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TIME 05 Zurich. Tracking in the High Rate Environment of the HERA-B Detector. A. Spiridonov. DESY Zeuthen / ITEP Moscow. HERA-B tracking detectors Tracking algorithms Performance in commissioning phase Final tracking performance Matching Tracks fitting
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TIME 05 Zurich Tracking in the High Rate Environment of the HERA-B Detector A. Spiridonov DESY Zeuthen / ITEP Moscow HERA-B tracking detectors Tracking algorithms Performance in commissioning phase Final tracking performance Matching Tracks fitting Momentum/mass resolution Summary
HERA-B Detector Fixed target experiment at 920 GeV p beam at HERA Trigger Chambers (TC) Pattern Chambers (PC) Magnet Vertex Detector System (VDS) A. Spiridonov
Recorded Data and Physics HERA-B was designed to study CP violation with B-mesons Achieved rejection factor for dilepton trigger of order 104 Dilepton trigger: 3×105 reconstructed J/Y (ee,mm modes) Minimum bias trigger: 210×106 events acquired Goals for physics study: B physics (cross sections); QCD studies; Charmonium spectroscopy; D physics. A. Spiridonov
Track Reconstruction Challenges Large track density Combination of different detector technologies with complicated geometry: double sided silicon micro-strip detectors; honeycomb drift tubes (5 and 10 mm); Micro-strip gaseous chambers (MSGC-GEM). Detector imperfections during the commissioning and first period of data taking A. Spiridonov
Track Reconstruction Strategy Trigger Chambers Pattern Chambers Magnet Chambers Vertex Detector ECAL & MUON Vertex Detector: track finding Pattern Chambers: track finding Magnet Chambers: track propagation Trigger Chambers: track propagation Matching of VDS and PC track segments Tracks fitting A. Spiridonov
Vertex Detector System of HERA-B double-sided Si detectors 50 mm pitch 12 mm resolution 5% peak occupancy 64 detectors, 8 superlayers 150,000 channels A. Spiridonov
CATS: Cellular Automation for Tracking Track finding in VDS, NIM A489 p.389 Track finding in OTR PC (data processing), NIM A490 p.546 See also TIME05 talk: I.Kisel on cellular automation in CBM Semi-global method using local formation of spacepoints in neighbored detector planes Cell (spacepoint): 3D track segment inside a superlayer Model of cellular automation for tracking can be regarded as local discrete form of the Denby-Peterson neural net Tracking efficiency 98% for VDS on real data A. Spiridonov
Main Tracker of HERA-B Outer Tracker (OTR) Honeycomb drift tubes 115,000 TDC channels 5 and 10 mm cells 0°,+5°,-5° stereo layers peak occupancy 5% Inner Tracker (ITR) Micro-Strip Gaseous Chambers (MSGS-GEM) 140,000 analog readout channels pitch 300 mm 0°,+5°,-5° stereo layers peak occupancy 30% A. Spiridonov
Performance of the Main Tracker Design Data before 2001 Data after 2001 Outer Tracker Resolution 400-500mm Efficiency 85-90% 10-18% channels turned off Resolution 360mm Efficiency 94-97% 3% channels turned off Resolution 200mm Efficiency 98% Inner Tracker Resolution 80mm Efficiency 95% Resolution 150mm Efficiency 85% Resolution 150mm Efficiency 85% Drastic improvement of the Outer Tracker after 2001 A. Spiridonov
Ranger: Track Following Algorithm NIM A395, p.169 Track candidates seeding in the Pattern Tracker Hit triplets are used as seeds Both left/right assignments for drift distances Propagate all branches in parallel, but reject inferior Maximize quality estimator Q = #step - #fault - w c2 Kalman Filter A. Spiridonov
Ranger: Track Propagation in the Magnet NIM A426, p.268 Inhomogeneous magnetic field 3D concurrent track evolution Kalman filter 4th, 5th order Runge-Kutta Timing for 2 interactions + 1 with J/Y Pattern Chamber track finding 0.4 s Magnet Chamber propagation 0.2 s Trigger Chamber propagation 0.04 s A. Spiridonov
Main Tracker Reconstruction before 2001 Real event with 150 tracks Reconstructed with magnet tracking Tracking efficiency about 80% A. Spiridonov
Tracking Efficiency before 2001 Monte Carlo: 2 minimum bias + 1 with J/Y(mm) Stand alone reconstruction in Pattern Tracker Ranger CATS Efficiency per m track 0.97±0.02 0.94±0.02 Full event reconstruction for real data before 2001 SLT seeds Default algorithms Ranger Ranger CATS 288±23 209±17 190±17 Reconstructed J/Y(mm) 1 0.85±0.04 0.81±0.04 Efficiency per m track More realistic simulation to obtain MC & data agreement A. Spiridonov
SLT Seeding in off-line Reconstruction Coarse tracking for dileptons by Second Level Trigger 3D track following of SLT seeds by Ranger off-line Number of following in parallel branches can be made bigger in the case of few seeds, enhancing efficiency Efficiency ~95% for tracks being of physical interest Finally, SLT seeds were implemented for CATS also Physics results (B, cC etc) were obtained before 2001 A. Spiridonov
Tracking Performance after 2001 Not triggered: efficiency estimation on data using KS(pp) One p made from VDS-ECAL/RICH and OTR is searched Efficiency 95-97% for not triggered tracks on data Efficiency 96-99% for triggered tracks CATS Ranger 1.8 106mm triggers 1209±48 1252±44 number of J/Y(mm) S/(S+B) 0.57±0.01 0.64±0.01 Full event reconstruction about 3 s on HERA-B farm Pattern recognition takes 20-25% only A. Spiridonov
Matching of VDS and PC track segments Pairs (x,y,tX,tY,1/p) for VDS and PC given (p not defined) One Kalman Filter step to estimate p and c2 Use the c2 as a quality estimator Wrong match Proper match Tail: Moliere scattering and pattern recognition fails A. Spiridonov
Performance of Matching on Real Data KS(pp) and J/Y(mm) were used to evaluate efficiency Event number in signals and background vs matching c2 J/Y(mm) KS(pp) For c2 < 200: 98% p and 100% m were matched Selected pairs (ambiguities also) stored as tracks, superior flagged A. Spiridonov
Track Fit in HERA-B Use of the Kalman Filter technique The system state vector (x,y,tX,tY,1/p) 4th, 5th order Runge-Kutta 3 filter/smoother iterations with outliers removal at last J/Y(mm) Mass 3093 MeV/c2 Width 38 MeV/c2 A. Spiridonov
Track Fit Performance on Real Data Was investigated on the sample of J/Y(mm) The sample was divided into a 4×4 grid Binning in muon momentum: 14, 26, 44, 72 GeV/c Relative deviations smaller then 3·10-3 A. Spiridonov
Momentum Resolution on Real Data The sample of J/Y(mm) divided into a 4×4 grid D(m) = m/2 ( D(p1)/p1 + D(p2)/p2 ) O Muons momenta p1, p2 4 values of D(p)/p fitted to 4×4 D(m) A. Spiridonov
S U M M A R Y Performances of VDS and OTR detectors close to designed were achieved Tracking efficiency 98% in VDS Tracking efficiency 98% for triggered and 96% for not triggered tracks in OTR Matching efficiency about 98% for VDS and OTR track segments For J/Y(mm) small relative mass bias about 10-3 and mass resolution 38 MeV/c2 Data taking completed, high statistics recorded Physics analysis in progress A. Spiridonov