CHARGE SYMMETRY-BREAKING IN (N)RIGHT-ARROW-(P)RIGHT-ARROW SCATTERING AT 183 MEV

We report the results of a precise test of charge symmetry in the scattering of polarized neutrons from polarized protons at a laboratory bombarding energy of 183 MeV. The observable sensitive to charge symmetry is the difference between the analyzing powers associated with the neutron spin [A(n)(theta)] and with the proton spin [A(p)(theta)]. Systematic errors and experimental ambiguities in the measurement of this difference are extensively discussed. Our result for DELTA-A = A(n) - A(p), averaged over the angular range 82.2-degrees less-than-or-equal-to theta(c.m.) less-than-or-equal-to 116.1-degrees, is (33.1+/-5.9+/-4.3) x 10(-4). With the statistical and systematic errors added in quadrature, this value is 3.4 standard deviations larger than the effect expected from pure photon exchange (the electromagnetic spin-orbit interaction) between the neutron and proton, and thus represents clear evidence of charge symmetry breaking in the strong interaction. We also extract information about the angular dependence of DELTA-A(theta), within limitations imposed by uncertainties in the measured beam and target polarizations. Both the angle-averaged value and the angular dependence measured for DELTA-A are in excellent agreement with predictions from meson-exchange theory, when these include both the effect of the n-p mass difference on one-pion exchange and the isospin mixing of rho-0 and omega-0 mesons. In particular, the Bonn nucleon-nucleon (NN) potential model accounts for the present results utilizing rho-NN and omega-NN coupling constant values deduced previously for this potential from fits to more conventional NN scattering data.