PRECISION-MEASUREMENT OF CHARGE-SYMMETRY BREAKING IN NP ELASTIC-SCATTERING AT 347 MEV

A nonzero difference of the analyzing powers due to charge symmetry br eaking has been measured with high precision in np elastic scattering at a neutron beam energy of 347 MeV. The neutron beam and proton targe t were alternately polarized for the measurements of A(n) and A(p). A mirror-symmetric detection system was used to cancel geometry-related systematic errors. From fits of the measured asymmetry angular distrib utions over the range of 53.4 degrees less than or equal to theta(cm)l ess than or equal to 86.9 degrees, the difference in the zero-crossing angles of the analyzing powers was determined to be 0.438 degrees+/-0 .054 degrees(stat.)+/-0.051 degrees(syst.) in the center-of-mass syste m. Using the experimentally determined slope of the analyzing power dA /d theta=(-1.35+/-0.05)x10(-2)deg(-1) (c.m.), this is equivalent to De lta A(p)=[59+/-7(stat.)+/-7(syst.)+/-2(syst.)]x10(-4). The shape of De lta A(theta) in the vicinity of the zero-crossing angle has also been extracted. Predictions of nucleon-nucleon interaction models based on meson exchange agree well with the results. [S0556-2813(98)06404-8].