JT: 1The Berkeley Lab

STAR

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/

JT: 2The Berkeley Lab

STARThe 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: 3The Berkeley Lab

STARA 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: 4The Berkeley Lab

STARTPC Gas Volume & Electrostatic Field Cage

• 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

Self supporting Inner Field Cage: Al on Kapton using Nomex honeycomb; 0.5% rad length

JT: 5The Berkeley Lab

STARPixel Pad Readout

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

JT: 6The Berkeley Lab

STAROuter and Inner Sectors of the Pad Plane

60 cm

190 cmOuter sector

6.2 × 19.5 mm pads3940 pads

Inner sector2.85 × 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: 7The Berkeley Lab

STAR

Sector Operation for 20:1 signal to noise

Sector gas gain anodevoltage

inner 3000 1150outer 1100 1380

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: 8The Berkeley Lab

STARTPC 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

JT: 9The Berkeley Lab

STARPixel Readout of a Pad Plane SectorA cosmic ray + deltaelectron

3 sigma threshold

JT: 10The Berkeley Lab

STARAu 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, 2000.

The first 12 events were captured on tape!

JT: 11The Berkeley Lab

STARAu 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: 12The Berkeley Lab

STAROffline Particle Identification by dE/dx

Aihong Tang (Kent State U)

Remaining issue : correlation of dE/dxbetween pad rows

No calibration 9 %

With calibration 7.5%

Design 6.7%

12

Kp

d

edE

/dx

(keV

/cm

)

0

8

4

Anti - 3He

dE/dx PID range:

~ 0.7 GeV/c for K/

~ 1.0 GeV/c for K/p

JT: 13The Berkeley Lab

STARDrift Velocity Control Using Lasers and Tracks

Alexei Lebedev, Bill Love, Jeff Porter (BNL)

Pressure (mbar)

5.44

5.45

Dri

ft v

eloc

ity

(cm

/s)

1010 1020

• Lasers for coarse value

• Fine adjustment from tracking matching both side of the TPC

See poster B24 by A. Lebedev

JT: 14The Berkeley Lab

STARSolenoidal Magnetic Field

• Magnetic Field

0.0 G

2.5 kG

5.0 kG

• Radial Uniformity

40 gauss

• Phi Uniformity

1 gauss

JT: 15The Berkeley Lab

STARB Field Map and Distortion Corrections

Field map allows parameter free calculation

Love, Foley (BNL), Trentalange (UCLA), JT (LBNL)

Calculated Distortion = E BrMeasured Br / Bz

20

60

100

140

-200 2000-100 100

180

Z (cm)

TPC fiducial volumeRad

ius

(cm

)

Br/Bz scale 0.8 %20

60

100

140

-200 2000-100 100

180

TPC fiducial volume

Z (cm)

Distortion scale 1 mm

Rad

ius

(cm

)

JT: 16The Berkeley Lab

STARElectric 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 VGround plane = 0 V

1.6 cm

Pad row #10 20 30

Data

Res

idu

al (

mm

)

0.2

0.1

-0.1

0.

Res

idu

al (

mm

)

Calculation

gap

Inner sector Outer sector

Radius (cm)

Wieman, JT (LBNL), Long, Trentalange (UCLA)

JT: 17The Berkeley Lab

STARMany Small Effects – B, E, Clock, Twist, CM …

Hui Long, Steve Trentelange(UCLA), JT (LBNL)

All calculated distortions

20

60

100

140

-200 2000-100 100

180

Z (cm)

Rad

ius

(cm

)

Distortion scale 1.5 mm

Outer sectorInner sector

Tra

ck R

esid

ual

s (c

m) Before

> 200 m

Inner sector

Outer sector

Tra

ck R

esid

ual

s (c

m) After

< 50 m

JT: 18The Berkeley Lab

STAR Particle ID via Topology & Combinatorics

Secondary vertex: Ks + p +

+ + K e++e-

Ks + + - K + + K- p + - + + -

from K+ K- pairs

K+ K- pairs

m inv

m inv

same event dist.mixed event dist.

background subtracted

dn/dm

dn/dm

“kinks”

K +

JT: 19The Berkeley Lab

STARSTRANGENESS! (Preliminary)

K0s

K+

bar

JT: 20The Berkeley Lab

STARSummary 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: 21The Berkeley Lab

STARTPC & 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