Shifting CRT T0 and T1 properly in CAFMaker

[jedori0228]

CRT T1 is a time reference to the trigger unlike T0 which is an absolute timestamp. When CRTUseTS0 is set to false and we are saving T1 in CRTHit::time, it should be shift by +srtrigger.trigger_within_gate

[miquelnebot]

@ jedori0228 I assume this goes with
SBNSoftware/sbnobj#72

And these are targeting production but not critical right now for a patch so they will be deferred to next production release early next year. Please say otherwise.

[miquelnebot]

@henrylay97 can you weigh in as in the obj one, please?

[henrylay97]

Of course. It's not an area of the code I'm familiar with so apologies if my question is naive.

Principle looks fine to me ✔️

I appreciate that this PR purely allows for a different reference time. Its not clear to me where its ensured that MC doesn't have this correction applied? Given this function is applied regardless of whether the event is MC or data? Is the value carefully set elsewhere to avoid this problem?

[jedori0228]

@ jedori0228 I assume this goes with SBNSoftware/sbnobj#72

And these are targeting production but not critical right now for a patch so they will be deferred to next production release early next year. Please say otherwise.

Yes, it only affects CAFMaker, and not critical for now.

[jedori0228]

Timings in MC is not understood fully yet (at least for me), and we are not doing this shifts for it; ReferenceCRTToBeam() can/should be set to false.

[henrylay97]

So my worry is that it currently defaults to true, so we would need to actively set it to false in icaruscode & sbndcode fcls

https://github.com/SBNSoftware/sbncode/blob/develop/sbncode/CAFMaker/CAFMakerParams.h#L332-L335

[jedori0228]

(Tagging @francescopoppi and @gputnam)
I made few more updates to properly shift and save T0. With FixCRTReferenceTimes(), we initially fill SRCRTHit::t0 (double) with sbn::crt::ts0()/1000. (int64_t). Here we already lose precision. I picked one CRTHit object and printed raw ts0() value and its converted version to SRCRTHit::t0;

crthits[i].ts0()             = 1 656 344 589 827 546 979 (ns)
srcrthits.back().t0          = 1.65634e+15 (us)
                      *1000 -> 1 656 344 585 695 133 696 (ns)

Also, assigning -srtrigger.beam_gate_time_abs/1e3 to double CRT_reference_time caused a problem:

(true value) srtrigger.beam_gate_time_abs = 1656344589830460080 ns
(when saved to a double) -srtrigger.beam_gate_time_abs/1e3 = -1.67904e+16 (us)

Note that the true value is ~1.65e18, so -1.65e18/1e3 should be ~-1.65e15; the order is different, and it comes from the fact that srtrigger.beam_gate_time_abs is unsigned.
To keep all the precision and pass correct reference time, now I shift the timings within Filler function, which was done before v09_63_00_01.

[miquelnebot]

trigger build SBNSoftware/sbnobj#72

[miquelnebot]

trigger build LArSoft/lar*@LARSOFT_SUITE_v09_65_01 SBNSoftware/sbnobj#72

[miquelnebot]

trigger build SBNSoftware/sbnobj#72 SBNSoftware/icarusalg#63 SBNSoftware/icaruscode#496

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