Author/Authors :
Gericke، نويسنده , , Michael and Page، نويسنده , , You S. and Ramsay، نويسنده , , D. and Alarcon، نويسنده , , R. and Balascuta، نويسنده , , S. and Barron، نويسنده , , L. and Bowman، نويسنده , , J.D. and Carlini، نويسنده , , R.D. and Chen، نويسنده , , W. and Chupp، نويسنده , , T.E. and Crawford، نويسنده , , C. and Covrig، نويسنده , , S. and Dabaghyan، نويسنده , , M. and Freedman، نويسنده , , S.J. and Gentile، نويسنده , , T.R. and Gillis، نويسنده , , R.C. and Greene، نويسنده , , G.L. and Hersman، نويسنده , , F.W. and Ino، نويسنده , , T. and Jones، نويسنده , , G.L. and Lauss، نويسنده , , B. and Leuschner، نويسنده , , M. and Losowki، نويسنده , , B. and Mahurin، نويسنده , , R. and Masuda، نويسنده , , Y. and Mei، نويسنده , , J. and Mitchell، نويسنده , , G.S. and Muto، نويسنده , , S. and Nann، نويسنده , , Mervi H. and Penttilن، نويسنده , , S.I. and Salas-Bacci، نويسنده , , A. and Santra، نويسنده , , S. and Seo، نويسنده , , P.-N. and Sharapov، نويسنده , , E. 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 has recently completed the first phase of a measurement to determine the size of the weak nucleon–nucleon interaction from cold neutron capture on a liquid hydrogen target. In the framework of the nearly 30 year old DDH model [B. Desplanques, J.F. Donoghue, B.R. Holstein, Annals of Physics 124 (1980) 449], the measured process is explained in terms of the weak pion–nucleon coupling, while the framework of modern effective field theory parameterizes the measured process in terms of the S 1 3 - P 1 3 , long range transition (essentially the Danilov parameter ρ t ) [S.L. Zhu et al., Nuclear Physics A 748 (2005) 435; C.-P. Liu, Phys. Rev. C 75 (2007) 065501]. The couplings in terms of either model are directly proportional to the parity violating up-down asymmetry in the angular distribution of gamma rays with respect to the neutron spin direction in the reaction n ⇒ + p → d + γ . The asymmetry has a predicted size of 5 × 10 - 8 and the aim of the NPDGamma collaboration is to measure it to 20%. The first phase of the measurement was completed at the Los Alamos National Laboratory Neutron Science Center Spallation Source with a preliminary result of ( - 1.1 ± 2.1 stat . ± 0.2 sys . ) × 10 - 7 . Here, we report on the measurements and the results obtained so far. The experiment is currently being installed at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory, for the remainder of its run time.
