The paper presents the results of measurement of three tensor analyzing power components for the ... more The paper presents the results of measurement of three tensor analyzing power components for the incoherent π 0-meson photoproduction on a deuteron in the photon energy range of 250-500 MeV, the proton energy range of 15-200 MeV, and the neutron energy range of 15-150 MeV. The incoherent π 0-meson electroproduction on a deuteron was used as a source of quasireal photons for the incoherent π 0-meson photoproduction. The experiment was performed using an internal tensor-polarized gas deuterium target of the VEPP-3 electron storage ring by the proton-neutron coincidence method. The results of measurement of the tensor analyzing power components are compared with the results of statistical modeling performed in the framework of a theoretical model.
Tensor analyzing-power components $$T_{20}$$ T 20 , $$T_{21}$$ T 21 , and $$T_{22}$$ T 22 for the... more Tensor analyzing-power components $$T_{20}$$ T 20 , $$T_{21}$$ T 21 , and $$T_{22}$$ T 22 for the reaction $$\gamma d\rightarrow np\pi ^0$$ γ d → n p π 0 have been studied for the first time in the photon energy range from 280 to 500 MeV. The data are extracted from the experimental statistics accumulated at the VEPP-3 storage ring in 2002–2003. The measured asymmetries are compared with the results of statistical simulations performed with the $$\gamma d\rightarrow np\pi ^0$$ γ d → n p π 0 amplitude from a spectator model, taking into account corrections for the final-state interaction. The comparison demonstrates quite good agreement between the experimental results and the theory.
Near-threshold coherent photoproduction of π0-meson on the deuteron is investigated. Numerical re... more Near-threshold coherent photoproduction of π0-meson on the deuteron is investigated. Numerical results for the unpolarized differential and total cross sections, the linear photon Σ-asymmetry, the vector T11 and tensor T2M (M = 0, 1, 2) deuteron spin asymmetries, and the spin asymmetry $$\tilde{T}_{20}$$ of the total cross section are presented. The role of D-wave component of the deuteron wave function on these physical observables is studied. The calculations are based on the impulse approximation in which we use the realistic and high-precision Bonn NN potential (full model) for the deuteron wave function and the unitary isobar MAID-2007 model for the elementary γN → πN amplitude that describes well the threshold region. We have found that the D-wave component has a negligible effect on the unpolarized cross sections and the vector deuteron T11-asymmetry at photon lab-energies close to threshold. On the contrary, we have obtained a significant role of the D-wave part of the deuteron wave function on the Σ, T2M, and $$\tilde{T}_{20}$$ spin asymmetries. The results for the unpolarized differential cross section are compared to the experimental data from TAPS and a satisfactory agreement within the uncertainties has been obtained at forward pion angles. At backward pion angles, our results underestimate the experimental data and a disagreement has been found.
Tensor target spin asymmetries [Formula: see text] ([Formula: see text]=0,1,2) in the reaction [F... more Tensor target spin asymmetries [Formula: see text] ([Formula: see text]=0,1,2) in the reaction [Formula: see text] are studied for photon energies from [Formula: see text]-threshold up to 1.5[Formula: see text]GeV with inclusion of rescattering effects. It is shown that the influence of rescattering effects on the tensor target spin asymmetries is sizable in the energy region near [Formula: see text]-threshold. At higher energies, much smaller influence of rescattering effects is seen. The sensitivity of the obtained results to the elementary pion photoproduction operator is investigated and a considerable dependence is found, in particular at forward pion angles. In addition, a comparison with results of other theoretical models is also given. The extracted spin asymmetries are compared with available experimental data and a qualitative agreement is obtained. The predictions presented here may be useful to interpret the recent measurements from the VEPP-3 electron storage ring.
We discuss possible uncertainties in theoretical predictions for γd → π 0 d observables near thre... more We discuss possible uncertainties in theoretical predictions for γd → π 0 d observables near threshold due to the use of different elementary γN → πN amplitudes using an approach which is based on time-ordered perturbation theory. Results are presented for unpolarized cross sections and all possible spin asymmetries of differential and total cross sections. Our results indicate that the estimations of the uncertainty on the γd → π 0 d observables show important sensitivity to the modeling of the elementary γN → πN operator. A comparison to presently available experimental data is given. The results presented here are of particular interest for the evaluation of the systematic uncertainties caused by the use of different elementary operators in the analyses of γd → π 0 d measurements to extract information on the free neutron amplitude from deuteron data.
The photoproduction of π 0-mesons from the nucleon and deuteron has been studied for incidents of... more The photoproduction of π 0-mesons from the nucleon and deuteron has been studied for incidents of photon energies up to 1.5 GeV. By using the MAID-2007 model for the process on the nucleon, we predict results for the unpolarized and helicity-dependent total cross sections of the semi-exclusive reaction γd→π 0 X (X=np+d) with the inclusion of rescattering effects. We find that rescattering effects yield a substantially large contribution. The extracted results are compared with the available experimental data and a satisfactory agreement is obtained. In addition, the contribution of γd→π 0 X (X=np+d) to the finite GDH integral has been evaluated by explicit integration up to 1.5 GeV and a total value of 256.96 µb has been obtained. Convergence of the GDH integral has been reached. Abstrak Fotoproduksi Meson-π0 dari Nukleon dan Deuteron. Fotoproduksi meson-π 0 dari nukleon dan deuteron telah dipelajari untuk energi-energi foton datang hingga 1.5 GeV. Dengan menggunakan model MAID-2007 untuk proses produksi pada nukleon, kami meramalkan hasil-hasil perhitungan penampang lintang total tidak-terpolarisasi dan penampang lintang total bergantung-helisitas dari reaksi semi-eksklusif γd→π 0 X (X=np+d) dengan memasukkan efek rescattering. Hasil studi memperlihatkan bahwa efek rescattering memberikan kontribusi sangat besar. Perbandingan hasil-hasil ekstraksi dengan data eksperimen yang tersedia memperlihatkan kecocokan yang memuaskan. Sebagai tambahan, kontribusi dari proses γd→π 0 X (X=np+d) pada integral GDH berhingga telah dihitung dengan menggunakan integrasi eksplisit hingga 1.5 GeV dan nilai total sebesar 256.96 µb telah diperoleh. Konvergensi dari integral GDH telah tercapai.
We study the sensitivity of polarization observables in $$\gamma d\to\pi^{0}d$$ reaction near thr... more We study the sensitivity of polarization observables in $$\gamma d\to\pi^{0}d$$ reaction near threshold to the choice of elementary $$\gamma N\to\pi N$$ amplitude and $$NN$$ potential model adapted for the deuteron wave function (DWF). Numerical results for various beam, target, and beam–target polarization observables are presented and systematic uncertainties caused by the use of different elementary operators and DWFs are evaluated. The calculations are based on a $$\gamma d\to\pi^{0}d$$ approach in which realistic models for the elementary pion production amplitude and the DWF are used. We find considerable dependencies of the estimated results for all possible polarization observables on the elementary amplitude. The spin asymmetries $$\Sigma$$ , $$T_{21}^{c}$$ , $$T_{10}^{l}$$ , and $$T_{20}^{l}$$ show large sensitivities to the DWF. In contrast, the asymmetries $$T_{11}$$ , $$T_{2M}$$ ( $$M=0,1,2$$ ), $$T_{10}^{c}$$ , and $$E$$ as well as the helicity difference $$d(\sigma^{P}-\sigma^{A})/d\Omega$$ have slight dependence on the DWF only at photon energies very close to $$\pi$$ -threshold. The unpolarized differential cross section is also predicted and compared with the available experimental data, and a satisfactory agreement is obtained only at forward pion angles. We expect that the results presented here may be useful to interpret the recent measurements from Jefferson Lab, TAPS@ELSA, A2 and GDH@MAMI Collaborations.
The influence of final-state NN-rescattering on the beam asymmetry Σ for linearly polarized photo... more The influence of final-state NN-rescattering on the beam asymmetry Σ for linearly polarized photons in π^- photoproduction on the deuteron in the energy range from π-threshold through the Δ(1232)-resonance has been investigated. Numerical results for this spin observable are predicted and compared with recent experimental data from the LEGS Spin collaboration. Final-state NN-rescattering is found to be quite important and leads to a better agreement with existing experimental data. Furthermore, the differences with other theoretical models have been discussed.
Incoherent photoproduction of pions on the deuteron in the Delta(1232) resonance region is invest... more Incoherent photoproduction of pions on the deuteron in the Delta(1232) resonance region is investigated in order to study the influence of final state NN and PiN rescattering. For the elementary production operator an effective Lagrangian model is used which describes well the elementary reaction. The interactions in the final two-body subsystems are taken in separable form. We found that the influence of rescattering effects on total and differential cross sections is significant. Inclusion of such effects leads to an improved and quite satisfactory agreement with experiment. Since several experiments to measure the spin asymmetry of the total photoabsorption cross section, which determines the GDH sum rule, are now being performed or planned at different laboratories, the contribution of incoherent pion photoproduction to the spin asymmetry for the deuteron is evaluated with inclusion of NN and PiN rescattering contributions. The effect of final state rescattering on the spin asym...
The influence of final-state NN-rescattering on the helicity structure of the γ⃗d⃗→π^-pp reaction... more The influence of final-state NN-rescattering on the helicity structure of the γ⃗d⃗→π^-pp reaction in the energy range from π-threshold up to 550 MeV has been investigated. The differential polarized cross-section difference for the parallel and antiparallel helicity states is predicted and compared with recent experimental data. It is shown that the effect of NN-rescattering is much less important in the polarized differential cross-section difference than in the previously studied unpolarized differential cross section. Furthermore, the contribution of γ⃗d⃗→π^-pp to the spin asymmetry of the deuteron is explicitly evaluated over the region of the Δ(1232)-resonance with inclusion of NN-rescattering. The effect of NN final-state interaction is found to be much larger in the asymmetry than in the total cross section and leads to an appreciable reduction of the spin asymmetry in the Δ-region.
Spin observables for the three charge states of the pion for the pion photoproduction reaction on... more Spin observables for the three charge states of the pion for the pion photoproduction reaction on the deuteron, γ d→π NN, with polarized photon beam and/or oriented deuteron target are predicted. For the beam-target double-spin asymmetries, it is found that only the longitudinal asymmetries T_20^ℓ and T_2± 2^ℓ do not vanish, whereas all the circular and the other longitudinal asymmetries do vanish. The sensitivity of spin observables to the model deuteron wave function is investigated. It has been found that only T_21 and T_22 are sensitive to the model deuteron wave function, in particular in the case of π^0-production above the Δ-region, and that other asymmetries are not.
Polarization observables in incoherent pion photoproduction from the deuteron are investigated in... more Polarization observables in incoherent pion photoproduction from the deuteron are investigated in the energy region from π-threshold up to the Δ (1232)-resonance with inclusion of all leading πNN effects. Formal expressions for polarization observables are derived and described by various beam, target and beam-target asymmetries for polarized photons and/or polarized deuterons. For the elementary pion photoproduction operator on the free nucleon, a realistic effective Lagrangian approach is used which includes seven nucleon resonances, in addition to Born and vector-meson exchange terms. The interactions in the final two-body su bsystems are taken from separable representations of realistic potenti als. Results are given for the unpolarized cross sections, t he doubly polarized cross sections for parallel and antiparallel helicity stat es, the linear photon asymmetry, the double polarization E-asymmetry and, the vector and tensor deuteron asymmetries for the γd ! π − pp, γd ! π + nn, and γd ! π 0 np channels. The contributions to the spin asymmetry and the Gerasimov-Drell-Hearn (GDH) integral from separate channels are evaluated by explicit integration up to a photon lab-energy of 350 MeV. Effects of final-state interaction ar e investigated and their role in these observables are found to be significant, specially for π 0 production. The extracted results are compared with available experimental data and predictions of other works, and a satisfactory agreement is obtained. The sensitivity of the γd ! πNN results to the elementary γN ! πN operator is also investigated and a considerable dependence is found. This indicates that it can serve as a filter for different elementary operators. W e expect that the results presented here may be useful to interpret the rec ent measurements from the high-intensity and high duty-factor electron accelerators MAMI, ELSA, Jefferson Lab, LEGS, and MAX-Lab.
Polarization observables of the three charge states of the pion for the γd → πNN reaction with po... more Polarization observables of the three charge states of the pion for the γd → πNN reaction with polarized photon beam and/or oriented deuteron target are evaluated over the whole ∆(1232)-resonance region adopting a nonrelativistic model based on time-ordered perturbation theory. Results for the π-meson spectra, linear photon asymmetry, vector and tensor target asymmetries are presented. Particular attention is given, for the first time, to double polarization asymmetries for which we present results for T ℓ 20 and T ℓ 2±2. We found that all other double polarization asymmetries of photon and deuteron target are vanished. 1.
The role of the final-state NN-rescattering (NN-FSI) in the polarization observables of the inclu... more The role of the final-state NN-rescattering (NN-FSI) in the polarization observables of the inclusive reaction d(γ,π −)pp, involving polarization of the photon beam and/or the deuteron target, is investigated. Various single- and double-spin asymmetries are studied with respect to the influence of such interaction effect and numerical predictions are given for forthcoming experiments. It has been found that the effect of NN-FSI is quite important for the single-spin asymmetries Σ, T20, T21 and T22 and the double-spin asymmetry T ℓ 20, whereas it is much less important for the vector target asymmetry T11 and other beam-target double-polarization asymmetries. Furthermore, we found that the inclusion of the NN-FSI improves the description of the LEGS data for the linear photon asymmetry.
Incoherent photoproduction of pions on the deuteron in the first resonance region is investigated... more Incoherent photoproduction of pions on the deuteron in the first resonance region is investigated with special emphasis on single-spin asymmetries. For the elementary pion production operator an effective Lagrangian model which includes the standard pseudovector Born terms and a resonance contribution from the ∆(1232)-excitation is used. Single-spin asymmetries, both for charged and neutral pion photoproduction on the deuteron, are analyzed and calculated in the first resonance region. The linear photon asymmetry Σ, vector target asymmetry T11 and tensor target asymmetries T20, T21, and T22 for the reaction d(γ,π)NN with polarized photon beam and/or oriented deuteron target are predicted for forthcoming experiments.
A new value b = 0.0205±0.0017 fm 2 of the slope of the neutron form factor G En (q 2) at q 2 = 0 ... more A new value b = 0.0205±0.0017 fm 2 of the slope of the neutron form factor G En (q 2) at q 2 = 0 compatible with deuteron properties has been extracted by using a linear relation between b and A 2 S (1 + η 2) we found for a class of nonlocal potential models having the experimental values of both r D and Q. Another model dependent value b MHKZ = 0.0206 ± 0.0014 fm 2 , which is also compatible with deuteron properties, has been determined by applying "constrained" unitary transformations to the local MHKZ potential model. The sensitivity of a small changes in the experimental values used for r D and Q on the value obtained for b is also investigated.
The paper presents the results of measurement of three tensor analyzing power components for the ... more The paper presents the results of measurement of three tensor analyzing power components for the incoherent π 0-meson photoproduction on a deuteron in the photon energy range of 250-500 MeV, the proton energy range of 15-200 MeV, and the neutron energy range of 15-150 MeV. The incoherent π 0-meson electroproduction on a deuteron was used as a source of quasireal photons for the incoherent π 0-meson photoproduction. The experiment was performed using an internal tensor-polarized gas deuterium target of the VEPP-3 electron storage ring by the proton-neutron coincidence method. The results of measurement of the tensor analyzing power components are compared with the results of statistical modeling performed in the framework of a theoretical model.
Tensor analyzing-power components $$T_{20}$$ T 20 , $$T_{21}$$ T 21 , and $$T_{22}$$ T 22 for the... more Tensor analyzing-power components $$T_{20}$$ T 20 , $$T_{21}$$ T 21 , and $$T_{22}$$ T 22 for the reaction $$\gamma d\rightarrow np\pi ^0$$ γ d → n p π 0 have been studied for the first time in the photon energy range from 280 to 500 MeV. The data are extracted from the experimental statistics accumulated at the VEPP-3 storage ring in 2002–2003. The measured asymmetries are compared with the results of statistical simulations performed with the $$\gamma d\rightarrow np\pi ^0$$ γ d → n p π 0 amplitude from a spectator model, taking into account corrections for the final-state interaction. The comparison demonstrates quite good agreement between the experimental results and the theory.
Near-threshold coherent photoproduction of π0-meson on the deuteron is investigated. Numerical re... more Near-threshold coherent photoproduction of π0-meson on the deuteron is investigated. Numerical results for the unpolarized differential and total cross sections, the linear photon Σ-asymmetry, the vector T11 and tensor T2M (M = 0, 1, 2) deuteron spin asymmetries, and the spin asymmetry $$\tilde{T}_{20}$$ of the total cross section are presented. The role of D-wave component of the deuteron wave function on these physical observables is studied. The calculations are based on the impulse approximation in which we use the realistic and high-precision Bonn NN potential (full model) for the deuteron wave function and the unitary isobar MAID-2007 model for the elementary γN → πN amplitude that describes well the threshold region. We have found that the D-wave component has a negligible effect on the unpolarized cross sections and the vector deuteron T11-asymmetry at photon lab-energies close to threshold. On the contrary, we have obtained a significant role of the D-wave part of the deuteron wave function on the Σ, T2M, and $$\tilde{T}_{20}$$ spin asymmetries. The results for the unpolarized differential cross section are compared to the experimental data from TAPS and a satisfactory agreement within the uncertainties has been obtained at forward pion angles. At backward pion angles, our results underestimate the experimental data and a disagreement has been found.
Tensor target spin asymmetries [Formula: see text] ([Formula: see text]=0,1,2) in the reaction [F... more Tensor target spin asymmetries [Formula: see text] ([Formula: see text]=0,1,2) in the reaction [Formula: see text] are studied for photon energies from [Formula: see text]-threshold up to 1.5[Formula: see text]GeV with inclusion of rescattering effects. It is shown that the influence of rescattering effects on the tensor target spin asymmetries is sizable in the energy region near [Formula: see text]-threshold. At higher energies, much smaller influence of rescattering effects is seen. The sensitivity of the obtained results to the elementary pion photoproduction operator is investigated and a considerable dependence is found, in particular at forward pion angles. In addition, a comparison with results of other theoretical models is also given. The extracted spin asymmetries are compared with available experimental data and a qualitative agreement is obtained. The predictions presented here may be useful to interpret the recent measurements from the VEPP-3 electron storage ring.
We discuss possible uncertainties in theoretical predictions for γd → π 0 d observables near thre... more We discuss possible uncertainties in theoretical predictions for γd → π 0 d observables near threshold due to the use of different elementary γN → πN amplitudes using an approach which is based on time-ordered perturbation theory. Results are presented for unpolarized cross sections and all possible spin asymmetries of differential and total cross sections. Our results indicate that the estimations of the uncertainty on the γd → π 0 d observables show important sensitivity to the modeling of the elementary γN → πN operator. A comparison to presently available experimental data is given. The results presented here are of particular interest for the evaluation of the systematic uncertainties caused by the use of different elementary operators in the analyses of γd → π 0 d measurements to extract information on the free neutron amplitude from deuteron data.
The photoproduction of π 0-mesons from the nucleon and deuteron has been studied for incidents of... more The photoproduction of π 0-mesons from the nucleon and deuteron has been studied for incidents of photon energies up to 1.5 GeV. By using the MAID-2007 model for the process on the nucleon, we predict results for the unpolarized and helicity-dependent total cross sections of the semi-exclusive reaction γd→π 0 X (X=np+d) with the inclusion of rescattering effects. We find that rescattering effects yield a substantially large contribution. The extracted results are compared with the available experimental data and a satisfactory agreement is obtained. In addition, the contribution of γd→π 0 X (X=np+d) to the finite GDH integral has been evaluated by explicit integration up to 1.5 GeV and a total value of 256.96 µb has been obtained. Convergence of the GDH integral has been reached. Abstrak Fotoproduksi Meson-π0 dari Nukleon dan Deuteron. Fotoproduksi meson-π 0 dari nukleon dan deuteron telah dipelajari untuk energi-energi foton datang hingga 1.5 GeV. Dengan menggunakan model MAID-2007 untuk proses produksi pada nukleon, kami meramalkan hasil-hasil perhitungan penampang lintang total tidak-terpolarisasi dan penampang lintang total bergantung-helisitas dari reaksi semi-eksklusif γd→π 0 X (X=np+d) dengan memasukkan efek rescattering. Hasil studi memperlihatkan bahwa efek rescattering memberikan kontribusi sangat besar. Perbandingan hasil-hasil ekstraksi dengan data eksperimen yang tersedia memperlihatkan kecocokan yang memuaskan. Sebagai tambahan, kontribusi dari proses γd→π 0 X (X=np+d) pada integral GDH berhingga telah dihitung dengan menggunakan integrasi eksplisit hingga 1.5 GeV dan nilai total sebesar 256.96 µb telah diperoleh. Konvergensi dari integral GDH telah tercapai.
We study the sensitivity of polarization observables in $$\gamma d\to\pi^{0}d$$ reaction near thr... more We study the sensitivity of polarization observables in $$\gamma d\to\pi^{0}d$$ reaction near threshold to the choice of elementary $$\gamma N\to\pi N$$ amplitude and $$NN$$ potential model adapted for the deuteron wave function (DWF). Numerical results for various beam, target, and beam–target polarization observables are presented and systematic uncertainties caused by the use of different elementary operators and DWFs are evaluated. The calculations are based on a $$\gamma d\to\pi^{0}d$$ approach in which realistic models for the elementary pion production amplitude and the DWF are used. We find considerable dependencies of the estimated results for all possible polarization observables on the elementary amplitude. The spin asymmetries $$\Sigma$$ , $$T_{21}^{c}$$ , $$T_{10}^{l}$$ , and $$T_{20}^{l}$$ show large sensitivities to the DWF. In contrast, the asymmetries $$T_{11}$$ , $$T_{2M}$$ ( $$M=0,1,2$$ ), $$T_{10}^{c}$$ , and $$E$$ as well as the helicity difference $$d(\sigma^{P}-\sigma^{A})/d\Omega$$ have slight dependence on the DWF only at photon energies very close to $$\pi$$ -threshold. The unpolarized differential cross section is also predicted and compared with the available experimental data, and a satisfactory agreement is obtained only at forward pion angles. We expect that the results presented here may be useful to interpret the recent measurements from Jefferson Lab, TAPS@ELSA, A2 and GDH@MAMI Collaborations.
The influence of final-state NN-rescattering on the beam asymmetry Σ for linearly polarized photo... more The influence of final-state NN-rescattering on the beam asymmetry Σ for linearly polarized photons in π^- photoproduction on the deuteron in the energy range from π-threshold through the Δ(1232)-resonance has been investigated. Numerical results for this spin observable are predicted and compared with recent experimental data from the LEGS Spin collaboration. Final-state NN-rescattering is found to be quite important and leads to a better agreement with existing experimental data. Furthermore, the differences with other theoretical models have been discussed.
Incoherent photoproduction of pions on the deuteron in the Delta(1232) resonance region is invest... more Incoherent photoproduction of pions on the deuteron in the Delta(1232) resonance region is investigated in order to study the influence of final state NN and PiN rescattering. For the elementary production operator an effective Lagrangian model is used which describes well the elementary reaction. The interactions in the final two-body subsystems are taken in separable form. We found that the influence of rescattering effects on total and differential cross sections is significant. Inclusion of such effects leads to an improved and quite satisfactory agreement with experiment. Since several experiments to measure the spin asymmetry of the total photoabsorption cross section, which determines the GDH sum rule, are now being performed or planned at different laboratories, the contribution of incoherent pion photoproduction to the spin asymmetry for the deuteron is evaluated with inclusion of NN and PiN rescattering contributions. The effect of final state rescattering on the spin asym...
The influence of final-state NN-rescattering on the helicity structure of the γ⃗d⃗→π^-pp reaction... more The influence of final-state NN-rescattering on the helicity structure of the γ⃗d⃗→π^-pp reaction in the energy range from π-threshold up to 550 MeV has been investigated. The differential polarized cross-section difference for the parallel and antiparallel helicity states is predicted and compared with recent experimental data. It is shown that the effect of NN-rescattering is much less important in the polarized differential cross-section difference than in the previously studied unpolarized differential cross section. Furthermore, the contribution of γ⃗d⃗→π^-pp to the spin asymmetry of the deuteron is explicitly evaluated over the region of the Δ(1232)-resonance with inclusion of NN-rescattering. The effect of NN final-state interaction is found to be much larger in the asymmetry than in the total cross section and leads to an appreciable reduction of the spin asymmetry in the Δ-region.
Spin observables for the three charge states of the pion for the pion photoproduction reaction on... more Spin observables for the three charge states of the pion for the pion photoproduction reaction on the deuteron, γ d→π NN, with polarized photon beam and/or oriented deuteron target are predicted. For the beam-target double-spin asymmetries, it is found that only the longitudinal asymmetries T_20^ℓ and T_2± 2^ℓ do not vanish, whereas all the circular and the other longitudinal asymmetries do vanish. The sensitivity of spin observables to the model deuteron wave function is investigated. It has been found that only T_21 and T_22 are sensitive to the model deuteron wave function, in particular in the case of π^0-production above the Δ-region, and that other asymmetries are not.
Polarization observables in incoherent pion photoproduction from the deuteron are investigated in... more Polarization observables in incoherent pion photoproduction from the deuteron are investigated in the energy region from π-threshold up to the Δ (1232)-resonance with inclusion of all leading πNN effects. Formal expressions for polarization observables are derived and described by various beam, target and beam-target asymmetries for polarized photons and/or polarized deuterons. For the elementary pion photoproduction operator on the free nucleon, a realistic effective Lagrangian approach is used which includes seven nucleon resonances, in addition to Born and vector-meson exchange terms. The interactions in the final two-body su bsystems are taken from separable representations of realistic potenti als. Results are given for the unpolarized cross sections, t he doubly polarized cross sections for parallel and antiparallel helicity stat es, the linear photon asymmetry, the double polarization E-asymmetry and, the vector and tensor deuteron asymmetries for the γd ! π − pp, γd ! π + nn, and γd ! π 0 np channels. The contributions to the spin asymmetry and the Gerasimov-Drell-Hearn (GDH) integral from separate channels are evaluated by explicit integration up to a photon lab-energy of 350 MeV. Effects of final-state interaction ar e investigated and their role in these observables are found to be significant, specially for π 0 production. The extracted results are compared with available experimental data and predictions of other works, and a satisfactory agreement is obtained. The sensitivity of the γd ! πNN results to the elementary γN ! πN operator is also investigated and a considerable dependence is found. This indicates that it can serve as a filter for different elementary operators. W e expect that the results presented here may be useful to interpret the rec ent measurements from the high-intensity and high duty-factor electron accelerators MAMI, ELSA, Jefferson Lab, LEGS, and MAX-Lab.
Polarization observables of the three charge states of the pion for the γd → πNN reaction with po... more Polarization observables of the three charge states of the pion for the γd → πNN reaction with polarized photon beam and/or oriented deuteron target are evaluated over the whole ∆(1232)-resonance region adopting a nonrelativistic model based on time-ordered perturbation theory. Results for the π-meson spectra, linear photon asymmetry, vector and tensor target asymmetries are presented. Particular attention is given, for the first time, to double polarization asymmetries for which we present results for T ℓ 20 and T ℓ 2±2. We found that all other double polarization asymmetries of photon and deuteron target are vanished. 1.
The role of the final-state NN-rescattering (NN-FSI) in the polarization observables of the inclu... more The role of the final-state NN-rescattering (NN-FSI) in the polarization observables of the inclusive reaction d(γ,π −)pp, involving polarization of the photon beam and/or the deuteron target, is investigated. Various single- and double-spin asymmetries are studied with respect to the influence of such interaction effect and numerical predictions are given for forthcoming experiments. It has been found that the effect of NN-FSI is quite important for the single-spin asymmetries Σ, T20, T21 and T22 and the double-spin asymmetry T ℓ 20, whereas it is much less important for the vector target asymmetry T11 and other beam-target double-polarization asymmetries. Furthermore, we found that the inclusion of the NN-FSI improves the description of the LEGS data for the linear photon asymmetry.
Incoherent photoproduction of pions on the deuteron in the first resonance region is investigated... more Incoherent photoproduction of pions on the deuteron in the first resonance region is investigated with special emphasis on single-spin asymmetries. For the elementary pion production operator an effective Lagrangian model which includes the standard pseudovector Born terms and a resonance contribution from the ∆(1232)-excitation is used. Single-spin asymmetries, both for charged and neutral pion photoproduction on the deuteron, are analyzed and calculated in the first resonance region. The linear photon asymmetry Σ, vector target asymmetry T11 and tensor target asymmetries T20, T21, and T22 for the reaction d(γ,π)NN with polarized photon beam and/or oriented deuteron target are predicted for forthcoming experiments.
A new value b = 0.0205±0.0017 fm 2 of the slope of the neutron form factor G En (q 2) at q 2 = 0 ... more A new value b = 0.0205±0.0017 fm 2 of the slope of the neutron form factor G En (q 2) at q 2 = 0 compatible with deuteron properties has been extracted by using a linear relation between b and A 2 S (1 + η 2) we found for a class of nonlocal potential models having the experimental values of both r D and Q. Another model dependent value b MHKZ = 0.0206 ± 0.0014 fm 2 , which is also compatible with deuteron properties, has been determined by applying "constrained" unitary transformations to the local MHKZ potential model. The sensitivity of a small changes in the experimental values used for r D and Q on the value obtained for b is also investigated.
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Papers by Eed Darwish