CA+KF Track Reconstruction in the STS

CA+KF Track ReconstructionCA+KF Track Reconstructionin the STSin the STS

S. Gorbunov and I. KiselS. Gorbunov and I. KiselGSI/KIP/LITGSI/KIP/LIT

CBM Collaboration MeetingCBM Collaboration MeetingDresden, September 26, 2007Dresden, September 26, 2007

26 September 2007, Dresden26 September 2007, Dresden Ivan Kisel, KIP, Uni-HeidelbergIvan Kisel, KIP, Uni-Heidelberg 22/12/12

CBM Note on SIMDized Kalman Filter Track FitCBM Note on SIMDized Kalman Filter Track Fit

Implemented:Implemented:in CbmL1CATrackerin CbmL1CATracker

Different CPU architecturesDifferent CPU architecturesDifferent CPU architecturesDifferent CPU architectures

The Kalman filter based track The Kalman filter based track fit works with single precision fit works with single precision floating point variables, and floating point variables, and we are now not far from we are now not far from implementing it in integers in implementing it in integers in order to port it later to FPGA.order to port it later to FPGA.


Cellular Automaton PseudocodeCellular Automaton Pseudocode

11 Create trackletsCreate tracklets 22 Collect tracksCollect tracks


Reconstruction Time vs. Number of MC TracksReconstruction Time vs. Number of MC Tracks

(2) all tracks(2) all tracks(1) all quasi-primary tracks(1) all quasi-primary tracks(0) fast quasi-primary tracks(0) fast quasi-primary tracks


Structure and DataStructure and Data

cbmroot/L1cbmroot/L1

L1AlgoL1Algo

L1GeometryL1Event

(L1Strips, L1Hits) L1Tracks

Strips:Strips: float vStripValues[NStrips]; // strip coordinates (32b)unsigned char vStripFlags [NStrips]; // strip iStation (6b) + used (1b) + used_by_dublets (1b)Hits:Hits:struct L1StsHit { unsigned short int f, b; // front (16b) and back (16b) strip indices };L1StsHitL1StsHit vHits[NHits];

unsigned short int vRecoHits [NRecoHits]; // hit index (16b)unsigned char vRecoTracks [NRecoTracks]; // N hits on track (8b)

class L1Triplet{ unsigned short int w0; // left hit (16b) unsigned short int w1; // first neighbour (16b) or middle hit (16b) unsigned short int w2; // N neighbours (16b) or right hit (16b) unsigned char b0; // chi2 (5b) + level (3b) unsigned char b1; // qp (8b) unsigned char b2; // qp error (8b)}

Input:Input:

Output:Output:

Internal:Internal:

• A standalone L1AlgoL1Algo module• About 300 kB300 kB per central event


Event DisplayEvent Display


CA Track Finder EfficiencyCA Track Finder Efficiency

MBias eventsMBias events Central eventsCentral events

Efficiency, %Efficiency, % Track categoryTrack category Efficiency, %Efficiency, %

98.0 + (0.7 + 1.3) Reference set (>1 GeV/c) 96.6 + (1.8 + 1.6)

95.4 + (1.1 + 3.5) All set (>=4 hits, >100 MeV/c) 93.5 + (2.9 + 3.6)

89.1 + (2.1 + 8.8) Extra set (<1 GeV/c) 85.9 + (5.9 + 8.2)

0.4 Clone 0.4

1.6 Ghost 4.7

140 MC tracks/event found 633

Standard geometry: 2M2P4SStandard geometry: 2M2P4S

Reconstructed + (Damaged + Good)


Low Momentum Tracks Low Momentum Tracks

1. In general, efficiency calculation is based on similarity 1. In general, efficiency calculation is based on similarity between parameters of generated and reconstructed tracks. between parameters of generated and reconstructed tracks. 2. The simplest efficiency calculation 2. The simplest efficiency calculation is is based on association based on association of hits used for track fitting. of hits used for track fitting. 3. In the region of low momentum tracks it 3. In the region of low momentum tracks it can becan be based on based on association of hits within the track road because of large association of hits within the track road because of large multiple scattering and high hit density. Therefore, ghost in multiple scattering and high hit density. Therefore, ghost in (2) can here contribute to (1).(2) can here contribute to (1).

Central eventsCentral events


Detector InefficiencyDetector Inefficiency

• Tracking is gathering of Tracking is gathering of 11//22D measurements into D measurements into 55D tracks, here combinatoricsD tracks, here combinatorics• Therefore, tracking is split into two parts: local (1) and global (2) Therefore, tracking is split into two parts: local (1) and global (2) • In the local part a gap between 1/2D and 5D is filled with triplets In the local part a gap between 1/2D and 5D is filled with triplets • If there is If there is no tripletno triplet in the local step, in the local step, no trackno track in the global step in the global step• Therefore, Therefore, short tracks are weak against detector inefficiencyshort tracks are weak against detector inefficiency

• Tracks interesting for physics are usually long (long vs. short tracks)Tracks interesting for physics are usually long (long vs. short tracks)• Specialized extra tracking step (usually indicates weakness of the detector)Specialized extra tracking step (usually indicates weakness of the detector)• Increase acceptance (<- RIncrease acceptance (<- Rinin, R, Routout ->) keeping N ->) keeping Nchch constant (longer or chained strips) constant (longer or chained strips)• Double stations – 4x-, 3x-, 2x-strip space points (no inefficiency, no dead zones)Double stations – 4x-, 3x-, 2x-strip space points (no inefficiency, no dead zones)


CA Track Finder EfficiencyCA Track Finder Efficiency

MBias eventsMBias events Central eventsCentral events

Standard geometry: 2M2P4SStandard geometry: 2M2P4S

Efficiency, %Efficiency, % Track categoryTrack category Efficiency, %Efficiency, %

96.4 + (1.1 + 2.5) Reference set (>1 GeV/c)

94.7 + (2.6 + 2.7)

93.3 + (1.6 + 5.1) All set (>=4 hits, >100 MeV/c)

91.1 + (3.9 + 5.0)

85.6 + (2.9 + 11.5) Extra set (<1 GeV/c)

82.1 + (7.1 + 10.8)

0.3 Clone 0.3

2.1 Ghost 5.9

136 <- 140100%

MC tracks/event found 617 <- 633100%

Reconstructed + (Damaged + Good)

Detector efficiency (MC points) 98%


CBM Note on Reconstruction of Decayed ParticlesCBM Note on Reconstruction of Decayed Particles

Implemented:Implemented:in CBM as CbmKFParticlein CBM as CbmKFParticlein ALICE as AliKFParticlein ALICE as AliKFParticle

DD00DD00

x, y, z, px, y, z, pxx, p, pyy, p, pzz, E, m, L, c, E, m, L, cx, y, z, px, y, z, pxx, p, pyy, p, pzz, E, m, L, c, E, m, L, c

KK--

++

In addition to vertices, which are now production and In addition to vertices, which are now production and decay points, all physical parameters of decayed decay points, all physical parameters of decayed particles together with the corresponding errors are particles together with the corresponding errors are provided by the package.provided by the package.


Summary and PlansSummary and Plans

SIMDized CA and KF algorithms are releasedSIMDized CA and KF algorithms are released Low momentum tracks down to 100 MeV/c are found by defaultLow momentum tracks down to 100 MeV/c are found by default CA track finder works with inefficient detectorsCA track finder works with inefficient detectors Need direct access to strips (fixed geometry at the level of modules)Need direct access to strips (fixed geometry at the level of modules) Further analysis of robustness of the CA track finderFurther analysis of robustness of the CA track finder

CA+KF Track Reconstruction in the STS

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