<div dir="ltr">Hi Andrew,<div><br></div><div>This is due to improper gas flow in layers 1 & 3 because they were manufactured and sent to us with a defect. Therefore they do not have uniform gas flow and the GEM foils bulge slightly inside. We have reduced gas flow in these layers to mitigate the effect. In the pdf attached below I have the plots showing this during GMn running. The color scale shows the average time sample peak. Clearly the layers except for 1 & 3 are uniform. Interestingly, in layer 1 & 3 you can clearly see the spacers on the GEMs. If you look at the picture I have attached of the GEM foil with the spacer it perfectly matches up with the timing hit map.</div><div><br></div><div>Best,</div><div>Sean</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, Apr 27, 2023 at 4:49 PM Andrew Puckett via Sbs_gems <<a href="mailto:sbs_gems@jlab.org">sbs_gems@jlab.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div class="msg-4671764791414041665">
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<p class="MsoNormal">Hello all, </p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">As you may remember, we saw that GEM layers 1 and 3 in BigBite exhibited significantly wider timing distributions during GMN (and GEN), even for the good signals. Recently, for the first time, I tried to get a closer look at the uniformity
(or lack thereof) of the signal timing for the GEMs, with some interesting findings. I wanted to solicit the opinions of the GEM hardware experts to see if this is something that has been seen before, and if the pattern has a simple explanation, what the physical
mechanism might be, and whether it could be mitigated in the future.</p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">The first picture shows the average signal timing (U+V)/2 on the x axis for the five BigBite GEM layers versus global “x” position of the hit on the y axis. As we can see, in UV layers 0 and 2, the timing is relatively uniform as a function
of vertical hit position, whereas for layers 1 and 3, there is a significant correlation that follows a similar x dependence. Layer 4 also exhibits an x dependence qualitatively similar to layers 1 and 3 but the magnitude is smaller compared to the resolution.
Also, in all cases the width of the good timing peak for layers 1 and 3 is wider (~10 ns) compared to layers 0, 2, and 4 (~6-7 ns), even after accounting for the non-uniformity versus position. The second attachment shows the correlation with the y-coordinate.
Here layers 1 and 3 still show a fairly significant correlation while layers 0, 2, and 4 show almost no correlation.
</p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">While this is something we can in principle measure and correct for if we want to apply tighter timing cuts in the analysis, I would love to hear people’s ideas for what is happening here. Thoughts?</p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">Best regards,</p>
<p class="MsoNormal">Andrew</p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal"><span><img width="2113" height="1207" style="width: 22.0104in; height: 12.5729in;" id="m_-7896495896050649658Picture_x0020_1" src="cid:187c5a0217e4cff311"></span></p>
<p class="MsoNormal"><span><img width="2113" height="1207" style="width: 22.0104in; height: 12.5729in;" id="m_-7896495896050649658Picture_x0020_2" src="cid:187c5a0217e5b16b22"></span></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
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<p class="MsoNormal"><span style="font-size:12pt;font-family:Century,serif;color:black">Andrew Puckett<br>
Associate Professor, Physics Department<br>
University of Connecticut<br>
196 Auditorium Road, Unit 3046<br>
Storrs, CT 06269-3046<br>
Office phone: (860) 486-7137<br>
</span><a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__puckett.physics.uconn.edu&d=DwMFaQ&c=CJqEzB1piLOyyvZjb8YUQw&r=IY9rjQPVeUBORHn2z0jGy7U2Cc-U0-dYM3Rqg9Kcgwk&m=mqnr-u03fz88sFWzNehQ_K9gIZ354OKqu8BXbauy_ozF8ZM098hMov7wraXZim1F&s=PWgMf4P2IDtkIF4iMhHRA-8Ko-zkQSdC33M2uBySJBo&e=" title="https://puckett.physics.uconn.edu" target="_blank"><span style="font-size:12pt;font-family:Century,serif">https://puckett.physics.uconn.edu</span></a><span style="font-size:12pt;font-family:Century,serif;color:black"><br>
</span><a href="mailto:andrew.puckett@uconn.edu" target="_blank"><span style="font-size:12pt;font-family:Century,serif">puckett@jlab.org</span></a></p>
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