[Halla_pi0] pi0 discussion and meeting

[richard lindgren]

Greetings,

JLab folks will  meet in Doug's office at JLab and UVa folks will meet in Room 120
at UVA at 1:30. Below is an email from Cole with a link to his website with a new cross section Table
with new replay by Khem incorporating fringe field effects in BigBite and (I think) Vince's HRS algorithm for phi and theta smaller acceptance due to not using the outer scintillators in the focal plane. Of course the replay includes corrections of any errors in the old scripts that Khem may have found. 

Here is a partial summary of our discussion last night.

To see effects of the changes in the BB field compare Nov and June data. Look at the Bottom plots  of acceptance (black points ) for W=1.07475, HRS=12.5 deg, and BB=48 deg. You will see that the black dots follow the red data  better at 48 deg.

However, there are still problems. Look at Nov data for the theta and phi distributions for W= 1.07475,  Q2=0.085 from HRS=14.5 degrees with the same kinematics from HRS=16.5 deg. The data at 14.5 deg overshoots all the calculations at all BB angles by about 30% whereas at 16.5 deg the data is pretty much in agreement
with all the calculations for the same Q value. Perhaps, HRS acceptance isn't quite right.

Similar disagreement also occurs at W= 1.07475,  Q2=0.065 from HRS=12.5 degrees with the same kinematics from HRS=14.5 deg at selected theta angles
like at theta = 130 and 150 deg.

This effect really shows up if you look at Coles total cross section plots vrs Q2 for different HRS settings. Click on  ΔW=0.5-3.5 FLAT vs SAMP

The Q2 dependence within the HRS for a given HRS setting is off. When you compare the total cross section at the same Q2 determined form different HRS angles but overlapping in Q2, you get disagreement.


The lowest Q2= 0.045  has the wrong bin size so do not take that point seriously.

THis is enough for now. See you at 1:30 PM.

Richard





> I've updated my Summary page with Khem's latest table:
> 
> http://clasweb.jlab.org/wiki/index.php/Summary
> 
> The new table results are under NOV 2011, the previous
> results are under JUN 2011.  I also compare to the
> new MAMI data by averaging our Q2 data on either side
> of the MAMI Q2 points.  The Legendre fits at Q2=0.047
> are unstable but I may be able to improve that.
> 
> The BB acceptance looks more consistent with the data
> than before and we are seeing smoother looking phi*
> distributions.  It looks like there are still some
> Q2 dependent normalization problems, but this may
> change when Khem looks at the Q2 vs e- phi cuts.
> 
> The radiative corrections are still crude, just
> a single number applied to all points.  When we decide
> on our final MM2 cut I will recalculate them.
> 
> Cole
> 


Dr. Richard Lindgren
Physics Department
University of Virginia




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