Lines to measure electron and muon tracking efficiencies for Run 3

MR of Bu2Jpsi2eeK_TagAndProbe.py and Bu2Jpsi2mumuK_TagAndProbe.py HLT2 lines.

These lines are designed to measure electron and muon tracking efficiencies from data for Run 3, using B+->K+Jpsi(->l+l-) decays. The kaon and one of the leptons are fully reconstructed long tracks (the tags). The other lepton is only reconstructed in the VELO (probe track). The details are given in this presentation given at the RTA Selections WP3 meeting on 8 Nov 2022: https://indico.cern.ch/event/1195028/contributions/5130840/attachments/2543241/4379164/TagAndProbe_November2022.pdf

Since the probe track is a VELO track, we only have information on its direction (and not its absolute momentum). This implies that the B+ momentum is wrong. In addition, since the pile-up is at around 7 in Run 3, the B+ can point to the "wrong" best PV. Therefore, we wrote a fitter to estimate the VELO candidate momentum and reconstruct the related kinematic of the decay. The fitter uses two algorithms:

• A jpsi constraint algorithm, where the dilepton system is forced to have the Jpsi mass. This algorithm is crucial to determine the best PV, defined as the one minimising the IP of the B+.
• A PV constraint algorithm, where the B+ momentum is forced to align with its flight distance vector. Using the fitter, we can apply requirements on kinematic quantities obtained with the fitter to remove a large fraction of the combinatorial background. The algorithm is called VeloToLongTrackEffFilter.cpp and the related MR is here: Rec!3188 (merged)

Rates obtained on upgrade_minbias_hlt1_filtered (reduced w.r.t. presentation due to tightening of cuts):

• Bu2Jpsi2eeK_TagAndProbe: (0.67 +/- 0.21) kHz
• Bu2Jpsi2mumuK_TagAndProbe: (0.73 +/- 0.22) kHz