The influence of final state N N -and πN -rescattering in incoherent pion photoproduction on the deuteron has been investigated. For the elementary photoproduction 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. While N N -rescattering shows quite a significant effect, particularly strong for neutral pion production, πN -rescattering is almost negligible. Inclusion of such effects leads to an improved and quite satisfactory agreement with experiment.PACS numbers: 13.60. Le, 21.45.+v, 25.20.Lj

Spin observables for the three charge states of the pion for the pion photoproduction reaction on the deuteron, γd → πN N , 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 ℓ 20 and T ℓ 2±2 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 ∆-region, and that other asymmetries are not.

The contribution of incoherent single pion photoproduction to the spin response of the deuteron, i.e., the asymmetry of the total photoabsorption cross section with respect to parallel and antiparallel spins of photon and deuteron, is calculated over the region of the ∆-resonance with inclusion of final state N Nand πN -rescattering. Sizeable effects, mainly from N N -rescattering, are found leading to an appreciable reduction of the spin asymmetry. Furthermore, the contribution to the Gerasimov-Drell-Hearn integral is explicitly evaluated by integration up to a photon energy of 550 MeV. Final state interaction reduces the value of the integral to about half of the value obtained for the pure impulse approximation.

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 T 11 and tensor target asymmetries T 20 , T 21 , and T 22 for the reaction d(γ, π)N N with polarized photon beam and/or oriented deuteron target are predicted for forthcoming experiments.Recent work in view of continuing technical improvements, such as ELSA in Bonn, LEGS in Brookhaven, CEBAF in Newport News, or MAMI in Mainz, for preparing polarized beams and targets and for polarimeters for the polarization analysis of ejected particles, has motivated the examination of certain aspects of the polarization observables in pion production on the deuteron that are fundamental to the process. Quasifree π − photoproduction on the deuteron via the γd → π − pp reaction has been investigated within a diagrammatic approach including NN-and πN-rescattering effects [1]. In that work, the authors reported predictions for the squared moduli of amplitudes | T f i | 2 , analyzing powers connected to beam polarization T 22,00 , to target polarization T 00,20 , and to polarization of one of the final protons P 1 y . It has been shown, that final state interaction effects play a noticeable role in the behaviour of these observables. In our previous evaluation [2,3], the energy dependence of the three charge states of the pion for the γd → πNN reaction over the whole ∆(1232)-resonance region has been evaluated. We have presented results for differential and total cross sections as well as the spin asymmetry and the Gerasimov-Drell-Hearn (GDH) sum rule for the deuteron.Notwithstanding this continuing effort to study this process, the wealth of information contained in it has not yet been fully exploited. Since the t-matrix has 12 independent complex amplitudes and in order to determine completely the t-matrix, one has to measure 23 independent observables. Up to present times, only a few observables have been measured and studied in details, e.g.,

The role of the final-state N N -rescattering (N N -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 N N -FSI is quite important for the single-spin asymmetries Σ, T 20 , T 21 and T 22 and the double-spin asymmetry T ℓ 20 , whereas it is much less important for the vector target asymmetry T 11 and other beam-target double-polarization asymmetries. Furthermore, we found that the inclusion of the N N -FSI improves the description of the LEGS data for the linear photon asymmetry.

The influence of final-state N N -rescattering on the helicity structure of the γ d → 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 N N -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 γ d → π − pp to the spin asymmetry of the deuteron is explicitly evaluated over the region of the ∆(1232)resonance with inclusion of N N -rescattering. The effect of N N 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 ∆-region.

The helicity dependence of the γ d → π − pp, γ d → π + nn, and γ d → π 0 np reaction channels is studied for incident photon energies from threshold up to the (1232) resonance with inclusion of leading πNN effects. The doubly polarized total and differential cross sections for parallel and antiparallel helicity states are predicted. Then the contribution of various channels to the deuteron spin asymmetry and the double polarization E asymmetry is calculated. In addition, the contribution to the Gerasimov-Drell-Hearn (GDH) integral from separate channels is evaluated by explicit integration up to a photon lab energy of 350 MeV. Sizeable effects from final-state interactions, specially for π 0 production, are found. The sensitivity of the results to the elementary pion photoproduction operator is also investigated. Considerable dependence of the results on the elementary amplitude is found. We expect that these results may be useful to interpret the recent measurements from LEGS@BNL, A2, and GDH@MAMI Collaborations.

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