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
A Toroidal LHC Apparatus HEP2007 Manchester, 19 July 2007 A.Andreazza - Status of the ATLAS Pixel Detector
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 > 1015 1 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
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: 4000 e- threshold dispersion: 40-90 e- noise: 140-180 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
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
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
System test: optical links error free region phase [ns] PiN threshold [DAC] 10 01 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
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
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
Cosmics data: noise measurements Occupancy: hit probability per bunch crossing of a pixel. Typical occupancy rate in noise runs is 1-3 10-8 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
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
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
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
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
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
Back-up transparencies
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
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
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
A.Andreazza - Status of the ATLAS Pixel Detector Specifications Radiation hardness: NIEL > 1015 1 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
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