Global Tracking for CBM Andrey Lebedev 1,2 Ivan Kisel 1 Gennady Ososkov 2 1 GSI Helmholtzzentrum...
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Transcript of Global Tracking for CBM Andrey Lebedev 1,2 Ivan Kisel 1 Gennady Ososkov 2 1 GSI Helmholtzzentrum...
Global Tracking for CBM
Andrey Lebedev 1,2
Ivan Kisel 1
Gennady Ososkov 2
1GSI Helmholtzzentrum für Schwerionenforschung GmbH , Darmstadt, Germany2Laboratory of Information Technologies, Joint Institute for Nuclear Research, Dubna, Russia
1st CBM Russia MeetingMay 18-22, 2009JINR, Dubna, Russia
2 A.Lebedev, I.Kisel, G.Ososkov, Global Tracking for CBM
Outline• Global tracking
– Geometries– Requirements – Tracking– Results
• Speed up of the tracking software
3 A.Lebedev, I.Kisel, G.Ososkov, Global Tracking for CBM
CBM setups
• “Muon” setup– STS+MUCH+(TRD)+(TOF)
• “Electron” setup– STS+(RICH)+(TRD)+(TOF)+(ECAL)
4 A.Lebedev, I.Kisel, G.Ososkov, Global Tracking for CBM
Segmented MUCH• 6 absorbers
– 225 cm of iron• 2 stations in first 5 gaps• 3 stations in the last gap
for trigger• 2 sides in each station
Back sideFront side
Optionally: STRAW TUBES in the last stations (V.Peshehonov et al)
V.NikulinE.KryshenM.Ryzhinskiy
Front side Back sideFront side Back sideFront side
5 A.Lebedev, I.Kisel, G.Ososkov, Global Tracking for CBM
Segmented TRD– Segmented geometry– 2 cm thick support frames– More dead zones
• Leads to detector inefficiency
6 A.Lebedev, I.Kisel, G.Ososkov, Global Tracking for CBM
Global tracking procedure• CbmLitFindGlobalTracks
– Tracking + Merging– Automatic configuration, depending on
the setup• STS+(TRD)+(TOF)• STS+MUCH+(TRD)+(TOF)
STS
MUCHTRD TOF
L1 STStracking
LIT tracking
Hit-to-track merging
7 A.Lebedev, I.Kisel, G.Ososkov, Global Tracking for CBM
Tracking• Initial seeds are tracks reconstructed
in STS (L1 tracking)• Tracking is based on
– Track following– Kalman Filter– Validation gate– Different hit-to-track association
techniques
8 A.Lebedev, I.Kisel, G.Ososkov, Global Tracking for CBM
Tracking methods• Branching
– Branch is created for each hit in the validation gate.
• Nearest Neighbor– The closest by a Euclidean statistical distance hit
from a validation gate is assigned to track.
• Weighting– Doesn’t allow track splitting, it collects all the hits in
the validation gate.
9 A.Lebedev, I.Kisel, G.Ososkov, Global Tracking for CBM
Simulation parameters• Events
– Muons: 1000 UrQMD at 25 AGeV + 10 mu in each event
– Electrons: 500 UrQMD at 25 AGeV + 10 electrons in each event
• Efficiency (CbmLitReconstructionQa)– Global tracking:
• STS – 4 MC STS points• STS+TRD(MUCH) – 4 MC STS and 8(12) MC TRD(MUCH)
points• STS+TRD(MUCH)+TOF - 4 MC STS and 8(12) MC
TRD(MUCH) points + TOF point– Local tracking and merging:
• TRD(MUCH) – STS as 100% + 8(12) MC points in TRD(MUCH)
• TOF merging – STS+TRD(MUCH) as 100% + TOF point
10 A.Lebedev, I.Kisel, G.Ososkov, Global Tracking for CBM
Muons
muonsall
STS STS+MUCH STS+MUCH+TOF MUCH TOF
all 74.9 90.0 90.7 92.1 98.7
reference 94.8 90.9 91.0 92.7 98.7
muons 98.0 91.4 91.0 93.1 98.7
Efficiency in %
11 A.Lebedev, I.Kisel, G.Ososkov, Global Tracking for CBM
Electrons
electronsall
STS STS+TRD STS+TRD+TOF TRD TOF
all 81.7 85.0 77.6 92.9 91.1
reference 95.5 91.3 83.1 94.9 91.1
electrons 96.6 87.9 74.5 89.3 84.6
Efficiency in %
12 A.Lebedev, I.Kisel, G.Ososkov, Global Tracking for CBM
Speed up [1]: number of branches• Motivation: The main problem with branching
algorithm is that its computational and memory requirements can grow with time and saturate computing system.
• Solution: Only a limited number of the nearest hits in the validation gate can start a new branch.
Maximum number of hits in the
validation gate30 20 15 10 7 5 4 3 2 1
Tracking efficiency,%
93.1 93.1 93.1 93.1 93.1 93.1 93.1 92.9 92.9 91.8
Time, s/event 1.91 1.63 1.37 1.05 0.8 0.62 0.52 0.44 0.34 0.20
MUCH tracking, UrQMD 25 AGeV Au-Au + 10 muons
4 times faster!
CPU: Intel C2D P8400
13 A.Lebedev, I.Kisel, G.Ososkov, Global Tracking for CBM
Speed up [2]: fast search of hitsMotivation -Hits are sorted by x position
-Binary search is used to find Min and Max index
2 2cov posdX k
pos Maximum measurement error on the station
Fast search of hits
Loop over MIN and MAX
indices
Loop over MIN and MAX
indices
2 times increase in speed!1.05 s/event -> 0.52 s/event(MUCH tracking, UrQMD+10mu)
CPU: Intel C2D P8400
14 A.Lebedev, I.Kisel, G.Ososkov, Global Tracking for CBM
Speed up [3]: simplification of the geometry• Simplified geometry
– TGeoManager: storage + navigation– Stations are approximated as planes
• Reduction of number of nodes from 800k to 100• 0.52 s/event 0.3 s/event
• Future plans– Custom navigation (assuming detector planes
are perpendicular to z)– Optimization of the step size in the track
propagation
CPU: Intel C2D P8400
15 A.Lebedev, I.Kisel, G.Ososkov, Global Tracking for CBM
Speed up: plans of further developments
• Magnetic field access (same as for L1)– approximation of the magnetic field
• Parallelism– SIMDization
46% of total track propagation costs is due to access to the magnetic field
Reachable gain of speed:
100? 1000?...
16 A.Lebedev, I.Kisel, G.Ososkov, Global Tracking for CBM
Summary and outlook• Summary:
– The Lit track reconstruction package has been significantly improved
• global tracking procedure implemented• algorithm speed up results in 0.3 s/event for
MUCH tracking• Outlook
– Continue speed up studies– MUCH trigger
18 A.Lebedev, I.Kisel, G.Ososkov, Global Tracking for CBM
Track propagation• Extrapolation. Two models:
– Straight line in case of absence of magnetic field.– Solution of the equation of motion in a magnetic field with the 4th order Runge-Kutta method.
• Material Effects.– Energy loss (ionization: Bethe-Bloch,
bremsstrahlung: Bethe-Heitler, pair production)– Multiple scattering (Gaussian approximation)
• Navigation.– Based on the ROOT TGeoManager.
The Algorithm:Trajectory is divided into steps. For each step: Straight line approximation for finding
intersections with different materials (geometry navigator)Geometrical extrapolation of the trajectory
Material effects are added at each intersection point
Track propagation components
19 A.Lebedev, I.Kisel, G.Ososkov, Global Tracking for CBM
Weighted track fit• Weight is assigned to each hit• Weight is proportional to the multivariate Gaussian
distribution and includes temperature parameter T• Weighted hit is calculated as a weighted mean of the
hits from the same station• Weighted track is fitted with standard KF• Temperature is gradually decreasing. Simulated
annealing is applied to track fit
1) The process starts at a high temperature, all hits have the same weights.2) Weights are updated at a lower temperature.3) Weights are frozen.