Measurement of Strange Quark Contributions to the Vector Form Factors of the Proton at Q2=0.22 (GeV/c)2

摘要

A new measurement of the parity violating asymmetry in elastic electron scattering on hydrogen at backward angles and at a four momentum transfer of Q2=0.22 (GeV/c)2 is reported here. The measured asymmetry is ALR=(-17.23±0.82stat±0.89syst)×10-6. The standard model prediction assuming no strangeness is A0=(-15.87±1.22)×10-6. In combination with previous results from measurements at forward angles, it is possible to disentangle for the first time the strange form factors at this momentum transfer, G=0.050±0.038±0.019 and G=-0.14±0.11±0.11.