Precision neutron interferometric measurements and updated evaluations of the n-p and n-d coherent neutron scattering lengths

Abstract

We have performed high-precision measurements of the coherent neutron scattering lengths of gas phase molecular hydrogen and deuterium using neutron interferometry. After correcting for molecular binding and multiple scattering from the molecule, we find b_{np} = (-3.7384 +/- 0.0020) fm and b_{nd} = (6.6649 +/- 0.0040) fm. Our results are in agreement with the world average of previous Measurements, b_{np} = (-3.7410 +/- 0.0010) fm and b_{nd} = (6.6727 +/- 0.0045) fm. The new world averages for the n-p and n-d coherent scattering lengths, including our new results, are b_{np} = (-3.7405 +/- 0.0009) fm and b_{nd} = (6.6683 +/- 0.0030) fm. We compare bnd with the calculations of the doublet and quartet scattering lengths of several nucleon-nucleon potential models and show that almost all known calculations are in disagreement with the precisely measured linear combination corresponding to the coherent scattering length. Combining the world data on b_{nd} with the modern high-precision theoretical calculations of the quartet n-d scattering lengths recently summarized by Friar et al., we deduce a new value for the doublet scattering length of ^{2}a_{nd} = [0.645 +/- 0.003(expt) +/- 0.007(theory)] fm. This value is a factor of 4, more precise than the previously accepted value of ^{2}a_{nd} = [0.65 +/- 0.04(expt)] fm. The current state of knowledge of scattering lengths in the related p-d system, ideas for improving by a factor of 5 the accuracy of the b_{np} and b_{nd} measurements using neutron interferometry, and possibilities for further improvement of our knowledge of the coherent neutron scattering lengths of 3H, 3He, and 4He are discussed.

22 pages, 19 figures

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• An accurate nucleon-nucleon potential with charge-independence breaking
• Construction of high-quality Nucleon-Nucleon potential models
• Quantum Monte Carlo calculations of nuclei with A \leq 7
• A New Expansion for Nucleon-Nucleon Interactions
• Effective Field Theory for Short-Range Forces
• The Three-Boson System with Short-Range Interactions
• Nucleon-Deuteron Scattering from an Effective Field Theory
• Study of bound and scattering states in three-nucleon systems
• Triton calculations with the new Nijmegen potentials
• The three- and four-nucleon systems from chiral effective field theory
• The complex Kohn variational method applied to N-d scattering
• Neutron-3H and Proton-3He Zero Energy Scattering
• The Three-Nucleon System Near the N-d Threshold
• Analyzing power in nucleon-deuteron scattering and three-nucleon forces

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