of the $σNN$ coupling constant. A new Coulomb $3N$ force between the third nucleon and dibaryon is found to be very important for a correct description of the Coulomb energy and r.m.s. charge radius in $^3$He. In view of the new results for Coulomb displacement energy obtained here for A=3 nuclei, an explanation for the long-term Nolen--Schiffer paradox in nuclear physics is suggested. The role of the charge-symmetry-breaking effects in the nuclear force is discussed.

nucl-th↗

The properties of the three-nucleon system with the dressed-bag model for nn interaction. I: New scalar three-body force

A multi-component formalism is developed to describe three-body systems with nonstatic pairwise interactions and non-nucleonic degrees of freedom. The dressed-bag model for $NN$ interaction based on the formation of an intermediate six-quark bag dressed by a $σ$-field is applied to the $3N$ system, where it results in a new three-body force between the six-quark bag and a third nucleon. Concise variational calculations of $3N$ bound states are carried out in the dressed-bag model including the new three-body force. It is shown that this three-body force gives at least half the $3N$ total binding energy, while the weight of non-nucleonic components in the $^3$H and $^3$He wavefunctions can exceed 10%. The new force model provides a very good description of $3N$ bound states with a reasonable magnitude of the $σNN$ coupling constant. The model can serve as a natural bridge between dynamical description of few-nucleon systems and the very successful Walecka approach to heavy nuclei and nuclear matter.

nucl-th↗

The properties of the three-nucleon system with the dressed-bag model for $NN$ interaction. II: Coulomb and CSB effects

Coulomb and charge-symmetry breaking effects in the $^3$He ground state within the dressed dibaryon model developed recently for $2N$ and $3N$ forces are examined in detail. Particular attention has been paid to the Coulomb displacement energy $ΔE_C=E_B(^3{\rm H})- E_B(^3{\rm He})$ and rms charge radii of $^3$H and $^3$He. A new scalar $3N$ force between the third nucleon a$ dibaryon is found to be very important for a correct description of the Coulomb energy and rms charge radius in $^3$He. In view of the new results for $ΔE_C$ obtained here, the role of the effects of charge symmetry breaking in the nuclear force is discussed.

nucl-th↗

To the nature of intermediate- and short-range nucleon-nucleon interaction

Instead of the Yukawa mechanism for intermediate- and short-range interaction some new approach based on formation of the symmetric six-quark bag in the state $|(0s)^6[6]_X,L=0>$ dressed due to strong coupling to $π$, $σ$ and $ρ$ fields are suggested. This new mechanism offers both a strong intermediate-range attraction which replaces the effective $σ$-exchange (or excitation of two isobars in the intermediate state) in traditional force models and also short-range repulsion. Simple illustrative model is developed which demonstrates clearly how well the suggested new mechanism can reproduce $NN$ data.

nucl-th↗

The new mechanism for intermediate- and short-range nucleon-nucleon interaction

Arguments against the traditional Yukawa-type approach to $NN$ intermediate- and short-range interaction due to scalar-isoscalar meson exchange are presented. Instead of the Yukawa mechanism for intermediate-range attraction some new approach based on formation of the symmetric six-quark bag in the state $|(0s)^6[6]_X,L=0>$ dressed due to strong coupling to $π$, $σ$ and $ρ$ fields are suggested. These new mechanism offers a strong intermediate-range attraction which replaces the effective $σ$-exchange (or excitation of two isobars in the intermediate state) in traditional force models. A similar mechanism with vector $ρ$-meson production in the intermediate six-quark state is expected to lead to a strong short-range spin-orbital nonlocal interaction in the $NN$ system, which may resolve the long-standing puzzle of the spin-orbit force in baryons and in two-baryon systems. Illustrative examples are developed which demonstrate clearly how well the suggested new model can reproduce $NN$ data. Strong interrelations have been shown to exist between the proposed microscopic model and the one-component Moscow $NN$ potential developed by the authors previously and also with some hybrid models and the one-term separable Tabakin potential. The new implications of the proposed model for nuclear physics are discussed.

nucl-th↗

An inversion procedure for coupled-channel scattering: determining the deuteron-nucleus tensor interaction

We present a practical $S$-matrix to potential inversion procedure for coupled-channel scattering. The inversion technique developed is applied to non-diagonal $S^J_{ll'}$ for spin one projectiles, yielding a tensor interaction $T_{\rm R}$, and is also applicable to spin-1/2 plus spin-1/2 scattering. The method is a generalization of the iterative-perturbative, IP, method. It is tested and evaluated and we investigate the degree of uniqueness of the potential, particularly for cases where there is insufficient information to define the potential uniquely. We examine the potentials which result when the $S$-matrix is generated from a $T_{\rm P}$ interaction. We also develop the generalisation, using established procedures, of IP $S$-matrix-to-potential inversion to direct observable-to-potential inversion. This `direct inversion' procedure is demonstrated to be an efficient method for finding a multi-component potential including a $T_{\rm R}$ interaction fitting multi-energy $σ$, ${\rm i}T_{11}$, $T_{20}$, $T_{21}$ and $T_{22}$ data for the scattering of spin-1 nuclei from spin-zero target. It is applicable to other channel spin 1 cases.

nucl-th↗

The complete version of Moscow NN potential

A complete version of the Moscow NN potential model is presented. The excellent description for all essential partial waves has been found in the energy range 0 -- 350 MeV. The one-channel version of the model includes the orthogonality condition to most symmetric six-quark states in all lowest partial waves and thus, from this point of view, the model generalizes the well known Saito's orthogonality condition model (OCM) for the baryon-baryon interaction case. The specific features of the presented model which distinguish it from many conventional force models are discussed in details. One of them is a specific tensor mixing between nodal and nodeless wavefunctions which results in very reasonable values of the OPE cut-off parameter Λ=0.78 GeV and the πNN-coupling constant value f^2=0.075 in nice agreement with modern trends. The model, in case of its confirmation in precise few-nucleon calculations, can lead to noticeable revisions for many nuclear properties given by conventional force models.

nucl-th↗

Spin 1 inversion: a Majorana tensor force for deuteron alpha scattering

We demonstrate, for the first time, successful S-matrix to potential inversion for spin one projectiles with non-diagonal $S^j_{ll'}$ yielding a $T_{\rm R}$ interaction. The method is a generalization of the iterative-perturbative, IP, method. We present a test case indicating the degree of uniqueness of the potential. The method is adapted, using established procedures, into direct observable to potential inversion, fitting $σ$, ${\rm i}T_{11}$, $T_{20}$, $T_{21}$ and $T_{22}$ for d + alpha scattering over a range of energies near 10 MeV. The $T_{\rm R}$ interaction which we find is very different from that proposed elsewhere, both real and imaginary parts being very different for odd and even parity channels.

nucl-th↗

Moscow-type NN-potentials and three-nucleon bound states

A detailed description of Moscow-type (M-type) potential models for the NN interaction is given. The microscopic foundation of these models, which appear as a consequence of the composite quark structure of nucleons, is discussed. M-type models are shown to arise naturally in a coupled channel approach when compound or bag-like six-quark states, strongly coupled to the NN channel, are eliminated from the complete multiquark wave function. The role of the deep-lying bound states that appear in these models is elucidated. By introducing additional conditions of orthogonality to these compound six-quark states, a continuous series of almost on-shell equivalent nonlocal interaction models, characterized by a strong reduction or full absence of a local repulsive core (M-type models), is generated. The predictions of these interaction models for 3N systems are analyzed in detail. It is shown that M-type models give, under certain conditions, a stronger binding of the 3N system than the original phase-equivalent model with nodeless wave functions. An analysis of the 3N system with the new versions of the Moscow NN potential describing also the higher even partial waves is presented. Large deviations from conventional NN force models are found for the momentum distribution in the high momentum region. In particular, the Coulomb displacement energy for nuclei ^3He - ^3H displays a promising agreement with experiment when the ^3H binding energy is extrapolated to the experimental value.

nucl-th↗

Improved $d$+$^4$He potentials by inversion, the tensor force and validity of the double folding model

Improved potential solutions are presented for the inverse scattering problem for $d$+$^4$He data. The input for the inversions includes both the data of recent phase shift analyses and phase shifts from RGM coupled-channel calculations based on the NN Minnesota force. The combined calculations provide a more reliable estimate of the odd-even splitting of the potentials than previously found, suggesting a rather moderate role for this splitting in deuteron-nucleus scattering generally. The approximate parity-independence of the deuteron optical potentials is shown to arise from the nontrivial interference between antisymmetrization and channel coupling to the deuteron breakup channels. A further comparison of the empirical potentials established here and the double folding potential derived from the M3Y effective NN force (with the appropriate normalisation factor) reveals strong similarities. This result supports the application of the double folding model, combined with a small Majorana component, to the description even of such a loosely bound projectile as the deuteron. In turn, support is given for the application of iterative-perturbative inversion in combination with the double folding model to study fine details of the nucleus-nucleus potential. A $d$-$^4$He tensor potential is also derived to reproduce correctly the negative $^6$Li quadrupole moment and the D-state asymptotic constant.

nucl-th↗