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The STAR Time Projection Chamber. Fabrice Reti è re (LBNL) for the STAR collaboration. TPC function Large acceptance gas detector | h |
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1
The STAR Time Projection Chamber
Fabrice Retière (LBNL)
for the STAR collaboration
2
Introduction
TPC functionLarge acceptance gas detector
||<1.8
Full azimuthal coverage
Momentum reconstructionTracking with design hit position resolution ~500 m
Pid using dE/dxDesign resolution : 7%
TPC design
Tuning the TPCPosition reconstruction
Drift velocity
Drift distortion
dE/dxUnderstanding ionization
Gain calibration
3
STAR detector
0.5 Tesla magnet0.25 for year 1
Trigger CTBZDCLevel 3
Year 1 detectorsTPCRICH1 SVT ladder
4
5
TPC gas volume
Gas : P10 (Ar-CH4 90%-10%) @ 1 atm
Drift voltage : -31 kV
6
Pad readout
2×12 super-sectors
60 cm
127 cm
190 cm
Outer sector6.2 × 19.5 mm2 pad
3940 pads
Inner sector2.85 × 11.5 mm2 pad
1750 pads
7
Electronic readout
FEE, custom design IC : SAS + SCA (512 time bins)Readout 140K channels, i.e. 70M pixels
Readout boardCarry ~1000 Channels to DAQ
SCAADC
SCAADC
X 16
MUX
TPCPad
PreampShaperAmp
AnalogMemory
Fiber optictransmitterto DAQ
SAS IC SCA + ADCIC
FEEBoard
ReadoutBoard
8
TPC at workFirst RHIC events
Detector very stableGood for physics without calibration
9
TPC at work dE/dx measurement before calibration
K pd
dEdx resolution good for Pid
e
10
Tuning the TPCProcesses to control
IonizationPid using dE/dx
Electron driftDrift distortion
Drift velocity (laser)
GainGas gain
Electronic gain
Particle
11
Electron drift Drift velocity under control
Pressure (mbar)Alexei Lebedev, Bill Love, Jeff Porter (BNL)
Dri
ft v
eloc
ity
(cm
/s)
5.44
5.45
1010 1020
Laser for coarse value
Fine adjustment from tracking matching both side of the TPC
12
Electron drift Drift correction in TPC
Distortion sourcesRadial B field (<2mm)
End cap location (800 m)
E field corrections to field cage (400 m)
0.5 mrad E/B field misalignment (400 m)
Detected using residual average over many tracks
Corrections using field maps and geometry survey
No tuning on data required
Ave
rage
res
idua
l (m
m)
0.3
-0.3
0.
60. 100. 140. Radius (cm)
13
Electron drift B field map correction
Field map allows parameter free calculation
TPC active volume TPC active volume
Calculated distortion = ExBrMeasured Br/Bz
Bill Love, Al Saulys (BNL), Jim Thomas (LBNL)
20
60
100
140
Rad
ius
(cm
)
20
60
100
140
Rad
ius
(cm
)
-200 2000-100 100Distance to central membrane (cm)
-200 2000-100 100Distance to central membrane (cm)
0.4
-0.8
-0.4
0.
Br/
Bz
(%)
R/
dis
tort
ion
(mm
)
0
-1.
1.
14
Electron driftInner/outer sector boundary
Data
Calculation
No wires at the boundary between inner and outer sector
E field leakE field radial component
ExB effect on R/
Radius (cm)
Outer sector Inner sector
Gating grid = -127 VGround plane = 0 V
1.6 cm
Pad row #10 20 30
Ave
rage
res
idua
l (m
m)
Ave
rage
res
idua
l (m
m)
0.2
0.1
-0.1
0.
gap
Inner sector
Inner sector
Outer sector
Outer sector
15
Electron driftdistortions under control
TPC active volume
Huan Huang, Hui Long and Steve Trentelange (UCLA)Jim Thomas (LBNL)
20
60
100
140
Rad
ius
(cm
)
-200 2000-100 100Distance to central membrane (cm)
R/
dis
tort
ion
(mm
)
0
-1.
1.
-2.Pad row #10 20 30
Ave
rage
res
idua
l (m
m)
0.2
-0.1
0.
Inner sector Outer sector
All calculated distortionsAverage residual
16
Gain uniformityGas gain
Eugene Yamamoto (UCLA)
Gain variationOver TPC sectors With time
PressureTemperature…
Correction using average dEdx
Require a lot of events to cancel out fluctuations
Gain monitor chamber being builtPulser for electronic gain calibration
1.3
1.4
1.5
Gai
n (a
rb. u
nit.)
1000
1.6
1010 1020 1030Pressure (mbar)
essure
essure
Gain
Gain
Pr
Pr7.3
17
Gain uniformityElectronic gain
To measure uniformity of electronic gain
8% sigma variation but 20% RMS (tail)Precise channel level correction
Pulser also identifies dead channels = 0.25%
Pad pl
ane
Anode
Groun
d plan
e
Gating
grid
Pulser
TPC drift volume
Inner sector
Outer sector
Pu
lser
am
plit
ude
(arb
. uni
t.)
18
Ionization and gain uniformity dEdx resolution
Remaining issue : correlation of dE/dx between pad rows
Yuri Fisyak (BNL)
No calibration 9 %
With calibration 7.5%
Design 6.7%
Track length (cm)
dE
/dx/
(dE
/dx)
(%
)
19
Conclusion particle identification
Aihong Tang (Kent State U)
K
p d
e
dE/d
x (k
eV/c
m)
0
12
8
4
20
The TPC is an excellent tool for physics
Approaching design performance
Good particle separation using dE/dx
7.5%
-proton separation : 1.3 GeV/c
Position resolution500 m
2-Track resolution2.5 cm
Momentum resolution 2%
Future challengesAchieve turn-key operationHandle increased luminosity
Lots of physics from the year 1 data
Collective flowIdentified particle spectraParticle correlationsEvent by event physicsStrangeness…