Phase shift parameters for p-d elastic scattering are extracted from new measurements of spin observables at E v = 3 MeV. The experimental phase shifts are compared with predictions obtained from Faddeev calculations. The agreement between theory and experiment is generally good. However, we find that there are significant discrepancies for the 2 Si phase shift and for the S-D mixing parameters.PACS numbers: 25.10. +S, 24.70.+S, 25.40.Cm There is currently a great deal of interest in understanding the nuclear three-body system. Over the last several years a substantial amount of progress has been made in the development of the theoretical means for addressing the three-body problem (for example, techniques for solving the Faddeev equations). It is now well established (see, for example, Ref.[1]) that conventional two-body NN forces are not sufficiently strong to reproduce the observed 3 H and 3 He binding energies, and the role of three-body forces in resolving this discrepancy has been studied extensively [2][3][4].Experimental results for n-d and p-d elastic scattering also have the potential to provide new information concerning the nature of the fundamental interactions in complex nuclear systems. As the theoretical capabilities continue to advance we can anticipate that the scattering data will begin to take on added importance. It has been known for some time that measurements of the nucleon analyzing power, A y , for N-d scattering are very sensitive to the NN 3 Pj partial waves [5], and this sensitivity has recently been exploited in an effort to constrain the NN 3 Pj forces [6]. It has also been suggested [5][6][7] that comparison of n-d and p-d results may provide information concerning possible charge independence and/or charge symmetry violation, and one can expect that N-d measurements will ultimately play an important role in understanding the nature and role of nuclear three-body forces.Our purpose in the present Letter is to present new measurements of spin observables for p-d elastic scattering. The measurements will be compared with existing state-of-the-art Faddeev calculations [8]. These calculations provide a good qualitative description of the data, but at the quantitative level there are discrepancies. The nature of the differences between the measured and calculated polarization observables will be studied by comparing phase shifts extracted from the data with the calculated phase shifts. Comparison of theory and experiment at the level of the phase shifts is clearly of value, since it is often possible to relate individual splittings or mixing parameters with specific components of the NN force. However, comparisons of this kind have not been fruitful in the past since the measurements have not been of sufficient quality to allow reliable and accurate determination of the phase shift parameters.We have obtained new measurements of the polarization observables for p-d elastic scattering at E p = 3 MeV and at the corresponding deuteron energy, Ed = 6 MeV. The new data set consists of mea...

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