<div dir="ltr"><div>And here is an example of one of the ways we can get around this problem.</div><div><img src="cid:ii_mhfcdl470" alt="image.png" width="578" height="429"><br><br></div></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Fri, Oct 31, 2025 at 2:17 PM William Henry via Color_transp <<a href="mailto:color_transp@jlab.org">color_transp@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">
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I don’t see any problem with 0.65 atm. LAD used 0.38 atm and R-SIDIS ran with 1 atm. However when filling to 1 atm we ran out of the C4F8O and I had to finish the fill with C4F10 but they have almost the same index of refraction. See (<a href="https://logbooks.jlab.org/entry/4418173" target="_blank">https://logbooks.jlab.org/entry/4418173</a>).
Assuming no one else requests a change below 0.65 atm I would just need to pump out some heavy gas.
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<div dir="ltr">William Henry</div>
<div dir="ltr"><br>
<blockquote type="cite">On Oct 31, 2025, at 2:19 PM, Sebouh Paul <<a href="mailto:sebouh.paul@gmail.com" target="_blank">sebouh.paul@gmail.com</a>> wrote:<br>
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<div dir="ltr"><span>Hi Dave and Bill,</span><br>
<span>Can you tell me more about this hole in the acceptance? This sounds</span><br>
<span>concerning to me.</span><br>
<span>Thanks,</span><br>
<span>Sebouh</span><br>
<span></span><br>
<span>On Fri, Oct 31, 2025, 13:29 Dave Gaskell <<a href="mailto:gaskelld@jlab.org" target="_blank">gaskelld@jlab.org</a>> wrote:</span><br>
<blockquote type="cite"><span></span><br>
</blockquote>
<blockquote type="cite"><span>Hi Sebouh -</span><br>
</blockquote>
<blockquote type="cite"><span></span><br>
</blockquote>
<blockquote type="cite"><span>In principle, 0.65 atm should not be a problem - I think one would</span><br>
</blockquote>
<blockquote type="cite"><span>expect about 15 photoelectrons at that pressure. However, there's a</span><br>
</blockquote>
<blockquote type="cite"><span>pretty big hole in the center of the acceptance that will need to be cut</span><br>
</blockquote>
<blockquote type="cite"><span>out.</span><br>
</blockquote>
<blockquote type="cite"><span></span><br>
</blockquote>
<blockquote type="cite"><span>I'm cc-ing Bill Henry here as he takes care of the Cherenkov</span><br>
</blockquote>
<blockquote type="cite"><span>configuration for the Hall C experiments. Bill - do you see any issue</span><br>
</blockquote>
<blockquote type="cite"><span>with running at 0.65 atm?</span><br>
</blockquote>
<blockquote type="cite"><span></span><br>
</blockquote>
<blockquote type="cite"><span>Cheers,</span><br>
</blockquote>
<blockquote type="cite"><span>Dave</span><br>
</blockquote>
<blockquote type="cite"><span></span><br>
</blockquote>
<blockquote type="cite"><span>On 10/31/25 12:35 PM, Sebouh Paul wrote:</span><br>
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<blockquote type="cite"><span>Hi Dave,</span><br>
</blockquote>
</blockquote>
<blockquote type="cite">
<blockquote type="cite"><span>We seek your advice regarding the HGC. In the Pion CT experiment at</span><br>
</blockquote>
</blockquote>
<blockquote type="cite">
<blockquote type="cite"><span>Hall C, we will want to detect pi+ and filter out kaons in the SHMS</span><br>
</blockquote>
</blockquote>
<blockquote type="cite">
<blockquote type="cite"><span>using the HGC. We calculated that in order to ensure that the index</span><br>
</blockquote>
</blockquote>
<blockquote type="cite">
<blockquote type="cite"><span>of refraction is less than 1/β for the highest momentum kaons within</span><br>
</blockquote>
</blockquote>
<blockquote type="cite">
<blockquote type="cite"><span>the acceptance in the SHMS at our highest momentum setting (the</span><br>
</blockquote>
</blockquote>
<blockquote type="cite">
<blockquote type="cite"><span>central momentum would be approx 9 GeV, exact value TBD), we'd need to</span><br>
</blockquote>
</blockquote>
<blockquote type="cite">
<blockquote type="cite"><span>have around 0.65 atm. Would this be feasible? Are there standard</span><br>
</blockquote>
</blockquote>
<blockquote type="cite">
<blockquote type="cite"><span>procedures we would need to follow, or anything else we would need to</span><br>
</blockquote>
</blockquote>
<blockquote type="cite">
<blockquote type="cite"><span>know, in order to set up the HGC for this experiment?</span><br>
</blockquote>
</blockquote>
<blockquote type="cite">
<blockquote type="cite"><span>Thanks,</span><br>
</blockquote>
</blockquote>
<blockquote type="cite">
<blockquote type="cite"><span>Sebouh</span><br>
</blockquote>
</blockquote>
<blockquote type="cite"><span></span><br>
</blockquote>
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