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  The Pixel L0 trigger  Alignment and Calibration  First experiences with LHC  Conclusions 2Vertex '09 / Putten (Nl)V. Manzari - ALICE ITS

ALICE (A Large Ion Collider Experiment) at LHC Size: 16 x 26 meters Weight: 10,000 tonnes  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) 3Vertex '09 / Putten (Nl)V. Manzari - ALICE ITS

What makes ALICE different?  With respect to ATLAS, CMS and LHCb.....and complementary to them Experiment designed for Heavy Ion collisions TeV per nucleon) - only dedicated experiment at LHC, must be comprehensive and be able to cover all relevant observables Extreme track densities dN ch /d  ~ 2000 – at r = 4 cm (1st pixel layer) up to 80/cm 2 (x500 compared to 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 p T range - from very soft (0.1 GeV/c) to fairly hard (100 GeV/c) Very low p T cutoff Excellent vertexing capability Modest luminosity and interaction rates - 10 kHZ (Pb-Pb) to 300 kHZ (pp) (< 1/1000 of 34 ) Irradiation levels at the innermost SPD layer: - 10 years standard running (10 8 s pp + 5x10 6 s Pb-Pb s Ar-Ar) TID ≈ 2.5kGy, F ≈ (1MeV n eq )/cm 2 The price to be paid  slow detectors 4Vertex '09 / Putten (Nl)V. Manzari - ALICE ITS central Au-Au ~130 GeV/nucleon CM energy STAR

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) 5 Size: 16 x 26 meters Weight: 10,000 tonnes Vertex '09 / Putten (Nl)V. Manzari - ALICE ITS

 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 p T 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 ( ≈ 3.9 cm) - Limited material budget - dE/dx information in 4 layers at least for particle ID in 1/  2 region The Inner Tracking System 6 < 60  m (r  ) for p t > 1 GeV/c Central Pb–Pb Track impact parameter resolution [  m] Vertex '09 / Putten (Nl)V. Manzari - ALICE ITS

Detector parameters Vertex '09 / Putten (Nl)V. Manzari - ALICE ITS7 LayerDet.Radius (cm) Lengt h (cm) Surface (m 2 ) Chan.Spatial precision (  m) Cell ( μ m 2 ) Max occupancy central PbPb (%) Power dissipation (W) rr zbarrelend-cap 1 SPD M x k SDD K x k1.75k SSD M x k  Integral of material thickness traversed by a perpendicular track originating ad the primary vertex versus radius Material budget

Pixel Half-stave Outer surface: 80 half-staves Beam pipe Outer layer Inner layer 13.5 mm 15.8 mm ~1200 wire-bonds ALICELHCb1 readout chip mixed signals 8192 cells 50x425  m 2 8Vertex '09 / Putten (Nl)V. Manzari - ALICE ITS 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 Inner surface: 40 half-staves Minimum distance inner layer-beam pipe  5 mm 2 layer barrel Total surface: ~0.24m 2 Power consumption ~1.4kW Evaporative cooling C 4 F 10 Operating at room temperature Material budget per layer ~1% X 0 MCM 5 Al layer bus + extender Ladder 1Ladder 2 MCM + extender + 3 fiber link Grounding foil

Drift Central Cathode at -HV E drift Voltage divider v d (e - ) Anodes  HV supply  LV supply  Commands  Trigger Data  Modules mounted on ladders Carbon fiber support Cables to power supplies and DAQ SDD layers into SSD Cooling (H 2 O) tubes 70.2 mm Layer# laddersMod./ladder# modules Vertex '09 / Putten (Nl)V. Manzari - ALICE ITS Front-end electronics (4 pairs of ASICs) -> Amplifier, shaper, 10-bit ADC, 40 MHz sampling -> Four-buffer analog memory

double-side Strip r  - overlap: z - overlap: L5: 34 ladders L6: 38 ladders L5: 22 modules L6: 25 modules Ladder End ladder electronics Sensor: double sided strip: 768 strips 95 um pitch P-side orientation 7.5 mrad N-side orientation 27.5 mrad Hybrid:identical for P- and N-side Al on polyimide connections 6 front-end chips HAL25 water cooled carbon fibre support module pitch: 39.1 mm Al on polyimide laddercables 10Vertex '09 / Putten (Nl)V. Manzari - ALICE ITS

“Russian doll” installation 11Vertex '09 / Putten (Nl)V. Manzari - ALICE ITS

 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 Prompt Pixel Trigger Vertex '09 / Putten (Nl)V. Manzari - ALICE ITS12 SPD Half Stave Half stave Sensor Pixel chips Readout MCM Sensor 141 mm 1

Pixel Trigger System Optical splitters ALICE Central Trigger Processor SPD LTU Clk40 & Serial C side A side Data TTC 36.6±0.2 m 107.6±0.15 m 38.5±0.2 m 60 C.R. PixelTrigger main outputs L0 in TTC Vertex '09 / Putten (Nl)13V. Manzari - ALICE ITS

Pixel Trigger System PROC CONTROL DDL SIU SRAM  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 OPTIN BRAIN Vertex '09 / Putten (Nl)14V. Manzari - ALICE ITS

Pixel Trigger crate Optical splitters C22 rack Pixel Trigger System Vertex '09 / Putten (Nl) 15V. Manzari - ALICE ITS

Pixel trigger algorithms 1Minimum Bias (I+O)  th IO,mb and I  th I,mb and O  th O,mb 2High Multiplicity 1 I  th I,hm1 and O  th O,hm1 3High Multiplicity 2 I  th I,hm2 and O  th O,hm2 4High Multiplicity 3 I  th I,hm3 and O  th O,hm3 5High Multiplicity 4 I  th I,hm4 and O  th O,hm4 6Past Future Prot (I+O)  th IO,pfp and I  th I,pfp and O  th O,pfp 7Background(0) I  O+ offset I 8Background(1) O  I+ offset O 9Background(2) (I+O)  th (I+O),bnd 10CosmicSelectable coincidence  I/O = number of active FastOr on Inner/Outer layer  Cosmic algorithm can be selected from Control Room out of the following : TOP_outer and BOTTOM_outer OR_OUTER and OR_INNER DLAYER (  2 FOs in the INNER and  2 FOs in the OUTER) TOP_outer and BOTTOM_outer and TOP_inner and BOTTOM_inner TOP_outer and BOTTOM_outer and OR_INNER GLOBAL_OR Vertex '09 / Putten (Nl)16V. Manzari - ALICE ITS

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 RunJun ÷ 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 17Vertex '09 / Putten (Nl)V. Manzari - ALICE ITS

Pixel: operation and calibration  106/120 modules stably running Dead+noisy pixels < 0.15% Typical threshold ≈ 2800e- Operating temperature ≈ design value Average leakage ≤50V ≈ 5.8 µA Average Bus current (≈ 4.4 A) Detector readout time: ≈ 320  s Detector dead time: - 0% up to ≈ 3kHz (multi-event buffering) -≈ 320  s at 40 MHz trigger rate max readout rate (100% dead time ) ≈ 3.3 kHz Temperature (°C) Leakage current (µA) 18Vertex '09 / Putten (Nl)V. Manzari - ALICE ITS  Prompt L0 trigger with ≈800 ns latency SPD Online Event Display - Cosmic Run Self-triggered coincidence of top outer and bottom outer layer

Drift: operation and calibration  247 out of 260 modules in DAQ  Calibration quantities monitored every ≈ 24h Fraction of bad anodes ≈ 2% ≈ 2.5 ADC counts - Signal for a MIP on anodes ≈ 100 ADC Drift speed from dedicated runs with charge injectors 19 Display of 1 injector event on 1 drift side of 1 module Drift speed on 1 drift side from fit to 3 injector points v drift =  E  T -2.4 Lower e - mobility / higher temperature on the edges Drift speed on 1 anode during 3 months of data taking Measurement of v drift vs. anode and vs. time crucial to reach the design resolution of 35  m along r  Vertex '09 / Putten (Nl)V. Manzari - ALICE ITS

Charge ‘ratio’ Cluster charge N-side Cluster charge P-side Strip: operation and calibration  1477/1698 modules in DAQ ≈86% of the surface Fraction of bad strips ≈ 1.5 % 11 %  Charge matching between p and n sides Relative calibration from 40k cosmic clusters Important to reduce noise and ghost clusters 20Vertex '09 / Putten (Nl)V. Manzari - ALICE ITS

Cosmic Runs  Pixel Trigger: coincidence between Top Outer Layer AND Bottom Outer Layer rate: 0.18 Hz  Statistics from 2008 cosmic runs: ≈10 5 good events (no B field) events  3 clusters in SPD events  4 clusters in SPD 21Vertex '09 / Putten (Nl)V. Manzari - ALICE ITS

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 22Vertex '09 / Putten (Nl)V. Manzari - ALICE ITS

Alignment with cosmics  After realignment with cosmics using SPD triggered data and Millepede: Effective r  resolution ~14  m (nominal detector position resolution r  12 µm)  = 20 μ m (vs 15 μ m in simulation without misalignment)‏ 23Vertex '09 / Putten (Nl)V. Manzari - ALICE ITS  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  = 48 μ m (vs 40 μ m in simulation without misalignment)‏ Track-to-“extra clusters” distance in transv. plane (sensor overlap) after alignment before alignment after alignment before alignment SPD only, 2008 B=0 data preliminary track-to-track  xy [cm]

Drift: calibration Vertex '09 / Putten (Nl)V. Manzari - ALICE ITS24  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

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. PYTHIA p+p events at √s = 10 TeV 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) Vertex '09 / Putten (Nl)V. Manzari - ALICE ITS

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 26Vertex '09 / Putten (Nl)V. Manzari - ALICE ITS Longitudinal tracks along one pixel module (  14 cm)  During following injection tests more ITS layers were active Injection event seen by the Drifts Injection event seen by Pixels

Beam induced background 27Vertex '09 / Putten (Nl)V. Manzari - ALICE ITS  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

First collision 28Vertex '09 / Putten (Nl)V. Manzari - ALICE ITS  In Sept 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 Collision of beam-halo particle with the first pixel layer: 7 reconstructed tracks from common vertex. Pixel trigger ITS standalone tracking

ALICE and ITS in 2009  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 29Vertex '09 / Putten (Nl)V. Manzari - ALICE ITS  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.

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 C 4 F 10 flow. -Air conditions in the innermost detector volume Control and monitoring of temperature and humidity Vertex '09 / Putten (Nl)V. Manzari - ALICE ITS30

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  8  m; 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 31Vertex '09 / Putten (Nl)V. Manzari - ALICE ITS

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 ~5 μ m square.  Measured Resolutions are: Δ x and Δ y~25 μ m Δ z~235 μ m Δθ x and Δθ y ~0.30e-3 ° Δθ z ~1.75e-3 ° 32Vertex '09 / Putten (Nl)V. Manzari - ALICE ITS