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Register a new userSpin observables in 71A MeV 6,8He-hydrogen scattering
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Predictions of cross sections and analyzing powers using g-folding optical potentials for the scattering of 71A MeV 6,8He ions from (polarized) hydrogen are compared with data. A g-folding model in which exchange amplitudes are evaluated explicitly was used with wave functions of 6,8He specified from a no-core shell model that used a complete (0+2+4)hw basis. The analyzing powers reveal some sensitivities to the details of the wave functions, especially in the case of halo nuclei.
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Various spin observables (analyzing powers and spin-correlation parameters) in $pd$ elastic scattering at $T_p = 800-1000$ MeV are analyzed within the framework of the refined Glauber model. The theoretical model uses as input spin-dependent $NN$ amplitudes obtained from the most recent partial-wave analysis and also takes into account the deuteron $D$ wave and charge-exchange effects. Predictions of the refined Glauber model are compared with the existing experimental data. Reasonable agreement between the theoretical calculations and experimental data at low momentum transfers $|t| lesssim 0.2$ (GeV/$c)^2$ is found for all observables considered. Moderate discrepancies found in this region are shown to be likely due to uncertainties in the input $NN$ amplitudes. Qualitative agreement at higher momentum transfers is also found for most observables except the tensor ones with mixed $x$ and $z$ polarization components. Possible reasons for observed deviations of the model calculations from the data at $|t| > 0.2$ (GeV/$c)^2$ are discussed.
A complete set of linearly independent observables in Compton scattering with arbitrarily polarised real photons off an arbitrarily polarised spin-1 target is introduced, for the case that the final-state polarisations are not measured. Adopted from the one widely used e.g. in deuteron photo-dissociation, it consists of 18 terms: the unpolarised cross section, the beam asymmetry, 4 target asymmetries and 12 asymmetries in which both beam and target are polarised. They are expressed by the helicity amplitudes and -- where available -- related to observables discussed by other authors. As application to deuteron Compton scattering, their dependence on the (isoscalar) scalar and spin dipole polarisabilities of the nucleon is explored in Chiral Effective Field Theory with dynamical Delta(1232) degrees of freedom at order $e^2delta^3$. Some asymmetries are sensitive to only one or two dipole polarisabilities, making them particularly attractive for experimental studies. At a photon energy of 100 MeV, a set of 5 observables is identified from which one may be able to extract the spin polarisabilities of the nucleon. These are experimentally realistic but challenging and mostly involve tensor-polarised deuterons. Relative to Compton scattering from a nucleon, sensitivity to the mixed spin polarisabilities $gamma_{E1M2}$ and $gamma_{M1E2}$ is increased because of interference with the D wave component of the deuteron and with its pion-exchange current. An interactive Mathematica 9.0 notebook with results for all observables at photon energies up to 120 MeV is available from [email protected]. Note May 2017/April 2018: This arXiv version presents the article including the corrections in the Errata Eur. Phys. J. A53 (2017) 113 and A54 (2018) 57 to ibid. A49 (2013) 100. This affects Eqs. (2.12) to (2.14), Figs. 4, 7 to 10, 12, 14 to 16, 18 to 20, 22 and 23, and the corresponding, related text.
We apply the cluster-folding (CF) model for $vec{p}+^{6}$He scattering at 200 MeV, where the potential between $vec{p}$ and $^{4}$He is fitted to data on $vec{p}+^{4}$He scattering at 200 MeV. For $vec{p}+^{6}$He scattering at 200 MeV, the CF model reproduces measured differential cross section with no free parameter, We then predict the analyzing power $A_y(q)$ with the CF model, where $q$ is the transfer momentum. Johnson, Al-Khalili and Tostevin construct a theory for one-neutron halo scattering, taking (1) the adiabatic approximation and (2) neglecting the interaction between a valence neutron and a target, and yield a simple relationship between the elastic scattering of a halo nucleus and of its core under certain conditions. We improve their theory with (3) the eikonal approximation in order to determine $A_y(q)$ for $^{6}$He from the data on $A_y(q)$ for $^{4}$He. The improved theory is accurate, when approximation (1)--(3) are good. Among the three approximations, approximation (2) is most essential. The CF model shows that approximation (2) is good in $0.9 < q < 2.4$ fm$^{-1}$. In the improved theory, the $A_y(q)$ for $^{6}$He is the same as that for $^{4}$He. In $0.9 < q < 2.4$ fm$^{-1}$, we then predict $A_y(q)$ for $vec{p}+^{6}$He scattering at 200 MeV from measured $A_y(q)$ for $vec{p}+^{4}$He scattering at 200 MeV. We thus predict $A_y(q)$ with the model-dependent and the model-independent prescription. The ratio of differential cross sections measured for $^{6}$He to that for $^{4}$He is related to the wave function of $^{6}$He. We then determine the radius between $^{4}$He and the center-of-mass of valence two neutrons in $^{6}$He. The radius is 5.77 fm.
Background: Theoretical calculations of the four-particle scattering above the four-cluster breakup threshold are technically very difficult due to nontrivial singularities or boundary conditions. Further complications arise when the long-range Coulomb force is present. Purpose: We aim at calculating proton-${}^3$He elastic scattering observables above three- and four-cluster breakup threshold. Methods: We employ Alt, Grassberger, and Sandhas (AGS) equations for the four-nucleon transition operators and solve them in the momentum-space framework using the complex-energy method whose accuracy and practical applicability is improved by a special integration method. Results: Using realistic nuclear interaction models we obtain fully converged results for the proton-${}^3$He elastic scattering. The differential cross section, proton and ${}^3$He analyzing powers, spin correlation and spin transfer coefficients are calculated at proton energies ranging from 7 to 35 MeV. Effective three- and four-nucleon forces are included via the explicit excitation of a nucleon to a $Delta$ isobar. Conclusions: Realistic proton-${}^3$He scattering calculations above the four-nucleon breakup threshold are feasible. There is quite good agreement between the theoretical predictions and experimental data for the proton-${}^3$He scattering in the considered energy regime. The most remarkable disagreements are the peak of the proton analyzing power at lower energies and the minimum of the differential cross section at higher energies. Inclusion of the $Delta$ isobar reduces the latter discrepancy.
Spin polarization observables of the deuteron photodisintegration at low energies are studied in a pionless effective field theory up to next-to-next-to-leading order (NNLO). The total and differential cross sections, induced neutron polarization $P_{y}$, and tensor analyzing powers $T_{20}$ and $T_{22}$ of the process are calculated at photon energies from the breakup threshold to 20~MeV. We find that the NNLO corrections in the cross sections and $P_{y}$ converge well whereas they turn out to be important contributions in $T_{20}$ and $T_{22}$. We discuss the discrepancy between theory and experiment in $P_{y}$ still persisting as well as an implication of our result to the first measurement of $T_{20}$ at low energies in the HIGS facility.
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