[Halld-offline] [EXTERNAL] Re: Fw: No TAGH Hits in Simulation

[Richard Jones]

Hello Igal et. al.,

Please create an issue on github describing this problem, and I will submit
a fix in a side branch. Once you have verified that this works, it will be
merged into the master branch.

-Richard Jones

On Tue, Jan 26, 2021 at 2:56 PM Igal Jaegle <ijaegle at jlab.org> wrote:

> *Message sent from a system outside of UConn.*
>
> Below an e-mail of Drew noting a bug in the tagger counter.
>
> tks ig.
>
> ------------------------------
> *From:* Drew Smith <andrew.p.smith at duke.edu>
> *Sent:* Tuesday, January 26, 2021 2:34 PM
> *To:* Alexander Somov <somov at jlab.org>; Igal Jaegle <ijaegle at jlab.org>;
> Tyler J Hague <tjhague at ncat.edu>
> *Subject:* [EXTERNAL] No TAGH Hits in Simulation
>
> Hi Guys,
>
>
> I believe I found the reason why there are no tagger hodoscope hits
> produced in my simulations for the region below the microscope minimum
> energy. As you recall, we decided to set the scaled_energy_range values for
> hodoscope counters 128-178 (the counters whose energies would otherwise
> span the microscope region) to 0. However, this introduces a problem in the
> 'addTaggerPhoton' function in hdgeant4 (defined in GlueXDetectorTAG.cc)
> which is responsible for generating tagger hits for beam photons.
> Specifically, if you look at lines 138-149 of GlueXDetectorTAG.cc it
> becomes clear that because this way of setting the scaled_energy_range
> table for the hodoscope will not work.
>
> For example, if there is a beam photon at 6 GeV, these lines of code will
> give a starting guess for the corresponding hodoscope counter of (line
> 139): int i = 274 * (6 GeV - 11.6061 GeV) / (0 GeV - 11.6061 GeV) = 132
> (this particular example uses the endpoint energy for run 61321). Next, the
> code compares whether the beam photon is less than the minimum energy for
> this tagger counter. If so, then it increments the counter number by 1 and
> re-checks this until it finds a counter where this is no longer true.
> However, for counter 132 the minimum energy is 0 GeV because the
> scaled_energy_range is set to 0. So, it does not increase the counter
> number until the actual counter is found, and in the end no tagger hits are
> constructed.
>
> The question then is how can we correct this? If the scaled_energy_range
> table is reverted to its previous state, then this will also be a problem
> (albeit a lesser problem). For example, with the old scaled_energy_table,
> if I generate events with gen_primex_compton for tagger hodoscope counter
> 200, then the photons will not be reconstructed in this counter but would
> instead be reconstructed in one or more of the counters between 128 and
> 178. The photon beam energy would be approximately right, but we would lose
> quite a lot of events because of gaps between adjacent counters.
>
> Alternatively, I can make a change to the hdgeant4 code where the
> hodoscope hits are registered to avoid this specific problem and allow us
> to keep counters 128-178 set to 0. However, I'm sure other GlueX people
> would not want me making changes to their simulation code, so I would
> probably only want to make this change to my own local installation of
> hdgeant4.
>
> Does anyone have suggestions on how to best handle this problem?
>
> Igal,
>
> In your simulations for the eta photoproduction, did you see tagger
> hodoscope hits registered for beam energies between ~4-7 GeV? I think below
> 4 GeV there should be no problem, and above the microscope energies there
> should also be no problem.
>
>
> Best,
> -- Drew
>
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