JT: 1 The Berkeley Lab O STAR The STAR Time Projection Chamber Jim Thomas Lawrence Berkeley National Laboratory for the STAR collaboration The Vienna Conference on Instrumentation Thursday February 22 nd,

JT: 2 The Berkeley Lab O STAR The Biggest in the World The STAR TPC is the biggest TPC in the world The biggest statue of Buddha in the world –Under a wooden roof –In a building without doors –Under a concrete roof –That rolls

JT: 3 The Berkeley Lab O STAR A TPC is at the heart of STAR at RHIC ZCal Barrel EM Calorimeter Endcap Calorimeter Magnet Coils TPC Endcap & MWPC ZCal FTPCs Vertex Position Detectors Central Trigger Barrel or TOF Time Projection Chamber Silicon Vertex Tracker RICH

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

JT: 5 The Berkeley Lab O STAR Pixel Pad Readout Readout arranged like the face of a clock - 5,690 pixels per sector

JT: 6 The Berkeley Lab O STAR Outer and Inner Sectors of the Pad Plane 60 cm 190 cm Outer sector 6.2 × 19.5 mm pads 3940 pads Inner sector 2.85 × 11.5 mm pads 1750 pads 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

JT: 7 The Berkeley Lab O STAR 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

JT: 8 The Berkeley Lab O STAR TPC Front End Electronics FEE –3 rd 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

JT: 9 The Berkeley Lab O STAR Pixel Readout of a Pad Plane Sector A cosmic ray + delta  electron 3 sigma threshold

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

JT: 11 The Berkeley Lab O STAR Au on Au Event at CM Energy ~ 130 GeV*A Two-track separation 2.5 cm Momentum Resolution < 2% Space point resolution ~ 500  m Rapidity coverage –1.5 <  < 1.5 A Central Event Typically 1000 to 2000 tracks per event into the TPC

JT: 12 The Berkeley Lab O STAR Offline Particle Identification by dE/dx Aihong Tang (Kent State U) Remaining issue : correlation of dE/dx between pad rows No calibration9 % With calibration7.5% Design6.7% 12  K p d e  dE/dx (keV/cm) Anti - 3 He dE/dx PID range: ~ 0.7 GeV/c for K /  ~ 1.0 GeV/c for K/p

JT: 13 The Berkeley Lab O STAR Drift Velocity Control Using Lasers and Tracks Alexei Lebedev, Bill Love, Jeff Porter (BNL) Pressure (mbar) Drift velocity (cm/  s) Lasers for coarse value Fine adjustment from tracking matching both side of the TPC See poster B24 by A. Lebedev

JT: 14 The Berkeley Lab O STAR Solenoidal Magnetic Field Magnetic Field 0.0 G  2.5 kG  5.0 kG Radial Uniformity  40 gauss Phi Uniformity  1 gauss

JT: 15 The Berkeley Lab O STAR B Field Map and Distortion Corrections Field map allows parameter free calculation Love, Foley (BNL), Trentalange (UCLA), JT (LBNL) Calculated Distortion = E  B r Measured B r / B z Z (cm) TPC fiducial volume Radius (cm) B r /B z scale  0.8 % TPC fiducial volume Z (cm) Distortion scale  1 mm Radius (cm)

JT: 16 The Berkeley Lab O STAR Electric Field Distortions No wires at the boundary between the inner and outer sectors –E field leak E field radial component ExB effect in R and  Outer sector Inner sector Gating grid = -127 V Ground plane = 0 V 1.6 cm Pad row # Data Residual (mm) Residual (mm) Calculation gap Inner sectorOuter sector Radius (cm) Wieman, JT (LBNL), Long, Trentalange (UCLA)

JT: 17 The Berkeley Lab O STAR Many Small Effects – B, E, Clock, Twist, CM … Hui Long, Steve Trentelange(UCLA), JT (LBNL) All calculated distortions Z (cm) Radius (cm) Distortion scale  1.5 mm Outer sector Inner sector Track Residuals (cm) Before > 200  m Inner sector Outer sector Track Residuals (cm) After < 50  m

JT: 18 The Berkeley Lab O STAR Particle ID via Topology & Combinatorics Secondary vertex: K s   +  p +    +   + K  e + +e - K s   + +  -   K + + K -   p +  -    + +  -  from K + K - pairs K + K - pairs m inv same event dist. mixed event dist. background subtracted dn/dm “ kinks ” K     +

JT: 19 The Berkeley Lab O STAR STRANGENESS! (Preliminary) K0sK0s  K+K+     bar   

JT: 20 The Berkeley Lab O STAR Summary of Performance Achieved to date Good particle separation using dE/dx – 7.5% dE/dx resolution –  -proton separation : > 1 GeV/c Position resolution –500  m –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  m 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 …

JT: 21 The Berkeley Lab O STAR 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