Neutron Interferometric Measurement of the Scattering Length Difference Between the Triplet and Singlet States of N-3 He.
Michael G. Huber, Muhammad D. Arif, Wei-Chen N. Chen, Thomas R. Gentile, Daniel S. Hussey, T C. Black, Dimitry A. Pushin, F. E. Wiefeldt, C.B Shahi, L Yang
We report a new determination of the n-Helium-3 scattering length difference Δ b = (−5.411 ± 0.031 (statistical) ± 0.039 (systematic) ) fm between the triplet and singlet states using a neutron interferometer. This revises our previous result Δ b = (−5.610 ± 0.027 (statistical) ± 0.032 (systematic) ) fm obtained using the same technique in 2008 [M. G. Huber, Phys. Rev. Lett. 20, 102 (2009) & M. G. Huber, Phys. Rev. Lett. 17, 103 (2009)]. This revision is due to a re-analysis of the 2008 experiment that includes allowing for an additional fit parameter and from measurements of magnetic field gradients near the Helium-3 cell. Further, 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 Helium- 3 aid in the interpretation of neutron scattering from quantum liquids. The difference Δ b was determined by measuring the relative phase shift between two incident neutron polarizations caused by the spin-dependent interaction with a polarized Helium-3 target. The target Helium-3 gas was sealed inside a small, flat windowed glass cell that was placed inside one beam path of the interferometer. The relaxation of Helium-3 polarization was monitored continuously with neutron transmission measurements. The neutron polarization and spin flipper efficiency were determined separately using Helium-3 analyzers and two different polarimetry analysis methods described in the text. A summary of the measured scattering lengths for n-Helium-3 with a comparison to nucleon interaction models is given.