1. Overview and status of the ATLAS Pixel Detector Attilio Andreazza Università di Milano and I.N.F.N. for the ATLAS Pixel Collaboration
Layout of the ATLAS Pixel Detector
Commissioning activities:
system test setup
measurement with cosmics on surface
Installation in ATLAS
Just few
selected topics

2. A Toroidal LHC Apparatus
HEP2007 Manchester, 19 July 2007
A.Andreazza - Status of the ATLAS Pixel Detector

3. The ATLAS Pixel Detector
The Pixel Detector is the vertex detector for the ATLAS experiment.
It consists of three barrel layers and six disks, covering with three precise measurement points the region up to 2.5.
Innermost layer (B-layer) at R=5 cm
There will be 1456 barrel modules and 288 forward modules, for a total of 80 million channels and a sensitive area of 1.6 m2.
Modules will operate in an environment temperature below 0ºC and within a 2T solenoidal magnetic field.
Barrel module are tilted by 20º in the R plane to overcompensate the Lorentz angle.
Components have been tested to be rad-hard up to:
NIEL > MeV n/cm2
dose > 500 kGy
Layer-1
B-Layer
B-Layer
B-Layer
Disks
Disks
Disks
Beampipe
HEP2007 Manchester, 19 July 2007
A.Andreazza - Status of the ATLAS Pixel Detector

4. A.Andreazza - Status of the ATLAS Pixel Detector
Module concept
60.8×16.4 mm2 × 250 m active silicon volume.
50 m (R) × 400 m () pixels
Bump bonds between sensor and 16 front-end electronics chips (both SnPb and In bumps used)
Module Controller Chip on flex hybrid to perform distribution of commands and event building.
Each channel can be individually tuned, to get uniform response:
threshold: e-
threshold dispersion: e-
noise: e-
Defective pixels
Layer 2: 0.29%
Layer 1: 0.20%
B-Layer: 0.07%
Disks: 0.20%
HEP2007 Manchester, 19 July 2007
A.Andreazza - Status of the ATLAS Pixel Detector

5. Timing in the pixels electronics
Ideal pulse shape is almost triangular with fast rise and slow return to baseline.
Timing of this signal is critical
Timewalk:
low pulse height signals arrive later than high pulse height;
if delay is too high, the pulse is associated to the subsequent bunch crossing.
uniform efficiency requires good synchronization.
Time over Threshold (ToT)
used to interpolate position of multi-hit clusters as a function of =Q2/(Q1+Q2)
Time over Threshold for a m.i.p. tuned to 30 clock cycles
timewalk
ToT
20 ns
In-time threshold
1 m.i.p.
HEP2007 Manchester, 19 July 2007
A.Andreazza - Status of the ATLAS Pixel Detector

6. A.Andreazza - Status of the ATLAS Pixel Detector
System test setup
Pixel endcap A
Service quarter panel
Commissioning of one full pixel detector endcap:
144 modules
Almost final services:
LV supply + rad-tolerant regulation system;
operation at -10 ºC, using evaporative cooling;
connection to off-detector readout electronics via optical fibres.
Goals:
test of services
setting up in-situ calibration tools
commissioning of DAQ
commissioning of the detector with cosmics ray and noise runs.
HEP2007 Manchester, 19 July 2007
A.Andreazza - Status of the ATLAS Pixel Detector

7. System test: optical links
error free region
phase [ns]
PiN threshold [DAC]
10
01
clock edge
Connection between on- and off-detector readout electronics is through optical link.
Each link can be tuned by setting:
signal phase
threshold
but size of error free region depends on the bias: one value for 7 channels.
Experience from system test operation:
dynamic range of channels is sensitive to temperature
matching of the 7 channels is not adequate at the design temperature.
Action:
install heaters to keep optobards at room temperature.
HEP2007 Manchester, 19 July 2007
A.Andreazza - Status of the ATLAS Pixel Detector

8. A.Andreazza - Status of the ATLAS Pixel Detector
Cosmics data-taking
Standalone running using the system test setup in December 2006:
Full Endcap A (144 modules, 112 readout)
trigger scintillator system (1 to 4 in the picture): 3 AND ( 1 OR 2 OR 4 )
20 cm iron block to provide a 230 MeV/c momentum cut.
Huge amount of random trigger data
About 1 M cosmics trigger
4% with reconstructed tracks through all three disks
Reference data for validation of pixel detector understanding
HEP2007 Manchester, 19 July 2007
A.Andreazza - Status of the ATLAS Pixel Detector

9. Cosmics data: module syncronization
Hits in time with trigger
Delay VS module number ns
Disk 0
10 ns
Flat noise distribution ns
Disk 1 ns
Timewalk spreads hits through different “bunch crossings”
This distribution is sensitive to module timing.
Checked module synchronization with resolution better than 1 ns.
Disk 2
HEP2007 Manchester, 19 July 2007
A.Andreazza - Status of the ATLAS Pixel Detector

10. Cosmics data: noise measurements
Occupancy: hit probability per bunch crossing of a pixel.
Typical occupancy rate in noise runs is per bunch crossing
Noise is concentrated on few hot pixels:
~90% are special pixels, marked during module characterization,
remaining can be removed with an additional masking step.
True random occupancy is order of 10-10
Signal
Noise
10-10
After masking
89 (out of 1.6×106)
pixels with occupancy
greater than 10-4
Occupancy
HEP2007 Manchester, 19 July 2007
A.Andreazza - Status of the ATLAS Pixel Detector

11. Cosmics data: efficiency
Efficiency can be computed using particles which crosses overlapping modules in the same disk
24% of tracks
fiducial cuts on both the initial and overlapping module (remove shallow tracks)
Average efficiency ~99%
not enough statistics to provide accurate per module measurement. *
Disk 0
Disk 1
Disk 2
HEP2007 Manchester, 19 July 2007
A.Andreazza - Status of the ATLAS Pixel Detector

12. Cosmics data: resolution
50 m pitch
resolution = 21 m
50 m pitch
resolution = 18 m
400 m pitch
resolution = 118 m
400 m pitch
resolution = 117 m
alignment
Due to the low extrapolation distance, overlap residuals are good for testing detector resolution and alignment.
Low momentum tracks and high incidence angles, results in not-optimal resolution:
MC expectation is 16 m for the precision coordinate (~9 m for high momentum/normal incidence tracks)
After a simple alignment the observed resolution in data matches well with MC expectation.
HEP2007 Manchester, 19 July 2007
A.Andreazza - Status of the ATLAS Pixel Detector

13. Installation: the last tests
Final part of the assembly performed on surface:
connection of all the services
test of leak tightness and conductor continuity
2.5 monthes of hard work to fully check the detector before installing in ATLAS.
As built detector quality:
Localised inefficiencies
2 unusable modules
3 dead FE chips
total of 0.12% localized inefficiencies
None of these in the B-layer!
Individual bad pixels 0.2%
Only 0.07% in B-layer
Most relevant failures:
disconnected bumps
noisy channels
reduced charge collection
HEP2007 Manchester, 19 July 2007
A.Andreazza - Status of the ATLAS Pixel Detector

14. A.Andreazza - Status of the ATLAS Pixel Detector
... and then diving
Pixel Package Lowered; 25 June
Pixel Package Installed; 29 June
HEP2007 Manchester, 19 July 2007
A.Andreazza - Status of the ATLAS Pixel Detector

15. A.Andreazza - Status of the ATLAS Pixel Detector
Conclusions
The ATLAS Pixel detector construction has been completed
Detailed information of each of the 80M channels:
the fraction of defective pixels is below 0.4%
One endcap has been used for system commissioning:
matching of optical components proved to be critical
reconstruction and simulation software validated using cosmics rays:
noise occupancy O(10-10)
efficiency >99%
resolution matches MC expectation.
The full pixel package has been installed in the heart of ATLAS.
Unfortunately final connection to the services will not be possible until Fall: operation only in Winter.
As Sleeping Beauty waiting
for Prince Charming
...to be awakened by
a cosmics’ kiss
HEP2007 Manchester, 19 July 2007
A.Andreazza - Status of the ATLAS Pixel Detector

16. Back-up transparencies

17. System test: evaporative cooling
Switching on cooling
Switching off cooling
Module calibration, T-10 ºC
Modules in stand by, T-18 ºC
The evaporative cooling system is critical for operation of the detector at low temperature (needed to reduce impact of radiation damage).
It operated for the whole period with high reliability.
HEP2007 Manchester, 19 July 2007
A.Andreazza - Status of the ATLAS Pixel Detector

18. Front-end electronics concept
Fast charge amplifier with constant current feedback.
Fast discriminator with tunable threshold (7-bit DAC)
Storage of hits during the trigger latency time in 64 “End of Column” memory buffers for each column pair of 2×160 pixels
HEP2007 Manchester, 19 July 2007
A.Andreazza - Status of the ATLAS Pixel Detector

19. A.Andreazza - Status of the ATLAS Pixel Detector
Module concept
Self-consistent detector unit.
Sensor (Oxygenated FZ Silicon):
active area 60.8 × 16.4 mm2
250 m thickness
pixel cell 50 m (R) × 400 m (Z)
extended cells (ganged and long pixels) to cover the otherwise dead region between FE chips.
Front-end electronics:
16 FE-I3 chips, 0.25 m IBM technology, with rad-hard design;
46080 channels/module
Interconnection by bump-bonding:
Solder (IZM, Berlin)
Indium (Selex, previously AMS, Rome)
Flex hybrid:
Module Controller Chip to perform communication and event building;
local decoupling and temperature monitoring.
Module Controller Chip
Flex hybrid
Sensor
16 FE chips
Pigtail
HV connection
HEP2007 Manchester, 19 July 2007
A.Andreazza - Status of the ATLAS Pixel Detector

20. A.Andreazza - Status of the ATLAS Pixel Detector
Specifications
Radiation hardness:
NIEL > MeV neq/cm2
500 kGy
Technical Design Report specification were:
Rf resolution 13 mm,
efficiency better than 97% at end of lifetime,
analog information was a high priority option.
Given the 25 ns beam crossing rate at the LHC:
must be able to assign each hit to the proper bunch crossing; (measuremens of timewalk effects on efficiency and resolution)
must be able to store the hit information during the trigger latency time of ~100 beam crossings. (measuremens of rate capability of the readout system with high intensity beam)
HEP2007 Manchester, 19 July 2007
A.Andreazza - Status of the ATLAS Pixel Detector

21. A.Andreazza - Status of the ATLAS Pixel Detector
ToT measurements
ToT
Single hit clusters
Two hits clusters
Three hits clusters
ToT for clusters associated to tracks for single, double and triple hits
red isto: MC
blue crosses: cosmics data
Using calibration constants
from production measurements
read from DB
Noise suppressed
Calibration data from production measurements appears to describe cosmics data well
HEP2007 Manchester, 19 July 2007
A.Andreazza - Status of the ATLAS Pixel Detector