Run 2 Turbo PV refitting issue

The issue

In order to obtain an unbiased (or less biased) measure of the displacement of a particle wrt a PV (eg, flight distance, decay time, etc), PVs must be refitted excluding the signal tracks. This is enabled by setting ReFitPVs = True on the appropriate algorithm (CombineParticles, FilterDesktop, etc). However, in order to trigger the generation of refitted PVs, the PVs must be accessed by the algorithm, eg, by a BPV * LoKi functor. When refitted PVs are generated, they are saved to the output mDST along with the particle PV relations tables and so are accessible for user analysis. If the refitted PVs aren't generated, they can't be recovered offline on the mDST Turbo output.

The majority of Turbo lines requesting PV refitting in some algorithm in their sequence didn't do so in conjunction with a BPV functor, and so the refitted PVs aren't persisted, and are lost.

The initial investigation by Alex is here.

The same applies to lines that should have requested PV refitting but didn't, but these aren't discussed here.

The effect

If one or more tracks from your signal candidate are included in the PV fit, this will pull the position of the PV towards those tracks and so will bias any displacement variables calculated wrt the PV. This is particularly important for time dependent analyses, as the decay time will be biased. This could potentially bias measurements of, eg, lifetimes, mixing, time dependent CPV.

Mitigating effects

The PV fit only includes tracks with (see here, here, and here). Thus, if you have strong enough displacement cuts (, , etc) in your selection, the signal tracks will never have been included in the PV fit anyway. Note however that there is a difference between the used by the PV fitter to include/exclude tracks and the that you'll get in your ntuples offline.

Partially unaffected lines

These are lines that requested PV refitting, and did so correctly. Lines that didn't request PV refitting aren't shown.

For all these lines, PV refitting is only requested for the part of the decay tree. If you access the PV for the or then you'll get the non-refitted PV.

Affected lines

These are lines that requested PV refitting in some way, but did it incorrectly. Many of these include some cuts, which will mitigate the effect, so these are also listed. The selection tree with all selection requirements for each of these lines can be found here.

Line	cuts
Hlt2CharmHadDpToKmKpKpTurbo	{'Hlt2CharmHadD2HHH_DpToKmKpKpCombiner': ['MIPCHI2DV(PRIMARY) > 4.0', 'AHASCHILD((MIPCHI2DV (PRIMARY)) > 10.0', 'ANUM(MIPCHI2DV (PRIMARY) > 4.0) >= 2'], 'Hlt2CharmHadSharedDetachedDpmChild_KFilter': ['MIPCHI2DV(PRIMARY) > 4.0']}
Hlt2CharmHadDpToKmKpPipTurbo	{'Hlt2CharmHadD2HHH_DpToKmKpPipCombiner': ['AHASCHILD((MIPCHI2DV (PRIMARY)) > 50.0', 'MIPCHI2DV(PRIMARY) > 4.0', 'ANUM(MIPCHI2DV (PRIMARY) > 10.0) >= 2'], 'Hlt2CharmHadSharedDetachedDpmChild_KFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedDpmChild_piFilter': ['MIPCHI2DV(PRIMARY) > 4.0']}
Hlt2CharmHadDpToKmPipPipTurbo	{'Hlt2CharmHadSharedDetachedDpmChild_KFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedDpmChild_piFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadD2HHH_DpToKmPipPipCombiner': ['AHASCHILD((MIPCHI2DV (PRIMARY)) > 50.0', 'MIPCHI2DV(PRIMARY) > 4.0', 'ANUM(MIPCHI2DV (PRIMARY) > 10.0) >= 2']}
Hlt2CharmHadDpToKmPipPip _ForKPiAsymTurbo	{'Hlt2CharmHadSharedNoPIDDetachedChild_piFilter': ['MIPCHI2DV(PRIMARY) > 3.0'], 'Hlt2CharmHadDetAsym_DpToKmPipPipCombiner': ['AHASCHILD((MIPCHI2DV (PRIMARY)) > 100.0', 'MIPCHI2DV(PRIMARY) > 25.0', 'ANUM(MIPCHI2DV (PRIMARY) > 49.0) >= 2'], 'Hlt2CharmHadSharedNoPIDDetachedChild_KFilter': ['MIPCHI2DV(PRIMARY) > 3.0']}
Hlt2CharmHadDpToKmPipPip _LTUNBTurbo	{}
Hlt2CharmHadDpToKpKpPimTurbo	{'Hlt2CharmHadD2HHH_DpToKpKpPimCombiner': ['AHASCHILD((MIPCHI2DV (PRIMARY)) > 50.0', 'MIPCHI2DV(PRIMARY) > 4.0', 'ANUM(MIPCHI2DV (PRIMARY) > 10.0) >= 2'], 'Hlt2CharmHadSharedDetachedDpmChild_TightKFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedDpmChild_piFilter': ['MIPCHI2DV(PRIMARY) > 4.0']}
Hlt2CharmHadDpToKpPimPipTurbo	{'Hlt2CharmHadD2HHH_DpToKpPimPipCombiner': ['AHASCHILD((MIPCHI2DV (PRIMARY)) > 50.0', 'MIPCHI2DV(PRIMARY) > 4.0', 'ANUM(MIPCHI2DV (PRIMARY) > 10.0) >= 2'], 'Hlt2CharmHadSharedDetachedDpmChild_KFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedDpmChild_piFilter': ['MIPCHI2DV(PRIMARY) > 4.0']}
Hlt2CharmHadDpToPimPipPipTurbo	{'Hlt2CharmHadD2HHH_DpToPimPipPipCombiner': ['AHASCHILD((MIPCHI2DV (PRIMARY)) > 50.0', 'MIPCHI2DV(PRIMARY) > 4.0', 'ANUM(MIPCHI2DV (PRIMARY) > 10.0) >= 2'], 'Hlt2CharmHadSharedDetachedDpmChild_piFilter': ['MIPCHI2DV(PRIMARY) > 4.0']}
Hlt2CharmHadDspToKmKpKpTurbo	{'Hlt2CharmHadD2HHH_DspToKmKpKpCombiner': ['MIPCHI2DV(PRIMARY) > 4.0', 'AHASCHILD((MIPCHI2DV (PRIMARY)) > 10.0', 'ANUM(MIPCHI2DV (PRIMARY) > 4.0) >= 2'], 'Hlt2CharmHadSharedDetachedDpmChild_KFilter': ['MIPCHI2DV(PRIMARY) > 4.0']}
Hlt2CharmHadDspToKmKpPip	{'Hlt2CharmHadSharedDetachedDpmChild_KFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadD2HHH_DspToKmKpPipCombiner': ['AHASCHILD((MIPCHI2DV (PRIMARY)) > 50.0', 'MIPCHI2DV(PRIMARY) > 4.0', 'ANUM(MIPCHI2DV (PRIMARY) > 10.0) >= 2'], 'Hlt2CharmHadSharedDetachedDpmChild_piFilter': ['MIPCHI2DV(PRIMARY) > 4.0']}
Hlt2CharmHadDspToKmKpPipTurbo	{'Hlt2CharmHadSharedDetachedDpmChild_KFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadD2HHH_DspToKmKpPipCombiner': ['AHASCHILD((MIPCHI2DV (PRIMARY)) > 50.0', 'MIPCHI2DV(PRIMARY) > 4.0', 'ANUM(MIPCHI2DV (PRIMARY) > 10.0) >= 2'], 'Hlt2CharmHadSharedDetachedDpmChild_piFilter': ['MIPCHI2DV(PRIMARY) > 4.0']}
Hlt2CharmHadDspToKmKpPip _LTUNBTurbo	{}
Hlt2CharmHadDspToKmPipPipTurbo	{'Hlt2CharmHadSharedDetachedDpmChild_TightKFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadD2HHH_DspToKmPipPipCombiner': ['AHASCHILD((MIPCHI2DV (PRIMARY)) > 50.0', 'MIPCHI2DV(PRIMARY) > 4.0', 'ANUM(MIPCHI2DV (PRIMARY) > 10.0) >= 2'], 'Hlt2CharmHadSharedDetachedDpmChild_piFilter': ['MIPCHI2DV(PRIMARY) > 4.0']}
Hlt2CharmHadDspToKpKpPimTurbo	{'Hlt2CharmHadD2HHH_DspToKpKpPimCombiner': ['AHASCHILD((MIPCHI2DV (PRIMARY)) > 50.0', 'MIPCHI2DV(PRIMARY) > 4.0', 'ANUM(MIPCHI2DV (PRIMARY) > 10.0) >= 2'], 'Hlt2CharmHadSharedDetachedDpmChild_KFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedDpmChild_piFilter': ['MIPCHI2DV(PRIMARY) > 4.0']}
Hlt2CharmHadDspToKpPimPipTurbo	{'Hlt2CharmHadD2HHH_DspToKpPimPipCombiner': ['AHASCHILD((MIPCHI2DV (PRIMARY)) > 50.0', 'MIPCHI2DV(PRIMARY) > 4.0', 'ANUM(MIPCHI2DV (PRIMARY) > 10.0) >= 2'], 'Hlt2CharmHadSharedDetachedDpmChild_KFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedDpmChild_piFilter': ['MIPCHI2DV(PRIMARY) > 4.0']}
Hlt2CharmHadDspToPimPipPipTurbo	{'Hlt2CharmHadD2HHH_DspToPimPipPipCombiner': ['AHASCHILD((MIPCHI2DV (PRIMARY)) > 50.0', 'MIPCHI2DV(PRIMARY) > 4.0', 'ANUM(MIPCHI2DV (PRIMARY) > 10.0) >= 2'], 'Hlt2CharmHadSharedDetachedDpmChild_piFilter': ['MIPCHI2DV(PRIMARY) > 4.0']}
Hlt2CharmHadDstp2D0Pip _D02KS0KS0_KS0DDTurbo	{'Hlt2CharmHadDstp2D0Pip_D02KS0KS0_KS0DDTurboCombCombiner': ['MIPCHI2DV(PRIMARY) > 4.0']}
Hlt2CharmHadDstp2D0Pip _D02KS0KS0_KS0LLTurbo	{'Hlt2CharmHadDstp2D0Pip_D02KS0KS0_KS0LLTurboCombCombiner': ['MIPCHI2DV(PRIMARY) > 9.0'], 'Hlt2SharedKsLLTFKsLLTF': ['MIPCHI2DV(PRIMARY)>36']}
Hlt2CharmHadDstp2D0Pip _D02KS0KS0_KS0LL_KS0DDTurbo	{'Hlt2CharmHadDstp2D0Pip_D02KS0KS0_KS0LL_KS0DDTurboCombCombiner': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2SharedKsLLTFKsLLTF': ['MIPCHI2DV(PRIMARY)>36']}
Hlt2CharmHadLcpToPpKmKpTurbo	{'Hlt2CharmHadLcXic2HHH_LcpToKmPpKpCombiner': ['AHASCHILD((MIPCHI2DV (PRIMARY)) > 16.0', 'MIPCHI2DV(PRIMARY) > 6.0', 'ANUM(MIPCHI2DV (PRIMARY) > 9.0) >= 2'], 'Hlt2CharmHadSharedDetachedLcChild_KFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedLcChild_pFilter': ['MIPCHI2DV(PRIMARY) > 4.0']}
Hlt2CharmHadLcpToPpKmPipTurbo	{'Hlt2CharmHadSharedDetachedLcChild_piFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedLcChild_pFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedLcChild_KFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadLcXic2HHH_LcpToKmPpPipCombiner': ['AHASCHILD((MIPCHI2DV (PRIMARY)) > 16.0', 'MIPCHI2DV(PRIMARY) > 6.0', 'ANUM(MIPCHI2DV (PRIMARY) > 9.0) >= 2']}
Hlt2CharmHadLcpToPpKmPip _LTUNBTurbo	{}
Hlt2CharmHadLcpToPpKpPimTurbo	{'Hlt2CharmHadLcXic2HHH_LcpToPimPpKpCombiner': ['AHASCHILD((MIPCHI2DV (PRIMARY)) > 16.0', 'MIPCHI2DV(PRIMARY) > 6.0', 'ANUM(MIPCHI2DV (PRIMARY) > 9.0) >= 2'], 'Hlt2CharmHadSharedDetachedLcChild_piFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedLcChild_KFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedLcChild_pFilter': ['MIPCHI2DV(PRIMARY) > 4.0']}
Hlt2CharmHadLcpToPpPimPipTurbo	{'Hlt2CharmHadSharedDetachedLcChild_piFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadLcXic2HHH_LcpToPimPpPipCombiner': ['AHASCHILD((MIPCHI2DV (PRIMARY)) > 16.0', 'MIPCHI2DV(PRIMARY) > 6.0', 'ANUM(MIPCHI2DV (PRIMARY) > 9.0) >= 2'], 'Hlt2CharmHadSharedDetachedLcChild_pFilter': ['MIPCHI2DV(PRIMARY) > 4.0']}
Hlt2CharmHadXic0ToPpKmKmPipTurbo	{'Hlt2CharmHadXic0ToPpKmKmPipTurbo_DetachedHHHHCombinerCombiner': ['ANUM(MIPCHI2DV (PRIMARY) > 6.0) >= 2', 'AHASCHILD((MIPCHI2DV (PRIMARY)) > 8.0', 'MIPCHI2DV(PRIMARY) > 4.0']}
Hlt2CharmHadXic0ToPpKmKmPip _LTUNBTurbo	{}
Hlt2CharmHadXiccp2LcpKmPim _Lcp2PpKmPipTurbo	{'Hlt2CharmHadSharedDetachedLcChild_piFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedLcChild_pFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedLcChild_KFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadLcXic2HHH_LcpToKmPpPipCombiner': ['AHASCHILD((MIPCHI2DV (PRIMARY)) > 16.0', 'MIPCHI2DV(PRIMARY) > 6.0', 'ANUM(MIPCHI2DV (PRIMARY) > 9.0) >= 2']}
Hlt2CharmHadXiccp2LcpKmPip _Lcp2PpKmPipTurbo	{'Hlt2CharmHadSharedDetachedLcChild_piFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedLcChild_pFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedLcChild_KFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadLcXic2HHH_LcpToKmPpPipCombiner': ['AHASCHILD((MIPCHI2DV (PRIMARY)) > 16.0', 'MIPCHI2DV(PRIMARY) > 6.0', 'ANUM(MIPCHI2DV (PRIMARY) > 9.0) >= 2']}
Hlt2CharmHadXiccp2LcpKpPim _Lcp2PpKmPipTurbo	{'Hlt2CharmHadSharedDetachedLcChild_piFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedLcChild_pFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedLcChild_KFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadLcXic2HHH_LcpToKmPpPipCombiner': ['AHASCHILD((MIPCHI2DV (PRIMARY)) > 16.0', 'MIPCHI2DV(PRIMARY) > 6.0', 'ANUM(MIPCHI2DV (PRIMARY) > 9.0) >= 2']}
Hlt2CharmHadXiccp2XicpPimPim _Xicp2PpKmPipTurbo	{'Hlt2CharmHadSharedDetachedLcChild_piFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedLcChild_pFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedLcChild_KFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadLcXic2HHH_LcpToKmPpPipCombiner': ['AHASCHILD((MIPCHI2DV (PRIMARY)) > 16.0', 'MIPCHI2DV(PRIMARY) > 6.0', 'ANUM(MIPCHI2DV (PRIMARY) > 9.0) >= 2']}
Hlt2CharmHadXiccp2XicpPimPip _Xicp2PpKmPipTurbo	{'Hlt2CharmHadSharedDetachedLcChild_piFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedLcChild_pFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedLcChild_KFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadLcXic2HHH_LcpToKmPpPipCombiner': ['AHASCHILD((MIPCHI2DV (PRIMARY)) > 16.0', 'MIPCHI2DV(PRIMARY) > 6.0', 'ANUM(MIPCHI2DV (PRIMARY) > 9.0) >= 2']}
Hlt2CharmHadXiccpp2LcpKmPimPip _Lcp2PpKmPipTurbo	{'Hlt2CharmHadSharedDetachedLcChild_piFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedLcChild_pFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedLcChild_KFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadLcXic2HHH_LcpToKmPpPipCombiner': ['AHASCHILD((MIPCHI2DV (PRIMARY)) > 16.0', 'MIPCHI2DV(PRIMARY) > 6.0', 'ANUM(MIPCHI2DV (PRIMARY) > 9.0) >= 2']}
Hlt2CharmHadXiccpp2LcpKmPipPip _Lcp2PpKmPipTurbo	{'Hlt2CharmHadSharedDetachedLcChild_piFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedLcChild_pFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedLcChild_KFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadLcXic2HHH_LcpToKmPpPipCombiner': ['AHASCHILD((MIPCHI2DV (PRIMARY)) > 16.0', 'MIPCHI2DV(PRIMARY) > 6.0', 'ANUM(MIPCHI2DV (PRIMARY) > 9.0) >= 2']}
Hlt2CharmHadXiccpp2LcpKpPimPip _Lcp2PpKmPipTurbo	{'Hlt2CharmHadSharedDetachedLcChild_piFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedLcChild_pFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedLcChild_KFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadLcXic2HHH_LcpToKmPpPipCombiner': ['AHASCHILD((MIPCHI2DV (PRIMARY)) > 16.0', 'MIPCHI2DV(PRIMARY) > 6.0', 'ANUM(MIPCHI2DV (PRIMARY) > 9.0) >= 2']}
Hlt2CharmHadXiccpp2XicpPim _Xicp2PpKmPipTurbo	{'Hlt2CharmHadSharedDetachedLcChild_piFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedLcChild_pFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadXiccpp2XicpPim_Xicp2PpKmPipTurboCombCombiner': ['MIPCHI2DV(PRIMARY) > -1.0'], 'Hlt2CharmHadLcXic2HHH_LcpToKmPpPipCombiner': ['AHASCHILD((MIPCHI2DV (PRIMARY)) > 16.0', 'MIPCHI2DV(PRIMARY) > 6.0', 'ANUM(MIPCHI2DV (PRIMARY) > 9.0) >= 2'], 'Hlt2CharmHadSharedDetachedLcChild_KFilter': ['MIPCHI2DV(PRIMARY) > 4.0']}
Hlt2CharmHadXiccpp2XicpPip _Xicp2PpKmPipTurbo	{'Hlt2CharmHadSharedDetachedLcChild_piFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedLcChild_pFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadXiccpp2XicpPip_Xicp2PpKmPipTurboCombCombiner': ['MIPCHI2DV(PRIMARY) > -1.0'], 'Hlt2CharmHadSharedDetachedLcChild_KFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadLcXic2HHH_LcpToKmPpPipCombiner': ['AHASCHILD((MIPCHI2DV (PRIMARY)) > 16.0', 'MIPCHI2DV(PRIMARY) > 6.0', 'ANUM(MIPCHI2DV (PRIMARY) > 9.0) >= 2']}
Hlt2CharmHadXicpToPpKmPipTurbo	{'Hlt2CharmHadSharedDetachedLcChild_piFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedLcChild_pFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadSharedDetachedLcChild_KFilter': ['MIPCHI2DV(PRIMARY) > 4.0'], 'Hlt2CharmHadLcXic2HHH_LcpToKmPpPipCombiner': ['AHASCHILD((MIPCHI2DV (PRIMARY)) > 16.0', 'MIPCHI2DV(PRIMARY) > 6.0', 'ANUM(MIPCHI2DV (PRIMARY) > 9.0) >= 2']}

Systematic checks

If you care about PV refitting and you're using an affected line:

• Firstly, check the distribution of the tracks in your data. If their minimum values are all > 12 then you should be safe.
• If you have full DST MC for your analysis you can check if the daughter tracks are ever included in the PV fit. Note that the PVs are constructed from HLT1 fitted VELO tracks, so you'll have to unpack these tracks and compare by LHCbIDs to your signal tracks. You can also evaluate the effect of refitting the PVs excluding signal tracks.
• Try tightening the displacement cuts (, , decay time, etc) in your selection and examine how your results vary.
• Apply a cut on PV n. tracks and vary its value. The greater the number of tracks in the PV, the less influence your signal candidate will have on the PV.

Possible workaround

Tracks can be refitted as VELO tracks and their weight in the PV recalculated, thus enabling the influence of the track to be removed from the PV. Initial studies of this are shown here. The caveats are:

• VELO clusters must be available for the tracks to be refitted.
• The tracks are removed from the PV offline, so any trigger cuts will still have been applied wrt the non-refitted PV which will affect, eg, efficiency vs decay time.
• PV track removal doesn't fully unbias the PV, even in ideal conditions, so there will still be some systematic to assign.

-- MichaelAlexander - 2019-06-19