[Halld-offline] diagnosis and fix to photon gun failure

[Naomi Jarvis]

This looks good.

New:

[image: fix.png]

Old:

[image: before.png]

& the new hddm file is 4x larger than the old one.

Naomi.

On Sun, Mar 3, 2019 at 8:27 AM Richard Jones <richard.t.jones at uconn.edu>
wrote:

> Hello Jon, Naomi, [posted to mailing list so it persists after git issue
> is resolved]
>
> What you uncovered turned out to be a nasty tracking bug in the internals
> of the G4 tracking library that was abandoning the tracking of neutral
> particles under certain special circumstances. Although those circumstances
> were relatively rare, only once per 10k events or so, if they happened to
> occur on the last track in an event, then the tracking of all subsequent
> events would fail because there are only neutrals coming from your particle
> gun. I have submitted a new pull request that fixes this bug, and I ran a
> single run over 1M events to verify it works. Here is the plot that I get.
> Prior to this, I got the same results you did after event ~340,000. Now it
> runs to 1M events no problem.
>
> [image: image]
> <https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fuser-images.githubusercontent.com%2F7832920%2F53695391-3de8ed80-3d89-11e9-9e69-2217f678fdd3.png&data=02%7C01%7CHallD-Offline%40jlab.org%7Ce6e4b6f1f69d4cc4b4f708d6a0570219%7Cb4d7ee1f4fb34f0690372b5b522042ab%7C1%7C0%7C636872692899916071&sdata=1J9Df2E4%2B0VrSGGcAdwmxlWkVD5X5Hj3ovdBegs%2BCaY%3D&reserved=0>
>
> Please execute the pending pull request and verify that it works for you
> before closing this issue. I will follow up with a detailed description of
> the diagnosis and fix, in case you are interested.
> -Richard
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