Simulation to compare the reconstructed decay length of D⁰ using TCFIT and KFParticle

1. 100k D⁰ with flat Pt in [0.1 ;5.0], |η|<1, 0<φ<2π
2. 1D⁰ per event so that the correlation with the reconstructed pair is easy

input GEANT check : here 

note : the BFC chain has been run over 50k, not all the 100k.

1- TCFIT
The MC decay length is calculated with the .fz (or .geant.root) by :

1. looping over the vertexTable
2. take the entry for which the particle Id = 37 (D⁰)
3. take its vertex position and calculate the decayGeant2D and decayGeant3D

The reco. decay length is calculated via .MuDst.root :

1. run the BFC chain (y2014, PIX in tracking only, not sure of the IST)
2. no particle Id
3. TCFIT gives the signed decay length and its error
4. TCFIT uses StDcaTrackGeometry and fit the 2 daughters particle to find their common point
5. negative decay length means that the product of the momentum vector and position vector (secondary vertex - primary vertex) is negative
6. KFParticle : no mass constraint, primary vertex constraint

preliminary :
Fig 1 : correlation between the GEANT decay and reco. decay 

Fig 2 : cosine(angle) vs. reco. decay : cosine(angle) is the angle between the momentum vector of the pair and the vector joining the PV and decay vertex.
Negative values are likely background.

Fig 3 : DL (reco) - DL (MC) vs. DL (MC) for 3 cuts

Fig 4 and Fig 5 : mean and resolution of DL (reco) - DL (MC) vs. DL (MC) for 3 cuts

1. <DL(reco)- DL(MC)>~0 means no deviation in the reco.
2. σ(DL(reco)- DL(MC)) ~ 40-50µm resolution for both daughters having PIX hits > 1

2- KFParticle
Fig 6 : DL (reco) - DL (MC) vs. DL (MC) for 3 cuts

Fig 7 and Fig 8 : mean and resolution of DL (reco) - DL (MC) vs. DL (MC) for 3 cuts

1. <DL(reco)- DL(MC)>~0 means no deviation in the reco.
2. σ(DL(reco)- DL(MC)) ~ 40-50µm resolution for both daughters having PIX hits > 1

3- other comment(s)
Fig 10 : requiring that both daughters have 2 or more PXL hits also improve the error of the reco. decay length (by taking advantage of the single track pointing resolution)