Search

High precision vector and tensor analyzing power data of the deuteron-proton elastic scattering at 130 MeV deuteron beam energy have been measured in a large range of angles. They are compared with theoretical predictions obtained in various approaches: with realistic potentials for pure NN interactions, with the inclusion of a three-nucleon force, and in the framework of chiral perturbation theory. All the theoretical calculations describe roughly the main features of the measured distributions, but none of them can reproduce all their details. This indicates the need for further development of the three-nucleon force models.

The differential cross sections and vector analyzing powers for nd elastic scattering at En=248 MeV were measured for 10°–180° in the center-of-mass (c.m.) system. To cover the wide angular range, the experiments were performed separately by using two different setups for forward and backward angles. The data are compared with theoretical results based on Faddeev calculations with realistic nucleon-nucleon (NN) forces such as AV18, CD Bonn, and Nijmegen I and II, and their combinations with the three-nucleon forces (3NFs), such as Tucson-Melbourne 99 (TM99), Urbana IX, and the coupled-channel potential with Delta-isobar excitation. Large discrepancies are found between the experimental cross sections and theory with only 2N forces for thetac.m.>90°. The inclusion of 3NFs brings the theoretical cross sections closer to the data but only partially explains this discrepancy. For the analyzing power, no significant improvement is found when 3NFs are included. Relativistic corrections are shown to be small for both the cross sections and the analyzing powers at this energy. For the cross sections, these effects are mostly seen in the very backward angles. Compared with the pd cross section data, quite significant differences are observed at all scattering angles that cannot be explained only by the Coulomb interaction, which is usually significant at small angles.

We have measured for the first time the cross section of the 2H(n,γ)3H reaction at an energy relevant to big-bang nucleosynthesis by employing a prompt discrete -ray detection method. The outgoing photons have been detected by means of anti-Compton NaI(Tl) spectrometers with a large signal-to-noise ratio. The resulting cross sections are 2.23±0.34,1.99±0.25, and 3.76±0.41µb at En=30.5,54.2, and 531 keV, respectively. At En=30.5 keV the cross section differs from the value reported previously by a factor of 2. Based on the present data the reaction rate has been obtained for temperatures in the range 107-1010 K. The astrophysical impact of the present result is discussed. The obtained cross sections are compared with a theoretical calculation based on the Faddeev approach, which includes meson exchange currents as well as a three-nucleon force.

The proton to proton polarization transfer coefficients K,K, and K, and the proton to deuteron polarization transfer coefficients K,K,K, K,K,K,K, and K were measured in d(p,p)d and d(p,d)p reactions, respectively, at E=22.7 MeV. The data were compared to predictions of modern nuclear forces obtained by solving the three-nucleon Faddeev equations in momentum space. Realistic (semi)phenomenological nucleon-nucleon potentials combined with model three-nucleon forces and modern chiral nuclear forces were used. The AV18, CD Bonn, and Nijm I and II nucleon-nucleon interactions were applied alone or combined with the Tucson-Melbourne 99 three-nucleon force, adjusted separately for each potential to reproduce the triton binding energy. For the AV18 potential, the Urbana IX three-nucleon force was also used. In addition, chiral NN potentials in the next-to-leading order and chiral two- and three-nucleon forces in the next-to-next-to-leading order were applied. Only when three-nucleon forces are included does a satisfactory description of all data result. For the chiral approach, the restriction to the forces in the next-to-leading order is insufficient. Only when going over to the next-to-next-to-leading order does one get a satisfactory description of the data, similar to the one obtained with the (semi)phenomenological forces.

A simultaneous measurement of the cross sections of the 3He(γ,p)D and 3He(γ,pp)n reactions has been performed for the first time using monoenergetic pulsed γ-rays at E=10.2 and 16.0 MeV. Charged fragments from the reactions were detected with an efficiency of 100% using a 4 time projection chamber containing 3He gas as an active target. The incident γ-ray flux was measured by a γ-ray detector. Both the track and energy loss signals of charged fragments were obtained in an off-line analysis and used to clearly identify the reaction channel. Thus, the (γ,p) and (γ,pp) cross sections have been determined with small uncertainty. A comparison of the new data to current theory based on the AV18+Urbana IX nuclear forces including π- and ρ-like meson exchange currents shows a severe discrepancy at 10.2 MeV, while at 16.0 MeV data and theory agree within about 12%. Three-nucleon force effects are small, but in general shift the theory in the correct direction.

The photon and 3He analyzing powers as well as spin correlation coefficients in the semiexclusive three-body photodisintegration of 3He are investigated for incoming photon laboratory energies E=12, 40 and 120 MeV. The nuclear states are obtained by solving three-body Faddeev equations with the AV18 nucleon-nucleon potential alone or supplemented with the UrbanaIX three-nucleon force. Explicit pi- and rho-meson exchange currents are taken into account, but we also compare to other models of the electromagnetic current. In some kinematical conditions we have found strong effects of the three-nucleon force for the 3He analyzing power and spin correlation coefficients, as well strong sensitivities to the choice of the currents. This set of predictions should be a useful guidance for the planning of measurements. In addition, we compare our results for two-body 3He breakup induced by polarized photons with a few existing data., Comment: 23 pages, 16 figures

We study within the Faddeev framework the 3He(e,e'p)d as well as the 3He(e,e'p)pn and 3He(e,e'n)pp reactions in order to extract information on the proton and neutron polarization in polarized 3He. We achieve clear analytical insight for simplified dynamical assumptions and define conditions for experimental access to important 3He properties. In addition we point to the possibility of measuring the electromagnetic proton form factors in the process 3He(e,e'p)d which would test the dynamical picture and put limits on medium corrections of the form factors.

The limitations for the use of the spectral function S in the process 3He(e,e′N) has been investigated in a kinematical regime constrained by the conditions that the three-nucleon (3N) center-of-mass energy E3Nc.m.≤150 MeV and the magnitude of the three-momentum transfer, ∣Q⃗∣≤600 MeV∕c . Results based on a full treatment of the final state interaction are compared to the spectral function approximation. In the case of proton knockout in the direction of the photon kinematical conditions have been identified where both response functions, RL and RT , can be well approximated by S . These conditions occur for certain low missing momenta and missing energies but not in all cases. So care is required. In case of neutron knockout only RT is a candidate for an approximate treatment by S . In the case of RL the concept of using S is not valid in the studied kinematical regime. This does not exclude the possibility that beyond that regime it might be useful. Possible applications using S for the extraction of electromagnetic form factors of the nucleons are pointed out.

The processes 3He→(e→,e′) and 3He→(e→,e′n) are theoretically analyzed with the aim to search for sensitivities in the electric form factor of the neutron, GEn. Faddeev calculations based on the high-precision NN force AV18 and using consistent mesonic exchange currents are employed. While the inclusive process is too insensitive, the semiexclusive one appears promising.