TPC: Add scaling of VDrift with T/P

[matthias-kleiner]

• scaling of the VDrift is automatically enabled
• the reference T/P is extracted for VDrift objects without stored T/P if firstTime and lastTime of VDrift object is in the range +-20 minutes of available temperature and pressure
• scaling with T/P can be disabled by setting 'TPCGasParam.Temperature=0;TPCGasParam.Pressure=0'
• reference T/P is extracted automatically for online created VDrift with ITSTgl and laser method
• add storing of temperature, pressure and used VDrift in timeseries

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[shahor02]

@matthias-kleiner I am wondering if this is what we want. The original reason behind this complicated normalizations was to have
a reasonable refVDrift constant over the whole, so that the residuals extraction calibration, which have granularity different from that of VDrift, would use the same refVDrift value, see

AliceO2/Detectors/TPC/calibration/SpacePoints/src/TrackInterpolation.cxx

Lines 1127 to 1133 in 89bef8a

	// Attention! For the refit we are using reference VDrift and TDriftOffest rather than high-rate calibrated, since we want to have fixed reference over the run
	if (v.refVDrift != mTPCVDriftRef) {
	mTPCVDriftRef = v.refVDrift;
	mTPCDriftTimeOffsetRef = v.refTimeOffset;
	LOGP(info, "Imposing reference VDrift={}/TDrift={} for TPC residuals extraction", mTPCVDriftRef, mTPCDriftTimeOffsetRef);
	o2::tpc::TPCFastTransformHelperO2::instance()->updateCalibration(*mFastTransform, 0, 1.0, mTPCVDriftRef, mTPCDriftTimeOffsetRef);
	}

.
Therefore, the variation of the full VDrift was provided via time-dependent corrFact.

In the current code, the normalize method does not modify the result of getVDrift(), it is just

1. setting the refVDrift to the requested newVRef if it is non-0 and readjusts the corrFact to have the full VDrift unchanged (used to make sure that the next calibration slot creates VDrift with the same reference),
   or
2. at the 1st call w/o argument normalizes refVDrift to full VDrift and therefore sets the corrections to 1 (to have the refVDrift as correct as possible).

This change will not only scale the final getVDrift() value by the relative T/P change (which is OK) but will also modify the refVDrift according to the current meteo condition. Should not instead just corrFact (and refTP) adjusted to account for changed T/P?

[matthias-kleiner]

Hi @shahor02 , thanks for the comment and information. I was not aware of that specific reason why we wanted to have a constant refVDrift. In that case, we should indeed simply adjust the corrFact to account for changes in the T/P.

[wiechula]

Looks fine for me. @shahor02 if you also agree, this can be merged.

[shahor02]

Before we merge it: was it tested with real data?

[matthias-kleiner]

Hello @shahor02 ,
I tested it with local reconstruction of real data and checking the DCAz. You can see the DCAz is indeed more flat after the correction and the slope of the VDrift as a function of T/P is 1 as expected. The jump in the second plot is because two different VDrift objects are uploaded for that run. The remaining bias of the DCAz is probably due to something else like change in the gas mixture or something else

[shahor02]

Thanks @matthias-kleiner !