Measurement of Strange Quark Contributions to the Vector Form Factors of the Proton atQ2=0.22(GeV/c)2

A new measurement of the parity violating asymmetry in elastic electron scattering on hydrogen at backward angles and at a four momentum transfer of $Q^2=0.22(\mathrm{GeV}/c{)}^2$ is reported here. The measured asymmetry is $A_{\mathrm{LR}}=(-17.23\pm {0.82}_{\mathrm{stat}}\pm {0.89}_{\mathrm{syst}})\times {10}^{-6}$. The standard model prediction assuming no strangeness is $A_0=(-15.87\pm 1.22)\times {10}^{-6}$. 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, $G_E^s=0.050\pm 0.038\pm 0.019$ and $G_M^s=-0.14\pm 0.11\pm 0.11$.