College Park, Maryland      June 6 - 10 , 2004

M4-B3 (4:30 PM): High-precision measurements of the n-p, n-d, and n-3He bound coherent scattering lengths

T. C. Black (University of North Carolina at Wilmington), P. R. Huffman (National Institute of Standards and Technology; North Carolina State University), M. Arif, D. L. Jacobson, S. A. Werner (National Institute of Standards and Technology), W. M. Snow (Indiana University; IUCF), K. Schoen (University of Missouri - Columbia)

Recent measurements of the n-d and n-3He bound coherent scattering lengths, conducted at the Neutron Interferometer and Optics Facility at NIST, are in significant disagreement with exact calculations of these observables using modern NN+3NF potentials. The bound coherent n-d scattering length was measured to be bnd = (6.665 0.004) fm, which yields a new world average for this parameter of bnd = (6.669 0.003) fm. In the n-3He system, the bound coherent scattering length was measured as bn-3He = (5.857 0.007) fm, which yields a new world average for this parameter of bn-3He = (5.854 0.007) fm. Combining these measurements with O. Zimmer's result for the bound incoherent scattering length of bi = (-2.365 0.020) fm, one obtains the free singlet and triplet scattering lengths for the n-3He system; a0 = (7.456 0.026) fm, and a1 = (3.364 0.010) fm, respectively. Our measured value of the n-p bound coherent scattering length, bnp = (-3.7384 0.0020) fm is in agreement with the previous world average value of bnp = (-3.7410 0.0020)fm. The extreme precision of these new measurements renders them suitable for use in contemporary EFT calculations.

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