1. The Silicon Drift Detector of the ALICE Experiment
M. Sitta, University of Eastern Piedmont and INFN, Italy - for the ALICE Collaboration
Rout=43.6 cm
Lout=97.6 cm
SPD
SSD
SDD
Silicon Pixel Detector (SPD):
~10M channels
240 sensitive vol. (60 ladders)
Silicon Drift Detector (SDD):
~133k channels
260 sensitive vol. (36 ladders)
Silicon Strip Detector (SSD):
~2.6M channels
1698 sensitive vol. (72 ladders)
Layer 4
22 Ladders
Layer 3
14 Ladders
Layer 3: 6 sensors/ladder
Layer 4: 8 sensors/ladder
260 sensors in total
The ALICE experiment
The Inner Tracking System
The Silicon Drift Detectors
PASCAL (Preamplifier, Analog Storage and Conversion from Analog to digital)
@ 20 or 40 MHz
dynamic ADC range
test pulse for gain calib.
-1800 V
256 anods (per side)
(33)
(1 per SDD module)
AMBRA (A Multievent Buffer Readout Archi-tecture) (input from PASCAL)
CARLOS (Compression and Run Length encOding Subsystem)
8 inputs in parallel from AMBRA
2D two threshold compression
Anode pitch μm
HV (nominal) V Bias voltage -40 V
Average resolution: z 25 μm rφ 35 μm
The SDD readout chain
An SDD in detail
Calibration Runs
Pedestal
Pulser
Injector
Preamplifier gain
Drift velocity
Baseline and noise
After common mode subtraction
Drift speed depends on
Dopant concentration
Temperature ( T-2.4)
Very high stability
Module temperature can be inferred from drift speed
ADC sampling set at 20 MHz
Charge calibration
Residual maps
Distribution of cluster charge from cosmic tracks fitted with a convolution of Landau+Gaussian
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 4, Ladder 14, Mod 428, Anode 200
Layer 3 was off
less heating
Layer 3, Ladder 6, Mod 275, Anode 200
July 11st 2008
October 14th 2008
Extract with good precision the conversion factor ADC → keV (most probable value for energy deposition of a MIP in 200 mm of Si = 82 keV)