[Color_transp] [EXTERNAL] HGC

[Dipangkar Dutta]

And here is an example of one of the ways we can get around this problem.
[image: image.png]


On Fri, Oct 31, 2025 at 2:17 PM William Henry via Color_transp <
color_transp at jlab.org> wrote:

> 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  (https://logbooks.jlab.org/entry/4418173 ).  Assuming
> no one else requests a change below 0.65 atm I would just need to pump out
> some heavy gas.
>
> William Henry
>
> On Oct 31, 2025, at 2:19 PM, Sebouh Paul <sebouh.paul at gmail.com> wrote:
>
> Hi Dave and Bill,
> Can you tell me more about this hole in the acceptance?  This sounds
> concerning to me.
> Thanks,
> Sebouh
>
> On Fri, Oct 31, 2025, 13:29 Dave Gaskell <gaskelld at jlab.org> wrote:
>
>
> Hi Sebouh -
>
>
> In principle, 0.65 atm should not be a problem - I think one would
>
> expect about 15 photoelectrons at that pressure.  However, there's a
>
> pretty big hole in the center of the acceptance that will need to be cut
>
> out.
>
>
> I'm cc-ing Bill Henry here as he takes care of the Cherenkov
>
> configuration for the Hall C experiments.  Bill - do you see any issue
>
> with running at 0.65 atm?
>
>
> Cheers,
>
> Dave
>
>
> On 10/31/25 12:35 PM, Sebouh Paul wrote:
>
> Hi Dave,
>
> We seek your advice regarding the HGC.  In the Pion CT experiment at
>
> Hall C, we will want to detect pi+ and filter out kaons in the SHMS
>
> using the HGC.  We calculated that in order to ensure that the index
>
> of refraction is less than 1/β for the highest momentum kaons within
>
> the acceptance in the SHMS at our highest momentum setting (the
>
> central momentum would be approx 9 GeV, exact value TBD), we'd need to
>
> have around 0.65 atm.  Would this be feasible?  Are there standard
>
> procedures we would need to follow, or anything else we would need to
>
> know, in order to set up the HGC for this experiment?
>
> Thanks,
>
> Sebouh
>
>
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