[Frost] target depolarization

[Michael Dugger]

Hi,

I have some results regarding the target polarization as a function of 
z-vertex that might be of interest. In short: it looks like we can see the 
downstream de-polarization of the target using the pi+ n reaction, and 
this de-polarization is a large effect.

Method:
1) Isolate regions of the gamma p -> pi+ n reaction where the E 
observable appears to be always less than -0.5. By looking at Brian's 
slides 
(http://www.jlab.org/Hall-B/secure/g9/morrison/brian_E_obs_2-10-2011.pdf), 
I chose the region in cos(theta_cm) between -0.4 and +0.7 for E_gamma 
between 1500 and 1600 MeV, and cos(theta_cm) between -0.7 and +0.8 for 
E_gamma between 1600 MeV and 1750 MeV.

2) Slice the data into 32 z-vertex bins from z-vertex = -4.0 to +4.0 cm.

3) Find the |E| observable, with no carbon subtraction or other 
background subtraction, for the missing mass (assumed reaction gamma p -> 
pi+ X) between 0.89 and 0.99 GeV/c^2. This was performed assuming that our 
current values of the beam*target polarization are correct.

4) Plotted the results.

You can see the results here:
http://www.jlab.org/~dugger/g9/g9a/polZ1.gif

Top panel is z-vertex of the denominator of E.
Bottom panel is the absolute value of E as a function of z-vertex.

This looks to be a huge effect. We need to figure out how to get an 
average polarization.

Questions: Can we quantify the region in z where the low field NMR 
measurement took place? Is there any pictures, or diagrams the show the 
placement of the low-field NMR coils?

We can try and use the high field NMR data but there are a lot of 
"anomalous" measurements that would leave gaps in our polarization 
tables. See the entries (red implies anomalous measurement) in the list 
given on 
http://clasweb.jlab.org/rungroups/g9/wiki/images/6/66/Clf_spreadsheet3_landscape.jpg 
.
Moreover, in general, the the high field NMR measurements made previous 
to re-polarization might be questionable.

When I look at the baseline subtracted high field NMR signals on the FROST
webpage:
http://clasweb.jlab.org/rungroups/g9/wiki/images/c/c1/P4_2_areas_edited.jpg
they look bad.

Question: Are these a fair representation of what the baseline subtracted
NMR signal looks like for the high field just previous to re-polarization?

All the other baseline subtracted NMR plots look OK:

High field after polarization ->
http://clasweb.jlab.org/rungroups/g9/wiki/images/c/ca/P1_1_areas_edited.jpg

Low field after right after polarization ->
http://clasweb.jlab.org/rungroups/g9/wiki/images/d/d4/P2_1_areas_edited.jpg

Low field just before polarization ->
http://clasweb.jlab.org/rungroups/g9/wiki/images/9/90/P3_2_areas_edited.jpg

Question:
Could the poor quality of the baseline subtracted high-field NMR plots be
due to the large gradients in the butanol polarization with respect to
the beam?

Thanks for your time.

-Michael