1 / 31

Results from the commissioning of the ALICE Inner Tracking System with cosmics

Results from the commissioning of the ALICE Inner Tracking System with cosmics. Francesco Prino ( INFN – Sezione di Torino ) for the ALICE COLLABORATION. QM 2009, Knoxville, 2009 April 2nd. ALICE at the LHC. Inner Tracking System (I). Six layers of silicon detectors Coverage: | h |<0.9

jvitale
Télécharger la présentation

Results from the commissioning of the ALICE Inner Tracking System with cosmics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Results from the commissioning of the ALICE Inner Tracking System with cosmics Francesco Prino (INFN – Sezione di Torino) for the ALICE COLLABORATION QM 2009, Knoxville, 2009 April 2nd

  2. ALICE at the LHC

  3. Inner Tracking System (I) • Six layers of silicon detectors • Coverage: |h|<0.9 • Three technologies • Pixels (SPD) • Drift (SDD) • Double-sided Strips (SSD)

  4. Inner Tracking System (II) • Design goals • Optimal resolution for primary vertex and track impact parameter • Minimize distance of innermost layer from beam axis (<r>≈ 3.9 cm) and material budget • Maximum occupancy (central PbPb) < few % • 2D devices in all the layers • dE/dx information in the 4 outermost layers for particle ID in 1/b2 region

  5. ITS role in ALICE physics (I) • Tracking: • Prolong tracks reconstructed in the TPC • Improve momentum and angle resolution • Track impact parameter crucial for heavy flavours • Standalone ITS tracking • Track and identify particles missed by TPC due to dead zones between sectors, decays and pT cut-off • pT resolution <≈6% for a pion in pT range 200-800 MeV Poster by E. Biolcati Central Pb–Pb MC simulations: p-p < 60 mm (rf) for pt > 1 GeV/c Track impact parameter resolution [mm]

  6. ITS role in ALICE physics (II) • Vertexing • Reconstruction of primary (interaction) vertex • From tracks: ITS crucial to obtain resolution better than 100 mm • From SPD tracklets: done before tracking and used as a starting point (seed) in the tracking phase. Allows for pileup tagging based on multiple vertices • Identification of secondary vertices from decays of hyperons and open charm and beauty hadrons Primary vertex resolution vs. multiplicity in p-p D+ K-p+p+ decay vertex resolution Resolution [mm] Vertex from tracks Interaction diamond: sx,y=50 mm

  7. ITS role in ALICE physics (III) • Charged particle pseudorapidity distributions from SPD • Pairs of clusters, one per SPD layer, aligned to the main interaction vertex (“tracklets”) • Advantages (wrt dN/dh from tracks): • Larger h and pT acceptance • Less stringent calibration needs • Suitable for the very first data • First measurement that ALICE will be able to perform, both in p-p and Pb-Pb dN/dh reconstruction @ 10 TeV (Pythia) Poster by M. Nicassio

  8. 13.5 mm 15.8 mm SPD 5 Al layer bus + extender • 2 layer barrel • Total surface: ~0.24m2 • Power consumption ~1.5kW • 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 in 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 Inner surface: 40 half-staves

  9. Cables to power supplies and DAQ Cooling (H2O) tubes SDD 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

  10. End ladder electronics SSD r- overlap: L5: 34 ladders L6: 38 ladders 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

  11. ITS Commissioning data taking TIME • Detector installation completed in June 2007 • Run 1 : December 2007 • First acquisition tests on a fraction of modules • Run 2 : Feb/Mar 2008 • ≈ 1/2 of the modules in acquisition due to cooling and power supply limitations • Calibration tests + first atmospheric muons seen in ITS • Installation of services completed in May 2008 • Run 3 : June/October 2008 • Subdetector specific calibration runs • Frequent monitoring of dead channels, noise, gain, drift speed … • Cosmic runs with SPD FastOR trigger • First alignment of the ITS modules + test TPC/ITS track matching • Absolute calibration of the charge signal in SDD and SSD

  12. Temperature (°C) Leakage current (µA) SPD operation and calibration Example from PVSS online detector control and monitoring • 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 • FastOr trigger with ≈ 800 ns latency June 15, 2008 First “signs of life” of the LHC SPD online event display – Cosmic run Side view View along z Longitudinal tracks along one half-stave (14 cm)

  13. SDD operation and calibration Display of 1 injector event on 1 drift side of 1 module • 247 out of 260 modules in DAQ • Calibration quantities monitored every ≈ 24 h • 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 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

  14. SSD operation and calibration Charge ‘ratio’ • 1477 out of 1698 modules in DAQ • Fraction of bad strips ≈ 1.5 % • Charge matching between p and n sides • Relative calibration from 40k cosmic clusters • Important to reduce noise and ghost clusters 11 % Cluster charge N-side Cluster charge P-side

  15. Triggering and tracking the cosmics • Trigger: SPD FastOR • Coincidence between top outer SPD layer and bottom outer SPD layer • rate: 0.18 Hz AND • ITS Stand-Alone tracker adapted for cosmics • “Fake” vertex = point of closest approach between two “tracklets” built in the top and bottom SPD half-barrels • Search for two back-to-back tracks starting from this vertex

  16. Cosmic data sample • Statistics collected ≈ 105 good events • Goals: • Alignment of each of the 2198 ITS sensors with a precision < than its resolution (≈ 8 mm for SPD ! ) • Fundamental to reach e.g. the required resolution on track impact parameter for heavy flavour studies • dE/dx calibration in SDD and SSD Talk by A. Dainese Layer 5 (SSD) Layer 4 (SDD) Layer 1 (SPD) Layer 4 (SDD) Layer 4 (SDD) Layer 1 (SPD) Layer 1 (SPD)

  17. Alignment Poster by A. Rossi • Two track-based methods to extract the alignment objects (translations and rotations) for the 2198 ITS modules: • Millepede (default method, as for all LHC experiments) • Determine alignment parameters of “all” modules in one go, by minimizing the global c2 of track-to-points residuals for a large set of tracks • Iterative approach • Align one module at a time by fitting tracks in the other modules and minimizing the residuals in the module under study • Plus and hardware (based on collimated laser beams, mirrors and CCD cameras) alignment monitoring system • Monitor physical movements of ITS with respect to TPC • Strategy for the track-based alignment: • Use geometrical survey data as a starting point • Measurements of sensor positions on ladders during SDD and SSD construction • Hierarchical approach: • Start from SPD sectors (10) , then SPD half staves (120), then SPD sensors (240) • After fixing SPD, align SSD barrel (w.r.t. SPD barrel), then SSD ladders (72) … • After fixing SPD and SSD, move to SDD (which need longer time for calibration) • Include SDD calibration parameters: • Time Zero = time after the trigger for a particle with zero drift distance • Drift speed for modules with mal-functioning injectors

  18. Alignment: Survey for SSD • Three methods to validate SSD survey information • Fit track on one SSD layer (2 points)  residuals on other SSD layer • Fit one track on outer layer, one track on inner layer  distance and angles between the two tracks • Extra clusters from acceptance overlaps  distance between two clusters attached to same track on contiguous modules ALICE Preliminary

  19. Alignment: Millepede on SPD sDxy=52 mm   sspatial=14 mm (MC ideal geometry: sspatial=11 mm) Realigned y Track-to-track Dxy at y=0 ALICE Preliminary x Dxy [cm] Clusters attached to same track in acceptance overlaps sDxy=18 mm  sDxy=sspatial2  sspatial=14 mm (MC ideal geometry: sspatial=11 mm) not realigned realigned

  20. Alignment: Millepede on SDD • Interplay between alignment and calibration • TimeZero and DriftSpeed for modules with mal-functioning injectors included as free parameters in the Millepede • Resolution along drift direction affected by the jitter of the SPD FastOR trigger (at 10 MHz  4 SDD time bins) with respect to the time when the muon crosses the SDD sensor Geometry only Geometry + calibration

  21. dE/dx calibration • SDD • Larger drift distance  larger charge diffusion  wider cluster tails cut by the zero suppression • Effect quantitatively reproduced by Monte Carlo simulations • SSD • Cosmics with field (0.5 T) • Tracks reco in TPC+ITS • Muon Most Probable Value of dE/dx for 300 mm of silicon from AD&NDT 78 (2001) 183 ALICE Preliminary

  22. Conclusions • Successful commissioning run with cosmics during summer 2008 for the ALICE Inner Tracking System • Several calibration runs to check the stability of operation and performance over ≈ 3 months of data taking • Collected statistics of cosmic tracks allowed for: • Most of SPD modules realigned to  8mm. ≈ 1/2 of SSD modules (the ones close to the vertical with higher statistics) realigned. SDD on the way • dE/dx signal calibration in SDD and SSD • ITS ready for the first LHC collisions 7-track event collected with circulating LHC beam2 on Sept. 11th 2008

  23. Backup

  24. SDD performance vs. time

  25. SDD correction maps • All the 260 SDD modules have undergone a complete characterization (map) before assembling in ladders • Charge injected with an infrared laser in > 100,000 known positions on the surface of the detector • For each laser shot, calculate residual between the reconstructed coordinate and the laser position along the drift direction • Systematic deviations due to: • Non-constant drift field due to non-linear voltage divider • Parasitic electric fields due to inhomogeneities in dopant concentration Ideal Module Non-linear volt. divider Dopant inhomogeneties

  26. Alignment: SSD survey • Three methods to validate SSD survey information • Fit track on one SSD layer (2 points)  residuals on other SSD layer • Fit one track on outer layer, one track on inner layer  distance and angles between the two tracks • Extra clusters from acceptance overlaps  distance between two clusters attached to same track on contiguous modules Extra Clusters - With survey Extra clusters - No survey • xy=25 m • point=25/√2=18 m • misal=0 m • xy =48 m • point=48/√2=34 m • misal=27 m Dxy [cm] Dxy [cm]

  27. Alignment: Iterative on SPD Poster by A. Rossi • Minimization track-to-track residuals at Y=0 • Result from iterative approach

  28. Alignment: Millepede SPD+SSD • SSD Millepede realignment at ladder level + survey data for modules • Single track impact parameter resolution ≈ 30/2 ≈ 21 mm Talk by A. Dainese DATA, B=0 realigned (Millepede) ALICE Preliminary s ~ 30 mm

  29. LHC injection tests Aug/Sep 2008 • The SPD was operational during the beam injection tests and provided relevant information on the background levels in ALICE

  30. SDD dE/dx vs. drift time • Cluster charge dependence on drift distance • Larger drift distance  larger charge diffusion  wider cluster tails cut by the zero suppression • Effect quantitatively reproduced by Monte Carlo simulations • Cross checked with cosmic clusters collected with and without zero suppression • No dependence of cluster charge on drift distance observed without Zero Suppression Muons from test setup 3 scintillator trigger No Zero Supp With Zero Supp

  31. ITS Alignment Monitoring System • Laser based system which uses a spherical mirror (1x magnification) to determine the movement of the laser/camera module and the mirror relative to each other. • Any 3 mirror/camera pairs yield movement measurements for all 6 degrees of freedom. • Resolution is limited only by CMOS pixel size ~5μm square. • Measured Resolutions are: Δx and Δy ~25μm Δz ~235μm Δθx and Δθy ~0.30e-3 ° Δθz ~1.75e-3 °

More Related