[Color_transp] [EXTERNAL] HGC

[William Henry]

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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