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A first look at the Gigatracker simulation

A first look at the Gigatracker simulation. Massimiliano Fiorini CERN. NA62 Gigatracker Working Group 28 July 2009. Software. NA62 MonteCarlo fast simulation of the beam line based on Flyo called by Geant4 to generate primary particles

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A first look at the Gigatracker simulation

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  1. A first look at the Gigatracker simulation Massimiliano Fiorini CERN NA62 Gigatracker Working Group 28 July 2009

  2. Software • NA62MonteCarlo • fast simulation of the beam line based on Flyo • called by Geant4 to generate primary particles • beam particle passed to Geant4 at a given position along the beam line • default: beam track passed just in front of the 1st Gigatracker station • only Gigatracker enabled: all other detectors excluded • 3×106 events generated with two different “range cuts” for electrons in silicon: • 1st case: 1 mm (corresponds to 541 keV) • 2nd case: 1 m(corresponds to 990 eV) • numbers and plots refer only to 1st Gigatracker station

  3. Beam Spectrometer Layout • 3 Gigatracker (GTK) stations: 60mm × 27 mm dimension • 300 m × 300 mpixel cells • pixel structure and GTK geometry implemented in MonteCarlo by S. Bifani (see presentation on April 2009 Meeting): • Si sensor (200 m thickness), Sn-Pb bump bond (15 mthickness, 10 m diameter cylinder), Si read-out chip (100 m thickness), carbon fiber support (100 m thickness) 2ndachromat pπ θπK pK 13.2 m 9.6m pυ pυ GTK3 GTK1 60 mm GTK2

  4. 1st case

  5. Number of hits on GTK1

  6. Number of hits on GTK1 (zoom) Fraction of events with more than 1 hit: 0.72 %

  7. New classes added (1) • class GigaTrackerPixel • gathers all the hits’ energy belonging to the same pixel sensitive volume • methods implemented: • AddEnergy(Double_t) • GetNHit() • GetEnergy() • GetPixelID() • GetPositionX() • GetPositionY() • SetClusterID(Int_t) • GetClusterID()

  8. New classes added (2) • class GigaTrackerCluster • collection of adjacent pixels (side-side, corner-corner) in a C++ vector • methods implemented: • AddPixel(GigaTrackerPixel) • GetNPixels() • GetPixelVector() • GetDistance(GigaTrackerCluster) • GetEnergy() • GetPositionX() • GetPositionY() • GetWPositionX() • GetWPositionY()

  9. Number of pixels GTK1 • Fraction of events with more than 1 pixel: 0.3%

  10. Number of hits per pixel GTK1 • Fraction of pixels with more than 1 hit: 1.0 %

  11. Number of clusters GTK1 • Fraction of events with more than 1 cluster: 0.03 %

  12. Number of pixels per cluster GTK1 • Fraction of clusters with more than 1 pixel: 0.3 %

  13. Energy release GTK1 per event • mean energy: 72.4 keV (~20k e-h) • most probable energy: 53.7 keV (~15k e-h) • FWHM: ~25 keV (~7k e-h) • minimum energy: ~29 keV (~8k e-h)

  14. Hit position (X-Y) inside a pixel • uniform pixel population (average on all pixel of one GTK station) • r.m.s. = 86.8 m for both X and Y [300 m/SQRT(12) = 86.6 m]

  15. Hit position (Z) inside a pixel • in all cases the energy is released just at the entrance of the silicon sensor • only for multiple hits, the energy is deposited also at different depths along the sensor, up to the full thickness (200 µm)

  16. Hit position spread GTK1 • hit position spread (with respect to first hit) in GTK1 • r.m.s. (from un-zoomed plots) ~500 m for both X and Y

  17. Position resolution • single cluster • arithmetic pixel position average (no weight) • r.m.s. = 86.8 m for both X and Y

  18. Charge sharing among pixels • analyze single cluster formed by 2 pixels only (0.2%) • pixel ordering given by Geant4 • if both pixels have an energy below 28.8 keV (8 ke-h) the event is inefficient • found 9 inefficient events over 5595  (0.16 ± 0.05) % inefficiency

  19. 2nd case

  20. Number of hits on GTK1

  21. Number of pixels GTK1 • Fraction of events with more than 1 pixel: 2.4%

  22. Number of hits per pixel GTK1 • Fraction of pixels with more than 1 hit: 97.2 %

  23. Number of clusters GTK1 • Fraction of events with more than 1 cluster: 0.06 %

  24. Number of pixels per cluster GTK1 • Fraction of clusters with more than 1 pixel: 2.4 %

  25. Hit position (Z) inside a pixel • in all cases the energy is still released at the entry face of the silicon sensor • now the energy is deposited much more often also at different depths along the sensor, up to the full thickness

  26. Hit position spread GTK1 • hit position spread (with respect to first hit) in GTK1 • r.m.s. (from un-zoomed plots) ~100 m for both X and Y (before was ~500m)

  27. Position resolution • single cluster • arithmetic pixel position average (no weight) • r.m.s. = ~86 m for both X and Y

  28. Charge sharing among pixels • analyze single cluster formed by 2 pixels only • pixel ordering given by Geant4 • if both pixels have an energy below 28.8 keV (8 ke-h) the event is inefficient • Found 28 inefficient events over 58498  (0.05 ± 0.01) % inefficiency

  29. Conclusions and To Do List • use of new NA62 MonteCarlo with the aim of studying charge sharing effects among Gigatracker pixels • two classes implemented for reconstruction purposes • very preliminary results show a low inefficiency for particle detection in case that charge is distributed among 2 adjacent pixels • To Do list • increase statistics • variations of other Geant4 parameters from the PhysicsList • more detailed study of δ-rays production and “tracking” by Geant4 • take into account other effects after-generation (diffusion, drift)

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