Measurement of the Weak Neutral Current Form Factor of the Proton at high momentum transfer*

The elastic form factors of the proton and neutron are fundamental observables representing a projection of the internal structure of the nucleon. Measurements of the electromagnetic form factors of the proton and neutron can be combined to separately determine contributions from the u and d constituents of the nucleon, however, this interpretation relies on assumptions of both charge symmetry and negligible contributions from strangeness form factors. These assumptions are virtually untested at high momentum transfer, introducing a large uncertainty in flavor-separated form factors. An improvement in the uncertainty in flavor decomposition of u-quark and d-quark contributions to the nucleon form factors requires more stringent limits on possible strangeness contributions, well beyond those from existing data or lattice QCD calculations. The COIN experimental (E12-23-004) at Jefferson Lab In Hall C aims to measure parity-violation with coincidence detection of electron-proton elastic scattering at Q2=2.5 GeV/c2, to determine the weak form factor of the proton at high momentum transfer. This measurement would present an important development in the experimental study of the strangeness content of the nucleon form factor flavor decomposition. The result will provide a crucial check of the assumptions of both charge symmetry and negligible contributions from strangeness form factors which will greatly improve the precision of the flavor-separated electromagnetic nucleon form factors.