Researchers at NIST have made precise measurements of the neutron scattering length for helium-4 using neutron interferometry. The scattering length is a fundamental property that describes the interaction between neutrons and helium nuclei. The new measurement, with an uncertainty reduced by a factor of six, provides a more accurate benchmark for nuclear theory and effective field theory calculations.
The experiment involved using a neutron interferometer to create two entangled neutron paths, with one path passing through a helium gas-filled chamber and the other through a vacuum chamber. The phase shift caused by the helium gas was measured and found to be proportional to the scattering length. The researchers also identified and corrected for various systematic effects, including cell wall deformation under pressure.
The final result for the neutron-helium-4 scattering length is 3.0982 ± 0.0035 femtometers, a 2% downward shift from the previously accepted value. This improved measurement will help refine nuclear potential models and constrain low-energy constants in chiral effective field theory, potentially bringing few-nucleon theory and experiment into better agreement.
Keywords: neutron scattering, effective field theory, scattering length
