[Halld-tagger] DBeamPhoton tests

[Alexander Austregesilo]

Dear beamline group,

I produced 3 runs from the current data taking period with three 
different versions of the beam photon factory:

runs:
71463: 150nA
71469: 250nA
71724: 350nA

versions:
ver09: master (April 7th)
ver10: sdobbs_beamphoton_mod (merged with master April 7th)
ver11: tagm_fixes_for_2020_rtj (merged with master April 7th)

 From a first look at the monitoring plots (easiest with version browser 
https://halldweb.jlab.org/cgi-bin/data_monitoring/monitoring/versionBrowser.py), 
I see almost no difference for the 350nA run:

version | rho yield | DBeamPhotons
ver09  |  5.08    |  67.7
ver10  |  4.96    |  65.2
ver11  |  5.03    |  67.6

For the other 2 runs, I see a significant decrease in the number of beam 
photons from Sean's branch (~20%), while the decrease is smaller for 
Richard's. Both branches show a loss of about 10% in rho yields.

All merged histogram files can be found here:

/cache/halld/offline_monitoring/RunPeriod-2019-11/ver{09,10,11}/hists/hists_merged

Please have a look for yourself. I hope somebody can summarize this 
study during the production and analysis meeting tomorrow.

Cheers,

Alex