Measurement of the Weak Neutral Current Form Factor of the Proton at 2.5 (GeV/c)2*

The proposed COIN experiment at Jefferson Laboratory will determine the weak neutral current form-factor of the proton at 2.5 (GeV/c)2 via a measurement of the parity-violating asymmetry in elastic longitudinally polarized beam electron-proton scattering. The result will find or place an upper limit on the strangeness form factor at large momentum transfer. This is key to the flavor decomposition of u-quark and d-quark contributions to the nucleon form factors, which requires more stringent limits on possible strangeness contributions, well beyond those from existing data or lattice QCD calculations. Motivating this measurement is the experimental observation that u-quark and d-quark contributions to the Pauli and Dirac factors are nearly constant in ratio at low Q2, while the d-quark component drops relative to the u-quark component with increasing Q2  This measurement would present an important development in the experimental study of the strangeness content of the nucleon form factor flavor decomposition.