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The first observation of the phenomenom of deuteron spin dichroism in the energy region of 6-20 MeV is described. Experimental values of this effect for deuterons after passage of an unpolarized carbon target are reported., Comment: 10 pages, Latex, 16 eps figures, typos are corrected

We measured the cross sections and tensor analyzing powers of the 1H(→d, pp)n breakup reaction at Ed=19 MeV in four symmetric constant relative energy (SCRE) configurations. The data are compared with theoretical predictions from four different approaches: the first based on high-precision (semi)phenomenological potentials alone or, the second, combined with model three-nucleon forces, and the third based on chiral forces up to next-to-next-to-leading order (NNLO) in the chiral expansion. In these cases the Coulomb interaction is not included. In addition, a fourth approach consists in a comparison with predictions based on CD Bonn including the Δ excitation and the Coulomb force. In all cases the measured cross sections are significantly below the theoretical values, whereas the magnitudes of the tensor analyzing powers agree within the error bars in three of the four cases. The apparent discrepancies in the breakup cross sections are similar to the known differences for the space-star breakup. This adds to the data base of unsolved low-energy discrepancies (puzzles).

We measured the cross sections and tensor analyzing powers of the H-1(d,pp)n breakup reaction at E-d=19 MeV in four symmetric constant relative energy (SCRE) configurations. The data are compared with theoretical predictions from four different approaches: the first based on high-precision (semi)phenomenological potentials alone or, the second, combined with model three-nucleon forces, and the third based on chiral forces up to next-to-next-to-leading order (NNLO) in the chiral expansion. In these cases the Coulomb interaction is not included. In addition, a fourth approach consists in a comparison with predictions based on CD Bonn including the Delta excitation and the Coulomb force. In all cases the measured cross sections are significantly below the theoretical values, whereas the magnitudes of the tensor analyzing powers agree within the error bars in three of the four cases. The apparent discrepancies in the breakup cross sections are similar to the known differences for the space-star breakup. This adds to the data base of unsolved low-energy discrepancies (puzzles).