G. L. Jones

SANS Polarization Analysis with Nuclear-Spin-Polarized 3He

A neutron spin filter based on transmission through nuclear-spin-polarized 3He gas has been applied to polarization analysis of small angle neutron scattering (SANS). Such spin filters, which are based on the large spin dependence of the absorption of neutrons by 3He, make SANS polarization analysis possible because of their large angular acceptance. In the present experiment, a 3He-based analyzer was employed to separate nuclear scattering into its coherent and spin-incoherent components. Polarized 3He analyzers were prepared by two different optical pumping methods and installed on the NG3 SANS instrument at the NIST Center for Neutron Research (NCNR). Measurements were taken on cellophane tape and silica gel, for which the scattering is almost completely incoherent and coherent, respectively, and on a combined sample. For the combined sample, separation of the coherent part from the incoherent part was successfully demonstrated using polarization analysis.

Spin exchange optical pumping at pressures near 1 bar for neutron spin filters

Motivated by applications to neutron spin filters and recent advances in spectrally narrowed laser diode arrays (LDAs), we are exploring spin exchange optical pumping of 3He at pressures near 1 bar. Among our more interesting results has been the production of glass cells with extremely long relaxation times. The best of these has a lifetime of T1=840 h [where the polarization decays versus time, t, as exp(−t/T1)], dominated by the dipole–dipole contribution of 950 h at a 3He partial pressure of 0.85 bar. Using a broadband LDA, we have obtained 55% 3He nuclear polarization in this cell. These results are particularly relevant to the application of 3He-based neutron spin filters to neutron scattering and weak interaction experiments. Applications to magnetometry and polarized gas magnetic resonance imaging are also possible.

Compressing Spin-Polarized 3 He With a Modified Diaphragm Pump

Nuclear spin-polarized 3He gas at pressures on the order of 100 kPa (1 bar) are required for several applications, such as neutron spin filters and magnetic resonance imaging. The metastability-exchange optical pumping (MEOP) method for polarizing 3He gas can rapidly produce highly polarized gas, but the best results are obtained at much lower pressure (~0.1 kPa). We describe a compact compression apparatus for polarized gas that is based on a modified commercial diaphragm pump. The gas is polarized by MEOP at a typical pressure of 0.25 kPa (2.5 mbar), and compressed into a storage cell at a typical pressure of 100 kPa. In the storage cell, we have obtained 20 % to 35 % 3He polarization using pure 3He gas and 35 % to 50 % 3He polarization using 3He-4He mixtures. By maintaining the storage cell at liquid nitrogen temperature during compression, the density has been increased by a factor of four.

New limit on time-reversal violation in beta decay.

We report the results of an improved determination of the triple correlation DP·(p(e)×p(v)) that can be used to limit possible time-reversal invariance in the beta decay of polarized neutrons and constrain extensions to the standard model. Our result is D=[-0.96±1.89(stat)±1.01(sys)]×10(-4). The corresponding phase between gA and gV is ϕAV=180.013°±0.028° (68% confidence level). This result represents the most sensitive measurement of D in nuclear β decay.

Search for a T-odd, P-even Triple Correlation in Neutron Decay

Search for a T-odd, P-even Triple Correlation in Neutron Decay T.E. Chupp, 1 R.L. Cooper, 1 K.P. Coulter, 1 S.J. Freedman, 2 B.K. Fujikawa, 2 A. Garc´ia, 3, 4 G.L. Jones, 5 H.P. Mumm, 6 J.S. Nico, 6 A.K. Thompson, 6 C.A. Trull, 7 F.E. Wietfeldt, 7 and J.F. Wilkerson 3, 8, 9 University of Michigan, Ann Arbor, Michigan 48104, USA Physics Department, University of California, Berkeley, and Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA CENPA and Physics Department, University of Washington, Seattle, WA 98195 USA Department of Physics, University of Notre Dame, Notre Dame, IN 46556 USA Physics Department, Hamilton College, Clinton, NY 13323, USA National Institute of Standards and Technology, Gaithersburg, MD 20899, USA Physics Department, Tulane University, New Orleans, LA 70118, USA Department of Physics and Astronomy, University of North Carolina, Chapel Hill, North Carolina 27599, USA Oak Ridge National Lab, Oak Ridge, TN, 37831 USA Background: Time-reversal-invariance violation, or equivalently CP violation, may explain the observed cosmological baryon asymmetry as well as signal physics beyond the Standard Model. In the decay of polarized neutrons, the triple correlation D J n ·(p e ×p ν ) is a parity-even, time-reversal- odd observable that is uniquely sensitive to the relative phase of the axial-vector amplitude with respect to the vector amplitude. The triple correlation is also sensitive to possible contributions from scalar and tensor amplitudes. Final-state effects also contribute to D at the level of 10 −5 and can be calculated with a precision of 1% or better. Purpose: We have improved the sensitivity to T-odd, P-even interactions in nuclear beta decay. Methods: We measured proton-electron coincidences from decays of longitudinally polarized neutrons with a highly symmetric detector array designed to cancel the time-reversal-even, parity-odd Standard-Model contributions to polarized neutron decay. Over 300 million proton-electron coincidence events were used to extract D and study systematic effects in a blind analysis. Results: We find D = [−0.94 ± 1.89(stat) ± 0.97(sys)] × 10 −4 . Conclusions: This is the most sensitive measurement of D in nuclear beta decay. Our result can be interpreted as a measurement of the phase of the ratio of the axial-vector and vector coupling constants (C A /C V = |λ|e iφ AV ) with φ AV = 180.012 ◦ ±0.028 ◦ (68% confidence level) or to constrain time-reversal violating scalar and tensor interactions that arise in certain extensions to the Standard Model such as leptoquarks. This paper presents details of the experiment, analysis, and systematic- error corrections. PACS numbers: 24.80.+y, 11.30.Er, 12.15.Ji, 13.30.Ce DISCLAIMER: This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor the Regents of the University of Cal- ifornia, nor any of their employees, makes any warranty, express or implied, or assumes any le- gal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, prod- uct, or process disclosed, or represents that its use would not infringe privately owned rights. Refer- ence herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommen- dation, or favoring by the United States Govern- ment or any agency thereof, or the Regents of the University of California. The views and opin- ions of authors expressed herein do not necessar- ily state or reflect those of the United States Gov- ernment or any agency thereof or the Regents of the University of California. I. INTRODUCTION The symmetries of physical processes under the trans- formations of charge conjugation (C), parity (P), and time reversal (T) have played a central role in the de- velopment of the Standard Model of elementary-particle interactions [1]. Time-reversal-symmetry violation (or T violation), which is equivalent to CP violation assum- ing CPT symmetry, has been of particular interest be- cause it is sensitive to many kinds of new physics. The CP-violating parameters of the Standard Model are the Cabibbo-Kobayashi-Maskawa (CKM) phase, which en- ters in the mixing of three generations of quarks, and the parameter θ QCD . The effect of the CKM phase is strongly suppressed in the permanent electric dipole mo- ments (EDMs) of the neutron [2] and heavy atoms [3, 4], and recent EDM results combine to set upper limits on θ QCD . All laboratory measurements to date are consis- tent with a single source of CP violation, i.e. the phase in the CKM matrix. An exception may be the 3.2 sigma deviation observed recently as an asymmetry in the pro- duction of pairs of like-sign muons reported by the D0

A measurement of parity-violating gamma-ray asymmetries in polarized cold neutron capture on 35Cl, 113Cd, and 139La

Abstract An apparatus for measuring parity-violating asymmetries in gamma-ray emission following polarized cold neutron capture was constructed as a 1/10th scale test of the design for the forthcoming n → + p → d + γ experiment at LANSCE. The elements of the polarized neutron beam, including a polarized 3 He neutron spin filter and a radio frequency neutron spin rotator, are described. Using CsI(Tl) detectors and photodiode current mode readout, measurements were made of asymmetries in gamma-ray emission following neutron capture on 35 Cl , 113 Cd , and 139 La targets. Upper limits on the parity-allowed asymmetry s n ·( k γ × k n ) were set at the level of 7×10 −6 for all three targets. Parity-violating asymmetries s n · k γ were observed in 35 Cl , A γ =(−29.1±6.7)×10 −6 , and 139 La , A γ =(−15.5±7.1)×10 −6 , values consistent with previous measurements.

Consequence for Wavefunction Collapse Model of the Sudbury Neutrino Observatory Experiment

It is shown that data on the dissociation rate of deuterium obtained in an experiment at the Sudbury Neutrino Observatory provides evidence that the Continuous Spontaneous Localization wavefunction collapse model should have mass–proportional coupling to be viable.

Electrical heating for SEOP-based polarized 3He system

Development of neutron spin filters based on polarized 3He is underway at Spallation Neutron Source (SNS). We report the progress of electrical heating tests in polarized 3He based on Spin-Exchange Optical Pumping (SEOP) method. We first test the system performance based on electrical heating via non-inductance heating pads. We observe a contribution of 955 hours to the relaxation time T1 from the heating pads. We then test the electrical heating SEOP pumping system at the SNS beamline Magnetic Reflectometer. We currently obtain 73% 3He polarization in a cell with 820 cm3 in volume.

Precision Measurement of Parity Violation in Polarized Cold Neutron Capture on the Proton: the NPDγ Experiment

The NPDγ experiment at the Los Alamos Neutron Science Center (LANSCE) is dedicated to measure with high precision the parity violating asymmetry in the γ emission after capture of spin polarized cold neutrons in para‐hydrogen. The measurement will determine unambiguously the weak pion‐nucleon‐nucleon (πNN) coupling constant fπ1.The NPDGamma experiment at the Los Alamos Neutron Science Center (LANSCE) is dedicated to measure with high precision the parity violating asymmetry in the

He3 polarization via optical pumping in a birefringent cell

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