<html><head><meta http-equiv="Content-Type" content="text/html charset=windows-1252"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div>Richard, the shift corresponds to a change of 25 MeV in beam energy. I have computed it from the data (g, p -> 4pi, p (nothing missing)) and have plotted it at:</div><div><br></div><div><a href="https://logbooks.jlab.org/entry/3416791">https://logbooks.jlab.org/entry/3416791</a></div><div><br></div><div>So it’s about a whole counter. </div><div><br></div><div> - Paul</div><br><div><div>On Aug 9, 2016, at 3:33 PM, Richard Jones <<a href="mailto:richard.t.jones@uconn.edu">richard.t.jones@uconn.edu</a>> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div dir="ltr">Hello Paul and all, related to discussion at today's analysis meeting:<div><br></div><div>Brendan and I did a quick estimate of the sensitivity of the missing-mass-squared to the tagger energy scale in the region of the step revealed in the plots you showed today, around 4 GeV photon energy. We conclude that an offset as small as 6-8 MeV in the mean tagged photon energy associated with a given tagger counter could explain this step. The tagging counters in this region subtend about 25 MeV. So the observed step could be generated by systematic shifts in the position of the tagger hodoscope counters by as little as 1/3 of their width. Their width in this region is only 3mm wide, so the required scale for the shift would be 1mm. We looked at the geometry of the tagger and we think there is a large physical path-length distance between sets of counters with a boundary close to the region where your step occurs. The fact that one data point seems to interpolate across the step is not surprising, given Dan Sober's observation that beam divergence and multiple scattering effects create significant cross-over of tagged electrons between neighboring tagger bins. This break appears because the counters are arranged in rows with different distances from the focal plane, and at the downstream end of the hodoscope the path length between rays that hit the front row blocks and the back row is large compared to their spacing within a row.</div><div><br></div><div>All of this is to say that shifts of order 0.010 - 0.015 GeV^2 in missing-mass-squared are expected based on the present precision (~10MeV) of the calibration of the position of the boundaries of the tagger energy bins in this region. In the region of the microscope, I expect that the precision is better, of order 5MeV, but not by an order of magnitude.</div><div><br></div><div>-Richard Jones</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Mon, Aug 8, 2016 at 11:37 AM, Paul Mattione <span dir="ltr"><<a href="mailto:pmatt@jlab.org" target="_blank">pmatt@jlab.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">The next analysis working group meeting will be tomorrow at 1:30pm in room A110. The agenda is posted at:<br>
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<a href="https://halldweb.jlab.org/wiki/index.php/August_9,_2016,_Analysis_Working_Group" rel="noreferrer" target="_blank">https://halldweb.jlab.org/<wbr>wiki/index.php/August_9,_2016,<wbr>_Analysis_Working_Group</a><br>
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- Paul<br>
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