Post on 13-Jan-2016
description
120-23 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
220-23 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)
*
320-23 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
420-23 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 m3
Ne-CO2-N2: 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
2.5 m
520-23 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
620-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja
Drift voltage systemComponents
Resistor rods
Voltage dividers' network
Provide constant electric field Water cooled voltage dividers
→ remove dissipated power Control of water conductivity Radiation length X / X0 of Field Cage
1.367 % - inner FC 0.607 % - gas 2.153 % - outer FC
Very stable operationFew well understood trips
(beam loss) Tomography of FC in good
agreement with MC
720-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja
Recirculating gas system
Precise control of gas mixture O2 and H2O contamination
removed by Cu catalyser To minimize signal loss
(e- attachment) Contamination:
~ 1 ppm O2 (design < 5)
Humidity kept at fixed level
→ to avoid aging of components
In operation since 2006
Components
820-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja
Cooling systemProvide 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
920-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja
Detector Control SystemEnsure 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
1020-23 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
1120-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja
Gain calibration using 83KrCalibration
main peak (41.6 keV)
OROCResolution 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 83Kr Characteristic decay spectrum Dedicated clusterizer Fit the main peak (41.6 keV) Parabolic fit Calibration constants
3 different HV settings (gains) High statistics: several 108 Kr events Accuracy of peak position: << 1%
(design: 1.5%) Repeated after electronic maintenance
or every year
1220-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja
Kr calibration - systematics
IROC
OROC
short mid 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
1320-23 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.
1420-23 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
1520-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja
Drift velocity measurements d = d(E, B, (Tin, Patm), CCO2, CN2)
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
1620-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja
Drift velocity measurements d = d(E, B, (Tin, Patm), CCO2, CN2)
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
1720-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja
Space point resolutionPerformance
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
1820-23 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 pT at vertex gives resolution
Statistics: ~ 5 106 events Low momentum tracks
Deduced from the width of K0S mass
peak Current status (w/o many corrections):
(pT/pT)2 = (0.01)2 + (0.007pT)2
Achieved: ~ 7 % @ 10 GeV/c
~ 1 % below 1 GeV/c Place for improvement:
~ 4 % @ 10 GeV/c
Performance
1920-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja
dE/dx resolution - cosmicsAllows particle identification up to 50 GeV/c Statistics: 8.3106 cosmic tracks in 2008 Design goal: 5.5 % Measured: < 5 %
Performance
TPC cosmic data
500 < p < 550 MeV
p d
e
e
p
2020-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja
dE/dx spectrum in dataPerformance
2120-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja
Material budgetVertices from conversion photonsRadial distribution
Agreement between MC and DATA: 5 ~ 15 %
Performance
TPC begins here
2220-23 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
2320-23 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
2420-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja
The ALICE TPC collaborationHarald Appelshaeuser6, Peter Braun-Munzinger7, Peter Christiansen9, Panagiota
Foka7, Ulrich Frankenfeld7, Chilo Garabatos7, Peter Glassel8, Hans-Ake Gustafsson9, Haavard Helstrup1, Marian Ivanov7, Rudolf Janik2, Alexander Kalweit5, Ralf Keidel11, Marek Kowalski10, Dag Toppe Larsen1, Christian Lippmann3, Magnus
Mager3, Adam Matyja10,12 , Luciano Musa3, Borge Svane Nielsen4, Helmut Oeschler5, Miro Pikna2, Attiq Ur Rehman3, Rainer Renfordt6, Stefan Rossegger3,
Dieter Roehrich1, Hans-Rudolf Schmidt7, Martin Siska2, Brano Sitar2, Carsten Soegaard4, Johanna Stachel8, Peter Strmen2, Imrich Szarka2, Danilo Vranic7, Jens
Wiechula8
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.
2520-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja
BACKUP
2620-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja
PID
2720-23 September 2010, Etretat, Rencontres QGP-France 2010, Adam Matyja
Cluster finderTrack
Pad
Pad
-row
Track
Fired pad
Cluster
Pad
Pad
-row
Krypton
Fired pad
Cluster
Decay point