New Measurements of the Beam Normal Spin Asymmetries at Large Backward Angles with Hydrogen and Deuterium Targets

New measurements of the beam normal single spin asymmetry in the electron elastic and quasielastic scattering on the proton and deuteron, respectively, at large backward angles and at ⟨Q^{2}⟩=0.22  (GeV/c)^{2} and ⟨Q^{2}⟩=0.35  ( GeV/c)^{2} are reported. The experimentally observed asymmetries are compared with the theoretical calculation of Pasquini and Vanderhaeghen [Phys. Rev. C 70, 045206 (2004).PRVCAN0556-281310.1103/PhysRevC.70.045206]. The agreement of the measurements with the theoretical calculations shows a dominance of the inelastic intermediate excited states of the nucleon, πN and the Δ resonance. The measurements explore a new, important parameter region of the exchanged virtual photon virtualities.

Measurement of strange quark contributions to the vector form factors of the proton at Q2 = 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 (Ge V / c);{2} is reported here. The measured asymmetry is A_{LR} = (-17.23 +/- 0.82_{stat} +/- 0.89_{syst}) x 10;{-6}. The standard model prediction assuming no strangeness is A_{0} = (-15.87 +/- 1.22) x 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 +/- 0.038 +/- 0.019 and G_{M};{s} = -0.14 +/- 0.11 +/- 0.11.