[Tpe] systematic uncertainty for the test run

[Larry Weinstein]

Dear Folks,

Dasuni has run her simulation for the test run, offsetting the 2-cm rad 
phi collimator by 1 mm.  The results are shown in ENOTE 405.  She finds 
that a 1 mm offset changes the e+/e- incident lepton ratio by 8%.  Yikes!

Dave Kashy sent me the survey information for the test run (see link 
below).  It appears as though the collimator was offset by -0.24 mm with 
an uncertainty of about 0.15 mm.  (I can check with the survey group to 
find out their measurement uncertainty.)

If we blindly assume that the effect of the radphi collimator offset is 
linear with offset, then a 0.24 mm offset indicates a 2% shift in the 
e+/e- incident lepton yield.  If so, then John's systematic uncertainty 
is correct.

Note that we have a lot more statistics in the incident lepton ratio 
than Maryam so we can improve on that 0.990+/-0.006 that she reported.  
(We achieved the statistics by killing all particles with E < 0.5 GeV.)

Should we redo this simulation for the measured collimator offset?

Dasuni - in which direction did you offset the collimator?  Is that the 
same direction that the survey group finds that the collimator was offset?

- Larry

-------- Original Message --------
Subject: 	Re: TPE run
Date: 	Thu, 12 Aug 2010 14:31:02 -0400
From: 	David Kashy <kashy at jlab.org>
To: 	Larry Weinstein <weinstei at jlab.org>



Hi Larry,
I believe the brass collimator was a nice fit inside the lead
collimator. The lead collimator was surveyed on Transmittal B1077 and
you can find a copy here!
http://www.jlab.org/accel/survalign/documents/dthallb/B1077.pdf

I would guess the accuracy of this at +/- 0.15mm or better!

If you need to know more we will have to contact the survey group.
Dave





Larry Weinstein wrote:
>  Dear Dave,
>
>  How accurately positioned was the 2 cm brass collimator before the rad
>  phi wall during the 2006 TPE test run?  This has a crucial impact on
>  our systematic uncertainty for that measurement.
>  +/-1 mm
>  +/- 0.5 mm
>  +/- 0.25 mm
>

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