Measurement of the beam-normal single-spin asymmetry for elastic electron scattering from 12C and 27Al

Le résumé fourni par la source

We report measurements of the parity-conserving beam-normal single-spin\nelastic scattering asymmetries $B_n$ on $^{12}$C and $^{27}$Al, obtained with\nan electron beam polarized transverse to its momentum direction. These\nmeasurements add an additional kinematic point to a series of previous\nmeasurements of $B_n$ on $^{12}$C and provide a first measurement on $^{27}$Al.\nThe experiment utilized the Qweak apparatus at Jefferson Lab with a beam energy\nof 1.158 GeV. The average lab scattering angle for both targets was 7.7\ndegrees, and the average $Q^2$ for both targets was 0.02437 GeV$^2$ (Q=0.1561\nGeV). The asymmetries are $B_n$ = -10.68 $\\pm$ 0.90 stat) $\\pm$ 0.57 (syst) ppm\nfor $^{12}$C and $B_n$ = -12.16 $\\pm$ 0.58 (stat) $\\pm$ 0.62 (syst) ppm for\n$^{27}$Al. The results are consistent with theoretical predictions, and are\ncompared to existing data. When scaled by Z/A, the Q-dependence of all the\nfar-forward angle (theta < 10 degrees) data from $^{1}$H to $^{27}$Al can be\ndescribed by the same slope out to $Q \\approx 0.35$ GeV. Larger-angle data from\nother experiments in the same Q range are consistent with a slope about twice\nas steep.

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