arXiv subjects

M. I. Levchuk

Publications and source records attributed to M. I. Levchuk.

17 recordsLinked to original sources

arXiv2026

Tensor analyzing power $T_{20}$ in the reaction $γ\vec{d}\to pn$ at photon energies 350-680 MeV

We present measurements of the tensor analyzing power $T_{20}$ in the reaction $γ{d}\to pn$ at photon energies $E_γ= 350$-$680$~MeV. The experiment was performed at the VEPP-3 storage ring using an internal tensor-polarized deuterium gas target and a tagged quasi-real photon beam. The data were obtained for proton emission angles $Θ_p = 70^\circ$-$102^\circ$. Comparison with modern meson-baryon calculations shows generally satisfactory agreement within the present uncertainties. A theoretical analysis of an extended data set, covering the energy range from threshold to 680~MeV and including both the new data and the previous results from 2007, is presented.

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arXiv2013

On extraction of the total photoabsorption cross section on the neutron from data on the deuteron

An improved procedure is suggested for finding the total photoabsorption cross section on the neutron from data on the deuteron at energies < 1.5 GeV. It includes unfolding of smearing effects caused by Fermi motion of nucleons in the deuteron and also takes into account non-additive contributions to the deuteron cross section due to final-state interactions of particles in single and double pion photoproduction. This procedure is applied to analysis of existing data.

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arXiv2011

Structure of the nucleon and spin-polarizabilities

Spin-polarizabilities are predicted by calculating the cross-section difference $σ_{3/2}-σ_{1/2}$ from available data for the resonance couplings $A_{3/2}$ and $A_{1/2}$ and CGLN amplitudes. The forward spin-polarizabilities are predicted to be $γ^{(p)}_0=-0.58\pm 0.20$ and $γ^{(n)}_0=+0.38\pm 0.22$ in units of $10^{-4}$fm$^4$ where the different signs are found to be due to the isospin dependencies of the $E_{0+}$ and the $(M,E)^{(1/2)}_{1+}$ amplitudes. The backward spin-polarizabilities are predicted to be $γ^{(p)}_π=-36.6$ and $γ^{(n)}_π=+58.3$, to be compared with the experimental values $γ^{(p)}=-36.4\pm 1.5$ and $γ^{(n)}_π=+58.6\pm 4.0$. Electric $γ_E$ and magnetic $γ_M$ spin-polarizabilities are introduced and discussed in terms of the $E1$ and $M1/E2$ components of the photo-absorption cross section of the nucleon.

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arXiv2010

Helicity-dependent reaction \vec γ\vec d\to πNN and its contribution to the GDH sum rule for the deuteron

Helicity-dependent incoherent pion photoproduction in the reaction \vec γ\vec d\to πNN is studied in the framework of the diagrammatic approach. Contributions to the reaction amplitude from diagrams corresponding to impulse approximation as well as NN and πN interactions in the final state have been evaluated. The elementary γN\to πN operator is taken from the MAID and SAID models. A detailed comparison of the predictions with recent experimental data by the GDH and A2 collaborations at energies below 500 MeV is presented. Reasonable agreement with the data on the yields and cross sections for polarized beam and polarized target has been achieved in all channels. The unpolarized data of the GDH and A2 collaborations have also been analyzed within the approach. A strong overestimation for the neutral channel has been found. At the same time, the model provides a quite satisfactory description of the unpolarized data for the charged channels. The sensitivity of the obtained results to the choice of the elementary γN\to πN operator is discussed in detail. The contribution of the γd\to πNN reaction to the GDH sum rule for the deuteron up to a photon energy of 1.65 GeV has been evaluated with the result of 235\pm 25 \mub.

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arXiv2006

Incoherent pion photoproduction on the deuteron in the first resonance region

Incoherent pion photoproduction on the deuteron is studied in the first resonance region. The unpolarized cross section, the beam asymmetry, and the vector and tensor target asymmetries are calculated in the framework of a diagrammatic approach. Pole diagrams and one-loop diagrams with $NN$ scattering in the final state are taken into account. An elementary operator for pion photoproduction on the nucleon is taken in various on-shell forms and calculated using the SAID and MAID multipole analyses. Model dependence of the obtained results is discussed in some detail. A comparison with predictions of other works is given. Although a reasonable description of many available experimental data on the unpolarized total and differential cross sections and photon asymmetry has been achieved, in some cases a significant disagreement between the theory and experiment has been found. Invoking known information on the reactions $γd\toπ^0 d$ and $γd\to np$ we predict the total photoabsorption cross section for deuterium. We find that our values strongly overestimate experimental data in the vicinity of the $Δ$ peak.

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arXiv2005

Structure of the $σ$-meson and diamagnetism of the nucleon

The structure of the $σ$ meson and the diamagnetism of the nucleon are shown to be topics which are closely related to each other. Arguments are found that the $σ$ meson couples to two photons via its non-strange $q\bar{q}$ structure component. This ansatz leads to a quantitative explanation of the $t$-channel component of the difference of electromagnetic polarizabilities, (α-β)^t$, containing the diamagnetism of the nucleon. The prediction is $(α-β)^t_{p,n}=(5α_e g_{πMM})/(6π^2 m^2_σf_π)=15.3$ in units of $10^{-4}{\rm fm}^3$ to be compared with the experimental value $(α-β)^t_p=15.1\pm 1.3$ for the proton and $(α-β)^t_n=14.8\pm 2.7$ for the neutron. The equivalent approach to exploit the $ππ$ structure component of the $σ$ meson via the BEFT sum rule leads to $(α-β)^t_{p,n}=14\pm 2$, what also is in agreement with the experimental results.

hep-ph↗

arXiv2003

Quasi-free $π^0$ Photoproduction from the Bound Nucleon

Differential cross-sections for quasi-free $π^0$ photoproduction from the proton and neutron bound in the deuteron have been measured for $E_γ= 200 - 400$ MeV at $θ^{\rm lab}_γ= 136.2^\circ$ usind the Glasgow photon tagger at MAMI, the Mainz 48 cm $\varnothing$ $\times$ 64 cm NaI(Tl) photon detector and the Göttingen SENECA recoil detector. For the proton measurements made with both liquid deuterium and liquid hydrogen targets allow direct comparison of "free" $π^0$ photoproduction cross-sections as extracted from the bound proton data with experimental free cross sections which are found to be in reasonable agreement below 320 MeV. At higher energies the "free" cross sections extracted from quasifree data are significantly smaller than the experimental free cross sections and theoretical predictions based on multipole analysis. For the first time, "free" neutron cross sections have been extracted in the $Δ$-region. They are also in agreement with the predictions from multipole analysis up to 320 MeV and significantly smaller at higher photon energies.

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arXiv2003

Compton Scattering from the Deuteron and Extracted Neutron Polarizabilities

Differential cross sections for Compton scattering from the deuteron were measured at MAX-lab for incident photon energies of 55 MeV and 66 MeV at nominal laboratory angles of $45^\circ$, $125^\circ$, and $135^\circ$. Tagged photons were scattered from liquid deuterium and detected in three NaI spectrometers. By comparing the data with theoretical calculations in the framework of a one-boson-exchange potential model, the sum and difference of the isospin-averaged nucleon polarizabilities, $α_N + β_N = 17.4 \pm 3.7$ and $α_N - β_N = 6.4 \pm 2.4$ (in units of $10^{-4}$ fm$^3$), have been determined. By combining the latter with the global-averaged value for $α_p - β_p$ and using the predictions of the Baldin sum rule for the sum of the nucleon polarizabilities, we have obtained values for the neutron electric and magnetic polarizabilities of $α_n= 8.8 \pm 2.4$(total) $\pm 3.0$(model) and $β_n = 6.5 \mp 2.4$(total) $\mp 3.0$(model), respectively.

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arXiv2003

Quasi-free Compton Scattering and the Polarizabilities of the Neutron

Differential cross sections for quasi-free Compton scattering from the proton and neutron bound in the deuteron have been measured using the Glasgow/Mainz tagging spectrometer at the Mainz MAMI accelerator together with the Mainz 48 cm $\oslash$ $\times$ 64 cm NaI(Tl) photon detector and the Göttingen SENECA recoil detector. The data cover photon energies ranging from 200 MeV to 400 MeV at $θ^{LAB}_γ=136.2^\circ$. Liquid deuterium and hydrogen targets allowed direct comparison of free and quasi-free scattering from the proton. The neutron detection efficiency of the SENECA detector was measured via the reaction $p(γ,π^+ n)$. The "free" proton Compton scattering cross sections extracted from the bound proton data are in reasonable agreement with those for the free proton which gives confidence in the method to extract the differential cross section for free scattering from quasi-free data. Differential cross sections on the free neutron have been extracted and the difference of the electromagnetic polarizabilities of the neutron have been obtained to be $α-β= 9.8\pm 3.6(stat){}^{2.1}_1.1(syst)\pm 2.2(model)$ in units $10^{-4}fm^3$. In combination with the polarizability sum $α+β=15.2\pm 0.5$ deduced from photoabsorption data, the neutron electric and magnetic polarizabilities, $α_n=12.5\pm 1.8(stat){}^{+1.1}_{-0.6}\pm 1.1(model)$ and $β_n=2.7\mp 1.8(stat){}^{+0.6}_{-1.1}(syst)\mp 1.1(model)$ are obtained. The backward spin polarizability of the neutron was determined to be $γ^{(n)}_π=(58.6\pm 4.0)\times 10^{-4}fm^4$.

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arXiv2002

Neutron polarizabilities investigated by quasi-free Compton scattering from the deuteron

Measuring Compton scattered photons and recoil neutrons in coincidence, quasi-free Compton scattering by the neutron has been investigated at MAMI (Mainz) at $theta^{lab}_γ=136^o$ in an energy range from 200 to 400 MeV. From the data a polarizability difference of $α_n - β_n = 9.8 \pm 3.6(stat)^{+2.1}_{-1.1}(syst)\pm 2.2(model)$ in units of $10^{-4}fm^3$ has been determined. In combination with the polarizability sum $α_n+β_n= 15.2\pm 0.5$ deduced from photo absorption data, the neutron electric and magnetic polarizabilities, $α_n=12.5\pm 1.8(stat)^{+1.1}_{-0.6}(syst)\pm 1.1(model)$ and $β_n = 2.7\mp 1.8(stat)^{+0.6}_{-1.1}(syst)\mp 1.1(model)$, are obtained.

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arXiv2001

Backward spin polarizability $γ_π$ of the proton

Using the Mainz $48 cm Ø\times 64 cm$ NaI(Tl) detector and the segmented Göttingen recoil detector SENECA in coincidence, Compton scattering by the proton at $θ^{lab}_γ= 136^\circ$ has been measured at MAMI (Mainz) in the energy range from 200 to 470 MeV. The new data confirm the previous observation that there is a systematic discrepancy between MAMI and LEGS (Brookhaven) data leading to different spin polarizabilities $γ_π= - 38.7 \pm 1.8$ and $-27.2 \pm 3.1$ $(\times 10^{-4}fm^4)$, respectively.

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arXiv2000

The inclusive reaction d(γ,π)NN in the first resonance region

Inclusive single pion photoproduction on the deuteron is studied in the first resonance region. The calculation is based on the use of the diagrammatic approach. Pole diagrams and one-loop diagrams with NN rescattering in the final state are taken into account. The elementary operator for pion photoproduction from the nucleon is taken in on-shell form and calculated using the SAID and MAID multipole analyses. Our predictions for total and differential cross section show good agreement with the available experimental data. Invoking some information on the reactions $gamma d\toπ^0 d and $γd\to np$ we predict the total photoabsorption cross section for deuterium. We find that our results overestimate the experimental data in the center of the Δ-peak (\sim 320 MeV) by about 10%.

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arXiv2000

Deuteron Compton scattering and electromagnetic polarizabilities of the nucleon

Differential cross section of deuteron Compton scattering has been calculated using the Bonn NN-potential, a consistent set of meson-exchange currents and seagulls, and lowest- and higher-order electromagnetic polarizabilities of the nucleon. Estimates of the polarizabilities of the neutron are obtained from recent experimental data.

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arXiv2000

Deuteron Compton scattering below pion photoproduction threshold

Deuteron Compton scattering below pion photoproduction threshold is considered in the framework of the nonrelativistic diagrammatic approach with the Bonn OBE potential. A complete gauge-invariant set of diagrams is taken into account which includes resonance diagrams without and with NN-rescattering and diagrams with one- and two-body seagulls. The seagull operators are analyzed in detail, and their relations with free- and bound-nucleon polarizabilities is discussed. It is found that both dipole and higher-order polarizabilities of the nucleon are needed for a quantitative description of recent experimental data. An estimate of the isospin-averaged dipole electromagnetic polarizabilities of the nucleon and the polarizabilities of the neutron is obtained from the data.

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arXiv2000

The reaction $^2H(γ,π^0)np$ in the threshold region

Neutral pion photoproduction on the deuteron in the inelastic channel is studied in the threshold region from 142 to 160 MeV. The calculation is based on the use of the diagrammatic approach. Contributions from the pole diagrams, one-loop diagrams both with $n$-$p$ and $π$-$N$ rescattering as well as two-loop diagrams with simultaneous inclusion of these rescattering mechanisms are taken into account. We have found a reasonable agreement with a very simple calculation by J.C. Bergstrom et al. [Phys. Rev. C 57 (1998) 3203]. It is shown that the `effective' electric dipole deuteron amplitude $E_d$ is negative in agreement with a prediction of ChPT. We conclude that a deviation of about 20% from a ChPT prediction for $E_d$ discovered in an experiment on coherent $π^0$ photoproduction off the deuteron cannot be attributed to inadequate estimates of inelastic channel contributions. We suggest that $π$-$N$ rescattering is responsible for the deviation of the free-nucleon $p_1$ threshold amplitude from the value measured in that experiment

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arXiv1999

On the reaction $ep \to ep γ$

We have studied the reaction $ep \to ep γ$ in the kinematics corresponding to electron scattering at small angles and photon scattering at large angles, where proton bremsstrahlung dominates. The analysis is based on the direct evaluation method of the matrix elements in the so-called diagonal spin basis. The results of numerical calculations for electron beam energy $E_{e}=200 MeV$ in the above kinematics show that the relative contribution of the Bethe-Heitler and interference terms to the reaction cross section is less than 10 %, and the cross section for the reaction $ep \to ep γ$ is quite sensitive to the proton polarizability. Owing to the factorization of the squared electric and magnetic form factors of the proton, a compact expression has been obtained for the differential cross section of the Bethe-Heitler emission of a linearly polarized photon by an electron, taking into account the proton recoil and form factors. A covariant expression has been obtained for the lepton tensor in which contributions of states with transverse and longitudinal polarizations of the virtual photon are separated.

hep-ph↗

arXiv1998

Deuteron Compton scattering below pion photoproduction threshold

Deuteron Compton scattering below pion photoproduction threshold is considered in the framework of the non-relativistic diagrammatic approach with the Bonn OBE potential. The complete gauge-invariant set of diagrams is taken into account which includes resonance diagrams without and with rescattering and diagrams with one- and two-body seagulls. The obtained results are compared with predictions of other models and with experimental data. A possibility of determining isospin-averaged electromagnetic polarizabilities of the nucleon is discussed.

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