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The STAR Time Projection Chamber

The STAR Time Projection Chamber. Jim Thomas Lawrence Berkeley National Laboratory for the STAR collaboration The Vienna Conference on Instrumentation Thursday February 22 nd , 2001. http://www.star.bnl.gov/. The Biggest in the World. The STAR TPC is the biggest TPC in the world.

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The STAR Time Projection Chamber

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  1. The STAR Time Projection Chamber Jim Thomas Lawrence Berkeley National Laboratory for the STAR collaboration The Vienna Conference on Instrumentation Thursday February 22nd, 2001 http://www.star.bnl.gov/

  2. The Biggest in the World The STAR TPC is the biggest TPC in the world • Under a concrete roof • That rolls • The biggest statue of Buddha in the world • Under a wooden roof • In a building without doors

  3. Time Projection Chamber Magnet Coils Silicon Vertex Tracker TPC Endcap & MWPC FTPCs ZCal ZCal Endcap Calorimeter VertexPositionDetectors Barrel EM Calorimeter Central Trigger Barrel or TOF RICH A TPC is at the heart of STAR at RHIC

  4. Gas: P10 ( Ar-CH4 90%-10% ) @ 1 atm Voltage :- 31 kV at the central membrane 148 V/cm over 210 cm drift path 420 CM TPC Gas Volume & Electrostatic Field Cage Self supporting Inner Field Cage:Al on Kapton using Nomex honeycomb; 0.5% rad length

  5. Pixel Pad Readout Readout arranged like the face of a clock - 5,690 pixels per sector

  6. 60 cm 190 cm Outer and Inner Sectors of the Pad Plane • 24 sectors (12 on a side) • Large pads good dE/dx resolution in the Outer sector • Small pads for good two track resolution in the inner sector Inner sector 2.85 × 11.5 mm pads 1750 pads Outer sector 6.2 × 19.5 mm pads 3940 pads

  7. TPC Sector Detail • Gating Grid • Ground Plane of Wires • Anodes • No field shaping wires • Simple and reliable • Individually terminated anode wires limit cross-talk • Low gain • Pad Plane

  8. TPC Front End Electronics • FEE • 3rd generation electronics • very compact • First chip is pre-amp, shaper & buffer • Second chip is switched capacitor array & (slow) ADC • Analog and Digital are not synchronous • 512 time buckets per ch • 32 channels per board • Readout (RDO) board • Multiplex and tag data • 6 RDOs per sector • 144 total • Data sent to DAQ on gigabit fiber link

  9. Pixel Readout of a Pad Plane Sector A cosmic ray + deltaelectron 3 sigma threshold

  10. Au on Au Event at CM Energy ~ 130 GeV*A Data taken June 25, 2000. The first 12 events were captured on tape! Real-time track reconstruction Pictures from Level 3 online display. ( < 70 mSec )

  11. Au on Au Event at CM Energy ~ 130 GeV*A A Central Event Typically 1000 to 2000 tracks per event into the TPC Two-track separation 2.5 cm Momentum Resolution < 2% Space point resolution ~ 500 mm Rapidity coverage –1.5 < h < 1.5

  12. Remaining issue : correlation of dE/dx between pad rows 12 d p 8 K dE/dx (keV/cm)  4 m e 0 Anti - 3He Offline Particle Identification by dE/dx Aihong Tang (Kent State U) dE/dx PID range: ~ 0.7 GeV/c for K/ ~ 1.0 GeV/c for K/p

  13. Lasers for coarse value Fine adjustment from tracking matching both side of the TPC 5.45 Drift velocity (cm/ms) 5.44 1010 1020 Pressure (mbar) Drift Velocity Control Using Lasers and Tracks Alexei Lebedev, Bill Love, Jeff Porter (BNL) See poster B24 by A. Lebedev

  14. Solenoidal Magnetic Field • Magnetic Field 0.0 G ± 2.5 kG ± 5.0 kG • Radial Uniformity ±40 gauss • Phi Uniformity ± 1 gauss

  15. Calculated Distortion = E ´ Br Measured Br / Bz 180 180 140 140 Radius (cm) 100 Radius (cm) 100 TPC fiducial volume TPC fiducial volume 60 60 Br/Bz scale ± 0.8 % Distortion scale ± 1 mm 20 20 -200 -100 0 100 200 -200 -100 0 100 200 Z (cm) Z (cm) Field map allows parameter free calculation B Field Map and Distortion Corrections Love, Foley (BNL), Trentalange (UCLA), JT (LBNL)

  16. No wires at the boundary between the inner and outer sectors E field leak E field radial component ExB effect in R and f 0.2 Data 0.1 Residual (mm) 0. -0.1 10 20 30 Pad row # Calculation 1.6 cm Gating grid = -127 V Residual (mm) Ground plane = 0 V gap Inner sector Outer sector Inner sector Outer sector Radius (cm) Electric Field Distortions Wieman, JT (LBNL), Long, Trentalange (UCLA)

  17. All calculated distortions Before > 200 mm 180 Track Residuals (cm) Inner sector 140 Outer sector 100 Radius (cm) After < 50 mm 60 Distortion scale ± 1.5 mm 20 Track Residuals (cm) -200 -100 0 100 200 Inner sector Outer sector Z (cm) Many Small Effects – B, E, Clock, Twist, CM … Hui Long, Steve Trentelange(UCLA), JT (LBNL)

  18. f from K+ K- pairs dn/dm background subtracted m inv dn/dm K+ K- pairs same event dist. mixed event dist. m inv Particle ID via Topology & Combinatorics Secondary vertex: Ks p + p  L p + p X  L + p  W L + K g  e++e- Ks p + + p - f  K + + K- L  p + p - r  p + + p - “kinks” K  + 

  19. STRANGENESS! (Preliminary) W- Lbar K+ W+ f K0s L X- X+ K*

  20. Good particle separation using dE/dx 7.5% dE/dx resolution p-proton separation : > 1 GeV/c Position resolution 500 mm Function of dip angle and crossing angle 2-Track resolution 2.5 cm Momentum resolution 2% Unique features of the STAR TPC 4 meter by 4 meter scale length No field wires in the anode planes Low gain Very compact FEE electronics Analog and Digital are not synchronous Data delivered via optic fiber Uniform B and E field Distortions correctable to 50 mm Lots of physics from the year 1 data Collective flow Identified particle spectra Particle correlations Event by event physics Strangeness Future challenges Achieve turn-key operation Handle increased luminosity … Summary of Performance Achieved to date

  21. TPC & Related Systems Project Leaders • TPC Project Leader - Howard Wieman (LBL) • Software - Iwona Sakrejda (LBL) • Anode - Declan Keane (Kent State) • Drift Velocity Control - Tom Trainor, Greg Harper (UW) • Gas System - L. Kotchenda (PNPI), B. Stringfellow (Purdue) • Slow Controls - Mike Cherney (Creighton) • Laser - Alexei Lebedev ( MEPHI & BNL ) • Magnet - Ken Foley, Ralph Brown (BNL) • Magnet Mapping - Steve Trentalange (UCLA), • Trigger - Hank Crawford (UCB) • CTB - Gary Epply, Ed Platner, Gordon Mutchler (Rice) • FEE - Spencer Klein, Fred Beiser (LBL) • DAQ - Mike Levine, Tonko Ljubicic (BNL) • Gating Grid & Pad Plane Pulser - Vahe Ghazikhanian (UCLA) • Mechanical Engineering - Russ Wells, Bill Edwards, Roger Stone, Ralph Brown

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