[Halld-pid-upgrade] [New Logentry] Follow-up Re: DIRC bar-by-bar diagnostics: early Fall 2019

[yunjiey at jlab.org]

Logentry Text:
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As a follow-up, I show some results of an analysis of the photon yields within the FastDIRC framework.

To help interpretation, I will give a brief description of how these numbers are obtained:
1) Given an extrapolated track with its kinematics (position, angle and momentum), FastDIRC performs a per-track fast Cherenkov photon generation and ray-tracing (50k photons per track for this study) given the geometry model. The result of this is O(50k) photons (i.e. the support points) each with its (x,y,t) locations at the photo-detection plane (note that so far it doesn't involve any modeling of the detection resolution, both timing and position).
2) For each observed hit on given its pixel and hit time, I select this hit if (i) it arrives within +/- 5 ns and (ii) within 8.5 mm (~ 6mm*sqrt(2), radius of 1 pixel) of any one of the 50k support points. For each track, the number of the observed hits that pass the above selection contributes one entry in each of the histograms.

I'd like to emphasize that this observable doesn't involve FastDIRC's PDF-based reconstruction and doesn't assume any detection resolution model, or the so-called distance measure. It is an independent modeling of our bar box + optical box geometry as well as the photon generation and propagation.

Attached are three files. 
Nph_Bar_XBin.pdf: it divides things into individual bars and different locations in x. Each page corresponds to one bar. To compare with Justin's DataBarNphotons.pdf
Nph_Bar.pdf: it integrates over x-bins along the bar. I organized them into 4 columns corresponding to the 4 bar boxes (bar box numbers from left to right: 10, 11, 1 and 0) and 12 rows corresponding to 12 bars in each bar box (from top to bottom corresponding to going away from beamline). Each row in columns 1 vs 3, and 2 vs 4 are in "mirror" locations w.r.t to the beamline for easy comparison.
Nph_BB.pdf: it integrates over bars and are divided only into the 4 bar boxes.

The tracks have rho and phi selection, as well as some track quality selections (which may not be optimal since more calibration of the other detectors are needed), performed by the dirc_tree plugin from the same run range and track reconstruction as Justin's results. The momentum requirement is more than 4 GeV. The results have lower stats in the sample compared to Justin's likely due to rho, phi selection and other track quality selections.

Nonetheless, they seem to point the same picture as Justin's results, i.e. bar box 0 (uppermost bar box) seems to have a consistently lower photon yield compare to the other boxes (especially bar box 11, the bottommost one, which is at the "mirror" location w.r.t. bar box 0). The photon yield numbers also seem to be consistent between the two independent analysis frameworks.

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