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Background rejection of Vertex Detector

Background rejection of Vertex Detector. T adashi Nagamine Tohoku University ILC 測定器学術創成会議 @ KEK, 28 Jun 2006. Outline. Introduction FPCCD Vertex Detector Structure Simulation Tools Geometry in Simulation Study Background Rejection by Cluster Shape. Introduction.

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Background rejection of Vertex Detector

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  1. Background rejection of Vertex Detector Tadashi Nagamine Tohoku University ILC測定器学術創成会議@ KEK, 28 Jun 2006

  2. Outline • Introduction • FPCCD Vertex Detector Structure • Simulation Tools • Geometry in Simulation Study • Background Rejection by Cluster Shape

  3. Introduction • Accelerator technology changed. • Warm -> Cold Cavity • Longer beam train • 192 -> 2820 bunches / train • 15.7 or more times pair background / train • Need to find reduce this background to manageable level • Use smaller pixel detector (more pixels / mm^2) • Smaller track finding window by closing adjacent layer (use doublets structure)

  4. Small Pixel Size • Left: 20x20 micron^2 pixel -> occupancy = 3 / 25 • Right: 5x5 micron^2 pixel -> occupancy = 3 / 400

  5. Track Finding Window • Track finding window proportional to multiple scattering angle X distance between layers

  6. Software for Simulation • SimTools-1-01 with geant4.7.0 p01 (For Impact Parameter Study) • SimTools-1-02 with geant4.8.0 p01 (For Cluster Shape Study) • Track fitting: Kalman filter based. (Fitting with semeared true hits, since No Track Finder yet!) • Geometry data file: glddec05_2m.dat • Pair Background generation: Cain v2.3 (data had been prepared by T. Fujikawa and N. Tani) SimTools ref: http://acfahep.kek.jp/subg/sim/simtools/index.html

  7. FPCCD Vertex DetectorGeometry in Simulation Study L3 • Cylindrical shape used for each layer • No support material • Layer thickness : 80m • 3 configurations are studied • Layer 1 : R=20mm • Layer 2 : R=32mm • Layer 3 : R=58mm • Hit position resolution: 2m L2 L1

  8. Cluster Shapes for Low PT and High PT tracks • Pair Background (e+e-) : Lower PT (blue line) • Most particles in Interaction : Higher PT (green line) CCD IP

  9. Energy Deposit of muon track cluster • Distribution of energy deposit of 1GeV/c - • Isolated Delta-ray only cluster excluded • Geant4 parameter • Range Cut : 0.3 m • Max Step Size : 1 m

  10. Energy Deposit of muon track cluster (2) • Distribution of energy deposit of 1GeV/c - • Z dependence • Edep>2KeV

  11. Energy Deposit of Pair Background • Distribution of energy deposit of pair background • Delta-ray only cluster included • Geant4 parameter • Range Cut : 0.3 m • Max Step Size : 1 m

  12. Energy Deposit of Pair Background(2) • No Z Dependence

  13. Cluster Width Distribution (muon) • 1GeV/c - • D distribution • D = 1~2

  14. Cluster Width Distribution (muon)(2) • 1GeV/c - • Dz distribution • Dz

  15. Cluster Width Distribution (Pair Background) • Pair background • D distribution • D = 1~12

  16. Cluster Width Distribution (Pair Background)(2) • Pair background • Dz distribution • Dz = 1~15 peaked at 3

  17. Distributions of Cluster Width v.s. Z (muon) • 1GeV/c - • D distribution • No Z dependence

  18. Distributions of Cluster Width v.s. Z (muon)(2) • 1GeV/c - • Dz distribution • Large Z dependence

  19. Distributions of Cluster width v.s. Z(Pair Background) • Pair background • D distribution • No Z dependence

  20. Distributions of Cluster width v.s. Z(Pair Background)(2) • Pair background • Dz distribution • No Z dependence

  21. Pair Background hits distribution in Z • BLACK: all hits • RED: after rejection

  22. Efficiency (rejection factor) vs Z Pair Background hits • 1/20 rejection is achieved for Z>5000(pixels)

  23. Hit Efficiency for Muon Track • BLACK: all hits • RED: after rejection

  24. Hit Efficiency for Muon Track(2) • Efficiency > 98% for most region

  25. Summary • Pair background can be reduced by using cluster shape by factor of 1/10 ~ 1/20 for z > 1/2 Layer length • Need to development track finder work well for z<1/2 utilizing narrow gap of doublet structure.

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