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THE LHCB TRACKS RECONSTRUCTION INRUN 2: STRATEGY AND PERFORMANCELaurent Dufour1, Renata Kope�ná2, Alex Pearce3, Maarten van Veghel1on behalf of the LHCb collaboration
1Nikhef National Institute for Subatomic Physics, the Netherlands2Physikalisches Institut, Heidelberg University, Germany3CERN, Switzerland
39th ICHEP, Seoul, July 2018
LHCB DETECTOR1 [1] [2]
RECONSTRUCTION IMPROVEMENTS IN RUN 2⇤ Major improvements in the pattern recognition algorithms⇤ Factor of 2 speed-up, without loss in performance⇤ Extensive use of machine-learning techniques⇤ Example: Improved fake-track reduction⇤ Fake tracks: not corresponding to a real particle’s trajectory⇤ Sped up by O(90%): allow the use in the online event selection⇤ Ghost rate in online event selection reduced from 22% to 14%
2
]2 [MeV/cπKm1800 1850 1900
)2ca
ndid
ates
/ (4
MeV
/c
0
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LHCbpreliminary
π K→0all Dfakes
[4]
MEASUREMENT OF TRACKING EFFICIENCY⇤ All data selected and stored in software trigger: “TurCal” [5]⇤ O�ine-quality event reconstruction available online⇤ Detector calibration ran online: o�ine-quality data⇤ Data immediately available for analyses
⇤ E�ciency from data using tag-and-probe method⇤ Track parameter inference independent of standard track re-
construction⇤ Exploit two-particle decays⇤ First track from the decay is fully reconstructed (tag track)⇤ Second track is reconstructed excluding the probed subdetec-
tor (probe track)
⇤ Tracking e�ciencies easily accessible using “TrackCalib” tool⇤ Transparent and easy e�ciency estimation⇤ User-defined track-quality cuts, binning and variables⇤ Available for all users
MUON TRACKING EFFICIENCY⇤ J/ ! µ+µ� decay is used [3]⇤ µµ pair ideal to probe the whole tracking system⇤ J/ gives a clear signal in the detector
⇤ J/ coming from B+ ! J/ X (data) and B+ ! J/ K (MC)⇤ Detached J/ for clean signal⇤ Unbiased selection by dedicated trigger
Long Method T-station method Velo method
Final method = Long method + (VELO method � T-station method)
3
η2 2.5 3 3.5 4 4.5
ε
0.86
0.88
0.9
0.92
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0.96
0.98
1
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1.04 LHCb preliminary
Data (50ns) 2015
Data (50ns) 2012
]c [GeV/p20 40 60 80 100 120 140 160 180 200
ε
0.86
0.88
0.9
0.92
0.94
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0.98
1
1.02
1.04 LHCb preliminary
Data (50ns) 2015
Data (50ns) 2012
ELECTRON TRACKING EFFICIENCYElectrons have a considerably di�erent behaviour compared to muons⇤ Significant energy loss (bremsstrahlung) along trajectory⇤ Decreases reconstruction e�ciency downstream of VELO
New method for measuring reconstruction e�ciencies for electrons:Kinematically constrained VELO tracks originating fromB+ ! J/ (! e+e�)K+
⇤ E�cient VELO reconstruction(⇡98%)
⇤ Applicable also to muons &hadrons
)2 c
Can
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LHCb simulation preliminary
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]2c[MeV/±K�/Jm5200 5400 5600
Kinematics⇤ Direction inferred from VELO
segment⇤ Probe momentum inferred
from J/ mass constraint⇤ Use B+ mass with J/ mass
constraint to distinguishbetween signal andbackground
REFERENCES[1] A. A. Alves Jr. et al. [LHCb collaboration], JINST 3 (2008) S08005[2] R. Aaij et al. [LHCb collaboration], Int. J. Mod. Phys. A30 (2015) 1530022[3] R. Aaij et al. [LHCb Collaboration], JINST 10, no. 02, P02007 (2015)[4] M. De Cian et al., LHCb-PUB-2017-011 (2017)[5] S. Benson et al., J. Phys.: Conf. Ser. 664 (2015) 082004