Neutron interferometric measurement of the scattering length difference between the triplet and singlet states of n-$^3$He

TL;DR

This study precisely measures the difference in scattering lengths between triplet and singlet states of neutron-$^3$He using neutron interferometry, refining previous results with additional data and improved analysis.

Contribution

The paper provides a more accurate measurement of the n-$^3$He scattering length difference, including a re-analysis of past data and new experimental data, enhancing the reliability of these fundamental nuclear parameters.

Findings

Measured $ riangle b'$ as (-5.411 ± 0.031 (stat) ± 0.039 (sys)) fm.

Revised previous measurement with improved analysis and additional data.

Compared scattering lengths with nuclear models and discussed implications.

Abstract

We report a determination of the n-$^3$He scattering length difference $\Delta b^{\prime} = b_{1}^{\prime}-b_{0}^{\prime} = $ ($-5.411$ $\pm$ $0.031$ (statistical) $\pm$ $0.039$ (systematic)) fm between the triplet and singlet states using a neutron interferometer. This revises our previous result $\Delta b^{\prime} = $ (-5.610 $\pm$ $0.027$ (statistical) $\pm$ $0.032$ (systematic) fm obtained using the same technique in 2008. This revision is due to a re-analysis of the 2008 experiment that includes a more robust treatment of the phase shift caused by magnetic field gradients near the $^3$He cell. Furthermore, we more than doubled our original data set from 2008 by acquiring six months of additional data in 2013. Both the new data set and a re-analysis of the older data are in good agreement. Scattering lengths of low Z isotopes are valued for use in few-body nuclear effective field theories, provide important tests of modern nuclear potential models and in the case of $^3$He aid in the interpretation of neutron scattering from quantum liquids. The difference $\Delta b^{\prime}$ was determined by measuring the relative phase shift between two incident neutron polarizations caused by the spin-dependent interaction with a polarized $^3$He target. The target $^3$He gas was sealed inside a small, flat windowed glass cell that was placed in one beam path of the interferometer. The relaxation of $^3$He polarization was monitored continuously with neutron transmission measurements. The neutron polarization and spin flipper efficiency were determined separately using $^3$He analyzers and two different polarimetry analysis methods. A summary of the measured scattering lengths for n-$^3$He with a comparison to nucleon interaction models is given.