[Hallc_sidis_analysis] HMS gas cherenkov counter

[bosted at jlab.org]

According to my notes, we actually had 0.45 atm of C4F8O in the HMS
Cerenkov (at least in the Spring 2018). Looking at run 6025 (central
momentum 4.5 GeV), I can see the pion signal starting to vanish at dp/p <
-10%, so
the threshold appears to be around 4.2 GeV. All of the CSV runs have
HMS momenta above 4.2 GeV, so the negative pions are always making a
signal, increasing with momentum to be almost the same as the electrons at
the
highest momentum (6.2 GeV). So, the HMS Cerenkov is not terribly
useful in rejecting pi- for this experiment.
My choice is to just put a threshold of 1 or 2 pe for the HMS Cerenkov,
and mainly use the shower counter to sperate pi and e. I'm using a cut of
about 0.75 in the shower track total energy.

However, if you want to use a higher cut of 4 or 5 p.e., if might give
a better result. I suggest to try both and see which one minimizes the
final error bar (or include as part of the systematic studies).

Peter

> 0.5 atm of C4F8O should have pion threshold of around 3.8 or 3.9 GeV/c,
> I think.
>
> -- Brad
>
> On Wed, 11 Dec 2019, bosted at jlab.org wrote:
>
>> Hi all,
>>    In case you didn't see this, here is a nice review of Cherenkov
>> counters:
>> https://www.jlab.org/indico/event/296/session/11/contribution/11/material/slides/0.pdf
>>    So the HMS should have 0.5 atm of C4Fsomething. I didn't see the pion
>> threshold mentioned. Brad, can you give us the number?
>> I imagine that it is aobut 5.2 GeV.
>>    Of particular note: one HMS mirror was broken until it was fixed in
>> summer 2018. I use a cut dp/p > -5% for runs in Spring18 to keep an
>> efficiency >98%.
>>    Peter
>> p.s. Sorry I left the meeting early: my computer crashed.  If anyone is
>> interested in using my "fiducial acceptance" regions for each
>> spectrometer, let me know. But maybe just as a starting point: you may
>> want to make your own. I know I should make a writeup, but I am swamped
>> with music gigs at the moment and won't be doing much physics until
>> after
>> Jan. 5.
>>
>> > Hi All,
>> > We will have the regular SIDIS analysis meeting tomorrow (Wednesday)
>> at
>> > Noon EDT.
>> > For those at JLab Room F227 has been reserved.
>> >
>> > The Meeting URL is
>> > https://bluejeans.com/648672553/
>> >
>> >
>> > Please plan on showing a few slides on your work and please upload the
>> > slides to the SIDIS elog at:
>> > https://hallcweb.jlab.org/elogs/SIDIS+Pt+and+CSV+Experiments+Analysis/
>> > <https://hallcweb.jlab.org/wiki/index.php/SIDIS#Weekly_Meetings>
>> >
>> > Cheers
>> > Dipangkar
>> > _______________________________________________
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>> > Hallc_sidis_analysis at jlab.org
>> > https://mailman.jlab.org/mailman/listinfo/hallc_sidis_analysis
>> >
>>
>>
>>
>