Precision Measurement of the Neutron Scattering Length of ~4He Using Neutron Interferometry

摘要

We report a 0.08% measurement of the bound neutron scattering length of He-4 using neutron interferometry. The result is b = (3.0982 +/- 0.0021 [stat] +/- 0.0014[syst]) fm. The corresponding free atomic scattering length is a = (2.4746 +/- 0.0017[stat] +/- 0.0011 [syst]) fm. With this result the world average becomes b = (3.0993 +/- 0.0025) fm, a 2% downward shift and a reduction in uncertainty by more than a factor of six. Our result is in disagreement with a previous neutron interferometric measurement but is in good agreement with earlier measurements using neutron transmission.