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The ALICE Inner Tracking System: commissioning and running experience

The ALICE Inner Tracking System: commissioning and running experience. V. Manzari / INFN Bari on behalf of the ITS project in the ALICE Collaboration. Outline. The Inner Tracking System Pixel, Drift and double-side Strip detectors Commissioning and Operation with cosmics

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The ALICE Inner Tracking System: commissioning and running experience

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  1. The ALICE Inner Tracking System: commissioning and running experience V. Manzari / INFN Bari on behalf of the ITS project in the ALICE Collaboration

  2. Outline • The Inner Tracking System • Pixel, Drift and double-side Strip detectors • Commissioning and Operation with cosmics • The Pixel L0 trigger • Alignment and Calibration • First experiences with LHC • Conclusions V. Manzari - ALICE ITS

  3. ALICE (A Large Ion Collider Experiment) at LHC • Ultra-relativistic nucleus-nucleus collisions • study behavior of strongly interacting matter under extreme conditions of compression and heat • Proton-Proton collisions • reference data for heavy-ion program • unique physics (momentum cutoff <100MeV/c, excellent PID, efficient minimum bias trigger) Size: 16 x 26 meters Weight: 10,000 tonnes V. Manzari - ALICE ITS

  4. What makes ALICE different? STAR • With respect to ATLAS, CMS and LHCb.....and complementary to them • Experiment designed for Heavy Ion collisions (Pb-Pb @ 2.75+2.75 TeV per nucleon) • only dedicated experiment at LHC, must be comprehensive and be able to cover all • relevant observables • Extreme track densitiesdNch/dh ~ 2000 – 8000 • - at r = 4 cm (1st pixel layer) up to 80/cm2 (x500 compared to pp @ LHC) • - high-granularity detectors with many space points per track • - very low material budget and moderate magnetic field • - very robust tracking • Hadrons, Leptons and Photons PID over a large pT range • - from very soft (0.1 GeV/c) to fairly hard (100 GeV/c) • Very low pT cutoff • Excellent vertexing capability • Modest luminosity and interaction rates • - 10 kHZ (Pb-Pb) to 300 kHZ (pp) (< 1/1000 of pp@1034) • Irradiation levels at the innermost SPD layer: - 10 years standard running (108s pp + 5x106s Pb-Pb + 106s Ar-Ar) TID ≈ 2.5kGy, F ≈ 3•1012 (1MeV neq)/cm2 • The price to be paid  slow detectors central Au-Au event @ ~130 GeV/nucleon CM energy V. Manzari - ALICE ITS

  5. ALICE Inner Tracking System • 6 barrel layer • 3 different silicon detector technologies, • 2 layers each, as seen by produced particles: • - Pixels (SPD), Drift (SDD), double-side Strips (SSD) Size: 16 x 26 meters Weight: 10,000 tonnes V. Manzari - ALICE ITS

  6. The Inner Tracking System • The ITS role in ALICE • - Improve primary vertex reconstruction and momentum resolution • - Secondary vertexing capability (c, b and hyperon decays) • - Track impact parameter resolution • - Tracking and PID of low pT particles • - Prompt L0 trigger capability (<800 ns) • - Charged particle pseudorapidity distribution • (First Physics measurement both in p-p and Pb-Pb) • Detector requirements • - 2D detectors • - High spatial precision • - High efficiency • - High granularity (≈few% occupancy) • - Minimize distance of innermost layer from beam axis (<r> ≈ 3.9 cm) • - Limited material budget • - dE/dx information in 4 layers at least for particle ID in 1/b2 region Central Pb–Pb < 60 mm (rf) for pt > 1 GeV/c Track impact parameter resolution [mm] V. Manzari - ALICE ITS

  7. Detector parameters Material budget • Integral of material thickness traversed • by a perpendicular track originating ad • the primary vertex versus radius V. Manzari - ALICE ITS

  8. Pixel 13.5 mm 15.8 mm 5 Al layer bus + extender • 2 layer barrel • Total surface: ~0.24m2 • Power consumption ~1.4kW • Evaporative cooling C4F10 • Operating at room temperature • Material budget per layer ~1% X0 MCM + extender + 3 fiber link Ladder 1 Ladder 2 MCM Grounding foil Half-stave ~1200 wire-bonds Outer surface: 80 half-staves • ALICELHCb1 • readout chip • mixed signals • 8192 cells • 50x425mm2 Inner layer Beam pipe Outer layer • Unique L0 trigger capability • Prompt FastOR signal from each chip • Extract and synchronize 1200 FastOR signals from the 120 half-staves • User defined programmable algorithms Minimum distance inner layer-beam pipe 5 mm V. Manzari - ALICE ITS Inner surface: 40 half-staves

  9. Drift Cables to power supplies and DAQ Cooling (H2O) tubes Modules mounted on ladders Voltage divider Central Cathode at -HV Carbon fiber support Anodes SDD layers into SSD Edrift vd (e-) HV supply 70.2 mm vd (e-) Edrift • LV supply • Commands • Trigger • Data  Front-end electronics (4 pairs of ASICs) -> Amplifier, shaper, 10-bit ADC, 40 MHz sampling -> Four-buffer analog memory V. Manzari - ALICE ITS

  10. double-side Strip End ladder electronics L5: 34 ladders L6: 38 ladders r- overlap: Ladder • carbon fibre support • module pitch: 39.1 mm • Al on polyimide laddercables z - overlap: L5: 22 modules L6: 25 modules Hybrid:identical for P- and N-side Al on polyimide connections 6 front-end chips HAL25 water cooled Sensor: double sided strip: 768 strips 95 um pitch P-side orientation 7.5 mrad N-side orientation 27.5 mrad V. Manzari - ALICE ITS

  11. “Russian doll” installation V. Manzari - ALICE ITS

  12. Prompt Pixel Trigger • 120 SPD modules, each contains 10 readout pixel chips • Pixel chip prompt trigger signal (Fast-OR) • Active if at least one pixel hit in the chip matrix • 10 bits on each of 120 optical links (1200) • Transmitted every 100 ns SPD Half Stave Readout MCM Half stave 141 mm Sensor 1 Sensor Pixel chips V. Manzari - ALICE ITS

  13. Pixel Trigger System TTC Clk40 & Serial 107.6±0.15 m C.R. 60 C side A side 36.6±0.2 m Data ALICE Central Trigger Processor Optical splitters TTC 38.5±0.2 m SPD LTU PixelTriggermain outputs L0 in TTC V. Manzari - ALICE ITS

  14. Pixel Trigger System • Router + Link-Rx (SPD readout) • Fast-OR signals in the data stream • OPTIN board • Fast-OR extraction and syncronization • BRAIN board • Pre-defined algorithm processing PROC CONTROL SRAM DDL SIU OPTIN BRAIN V. Manzari - ALICE ITS

  15. C22 rack Pixel Trigger System Optical splitters Pixel Trigger crate V. Manzari - ALICE ITS

  16. Pixel trigger algorithms • I/O = number of active FastOron Inner/Outer layer • Cosmic algorithm can be selected from Control Room out of the following : • TOP_outerandBOTTOM_outer • OR_OUTER andOR_INNER • DLAYER (2 FOs in the INNER and 2 FOs in the OUTER) • TOP_outerandBOTTOM_outerandTOP_innerandBOTTOM_inner • TOP_outerandBOTTOM_outerandOR_INNER • GLOBAL_OR V. Manzari - ALICE ITS

  17. ITS commissioning with cosmics • Detector installation Jun ‘07 • Completion of service connections Nov ’07 • 1st Cosmic Run Dec’07 • First acquisition tests on a fraction of modules • 2nd Cosmic Run Feb÷Mar ‘08 • ≈ 50 % of the ITS operable (cooling and power supply availability) • Calibration tests + first cosmic muons seen in ITS • Completion of Power Supply deployment May ‘08 • 3rd Cosmic Run Jun÷Oct ‘08 • Subdetector specific calibration runs • Maps of dead and noise channels, gain, drift speed, … • Cosmic runs with Pixel trigger • First alignment of the ITS modules + test TPC/ITS track matching • Calibration of the charge signal (dE/dx) in SDD and SSD V. Manzari - ALICE ITS

  18. Pixel: operation and calibration Temperature (°C) Leakage current (µA) • 106/120 modules stably running • Dead+noisy pixels < 0.15% • Typical threshold ≈ 2800e- • Operating temperature ≈ design value • Average leakage current @ ≤50V ≈ 5.8 µA • Average Bus current (≈ 4.4 A) • Detector readout time: ≈ 320 ms • Detector dead time: - 0% up to ≈ 3kHz (multi-event buffering) • ≈ 320 ms at 40 MHz trigger rate • max readout rate (100% dead time ) ≈ 3.3 kHz • Prompt L0 trigger with ≈800 ns latency SPD Online Event Display - Cosmic Run Self-triggered coincidence of top outer and bottom outer layer V. Manzari - ALICE ITS

  19. Drift: operation and calibration • 247 out of 260 modules in DAQ • Calibration quantities monitored every ≈ 24h • Fraction of bad anodes ≈ 2% • <Noise> ≈ 2.5 ADC counts - Signal for a MIP on anodes ≈ 100 ADC • Drift speed from dedicated runs with charge injectors Display of 1 injector event on 1 drift side of 1 module Drift speed on 1 anode during 3 months of data taking Drift speed on 1 drift side from fit to 3 injector points Measurement of vdrift vs. anode and vs. time crucial to reach the design resolution of 35 mm along rf vdrift = mE T-2.4 Lower e- mobility / higher temperature on the edges V. Manzari - ALICE ITS

  20. Strip: operation and calibration • 1477/1698 modules in DAQ • ≈86% of the surface • Fraction of bad strips ≈ 1.5 % Charge ‘ratio’ 11 % Cluster charge N-side • Charge matching between p and n sides • Relative calibration from 40k cosmic clusters • Important to reduce noise and ghost clusters Cluster charge P-side V. Manzari - ALICE ITS

  21. Cosmic Runs • Pixel Trigger: • coincidence between Top Outer Layer AND Bottom Outer Layer • rate: 0.18 Hz • Statistics from 2008 cosmic runs: ≈105 good events (no B field) • 65000 events  3 clusters in SPD • 35000 events  4 clusters in SPD V. Manzari - ALICE ITS

  22. Alignment methods • Dedicated talk by A. Dainese in session “Alignment” on 15/09 • Two track-based methods to extract the alignment parameters (translations and rotations) of the 2198 ITS modules: • Global minimization with Millepede (default method) • Iterative approach • Strategy: • Use geometrical survey data as a starting point - Measurements of sensor positions on ladders during SDD and SSD construction • Hierarchical approach: - Start with SPD barrel: 10 sectors  120 half staves  240 sensors - Align SSD barrel w.r.t. SPD barrel - Internal alignment of the SSD barrel: 72 ladders  … - Align SDD barrel (longer time for calibration) w.r.t. SPD+SSD • Include SDD calibration parameters: - Non-constant drift field due to non-linear voltage divider - Parasitic electric fields due to inhomogeneities in dopant concentration V. Manzari - ALICE ITS

  23. Alignment with cosmics • ITS Standalone tracker adapted for cosmics • Pseudo-vertex = point of closest approach between two “tracklets” in top and bottom SPD half-barrels • Search for two back-to-back tracks starting from this vertex Track-to-track (top vs bottom) distance in transv. plane Track-to-“extra clusters” distance in transv. plane (sensor overlap) SPD only, 2008 B=0 data SPD only, 2008 B=0 data before alignment before alignment after alignment after alignment preliminary preliminary track-to-track Dxy [cm]  = 48 μm (vs 40 μm in simulation without misalignment)‏  = 20 μm (vs 15 μm in simulation without misalignment)‏ • After realignment with cosmics using SPD triggered data and Millepede: • Effective rf resolution ~14 mm (nominal detector position resolution r 12 µm) V. Manzari - ALICE ITS

  24. Drift: calibration • Interplay between alignment and calibration • Space coordinates depends on T0 and drift speed, calibration is needed • With cosmics the resolution along drift direction is affected by the jitter of the Pixel trigger (at 10 MHz  4 SDD time bins) with respect to the time when the muon crosses the SDD sensor Geometry only Geometry + calibration V. Manzari - ALICE ITS

  25. Strip and Drift: energy loss • Simulations • The four outermost layers of the ITS (2xSDD + 2xSSD) contribute to the energy loss measurements by providing dE/dx values. • Cosmics • During the cosmic run campaigns of 2009 (field of 0.5 T) SSD and SDD were active in the acquisition. • Tracks reconstructed in TPC+ITS • Muon according to: • Atomic Data Tables 78, (2001) 183. • H. Bichsel, Rev. Mod. Phys. 60, (1988) 663 • H. Bichsel, NIM A562 (2006) 154 PYTHIA 6.214 p+p events at √s = 10 TeV V. Manzari - ALICE ITS

  26. First signs of life in LHC • ITS succesfully commissioned with cosmics in Summer 2008 • June 15, 2008: during the beam injection test in Tl2, the ITS pixel layers in self-triggering mode detected the first “sign of life” of LHC Injection event seen by Pixels Longitudinal tracks along one pixel module (14 cm) Injection event seen by the Drifts • During following injection tests more ITS layers were active V. Manzari - ALICE ITS

  27. Beam induced background • Study of the LHC screen related background in ALICE • ITS pixel layers in self-triggering mode during the beam injection tests provided relevant information on the background levels in ALICE V. Manzari - ALICE ITS

  28. First collision • In Sept. 2008 the ITS was ready to record the first collisions in LHC • «It's 9 a.m. and the Silicon Pixel Detector in ALICE lights • up with particle “debris“ created as beam in the transfer • line from the SPS hits the beam stop before Point 2.» • From CERN Courier –Nov. ’08 – LHC focus: “LHC first beam: a day to remember” • First LHC beam-induced interaction was recorded by the • ALICE ITS on 11 Sep ’08 • Pixel trigger • ITS standalone tracking • Collision of beam-halo particle with the first pixel layer: • 7 reconstructed tracks from common vertex. V. Manzari - ALICE ITS

  29. ALICE and ITS in 2009 • In Oct ‘08 ALICE has opted for a long shutdown to complete the installation of outer detectors and re-arrange all services (power, optical and cooling) on Side A of the central detectors, including the ITS, in order to allow an “easy” access to the TPC electronics. • Detector operations were resumed after the reconnection of all services in July ’09 • Re-commissioning and optimization in progress • Cosmics run with magnetic field: B=0.5T & 0.2T, both polarities, ongoing V. Manzari - ALICE ITS

  30. The lesson learnt so far.... • During the commissioning and the first operations we have learnt that: • We have developed and built performing and robust detectors • Performance well in agreement with the design specs and goals • They survive also to “unforeseen treatments” but.... • we underestimated services and accessibility • Optics require frequent check and cleaning • Power Supply • Cooling system • SDD-SSD water system: it has undergone a substantial upgraded in May ‘08 to fulfil the requirements of the two detectors • SPD evaporative system: the whole installation is undergoing a cleaning process to cure local inefficiencies which might be caused by lack of C4F10 flow. • Air conditions in the innermost detector volume • Control and monitoring of temperature and humidity V. Manzari - ALICE ITS

  31. Conclusions • The ALICE Inner Tracking System was successfully commissioned with cosmics during summer 2008 and was ready for the first collisions in September • Integration and operating stability with ALICE central services (ECS, DAQ, CTP and DCS), Alignment studies and Calibration runs were performed over several months of data taking • Alignment is very well advanced • Collected statistics of cosmic tracks allowed for: - Most of SPD modules alignement to  8mm; 50% of SSD modules (the ones close to the vertical with higher statistics) also aligned. SDD on the way - dE/dx signal calibration in SDD and SSD • Cosmic runs with different magnetic fields are ongoing • Final optimization of the detector performance is well advanced • Activities tuned with the LHC schedule V. Manzari - ALICE ITS

  32. Alignment Monitoring System • Laser based system which uses spherical mirrors and CCDs to monitor the movements of the ITS with respect to the TPC • Any 3 mirror/camera pairs yield movement measurements for all 6 degrees of freedom. • Resolution is limited by the CCD pixel size ~5μm square. • Measured Resolutions are: Δx and Δy ~25μm Δz ~235μm Δθx and Δθy ~0.30e-3 ° Δθz ~1.75e-3 ° V. Manzari - ALICE ITS

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