Precision neutron interferometric measurement of the n-3He coherent neutron scattering length -: art. no. 014004

A measurement of the n-He-3 coherent scattering length using neutron interferometry is reported. The result, b(c)=(5.8572 +/- 0.0072) fm, improves the measured precision of any single measurement of b(c) by a factor of eight; the previous world average, b(c)=(5.74 +/- 0.04) fm, now becomes b(c)=(5.853 +/- 0.007) fm. Measurements of the n-p, n-d, and n-He-3 coherent scattering lengths have now been performed using the same technique, thus allowing one to extract the scattering length ratios: parameters that minimize systematic errors. We obtain values of b(n3He)/b(np)=(-1.5668 +/- 0.0021) and b(nd)/b(np)=(-1.7828+/-0.0014). Using the new world average value of b(c) and recent high-precision spin-dependent scattering length data also determined by neutron optical techniques, we extract new values for the bound singlet and triple scattering lengths of b(o) =(9.949 +/- 0.027) fm and b(1)=(4.488 +/- 0.017) fm for the n-He-3 system. The free nuclear singlet and triplet scattering lengths are a(o)=(7.456 +/- 0.020) frn and a(1) =(3.363 +/- 0.013) fm. The coherent scattering cross section is sigma(c)=(4.305 +/- 0.007) b and the total scattering cross section is sigma(s)=(5.837+/-0.014) b. Comparisons of a(0) and a(1) to the only existing high-precision theoretical predictions for the n-He-3 system, calculated using a resonating group technique with nucleon-nucleon potentials incorporating three-nucleon forces, have been performed. Neutron scattering length measurements in few-body systems are now sensitive enough to probe small effects not yet adequately treated in present theoretical models.