Charge symmetry breaking in rvec n - rvec p 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 ({ital A}{sub {ital n}}({theta})) and with the proton spin ({ital A}{sub {ital p}}({theta})). Systematic errors and experimental ambiguities in the measurement of this difference are extensively discussed. Our result for {Delta}{ital A}{equivalent to}{ital A}{sub {ital n}}{minus}{ital A}{sub {ital p}}, averaged over the angular range 82.2{degree}{le}{theta}{sub c.m.}{le}116.1{degree}, is (33.1{plus minus}5.9{plus minus}4.3){times}10{sup {minus}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}{ital 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}{ital A} are in excellent agreement with predictions from meson-exchange theory, when these include both the effect of the {ital n}-{ital p} mass difference more » on one-pion exchange and the isospin mixing of {rho}{sup 0} and {omega}{sup 0} mesons. In particular, the Bonn nucleon-nucleon ({ital NN}) potential model accounts for the present results utilizing {rho}{ital NN} and {omega}{ital NN} coupling constant values deduced previously for this potential from fits to more conventional {ital NN} scattering data. « less