[Common] Fix TPC side determination in VDrift correction - #17846
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matthias-kleiner wants to merge 4 commits into
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matthias-kleiner
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alibuild,
ddobrigk,
dsekihat,
iarsene,
jgrosseo and
ktf
as code owners
September 9, 2026 15:05
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O2 linter results: ❌ 0 errors, |
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
ddobrigk
previously approved these changes
Sep 11, 2026
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Hi @matthias-kleiner, thanks a lot for this fix! However, I was wondering what will happen with data for which the TPC side flags are not stored: this is relevant, since those were added only in February this year. Further, since they were added "adiabatically" by taking unused bits in the flags integer, older datasets will appear to have all tracks only in one side, and thus the fix will break in that situation. Is there perhaps some way in which the TPC side information could be inferred from other parameters that existed already before? For instance, a combination of tgl and the sign of Z (given we store tracks at the position of their innermost update?)... Sorry if I am overlooking something. Thanks again! |
The TPCSideA/TPCSideC flags were only added to the AOD format in February 2026, so datasets produced before that always have neither bit set. Detect CE-crossing tracks from the track's asymmetric time margins and otherwise infer the side from a cross-check of Z and tgl sign, per TPC domain expert guidance, instead of silently skipping the correction for all tracks in older datasets. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Author
Hi @ddobrigk , |
shahor02
previously approved these changes
Sep 11, 2026
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Hi @matthias-kleiner, thanks a lot! I have one question and a request, if I may:
Thanks again - and please only worry about this whenever convenient and don't let me disturb your weekend! |
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Error while checking build/O2Physics/code-check for be7148b at 2026-09-14 04:43: Full log here. |
Introduce TPCVDriftManagerParam::useSideBasedCorrection (default off) to gate the new TPC-side-flag-based correction behind a ConfigurableParam, settable from any workflow via --configKeyValues without touching each task that owns a TPCVDriftManager instance. Keeps existing analyses on the legacy tgl-sign behaviour until explicitly opted in for testing. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Author
Hi @ddobrigk , I think it could in principle recover some efficiency loss: when the sign of the tgl disagrees with the actual TPC side, the old code shifts the tracks Z the wrong way instead of correcting it, which would hurt topological cuts. How much depends on how large the vDrift correction is and how often the vertex position/track topology puts tgl and Z sign at different sign. The best would be to make a direct A/B comparison with the switch. |
ddobrigk
approved these changes
Sep 14, 2026
ddobrigk
enabled auto-merge (squash)
September 14, 2026 13:21
ddobrigk
disabled auto-merge
September 14, 2026 15:13
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Error while checking build/O2Physics/staging for ec64032 at 2026-09-14 21:21: Full log here. |
Collaborator
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Hi @matthias-kleiner ! Thank you very much for the PR! I have taken the liberty to try out your changes in order to test whether the configurable is available in the The simplest alternative is maybe to add the variable My 2 cents. |
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| #include <CommonUtils/ConfigurableParam.h> | ||
| #include <CommonUtils/ConfigurableParamHelper.h> |
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| #include <CommonUtils/ConfigurableParam.h> | |
| #include <CommonUtils/ConfigurableParamHelper.h> |
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| struct TPCVDriftManagerParam : public o2::conf::ConfigurableParamHelper<TPCVDriftManagerParam> { | ||
| // Use the TPC side flags (with legacy-data fallback) instead of the tgl-sign-based correction. | ||
| // Off by default so that existing analyses see no change in results until this is explicitly | ||
| // enabled for testing. | ||
| bool useSideBasedCorrection = false; | ||
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| O2ParamDef(TPCVDriftManagerParam, "TPCVDriftManager"); | ||
| }; | ||
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| struct TPCVDriftManagerParam : public o2::conf::ConfigurableParamHelper<TPCVDriftManagerParam> { | |
| // Use the TPC side flags (with legacy-data fallback) instead of the tgl-sign-based correction. | |
| // Off by default so that existing analyses see no change in results until this is explicitly | |
| // enabled for testing. | |
| bool useSideBasedCorrection = false; | |
| O2ParamDef(TPCVDriftManagerParam, "TPCVDriftManager"); | |
| }; | |
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| class TPCVDriftManager | ||
| { | ||
| public: | ||
| void init(o2::ccdb::BasicCCDBManager* ccdb) noexcept | ||
| { | ||
| mCCDB = ccdb; | ||
| } |
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| class TPCVDriftManager | |
| { | |
| public: | |
| void init(o2::ccdb::BasicCCDBManager* ccdb) noexcept | |
| { | |
| mCCDB = ccdb; | |
| } | |
| void setUseSideBasedCorrection(bool value) noexcept | |
| { | |
| mUseSideBasedCorrection = value; | |
| } |
| // impose new Z coordinate | ||
| track.setZ(track.getZ() + ((track.getTgl() < 0.) ? -dDrift : dDrift)); | ||
| float zShift = 0.f; | ||
| if (!TPCVDriftManagerParam::Instance().useSideBasedCorrection) { |
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| if (!TPCVDriftManagerParam::Instance().useSideBasedCorrection) { | |
| if (!mUseSideBasedCorrection) { |
| @@ -156,6 +214,8 @@ | |||
| o2::ccdb::BasicCCDBManager* mCCDB{}; // reference to initialized ccdb manager | |||
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| bool mUseSideBasedCorrection{false}; |
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