Measurement Of Strange-Quark Contributions To The Nucleon'S Form Factors At Q(2)=0.230 (Gev/C)(2)

We report on a measurement of the parity-violating asymmetry in the scattering of longitudinally polarized electrons on unpolarized protons at a Q(2) of 0.230 (GeV/c)(2) and a scattering angle of theta(e)=30degrees-40degrees. Using a large acceptance fast PbF2 calorimeter with a solid angle of DeltaOmega=0.62 sr, the A4 experiment is the first parity violation experiment to count individual scattering events. The measured asymmetry is A(phys)=(-5.44+/-0.54(stat)+/-0.26(sys))x10(-6). The standard model expectation assuming no strangeness contributions to the vector form factors is A(0)=(-6.30+/-0.43)x10(-6). The difference is a direct measurement of the strangeness contribution to the vector form factors of the proton. The extracted value is G(E)(s)+0.225G(M)(s)=0.039+/-0.034 or F-1(s)+0.130F(2)(s)=0.032+/-0.028.