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Dear Folks,<br>
<br>
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!<br>
<br>
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.)<br>
<br>
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.<br>
<br>
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.)<br>
<br>
Should we redo this simulation for the measured collimator offset?<br>
<br>
Dasuni - in which direction did you offset the collimator? Is that the
same direction that the survey group finds that the collimator was
offset?<br>
<br>
- Larry<br>
<br>
-------- Original Message --------
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<th valign="BASELINE" nowrap="nowrap" align="RIGHT">Subject: </th>
<td>Re: TPE run</td>
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<th valign="BASELINE" nowrap="nowrap" align="RIGHT">Date: </th>
<td>Thu, 12 Aug 2010 14:31:02 -0400</td>
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<th valign="BASELINE" nowrap="nowrap" align="RIGHT">From: </th>
<td>David Kashy <a href="mailto:kashy@jlab.org"><kashy@jlab.org></a></td>
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<th valign="BASELINE" nowrap="nowrap" align="RIGHT">To: </th>
<td>Larry Weinstein <a href="mailto:weinstei@jlab.org"><weinstei@jlab.org></a></td>
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<br>
<br>
<pre>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!
<a href="http://www.jlab.org/accel/survalign/documents/dthallb/B1077.pdf">http://www.jlab.org/accel/survalign/documents/dthallb/B1077.pdf</a>
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
>
</pre>
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