One-nucleon Exchange Research Articles

Study of deuteron-proton backward elastic scattering at intermediate energies

We study deuteron- proton elastic scattering in the deuteron energy range between 500 MeV and 2 GeV at the cms scattering angle \theta^*\ge 140^\circθ*≥140∘. The reaction is considered in the relativistic multiple scattering expansion framework. The four reaction mechanisms are included into consideration: one-nucleon exchange, single scattering, double scattering, and the term corresponding to the delta excitation in the intermediate state.The model is applied to describe the angular dependence of the differential cross section at the deuteron energies of between 880 and 1300 MeV. Also the energy dependence of the differential cross section and polarisation observables such as tensor analyzing power T_{20}T20 and polarization transfer from the deuteron to proton \varkappa𝜘 are considered at the scattering angle equal to 180^\circ∘. Contributions of the different reaction mechanisms into the reaction amplitude are demonstrated in comparison with the existing experimental data.

Delta excitation in dp-elastic scattering at intermediate energies

In this report the deuteron-proton elastic scattering reaction is studied in the range of the deuteron kinetic energy from 500 MeV to 1300 MeV. dp-elastic scattering is considered in the relativistic multiple scattering expansion framework since the Faddeev calculation technique is not applicable at these energies. We start from the AGS-equations and iterate them up to a second-order of the nucleon-nucleon interaction. The four contributions are included into consideration: one-nucleon exchange (ONE), single scattering, double scattering, and the term corresponding the delta excitation in the intermediate state. The calculations are performed for four deuteron energies: 500, 880, 1200, and 1300 MeV. The results are presented in comparison with the experimental data on the dp-elastic scattering cross section.

One-nucleon exchange and the effective local potential in nucleus-nucleus scattering

The influence of one-nucleon exchange on the local nucleus-nucleus potential is investigated using the resonating group method. Neutron scattering on 4He and 16O nuclei is examined in detail. The results are compared to microscopic calculations.

Toward describing one-nucleon exchange in nucleus-nucleus scattering

The effect of one-nucleon exchanges on the potential of nucleus-nucleus interaction is considered on the basis of the resonating-group method. Corrections to the folding-model potential are obtained in the semiclassical approximation. Neutron scattering on 4He nuclei is considered as a model example.

Differential cross-section of dp elastic scattering at intermediate energies

The deuteron-proton elastic scattering is studied in the multiple-scattering expansion formalism. The contributions of the one-nucleon exchange, single and double scattering are taken into account. The Love and Franey parameterization of the nucleon-nucleon t -matrix is used, that gives an opportunity to include the off-energy-shell effects into calculations. Differential cross-sections are considered at four energies, T d = 390 , 500, 880, 1200MeV. The obtained results are compared with the experimental data.

THE ANGULAR DISTRIBUTIONS OF THE VECTOR Ay AND TENSOR Ayy, Axx, Axz ANALYZING POWERS IN THE dd → 3Hp AND dd → 3Hen REACTIONS AT Ed = 200 AND 270 MeV

The data on the vector Ay and tensor Ayy, Axx, Axz analyzing powers for the [Formula: see text] and [Formula: see text] reactions at Ed = 200 and 270 MeV are presented. The data demonstrate large values of analyzing powers and their strong variation versus the scattering angle. The observed negative sign of the tensor analyzing powers for these reactions at small angles clearly demonstrate the sensitivity to the D/S ratio of the 3H and 3He wave functions, respectively. The calculations performed within one-nucleon exchange model with the use of the standard three-nucleon bound state wave functions fail to reproduce the data on the tensor analyzing powers.

Polarization phenomena in elastic backward p-D scattering

The elastic backward proton-deuteron scattering is analyzed including both relativistic effects in the deuteron and the reaction mechanism. It is shown that inclusion of the graphs corresponding to the emission, rescattering and absorption of the virtual pion by a deuteron nucleon in addition to the one-nucleon exchange graph allows for a rather satisfactory description of all the experimental data on the differential cross section, tensor analyzing power of the deuteron and transfer polarization in this reaction.

Measurement of the vector A y and tensor A yy , A xx , A xz analyzing powers for the dd → 3H p reaction at 200 MeV

The data on the vector A y and tensor A yy , A xx , A xz analyzing powers for the $$ \vec d $$ d → 3H p reaction have been obtained at the energy of the initial deuteron of 200MeV in the angular range of 0–95 degrees in the c.m.s. The calculations performed within one-nucleon exchange model with the use of the standard three-nucleon bound state wave functions fail to reproduce the data on the tensor analyzing powers.

Analyzing powers Ayy , Axx , Axz and Ay in the dd → 3Hen reaction at 270 MeV

The data on the tensor Ayy, Axx, Axz and vector Ay analyzing powers in the dd → ^3Hen obtained at T d = 270 MeV in the angular range 0° - 110° in the c.m. are presented. The observed negative sign of the tensor analyzing powers Ayy, Axx and Axz at small angles clearly demonstrate the sensitivity to the ratio of the D - and S -wave component of the 3He wave function. However, the one-nucleon exchange calculations by using the standard 3He wave functions have failed to reproduce the strong variation of the tensor analyzing powers as a function of the angle in the c.m.

Measurement of the Analyzing Power inp→d→(pp)nwith a Fast ForwardS01Proton Pair

A measurement of the analyzing power A(y) of the p-->d--> (p p) + n reaction was carried out at the ANKE spectrometer at COSY at beam energies of 0.5 and 0.8 GeV by detection of a fast forward proton pair of small excitation energy E(pp) < 3 MeV. The S-wave dominance in the fast diproton is experimentally demonstrated in this reaction. While at T(p) = 0.8 GeV the measured analyzing power almost vanishes, it rises to nearly unity at T(p) = 0.5 GeV for neutrons emitted at theta(c.m.)(n) = 167 degrees. The results are compared with a model taking into account one-nucleon exchange, single scattering, and Delta(1232) excitation in the intermediate state. The model describes fairly well the unpolarized cross section obtained earlier and the analyzing power at 0.8 GeV; it fails to reproduce A(y) at 0.5 GeV.

The reaction pd→(pp)n at high momentum transfer and short-range NN properties

A recent cross section measurement of the deuteron breakup reaction pd→(pp)(0°)+n(180°), in the GeV region in a kinematics similar to backward pd elastic scattering, strongly contradicts predictions of a pd→dp model based on the one-nucleon exchange, single pN scattering and Δ excitation mechanisms, and on the wave functions of the Reid soft core and Paris NN potentials. We show within the same model that for the CD Bonn NN potential there is qualitative agreement with the data. It is attributed to a reduction of the one-nucleon exchange at energies above 1 GeV and an increase of the Δ(1232)-isobar contribution, both related to the short-range properties of the wave functions generated by this potential.

Exchange contributions to nucleus-nucleus potentials deduced from RGM phase shifts using inversion

Abstract We have determined, for certain representative cases, the representation in terms of local potentials of the contribution to the nucleus-nucleus interaction of one-nucleon exchange, core exchange and intermediate exchange terms. We do this by applying S l -to- V ( r ) inversion, using the IP method, to phase shifts from RGM calculations of Fujiwara and Tang, and LeMere et al. For tα at 18 MeV we find a shape parity dependence which is identical in nature to that found in other cases recently. For 3 He+ α at 60 MeV, a strong parity shape dependence still occurs, but of slightly different form. For α + 16 O, the 4N exchange generates a small parity dependence of the same nature, but this seems to disappear in the full RGM calculation. In the last two cases, we show the characteristic forms of potentials due to the different exchange terms. These calculations indicate the scope of inversion as a means of extracting information from microscopic calculations concerning the nucleus-nucleus interaction.

Spin structure of the deuteron from the d

The polarization observables in the elastic scattering of polarized deuterons on a polarized hydrogen target, with measurement of the recoil proton polarization, are considered. The observables are calculated in the one-nucleon exchange approximation, for the special case of backward scattering ([theta][sub c.m.]=180[degree]). Several new relations between polarization observables of the reaction are derived within the framework of this approximation. These relations can be used for detailed study of the deuteron structure and/or deuteron interaction at intermediate energy.

Pion-nucleon scattering in the P 33 channel in the linear sigma model

A consistent study of the NN interaction requires the investigation of the Δ resonance, as the Δ can affect the properties of the effective light σ meson originating from correlated two-pion exchange and vice versa. We study how the Δ appears as an effective degree of freedom in the linear σ model. Since the field-theoretic scattering amplitudes respect certain analytic properties, it is appropriate to use partial-wave dispersion relations for πN scattering, which produce non-linear integral equations that are solved by the N/ D method. We choose an amplitude that guarantees the correct threshold behavior and that gives a P 33 resonance with a driving term from one-nucleon exchange. Then we investigate the effect of adding the one-sigma-exchange force. With either a very heavy or a light σ meson, we can find a P 33 resonance. For intermediate σ masses, we find a πN bound state. We confirm that the calculated resonance mass depends sensitively on the short-range πN attraction. Nevertheless, the existence of a P 33 resonance is compatible with the existence of an effective light σ meson in this model.

Elastic backwardpd-scattering in ?-resonance region

Contribution ofΔ-resonance mechanism to elastic backwardpd-scattering overT 0 =0.5–0.8 GeV range of incident energy is analyzed. As distinct from [1–3], the parameters ofNN⇆NΔ amplitudes in the phenomenology of one-mesonπ- andρ-exchange are determined frompp→pnπ + reaction immediately in the kinematic region where the processpd→dp occurs. It has been found as a result that in the vicinity of the region whereΔ-isobar is present on-mass-shell, the coherent sum of the amplitudes ofΔ-resonance mechanism, relativistic one-nucleon exchange and single scattering predicts thepd→dp cross-section to be twice smaller than the experimental one and does not describe the tensor polarization oft 20 deuteron. Possible causes of this discrepancy as well as the relation between the mechanisms ofpd→dp process and the data on reactions of quasi-elastic knock-out of fast deuterons by protons (p,pd) from light nuclei, are discussed.

Exchange contributions in alpha +9Be elastic scattering.

The relative importance of the various exchange terms in the single-channel resonating group method calculations of ..cap alpha..+/sup 9/Be elastic scattering has been investigated by calculating in each case the l = 0 norm kernel ranges, the l = 0 to 7 phase shifts, and the differential cross sections in the c.m. incident energies in the range 0--8 MeV. A central two-nucleon interaction commonly taken in resonating group method calculations has been used, and for /sup 9/Be a cluster model wave function has been taken. The results have been compared with one another and with the experimental data at 6.06 and 7.01 MeV. It is concluded that the resonating group method in the single-channel approximation can describe reasonably well the ..cap alpha..+/sup 9/Be elastic scattering at incident energies of about 6 MeV and below. The one-nucleon exchange terms between the alpha particle and /sup 9/Be are by far the most significant, followed by those involving the exchange of the whole alpha clusters.

Meson-exchange approach to the tensor analyzing power in elastic pd backward scattering.

Motivated by a recent experiment, the differential cross section and the tensor analyzing power ${T}_{20}$ for elastic pd backward scattering is calculated in a microscopic model, which includes both the conventional one-nucleon exchange mechanism and rescattering contributions from the \ensuremath{\Delta}(1236) resonance. If supplemented by multiple scattering corrections, the model qualitatively accounts for the large negative values of ${T}_{20}$ for deuteron energies up to 2.3 GeV; however, it fails to reproduce the dip structures observed experimentally. Possible extensions of the model are briefly discussed.

Virtual state of the three nucleon system

The existence of a virtual state of the three nucleon system is established on the basis of three different analyses. Values for its pole position and residue in the doublet, $s$-wave, $n\ensuremath{-}d$ elastic scattering amplitude, are obtained from a fit to the experimental data, from partial wave dispersion relations, and from an exact three-particle, separable potential calculation. The calculations indicate that these parameters are determined mainly by the one-nucleon exchange mechanism and the doublet scattering length ${a}_{2}$. For ${a}_{2}=0.65$ fm our best calculation gives an energy of 0.482 MeV below the elastic threshold, on the second Riemann sheet, and a residue parameter ${{C}_{\ensuremath{\nu}}}^{2}=0.0504$, where ${{C}_{\ensuremath{\nu}}}^{2}$ is defined in analogy to the triton asymptotic normalization parameter.NUCLEAR REACTIONS Three-nucleon virtual state; fits to data; dispersion relations; separable potential calculations.

Effect of tensor force and one-nucleon exchange in the quasielastic ( 6Li, 6He) reaction

The effect of the tensor force and one-nucleon exchange is studied by applying the antisymmetrized DWBA method to the 48Ca( 6 Li, 6He) 48 Sc(π f 7 2 ν f 7 2 −1) J reaction. The exchange effect increases the cross sections but does not change the angular shapes. In contrast to the tensor force with Gaussian shape, the TWOPEP tensor contribution is larger than that of the central force and dominates the reaction for large L-transfer.

Dispersion relations for elastic n-d scattering

Partial wave N D equations for elastic n- d scattering are solved for the S = 1 2 , 3 2 channels. Three-particle contributions to unitarity for the decoupled S = 3 2 channels are approximately incorporated by using final state interactions between pairs in three-particle intermediate states. The equations for pairs of coupled S = 1 2 channels cannot be solved by standard methods and single channel Frye-Warnock equations with known inelasticities are considered instead. Driving forces are derived from single and double nucleon exchange. The latter are important down to the elastic threshold due to the anomalously long range of the one-nucleon exchange force. Real and imaginary parts of l = 0, 1, 2 phase shifts, differential cross sections and the binding energy of the triton are computed and found to be in general agreement with experiment. Threshold behaviour of the S = 1 2 , l = 0 phase and the position of the triton pole are shown to be sensitive to small changes in the input. The influences of vertex corrections, the virtual two-nucleon state, the break-up inelasticity and off-shell behaviour entering in the continuum approximation have been investigated in detail. In conclusion the N D approach is compared with the standard Fadde'ev-Lovelace potential theory.