The Silicon Drift Detector of the ALICE Experiment

The Silicon Drift Detector of the ALICE Experiment M. Sitta, University of Eastern Piedmont and INFN, Italy - for the ALICE Collaboration SSD SDD SPD Lout=97. 6 cm Rout=43. 6 cm Silicon Pixel Detector (SPD): • ~10 M channels • 240 sensitive vol. (60 ladders) Silicon Drift Detector (SDD): • ~133 k channels • 260 sensitive vol. (36 ladders) Layer 4 22 Ladders Layer 3 14 Ladders Layer 3: 6 sensors/ladder Layer 4: 8 sensors/ladder Silicon Strip Detector (SSD): • ~2. 6 M channels • 1698 sensitive vol. (72 ladders) 260 sensors in total The Silicon Drift Detectors The Inner Tracking System The ALICE experiment PASCAL (Preamplifier, Analog Storage and Conversion from Analog to digital) • @ 20 or 40 MHz • dynamic ADC range • test pulse for gain calib. 256 anods (per side) (1 per SDD module) (33) AMBRA (A Multievent Buffer Readout Architecture) (input from PASCAL) -1800 V Anode pitch 294 μm HV (nominal) -1800 V Bias voltage -40 V Average resolution: z 25 μm rφ 35 μm The SDD readout chain An SDD in detail CARLOS (Compression and Run Length enc. Oding Subsystem) • 8 inputs in parallel from AMBRA • 2 D two threshold compression Calibration Runs Pedestal Pulser Injector Baseline and noise Preamplifier gain Drift velocity After common mode subtraction Drift speed depends on Dopant concentration Temperature ( T-2. 4) Very high stability Charge calibration Distribution of cluster charge from cosmic tracks fitted with a convolution of Landau+Gaussian Module temperature can be inferred from drift speed ADC sampling set at 20 MHz Residual maps For all 260 SDD modules before assembling: • charge injected with an infrared laser in >100, 000 known positions • for each shot compute residual between reconstructed and know position • systematic deviations of drift speed (due to non-linear voltage divider or dopant concentration inhomogeneties) can be corrected at event reconstruction phase Layer 3, Ladder 6, Mod 275, Anode 200 Layer 3 was off less heating Layer 4, Ladder 14, Mod 428, Anode 200 Extract with good precision the conversion factor ADC → ke. V (most probable value for energy deposition of a MIP in 200 mm of Si = 82 ke. V) July 11 st 2008 October 14 th 2008