An initially unpolarized beam of deuterons is found to acquire tensor polarization after traversing a foil of spin-zero target nuclei. The effect, called nuclear spin dichroism, has been predicted theoretically, albeit resulting in small values of p zz of the order of 0.01 for energies around 10 MeV. The experiment was carried out at the Köln tandem accelerator using carbon targets bombarded by deuterons. The observed polarization is as large as p zz ¼ À0:28 AE 0:03 for a beam of 14.8 MeV and a 129 mg=cm 2 target. The results allow one to produce tensor-polarized deuterons with p zz around À0:30 (or þ0:25) from an initially unpolarized beam using a carbon target of appropriate thickness. DOI: 10.1103/PhysRevLett.104.222501 PACS numbers: 13.88.+e, 24.70.+s, 25.45.De, 29.27.Hj Nuclear spin dichroism leads to the appearance of tensor polarization in an initially unpolarized, forwardtransmitted beam of (spin 1) deuterons behind a target composed of spin-zero nuclei, like carbon [1]. The direction of primary and transmitted beam defines the quantization axis, and because of azimuthal symmetry, the beam behind the target is described by the tensor polarizationwhere is the number density of nuclei in the target (per unit of volume) and d its thickness (in units of length). The n m denote the normalized occupation numbers of deuterons in the magnetic substates m ¼ þ1, À1, and 0. The interaction of deuterons of energy E with spin-zero target nuclei is characterized by the total cross sections AE1 ðEÞ and 0 ðEÞ. Using the initial occupation numbers in the beam, n in þ1 ¼ n in À1 ¼ n in 0 ¼ 1 3 , the tensor polarization behind the target readswhere AE m ¼ R d 0 m ½EðxÞ dx, and EðxÞ is the deuteron energy at a penetration depth x into the target. When AE m ( 1, Eq. (2) reduces to p zz ð dÞ ¼ 2 3A nonzero cross-section difference is produced, for instance, by the nonspherical shape of the deuteron ground-state wave function. Recently, the deuteron-carbon interaction at deuteron energies of 5 to 20 MeV has been investigated theoretically [1]. The optical theorem relates the cross-section difference in Eq. (3) to the imaginary part of the coherent forward scattering amplitudes, When Eq. (3) is integrated over the range E in ¼ Eðx ¼ 0Þ to E out ¼ Eðx ¼ dÞ, deuterons decelerated from 20 to 11 MeV (or from 11 to 5.5 MeV) in a carbon target of areal density 180 ðor 70Þ mg=cm 2 are expected to acquire p zz ¼ þ0:014 (or p zz ¼ À0:0035) [1]. These predictions are to be compared with the experimental data obtained in this work.The measurements, presented here, were performed in two runs, in

We measured the cross sections of the 2 H(p,pp)n breakup reaction at Ep=16 MeV in three kinematical configurations: the np final-state interaction (FSI), the co-planar star (CST), and an intermediate-star (IST) geometry. The cross sections are compared with theoretical predictions based on the CD Bonn potential alone and combined with the updated 2π-exchange Tucson-Melbourne three-nucleon force (TM99'), calculated without inclusion of the Coulomb interaction. The resulting excellent agreement between data and pure CD Bonn predictions in the FSI testifies to the smallness of three-nucleon force (3NF) effects as well as the insignificance of the Coulomb force for this particular configuration and energy. The CST also agrees well whereas the IST results show small deviations between measurements and theory seen before in the pd breakup space-star geometries which point to possible Coulomb effects. An additional comparison with EFT predictions (without 3NF) up to order N 3 LO shows excellent agreement in the FSI case and a rather similar agreement as for CD Bonn in the CST and IST situations.

We measured the cross sections and tensor analyzing powers of the 1 H( 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 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). of the nucleon-deuteron (Nd) vector analyzing power A y at energies below ≈25 MeV by all modern NN potentials [1]. In both the proton-deuteron (pd) and neutron-deuteron (nd) elastic scattering, the theoretical prediction is about 30% below the data in the angular region of the analyzing power maximum [2][3][4]. For the same reaction, but for energies above ≈60 MeV, the minima of the differential cross section are also underpredicted if only two-nucleon (2N ) forces are used [5,6]. Although this discrepancy can be removed once three-nucleon forces (3NF s) are also taken into account, the low-energy A y problem has not been resolved yet.For the breakup process the low-energy nd space-star (SST) configuration in which all three nucleons are emerging in the c.m. system with equal magnitudes of momenta in a plane perpendicular to the incoming beam direction still presents 0556-2813/2006/73(6)/064001 (12) 064001-1

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The effect of nuclear spin dichroism, predicted by theoretical studies as the appearance of tensor polarization in initially unpolarized beams behind unpolarized or spinless targets, has been studied by measurements with the use of 9.5 to 18.7 MeV unpolarized deuteron beams from the Köln tandem accelerator and graphite targets of areal densities from 36 to 188 mg/cm 2 . Distinct deviations from the predicted weak effect were observed with a maximum vale of pzz = −(0.28 ± 0.03), measured behind a 129 mg/cm 2 target at 14.8 MeV initial beam energy. The present results will allow one to produce tensor-polarized deuteron beams with pzz about -0.30 or +0.25 from initially unpolarized beams by graphite targets of appropriate thickness.