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Measurement of the beam-normal single-spin asymmetry for elastic electron scattering from C12 and Al27
We report measurements of the parity-conserving beam-normal single-spin
elastic scattering asymmetries on C and Al, obtained with
an electron beam polarized transverse to its momentum direction. These
measurements add an additional kinematic point to a series of previous
measurements of on C and provide a first measurement on Al.
The experiment utilized the Qweak apparatus at Jefferson Lab with a beam energy
of 1.158 GeV. The average lab scattering angle for both targets was 7.7
degrees, and the average for both targets was 0.02437 GeV (Q=0.1561
GeV). The asymmetries are = -10.68 0.90 stat) 0.57 (syst) ppm
for C and = -12.16 0.58 (stat) 0.62 (syst) ppm for
Al. The results are consistent with theoretical predictions, and are
compared to existing data. When scaled by Z/A, the Q-dependence of all the
far-forward angle (theta < 10 degrees) data from H to Al can be
described by the same slope out to GeV. Larger-angle data from
other experiments in the same Q range are consistent with a slope about twice
as steep