2004/01/16 by A4 Collaboration, F. E. Maas, P. Achenbach +37 · 2 citations
Chemistry · Physics and Astronomy · #Advanced NMR Techniques and Applications #Particle physics theoretical and experimental studies #Quantum Chromodynamics and Particle Interactions #nucl-ex
paper · pdf · doi:10.1103/physrevlett.93.022002
published as Phys.Rev.Lett.93:022002,2004 · 5 pages, 3 figures, submitted to Phys. Rev. Letters on Dec 11, 2003
arxiv created 2004/01/16 · openalex publication_date 2004/07/07 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/30
We report on a measurement of the parity-violating asymmetry in the scattering of longitudinally polarized electrons on unpolarized protons at a Q2 of 0.230 (GeV/c)2 and a scattering angle of \ensuremathθe=30\ifmmode^∘\else\textdegree\fi--40\ifmmode^∘\else\textdegree\fi. Using a large acceptance fast PbF2 calorimeter with a solid angle of \ensuremathΔ\ensuremathΩ=0.62 sr, the A4 experiment is the first parity violation experiment to count individual scattering events. The measured asymmetry is Aphys=(\ensuremath-5.44\ifmmode±\else\textpm\fi0.54stat\ifmmode±\else\textpm\fi0.26sys)\ifmmode×\else\texttimes\fi10^\ensuremath-6. The standard model expectation assuming no strangeness contributions to the vector form factors is A0=(\ensuremath-6.30\ifmmode±\else\textpm\fi0.43)\ifmmode×\else\texttimes\fi10^\ensuremath-6. The difference is a direct measurement of the strangeness contribution to the vector form factors of the proton. The extracted value is GEs+0.225GMs=0.039\ifmmode±\else\textpm\fi0.034 or F1s+0.130F2s=0.032\ifmmode±\else\textpm\fi0.028.