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

© 2014 American Physical Society, https://dx.doi.org/10.1103/physrevc.90.064004We report a determination of the n-He-3 scattering length difference = b = = b = 1 -b = 0 = [-5.411 = 0.031 (statistical) = 0.039 (systematic)] fm between the triplet and singlet states using a neutron interferometer. This revises our previous result = b = = [-5.610 = 0.027 (statistical) = 0.032 (systematic)] fm obtained using the same technique in 2008 [ Huber et al., Phys. Rev. Lett. 102, 200401 (2009);,103, 179903(E) (2009)]. This revision is attributable to a reanalysis of the 2008 experiment that now includes a systematic correction caused by magnetic-field gradients near the 3He cell which had been previously underestimated. Furthermore, we more than doubled our original data set from 2008 by acquiring 6 months of additional data in 2013. Both the new data set and a reanalysis 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 3He, aid in the interpretation of neutron scattering from quantum liquids. The difference = b = was determined by measuring the relative phase shift between two incident neutron polarizations caused by the spin-dependent interaction with a polarized 3He target. The target 3He gas was sealed inside a small, flat-windowed glass cell thatwas placed in one beam path of the interferometer. The relaxation of 3He polarization was monitored continuously with neutron transmission measurements. The neutron polarization and spin-flipper efficiency were determined separately using 3He analyzers and two different polarimetry analysis methods. A summary of the measured scattering lengths for n-3He with a comparison to nucleon interaction models is given.U.S. Department of EnergyNational Institute of Standards and TechnologyNational Science Foundation: PHY-0555347, PHY-0855445, PHY-120534

Observation of the radiative decay mode of the free neutron

The theory of quantum electrodynamics (QED) predicts that beta decay of the neutron into a proton, electron and antineutrino should be accompanied by a continuous spectrum of soft photons. While this inner bremsstrahlung branch has been previously measured in nuclear beta and electron capture decay, it has never been observed in free neutron decay. Recently, the photon energy spectrum and branching ratio for neutron radiative decay have been calculated using two approaches: a standard QED framework(1-3) and heavy baryon chiral perturbation theory(4) (an effective theory of hadrons based on the symmetries of quantum chromodynamics). The QED calculation treats the nucleons as point-like, whereas the latter approach includes the effect of nucleon structure in a systematic way. Here we observe the radiative decay mode of free neutrons, measuring photons in coincidence with both the emitted electron and proton. We determined a branching ratio of (3.13 +/- 0.34) x 10(-3) (68 per cent level of confidence) in the energy region between 15 and 340 keV, where the uncertainty is dominated by systematic effects. The value is consistent with the predictions of both theoretical approaches; the characteristic energy spectrum of the radiated photons, which differs from the uncorrelated background spectrum, is also consistent with the calculated spectrum. This result may provide opportunities for more detailed investigations of the weak interaction processes involved in neutron beta decay.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62639/1/nature05390.pd

Searching for time reversal invariance violation in polarized neutron decay

Time reversal invariance violation is tightly constrained in the Standard Model, and the existence of a T-violating effect above the predicted level would be an indication of new physics. A sensitive probe of this symmetry in the weak interaction is the measurement of the D-coefficient in neutron decay. This parameter characterizes the triple-correlation of neutron spin, electron momentum, and neutrino (or proton) momentum, which changes sign under time reversal. The emiT experiment, now on line, attempts to improve the measurement of D,D, whose current average is 0.3±1.5×10−3.0.3±1.5×10−3. © 1997 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87907/2/399_1.pd

Overview of neutron interferometry at NIST

Neutron interferometry at the National Institute of Standards and Technology is a well-established program that performs experiments in a wide range of areas including materials science, quantum information, precision measurements of coherent and incoherent scattering lengths, and dark energy/fifth force searches. Central to the continued success of this program is the further understanding and elimination of instabilities and coherence-losses whether they are from thermal, vibrational, or dynamical sources. We have spent considerable effort in fabricating new interferometer crystals which have higher maximum fringe visibilities and that can be tailored to specific experiments. We describe the current facilities and a new post-machining fabrication process of crystal annealing

Overview of neutron interferometry at NIST

Neutron interferometry at the National Institute of Standards and Technology is a well-established program that performs experiments in a wide range of areas including materials science, quantum information, precision measurements of coherent and incoherent scattering lengths, and dark energy/fifth force searches. Central to the continued success of this program is the further understanding and elimination of instabilities and coherence-losses whether they are from thermal, vibrational, or dynamical sources. We have spent considerable effort in fabricating new interferometer crystals which have higher maximum fringe visibilities and that can be tailored to specific experiments. We describe the current facilities and a new post-machining fabrication process of crystal annealing

Progress on the BL2 beam measurement of the neutron lifetime

A precise value of the neutron lifetime is important in several areas of physics, including determinations of the quark-mixing matrix element |Vud|, related tests of the Standard Model, and predictions of light element abundances in Big Bang Nucleosynthesis models. We report the progress on a new measurement of the neutron lifetime utilizing the cold neutron beam technique. Several experimental improvements in both neutron and proton counting that have been developed over the last decade are presented. This new effort should yield a final uncertainty on the lifetime of 1 s with an improved understanding of the systematic effects

Measurement of the parity violating asymmetry AγAγ in +p→d+γn⃗+p→d+γ

The weak pion-nucleon coupling constant Hπ1Hπ1 remains poorly determined, despite many years of effort. The recent measurement of the 133Cs133Cs anapole moment has been interpreted to give a value of Hπ1Hπ1 almost an order of magnitude larger than the limit established in the 18F18F parity doublet experiments. A measurement of the gamma ray directional asymmetry AγAγ for the capture of polarized neutrons by hydrogen has been proposed at Los Alamos National Laboratory. This experiment will determine Hπ1Hπ1 independent of nuclear structure effects. However, since the predicted asymmetry is small, Aγ ≈ 5×10−8,Aγ≈5×10−8, systematic effects must be reduced to <5×10−9.<5×10−9. The design of the experiment will is presented, with an emphasis on the techniques used for controlling systematic errors. © 1999 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87690/2/247_1.pd