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The ATLAS Pixel Detector - Running Experience – Markus Keil – University of Geneva on behalf of the ATLAS Collaboration Vertex 2009 Putten, Netherlands, 13/09/2009. Outline. Introduction Timeline & Detector Status Calibrations Cosmic Ray Data Taking. Outline. Introduction

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Outline

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  1. The ATLAS Pixel Detector - Running Experience –Markus Keil – University of Genevaon behalf of the ATLAS CollaborationVertex 2009Putten, Netherlands, 13/09/2009

  2. Outline • Introduction • Timeline & Detector Status • Calibrations • Cosmic Ray Data Taking M. Keil - ATLAS Pixels: Running Experience

  3. Outline • Introduction • Timeline & Detector Status • Calibrations • Cosmic Ray Data Taking M. Keil - ATLAS Pixels: Running Experience

  4. The ATLAS Detector Length: 44 m Height: 25 m M. Keil - ATLAS Pixels: Running Experience

  5. Pixel Detector • Requirements: • Position resolution in rΦ-direction < 15μm • 3 track points for |η| < 2.5 • Time resolution < 25 ns • Hit detection efficiency > 97% • Basic Properties: • 1744 Pixel Modules on three barrel layers and 2 x 3 discs • 80M readout channels • Innermost layer at 5 cm • Radiation tolerance 500 kGy / 1015 1 MeVneqcm-2 • Evaporative C3F8 cooling integrated in local support structure → Module temperature below 0○C M. Keil - ATLAS Pixels: Running Experience

  6. The ATLAS Pixel Module • Sensor • 250 μm thick n-on-n Si sensor • 47232 (328 x 144) Pixels • Typical pixel size 50 x 400 μm(50 x 600 μm pixels in gaps between FE chips) • Bias voltage 150 – 600 V • Readout • 16 FE Chips with 2880 pixels each • Pulse height measured by means of Time over Threshold • Zero suppression in the FE chips, MCC chip builds module event • Data transfer 40 to 160 MHz depending on layer (occupancy) M. Keil - ATLAS Pixels: Running Experience

  7. Outline • Introduction • Timeline & Detector Status • Calibrations • Cosmic Ray Data Taking M. Keil - ATLAS Pixels: Running Experience

  8. Pixel Detector Operation 2008 and 2009 • Pixel Detector sign-off was foreseen to happen in a two-week period end of April / beginning of May 2008 • Cooling plant failure May 1st → Stopped until August • August 2008: Evaporative Cooling back, sign-off finished • September – October 2008: Combined cosmic ray data taking, pixel HV off during beam injection tests • November – December 2008: Calibration and Combined cosmic ray data taking • January – May 2009: Cooling plant consolidation • Jun 2009: ATLAS Cosmic ray data taking • July-August 2009: Detector consolidation M. Keil - ATLAS Pixels: Running Experience

  9. Detector Status • Leak-down measurements indicate a cooling fluid loss of 14 kg/year • Three leaky loops not operated in 2008; this year all loops will be operated unless a degradation should be observed. • Risk analysis of C3F8 in the N2 atmosphere of the inner detector ongoing (expected concentration < 0.1%) • Off-detector failures • Optical transmitter plugins in the readout crates (VCSEL arrays) had a failure rate of 1 per week of operation • All optical transmitter plugins in the readout crates have been exchanged; new plugins produced with stricter ESD protection requirements • 1.6% of the detector cannot be operated due to on-detector failures • Mostly due to problems in the optical links or the HV connections M. Keil - ATLAS Pixels: Running Experience

  10. Outline • Introduction • Timeline & Detector Status • Calibrations • Cosmic Ray Data Taking M. Keil - ATLAS Pixels: Running Experience

  11. Optical Data Link Tuning • Parameters to be adjusted: • On-detector laser power • Sampling threshold and phase • Bit error rate measurement for full parameter space to find the best parameter settings • Difficulty: one common laser power setting for 6/7 modules • In 2008: 97% of the detector successfully tuned • Now: Improved algorithms → Almost all links can be tuned automatically M. Keil - ATLAS Pixels: Running Experience

  12. Threshold and Noise • Threshold setting: 4000 e • Threshold tuned pixel by pixel, threshold dispersion after tuning ~ 40 e • Noise approx. 200 e for most pixels, slightly higher for special pixels • Threshold / Noise approx. 25 for normal pixels M. Keil - ATLAS Pixels: Running Experience

  13. Interchip Region M. Keil - ATLAS Pixels: Running Experience

  14. Time over Threshold • FE Chips provide Time over Threshold information for each hit • Nearly linear dependence on deposited charge • Pixel-by-pixel tuning; chosen tuning: 30 BC for 20 ke (corresponding to the signal of 1 mip) • Calibration by means of test charge injection • Charge measurement with ToT in cosmics data taking • Landau peak at 18300 (Simulation 19000 e): Confirms ToT Calibration M. Keil - ATLAS Pixels: Running Experience

  15. Outline • Introduction • Timeline & Detector Status • Calibrations • Cosmic Ray Data Taking M. Keil - ATLAS Pixels: Running Experience

  16. ATLAS Cosmic Ray Data Taking • Smooth integration into ATLAS data taking beginning of September 2008 • High voltage off during LHC beam injection (no stable beam) to protect FE chips→ no beam-splash events taken • Timing in with ATLAS → first cosmic ray track seen September 14 • 400k tracks taken with and without magnetic field • 96% of the modules operated (3 leaking cooling loops conservatively switched off) • Between day 35 and day 70: in-situ calibration of detector • 250k tracks taken in 2009 M. Keil - ATLAS Pixels: Running Experience

  17. Cosmic Ray Tracks • Track with 8 pixel hits on track (2 x 2 hits in module overlap regions) • Red: hits on track • Green: unassociated hits (noise) • Noise occupancy: ~ 10-10 hits/pixel/BC M. Keil - ATLAS Pixels: Running Experience

  18. Alignment • Alignment of pixel barrel modules from cosmics data • Beam data needed for endcap alignment • Alignment not yet perfect due to limited statistics, but large improvement w.r.t. nominal geometry and good starting point for alignment with beam: • Precision direction: 128 μm → 24 μm beam direction: 282 μm → 131 μm M. Keil - ATLAS Pixels: Running Experience

  19. Efficiency and Noise Occupancy • After alignment measured efficiency is >99.7% for active modules • Noise occupancy after masking of noisy pixels: ~ 10-10 • Fraction of masked pixels: 10-4 M. Keil - ATLAS Pixels: Running Experience

  20. Timing • Each hit has to be assigned to the correct bunch crossing (25 ns) • Module clocks have to be precisely aligned with the bunch crossing clock • In cosmics data taking: readout of 8 consecutive bunch crossings (plot shows hit time w.r.t. beginning of readout window) • Correction of propagation delays: • First step: time alignment of readout crates (scope measurements) • Second step: time alignment of modules (using cable length data) • Remaining effects: • Trigger jitter • Random phase of cosmics • Timewalk; “in-time” for less than 5400 e • Plan to start data taking with 5 BC readout, later reduce readout window to 1 BC External Delay = const - timewalk M. Keil - ATLAS Pixels: Running Experience

  21. Lorentz Angle Measurement • Cluster size vs. Track angle with and without magnetic field → Measurement of the Lorentz angle • Measured value close to expected value (225 mrad) • Theoretically expected dependence on mobility can be nicely seen when including modules of different temperature • Measured: (-0.78 ± 0.18) mrad/K, expected: -0.74 mrad/K M. Keil - ATLAS Pixels: Running Experience

  22. Summary • Pixel detector signed off and commissioned in very short time in 2008 • Calibration measurements show detector performance as expected • Noise approximately 200 e, Threshold dispersion approx. 40 e • Time over threshold allows for reliable charge measurement • Cosmic ray data taking with approximately 96% of the detector very useful for understanding of the detector • Good progress in alignment • Efficiency after alignment > 99.5% • Noise occupancy approximately 10-10 hits/pixel/BC • Useful input to detector simulation • Current status and next steps: • Calibration program has been rerun at lower temperature • Combined cosmic ray run Sept./Oct. • The Pixel Detector is ready for beam with ≥ 98% working modules! M. Keil - ATLAS Pixels: Running Experience

  23. Backup M. Keil - ATLAS Pixels: Running Experience

  24. Number of Masked Pixels M. Keil - ATLAS Pixels: Running Experience

  25. The Frontend Chip • One frontend chip contains 2880 pixel cells organised in 18 columns with 160 pixels each (400 x 50 mm) • Each pixel cell in the matrix contains preamplifier, discriminator and readout logic, which transfers hits to buffers at the bottom of the chip • Peripheral region contains hit buffers, logic for trigger coincidence and data serialisation and programmable DACs for the currents and voltages needed for the operation of the chip. • Hit transfer to EOC is done column pair wise, whereas pixel configuration is done with a 2880 bit long shift register that connects all pixels M. Keil - ATLAS Pixels: Running Experience

  26. The Pixel Cell M. Keil - ATLAS Pixels: Running Experience

  27. Preamplifier and Discriminator Signal Shapes • Time over threshold (length of discriminator signal) depends on • Deposited charge • Discriminator threshold • Feedback current • Information of the ToT (in units of 25 ns) is read out together with the hit information → possibility to measure the deposited charge M. Keil - ATLAS Pixels: Running Experience

  28. Optical Links M. Keil - ATLAS Pixels: Running Experience

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