Introduction

Sometime before this morning the spin rotators were changed as follows: blue beam rotator current was reduced by about 1 amp and yellow beam rotator current were reduced by 4-5 amps.  Runs 10097042-3 were taken after the change with about 3M events each.

Important

In order to help alleviate some of the confusion about which direction the beam is pointing, etc. I have changed my phi distribution to correspond to a more normal coordinate system.  Now phi=0 corresponds to the x=0 and phi increases as you move clockwise.  I've attached an excel spreadsheet that shows this binning in terms of slat number and how the L-R asymmetry is calculated for each phi point.

The fit is still Asin(x-B).  We know from analyzing the transverse data with this coordinate system that the angle given by the fit is the angle relative to vertical - i.e. that it gives an angle close to 0 when running transversely.

Results

These runs were part of fill 10505.  The average yellow beam polarization at flattop is 40.3+/-1.1%.  The average blue beam polarization at flattop is 38.8+/-1.1%. 

(1) Slat by slat asymmetires.

 (2) Phi asymmetries.

Interpretation

Does the new coordinate system make sense?  Well if you look at the slat by slat asymmetries for the east yellow forward scattering, you see an asymmetry in the horizontal slats.  It is positive for slats 1-4 and negative for slats 5-8.  This means that the yellow beam is pointing to the left.  The blue beam is the opposite, we see negative for slats 1-4 and positive for slats 5-8.  This means the blue beam is pointing to the right.  If this is so, I should get a an angle near -pi/2 for yellow and near +pi/2 for blue, which is what I fit.

Using the analyzing power of 7.5% I then get for the transverse components:

Yellow: fractional component 26.0 +/-  4.3% with an angle of -2.1 rad relative to vertical.

Blue: fractional component 22.4+/-2.5% with an angle of +1.6 rad relative to vertical.