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Zden ě k Dole ž al for the DEPFET beam test group 3rd Open Meeting of the Belle II Collaboration

DEPFET Beam Test 2008 Results. Zden ě k Dole ž al for the DEPFET beam test group 3rd Open Meeting of the Belle II Collaboration. Charles University in Prague. Introduction. Beam test 2008 tested ILC type of DEPFET detectors Test particles: pions 120 GeV

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Zden ě k Dole ž al for the DEPFET beam test group 3rd Open Meeting of the Belle II Collaboration

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  1. DEPFET Beam Test 2008 Results Zdeněk Doležal for the DEPFET beam test group 3rd Open Meeting of the Belle II Collaboration Charles University in Prague

  2. Introduction • Beam test 2008 tested ILC type of DEPFET detectors • Test particles: pions 120 GeV • Thickness of sensors: 450mm (Belle II: 50 mm) • Complication with multiple scattering • Pixel size ~ 24 – 32 mm (Belle II: ~ 60 – 90 mm) • Expected resolution < 2 mm (Belle II: ~ 8 mm) • Self-telescoping system • Special methods for data analysis (for separation of detector precision from other effects) • Belle II type of DEPFET detector expected for beam testing in 2010

  3. Introduction (2) Special scans performed: • Edge scan (to study edge effects) • Energy scan • Angle scan • Bias voltage scan • High statistics scan for stability checking

  4. The ‘underwear’: Power supplies

  5. Description of analysis Pre-tracking steps: • Common-mode noise correction • Gain correction • COG production (position error estimations) • Alignment and corrections in several steps Full resolution analysis with residuals, resolution analysis, track precision estimation, telescope resolutions etc. Verification of analysis with simulated data • GEANT4 simulation (TB2008 geometry, experimental detector resolutions simulated by Gaussian smear, analyzed in a standard way)

  6. Analysis results Total (cluster) charge Seed charge Cluster size

  7. Residuals Residuals (plots are in log scale): non-Gaussian tails at a 1 percent level Module 0 Module 1 Module 2 Module 3 Module 4 Module 5

  8. Verification of analysis with simulation data Resolutions reproduced from analysis of simulated data with realistic detector resolutions included Agreement in resolutions of all detectors within ±5% (±0,1 µm)‏

  9. Sub-pixel analysis results Typical results of DEPFET sub-pixel analysis: map of resolutions in pixel area. Color scale runs between 1 - 4 mm. First row shows modules #0, x and y axis , #1 x and y axis, second row shows modules #2 x and y axis , #3 x and y axis, third row shows modules #4 x and y axis and #5 x and y axis.

  10. Conclusion from bias scan • Changing bias affects seed and cluster size • Does not affect cluster charge and resolution Cluster charge Seed Cluster size Residuals Resolutions

  11. Conclusion from energy scan Relative deviations of resolutions, comparison of data and simulations. Solid circles are simulations, open circles are data; green - "diagonal" estimates, red - ML estimates. Simulation data are relative deviations of resolutions (green - "diagonal“ estimate, red - ML estimate) with energy, as seen in analysis of GEANT4 simulation data. For reference, we also plot residuals (blue). The data for each energy are based on analysis of 100 replicas of a data file containing 10,000 tracks. The plotted values are (xE - xtrue)=xtrue for simulations, and (xE - x120GeV )=x120GeV for data. The reasons of discrepancy are under study. Beam test results Beam test and simulation

  12. Cluster charge and seed in the angle scan • Expected behaviour: • rising cluster charge between 0 and ±4 deg (longer path) • effects of larger cluster size above ±4 deg • here 2x2 pixels summed only Linear increase of cluster size above ±1 deg.

  13. Resolution in the angle scan Best resolution within ±1 deg (agreement with simulations)

  14. Point Resolution in Z Point Resolution in Z At shallow angles cluster size gets extremely large and simple centre-of-gravity approach yields poor resolution due to inter-pixel charge fluctuations. Resolution is improved by means of η-algorithm (edge-technique) In many cases at normal incidence only one row is fired : resolution is limited by pixel size When track is inclined more than one row is fired -> resolution gets better A. Frey, MPI München 3/08/2006 DEPFET Workshop Bonn

  15. Conclusions • Analysis of DEPFET TB2008 is almost complete • Presented final results for: • individual detector resolutions • resolution vs. interpixel position • influence of edge voltage • energy scan • resolution vs. bias • resolution vs. incidence angle Summary of obtained resolutions: To do: high statistics scan analysis

  16. Conclusions • The analysis shows • Consistent behaviour of tested DEPFET modules over the whole course of the beam test. • Response to 120 GeV pions (110 keV deposited energy) was over 1600 ADU at ~13 ADU noise for the DUTs, which gives S/N over 120. • For modules thinned to 50 mm (prepared for Belle II)the S/N of 13 can be expected. An increase of 10 % can be gained with newly developed electronics (DEPFET sensor contributes to the measured noise by 10 % only, the rest comes from the current electronics). • The effects of different cluster size have to be tested. The expected resolutions for thinned sensor below 2 mm are very promising. • Detailed resolution scans show ~0.3 mm variation of resolution over the pixel area • Detailed results available in a DEPFET Note

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