Author/Authors :
S. and Barrَn Palos، نويسنده , , L. and Alarcon، نويسنده , , R. and Balascuta، نويسنده , , S. and Blessinger، نويسنده , , C. and Bowman، نويسنده , , J.D. and Chupp، نويسنده , , T.E. and Covrig، نويسنده , , S. and Crawford، نويسنده , , C.B. and Dabaghyan، نويسنده , , M. and Dadras، نويسنده , , J. and Dawkins، نويسنده , , M. and Fox، نويسنده , , W. and Gericke، نويسنده , , M.T. and Gillis، نويسنده , , R.C. and Lauss، نويسنده , , B. and Leuschner، نويسنده , , M.B. and Lozowski، نويسنده , , B. and Mahurin، نويسنده , , R. and Mason، نويسنده , , M. and Mei، نويسنده , , J. and Nann، نويسنده , , Mervi H. and Penttilن، نويسنده , , S.I. and Ramsay، نويسنده , , W.D. and Salas-Bacci، نويسنده , , A. and Santra، نويسنده , , S. and Seo، نويسنده , , P.-N. and Sharma، نويسنده , , M. and Smith، نويسنده , , T. and Snow، نويسنده , , W.M. and Wilburn، نويسنده , , W.S. and Yuan، نويسنده , , V.، نويسنده ,
Abstract :
The NPDGamma collaboration is performing a measurement of the very small parity-violating asymmetry in the angular distribution of the 2.2 MeV γ - rays from the capture of polarized cold neutrons on protons ( A γ ) . The estimated size of A γ is 5 × 10 − 8 , and the measured asymmetry is proportional to the neutron polarization upon capture. Since the interaction of polarized neutrons with one of the two hydrogen molecular states (orthohydrogen) can lead to neutron spin-flip scattering, it is essential that the hydrogen in the target is mostly in the molecular state that will not depolarize the neutrons ( ≥ 99.8 % parahydrogen). For that purpose, in the first stage of the NPDGamma experiment at the Los Alamos Neutron Science Center (LANSCE), we operated a 16-l liquid hydrogen target, which was filled in two different occasions. The parahydrogen fraction in the target was accurately determined in situ by relative neutron transmission measurements. The result of these measurements indicate that the fraction of parahydrogen in equilibrium was 0.9998 ± 0.0002 in the first data taking run and 0.9956 ± 0.0002 in the second. We describe the parahydrogen monitor system, relevant aspects of the hydrogen target, and the procedure to determine the fraction of parahydrogen in the target. Also assuming thermal equilibrium of the target, we extract the scattering cross-section for neutrons on parahydrogen.
Keywords :
Neutron polarization , Hadronic weak interaction , Orthohydrogen , Parahydrogen , Neutron capture , neutron scattering , Liquid hydrogen , parity violation
