1. 1 20-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja Commissioning and performance of the ALICE TPC Outline Components of TPC Calibration Performance results Summary Adam Matyja for the ALICE TPC collaboration Subatech, Nantes & INP PAN Kraków

2. 2 20-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja The ALICE detector * ALICE TPC Collaboration, J. Alme et al., "The ALICE TPC, a large 3-dimensional tracking device with fast readout for ultra-high multiplicity events.", Physics. Ins-Det/10011950 (2010) *

3. 3 20-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja The principle of the Time Projection Chamber → Based on multi-wire proportional chamber Charged particles ionize working gas atoms Ionization electrons drift with the constant velocity (v) in the direction of readout chambers due to the electric field Near the anode plane the strong electric field causes ionization avalanche It induces the signal on the pad plane  Collected charge gives the information about the energy loss It allows to obtain the information in two coordinates - (x,y) The third coordinate is inferred from the measurement of the electrons drift time measurement (z=vt) 3 coordinates give the space point on the track Main tracking device Allows to distinguish the charged particle species

4. 4 20-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja ALICE Time Projection Chamber General features:  Diameter  Length : 5 m  5 m  Azimuth angle coverage: 2   Pseudo-rapidity interval: |  |<0.9  Readout chambers: 72  Drift field: 400 V/cm  Maximum drift time: 94  s  Central electrode HV: 100 kV Gas:  Active volume: 90 m 3  Ne-CO 2 -N 2 : 85.7% - 9.5% - 4.8%  Cold gas - low diffusion  Non-saturated drift velocity  temperature stability and homogeneity  0.1 K Data readout:  Pads (3 types): 557 568  Samples in time direction: 1000  Data taking rate: ~ 2.8 kHz for p-p ~ 300 Hz for Pb-Pb 5 m 2.5 m

5. 5 20-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja ReadOut Chambers 2 sides with 18 sectors Sector consists of:  Inner chamber (IROC)  Outer chamber (OROC)  72 readout chambers Pad readout  3 sizes Components Stable operation

6. 6 20-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja Drift voltage system Components Resistor rods Voltage dividers' network Provide constant electric field Water cooled voltage dividers → remove dissipated power Control of water conductivity Radiation length X / X 0 of Field Cage  1.367 % - inner FC  0.607 % - gas  2.153 % - outer FC Very stable operation Few well understood trips (beam loss) Tomography of FC in good agreement with MC

7. 7 20-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja Recirculating gas system Precise control of gas mixture O 2 and H 2 O contamination removed by Cu catalyser To minimize signal loss (e - attachment)  Contamination: ~ 1 ppm O 2 (design < 5) Humidity kept at fixed level → to avoid aging of components In operation since 2006 Components

8. 8 20-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja Cooling system Provide temperature stability ~ 500 temperature sensors Leakless underpressure system with ~ 60 adjustable cooling circuits Thermal screening towards ITS and TRD Copper shields of service support wheel Cooling of ROC bodies Water cooling of FEE in copper envelope (~27 kW) Result: Temperature homogenity:  T = 0.046 K Components FEC with its cooling envelope Good agreement with design specifications

9. 9 20-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja Detector Control System Ensure a safe and correct operation of TPC Integrated into Experiment Control System Hardware architecture  Supervisory layer: user interface (PC) + databases  Control layer: hub - collect & process information from supervisory and field layers  Field layer: electronics to control equipment (power supplies, FEE, …) TPC is fully controlled by ALICE shifter Components

10. 10 20-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja Noise measurements Noise level improved during commissioning Mean noise level:  0.7 ADC count (700 e)  Designed - 1 ADC count (1000 e) Data volume of empty event:  non-zero suppressed (ZS): ~ 700MB  ZS event: ~ 30kB Typical size of the event with data:  0.1 - 0.2 MB (p - p) 360 kB TPC @ 7 TeV  ~ 30 MB (Pb - Pb, dN/dy = 2000) Calibration Current noise

11. 11 20-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja Gain calibration using 83 Kr Calibration main peak (41.6 keV) OROC Resolution of main peak: 4.0 % for IROCs 4.3 % for OROCs Gain variation Result: Relative gain variation C-side Determine gain for each pad Procedure:  Inject radioactive 83 Kr  Characteristic decay spectrum  Dedicated clusterizer  Fit the main peak (41.6 keV)  Parabolic fit  Calibration constants 3 different HV settings (gains) High statistics: several 10 8 Kr events Accuracy of peak position: << 1% (design: 1.5%) Repeated after electronic maintenance or every year

12. 12 20-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja Kr calibration - systematics IROC OROC shortmid long Edge effect well visible → Parabolic fit applied to avoid it Radial Azimuth The shape reflects a mechanical deformation of the pad plane Calibration Sector-by-sector

13. 13 20-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja Laser system 336 laser beams Used for:  E  B effect  Drift velocity measurements  Alignment Calibration Reconstructed laser tracks The principle of laser system for the TPC Laser features: = 266 nm or E = h = 4.66 eV Energy: 100 mJ/pulse Duration of pulse: 5 ns The ionization in the gas volume along the laser path occurs via two photon absorption by organic impurities.

14. 14 20-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja E  B effect Correction map from laser tracks Measure  r  For each laser track For several magnetic field settings Laser system  Calibration Caused by: Mechanical or electrical imperfections Imperfect B field  r   7 mm → for longest drift and nominal field Corrected to ~ 0.3 mm Detailed studies ongoing

15. 15 20-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja Drift velocity measurements  d =  d (E, B,  (T in, P atm ), C CO2, C N2 ) Crucial for track matching with other detectors How to obtain drift velocity correction factor:  Matching laser tracks and mirror positions  Matching TPC and ITS tracks  Matching tracks from two halves of TPC  Drift velocity monitor Required accuracy: 10 -4  update every 1h Calibration Photo electrons from central electrode monitor top-bottom arrival time offset caused by T and P gradients

16. 16 20-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja Drift velocity measurements  d =  d (E, B,  (T in, P atm ), C CO2, C N2 ) Crucial for track matching with other detectors How to obtain drift velocity correction factor:  Matching laser tracks and mirror positions  Matching TPC and ITS tracks  Matching tracks from two halves of TPC  Drift velocity monitor Required accuracy: 10 -4  update every 1h Calibration Photo electrons from central electrode monitor top-bottom arrival time offset caused by T and P gradients Corrected spectrum

17. 17 20-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja Space point resolution Performance Depends on:  Drift length  Inclination angle  Charge deposited on the anode wire In r  direction:  Y = 300 - 800  m  for small inclination angles (high momentum tracks) In drift direction:  Z = 300 - 800  m Good agreement with simulations

18. 18 20-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja Momentum resolution High momentum tracks  Cosmic muon tracks treated independently in two halves of TPC  Comparison of p T at vertex gives resolution  Statistics: ~ 5  10 6 events Low momentum tracks  Deduced from the width of K 0 S mass peak Current status (w/o many corrections): (  pT /p T ) 2 = (0.01) 2 + (0.007p T ) 2 Achieved: ~ 7 % @ 10 GeV/c ~ 1 % below 1 GeV/c Place for improvement: ~ 4 % @ 10 GeV/c Performance

19. 19 20-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja dE/dx resolution - cosmics Allows particle identification up to 50 GeV/c Statistics: 8.3  10 6 cosmic tracks in 2008 Design goal: 5.5 % Measured: < 5 % Performance TPC cosmic data 500 < p < 550 MeV p d e  e  p

20. 20 20-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja dE/dx spectrum in data Performance

21. 21 20-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja Material budget Vertices from conversion photonsRadial distribution Agreement between MC and DATA: 5 ~ 15 % Performance TPC begins here

22. 22 20-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja Life of TPC 2006 - first tests at the surface  No ZS  Only 2 sectors powered at a time 2007 - first commissioning underground  C-side successfully operated  Online ZS 2008 - commissioning with cosmics  Full TPC  Different run types implemented  Extensive calibration data taken _ 06. 12. 2009 - first  s = 900 GeV collisions _ 30. 03. 2010 - first  s = 7 TeV collisions

23. 23 20-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja Summary Physics results are well visible:  "Midrapidity antiproton-to-proton ratio in pp collisons at  s = 0.9 and 7 TeV measured by the ALICE experiment." - Phys. Rev. Lett. 105.072002 (2010)  "Two-pion Bose-Einstein correlations in pp collisions at  s = 900 GeV." - Phys. Rev. D 82, 052001 (2010)  "Transverse momentum spectra of charged particles in proton-proton collisions at  s = 900 GeV with ALICE at the LHC." - submitted to PLB (arXiv:1007.0719)  Other papers to be submitted soon: J/  production Particle spectra Strangeness D (*) -mesons ALICE TPC works stably during p-p data taking Calibration done → working on improvements Very good performance, close to specifications We are waiting for Heavy Ions

24. 24 20-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja The ALICE TPC collaboration Harald Appelshaeuser 6, Peter Braun-Munzinger 7, Peter Christiansen 9, Panagiota Foka 7, Ulrich Frankenfeld 7, Chilo Garabatos 7, Peter Glassel 8, Hans-Ake Gustafsson 9, Haavard Helstrup 1, Marian Ivanov 7, Rudolf Janik 2, Alexander Kalweit 5, Ralf Keidel 11, Marek Kowalski 10, Dag Toppe Larsen 1, Christian Lippmann 3, Magnus Mager 3, Adam Matyja 10,12, Luciano Musa 3, Borge Svane Nielsen 4, Helmut Oeschler 5, Miro Pikna 2, Attiq Ur Rehman 3, Rainer Renfordt 6, Stefan Rossegger 3, Dieter Roehrich 1, Hans-Rudolf Schmidt 7, Martin Siska 2, Brano Sitar 2, Carsten Soegaard 4, Johanna Stachel 8, Peter Strmen 2, Imrich Szarka 2, Danilo Vranic 7, Jens Wiechula 8 1.Department of Physics and Technology, University of Bergen, Bergen, Norway. 2.Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia. 3.European Organization for Nuclear Research (CERN), Geneva. 4.Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark. 5.Institut für Kernphysik, Technische Universität Darmstadt, Darmstadt, Germany. 6.Institut für Kernphysik, Johann-Wolfgang-Goethe Universität Frankfurt, Frankfurt, Germany. 7.Gesellschaft für Schwerionenforschung mbH (GSI), Darmstadt, Germany. 8.Physikalisches Institut, Ruprecht-Katls-Universität Heidelberg, Heidelberg, Germany. 9.Division of Experimental High Energy Physics, University of Lund, Lund, Sweden. 10.The Henryk Niewodniczański Institute of Nuclear Physics, Polish Academy of Sciences, Cracow, Poland. 11.Zentrum fur Technologietransfer und Telekommunikation (ZTT), Fachhochschule Worms, Worms, Germany. 12.Now at SUBATECH, Ecole des Mines de Nantes, Universite de Nantes, CNRS-IN2P3, Nantes, France.

25. 25 20-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja BACKUP

26. 26 20-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja PID

27. 27 20-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja Cluster finder Track Pad Pad-row Track Fired pad Cluster Pad Pad-row Krypton Fired pad Cluster Decay point