Parity violation and nucleon structure

Abstract

Measurements of proton and neutron spin structure functions indicate that a large fraction of the spin of the proton is not carried by valence quarks. This has stimulated theoretical interest in determining strange quark contributions to hadronic matrix elements. While the spin measurements determine s̄γμγ5s, the vector matrix element s̄γμs can be accessed through the nucleon’s neutral weak form factors as determined in parity violating electron scattering. Experiments are presently underway at MIT-Bates, Mainz and Jefferson Laboratory. The SAMPLE experiment at MIT-Bates recently published a measurement of the neutral weak magnetic form factor GMZ at low momentum transfer, from which the strange quark contribution GMs can be extracted. A summary of SAMPLE is presented, along with future plans at Jefferson Laboratory.