Spin-isospin selectivity in three-nucleon forces

Precision data are presented for the break-up reaction, (2)H((p) over right arrow, pp)n, within the framework of nuclear-force studies. The experiment was carried out at KVI using a polarized-proton beam of 190 MeV impinging on a liquid-deuterium target and by exploiting the detector, BINA. Some of the vector-analyzing powers are presented and compared with state-of-the-art Faddeev calculations including three-nucleon forces effect. Significant discrepancies between the data and theoretical predictions were observed for kinematical configurations which correspond to the (2)H((p) over right arrow,(2)He)n channel. These results are compared to the (2)H((p) over right arrow, d)p reaction to test the isospin sensitivity of the present three-nucleon force models. The current modeling of two and three-nucleon forces is not sufficient to describe consistently polarization data for both isospin states. (C) 2010 Elsevier B.V. All rights reserved

Investigation of nuclear forces in d + p elastic and p + d break-up reactions at intermediate energies

In this thesis, the break-up and elastic channels of the reaction at a proton-beam energy of 190~MeV were studied using BINA. After accelerating the polarized-proton beam from POLIS with AGOR, reactions of protons with deuterons from a liquid-deuterium target took place at the center of BINA. The cross section and analyzing powers are measured as a function of the kinematical variable S for different combinations of the polar coordinates of the outgoing particles. As a conclusion and regarding the uncertainties of the data, the deviations between the cross sections and theoretical predictions using solely NN potentials indicate the need for additional ingredients which are presently missing in the nuclear forces or in the framework which provides the predictions for the observables. The effect of 3NFs is predicted to be small and although adding the 3NF to the NN potentials helps to bridge the gap between data and the NN calculations, however, it cannot remedy the discrepancies observed for the cross section. The CDB+Relativistic predictions help to solve the discrepancies between data and theoretical calculations only in part of the phase space. That might be an indication that relativity is playing an important role at energies employed in this experiment, however, the approximations made for these calculations might not be sufficient. The analyzing power does not seem to be sensitive to Coulomb and relativistic effects. This observable is, therefore, a unique probe to study 3NF effects. In particular, at small azimuthal opening angles, 3NF effects can be observed and tested. In this region, however, the experimental data show that the presented 3NF potentials do not resolve the observed discrepancies. On the contrary, the disagreement between data and predictions by the Faddeev calculations increases by including all the 3N potentials.