[Sane-analysis] A_perp from SLAC data

[O. A. Rondon]

Hi,

Here is an updated plot of the perpendicular proton spin asymmetry
measured at SLAC, including a point that represents the average of all
data with <x> > 0.2 (label A_all)
http://twist.phys.virginia.edu/~or/sane/analysis/e155xap.pdf

Numerically it is A_all = -4.8e-3 +/- 1.4e-3. Since it integrates all
Q^2 from 1.8 to 6.7 GeV^2, and x from 0.16 to 0.53, it should be
comparable to our integrated asymmetries.

A(x_min > 0.2) = -8.0e-3 +/- 1.8e-3 is also definitely negative.

The expectation for SANE from these data would seem to be a small
negative A_80, but we need to keep in mind that there is a 2% to 5%
admixture of A_parallel ~ 0.4 at 80 degrees. Expressions for G2 for any
target field angle theta_N in terms of A_(near perp) and A_parallel are
posted here, on slide 2:
http://twist.phys.virginia.edu/~or/collmeet/siframes.htm

Solving for A_(near perp) in terms of G2, which could be calculated from
a model, and A_parallel is left as an exercise...

Cheers,

Oscar