  The parity-violating cross-section asymmetry in the elastic scattering of
polarized electrons from unpolarized protons has been measured at a
four-momentum transfer squared Q2 = 0.624 GeV and beam energy E =3.48 GeV to be
A_PV = -23.80 +/- 0.78 (stat) +/- 0.36 (syst) parts per million. This result is
consistent with zero contribution of strange quarks to the combination of
electric and magnetic form factors G_E^s + 0.517 G_M^s = 0.003 +/- 0.010 (stat)
+/- 0.004 (syst) +/- 0.009 (ff), where the third error is due to the limits of
precision on the electromagnetic form factors and radiative corrections. With
this measurement, the world data on strange contributions to nucleon form
factors are seen to be consistent with zero and not more than a few percent of
the proton form factors.
