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Simulation of Pixel Response in Test Beam with Diffusion Insights from SPD Group Meeting

This document provides an overview of the pixel response simulation undertaken during the Test Beam in 2002, as discussed in the SPD Group meetings led by Paul Nilsson. Critical updates include the integration of diffusion mechanisms in the AliRoot model, detailing how charge sharing occurs and its parameters. The impact of bias voltage, thresholds, and cluster sizes on simulation accuracy is highlighted. Future directions and unresolved issues, particularly with cluster sizes greater than three, are also outlined. The text emphasizes data analysis as a step towards refining simulation protocols.

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Simulation of Pixel Response in Test Beam with Diffusion Insights from SPD Group Meeting

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  1. Test Beam 2002 Pixel Response Simulation: Update Paul Nilsson, SPD Group Meeting , August 26, 2003 Jan Conrad (CERN, Pixel Group) SPD general meeting November, 2004 P. Nilsson, SPD Group Meeting

  2. Side remark • Ivanov’s talk: parameterization of errors on reconstructed points if response working, this can be done by MC (true-rec for different cluster sizes)  get parameterizations as function of incident angle and different cluster sizes. Simulation  Reconstruction Probably better: data analysis see talks of Domenico, Daniela,Pål P. Nilsson, SPD Group Meeting

  3. Contents • Main news: • Diffusion is included and working P. Nilsson, SPD Group Meeting

  4. Diffusion in AliRoot (Dubna) model • Energy is deposited in steps in the sensor volume (15-20 steps) • Charge sharing done by diffusion (see next slide).  Dependence on bias voltage. P. Nilsson, SPD Group Meeting

  5. Diffusion • Gaussian diffusion: charge cloud spreads out during the particle’s traversion • σdiff = k (T ldr,)1/2 • k = (2D/vdr)1/2D = 11cm2/s • vdr = μ E μ = 450 cm2/Vs • E = Vbias /dsensor σdiff  dsensor / √Vbias ≈ 5 – 15 μm P. Nilsson, SPD Group Meeting

  6. What is in the simulation @ present (default) ? • Charge sharing geometrical (Ba/Sa model) • Coupling parameters: 0. (no coupling) • Threshold: 2000 e, • noise/threshold 280 e • no dependence on bias voltage • no dependence on temperature P. Nilsson, SPD Group Meeting

  7. Geometry 2002 Trick: whole ladder Si (for segmentation, BN) No scintillators,no PCB VTT ladder: 300μ Chip: 725 μ Telescope: 300 μ Chip: 725 μ P. Nilsson, SPD Group Meeting

  8. Simulation • assume 300 mu detector, 80 V bias • threshold: 2300 e , Noise: 300 e • file: biasscan_chip03_th200_14-07 2002.root P. Nilsson, SPD Group Meeting

  9. Cluster Sizes including diffusion Long dimension Short dimension P. Nilsson, SPD Group Meeting

  10. How does it look without diffusion? No diffusion diffusion P. Nilsson, SPD Group Meeting

  11. Scans(slide taken from last SPD general meeting) Simulation ThresholdScan BIAS VOLTAGE? Data Angle Scan P. Nilsson, SPD Group Meeting

  12. Scans: present status P. Nilsson, SPD Group Meeting

  13. δ rays • Generated on correct level: • rule of thumb: 1 δ ray per mm Si per incident particle.  P. Nilsson, SPD Group Meeting

  14. Status summary and outlook • Cluster sizes 1 and 2 reproduced (zero tilt) • There is still a problem with cls >3 • Trigger simulation • more material details • FLUKA (M. Noriega) • More long term: • more effective diffusion routine ( CPU diff/nodiff = 7) • 2003 ! P. Nilsson, SPD Group Meeting

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