Abstract
We report on a measurement of the parity-violating asymmetry in the scattering of longitudinally polarized electrons on unpolarized protons at a of and a scattering angle of . Using a large acceptance fast calorimeter with a solid angle of , the A4 experiment is the first parity violation experiment to count individual scattering events. The measured asymmetry is . The standard model expectation assuming no strangeness contributions to the vector form factors is . The difference is a direct measurement of the strangeness contribution to the vector form factors of the proton. The extracted value is or .
- Received 11 December 2003
DOI:https://doi.org/10.1103/PhysRevLett.93.022002
©2004 American Physical Society