star time-projection chamber
DESCRIPTION
STAR Time-Projection Chamber. Huan Zhong Huang Department of Engineering Physics Tsinghua University & Department of Physics and Astronomy University of California, Los Angeles Thanks to Gene Van Buren, Jim Thomas, Blair Stringfellow and Howard Wieman. - PowerPoint PPT PresentationTRANSCRIPT
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STAR Time-Projection Chamber Huan Zhong Huang
Department of Engineering PhysicsTsinghua University
& Department of Physics and Astronomy University of California, Los Angeles
Thanks to Gene Van Buren, Jim Thomas, Blair Stringfellow and Howard Wieman
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STAR
Relativistic Heavy Ion Collider --- RHIC
Au+Au 200 GeV N-N CM energyPolarized p+p up to 500 GeV CM energy
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STAR Physics Approaches
Emphasis on Observables Sensitive to Early Partonic Stages:
1) High pT particles – Jet quenching? New baryon dynamics? 2) Particle fluctuations and large scale correlations – probe
conditions near phase boundary.3) Partonic collective flow observables especially for those particles
believed to have small hadronic re-scattering cross sections, D mesons and J/.
4) D meson production for initial gluon flux and structure function of nuclei.
5) J/ for possible color screening effect6) Direct and thermal photon production
Precision Measurements to Map Out Hadronic Evolution Dynamics
1) Resonances (,,f0, K*, , (1385) and(1520)) – Sensitive tohadronic evolution between chemical and kinetic freeze-out
2) Momentum-space-time relations at the kinetic freeze-out thrucorrelations of identical, non-identical pairs, and light clusters.
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STAR Schematic
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The STAR Detector
• Electron ID• energy loss in the tracking detectors (TPC dE/dx)• time of flight measurement (TOF)• calorimetric measurements (EMC)
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STAR TPC Geometry
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The STAR Time Projection Chamber
Inner and Outer Field Cages
Central Membrane
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Anode Wire-Pad Plane Readout
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Typical TPC Readout
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Limitations on Wire-Pad Readout1) The induced charge distribution on the pad plane is much wider than the intrinsic avalanche width --- wire-pad readout scheme not matching the true two-hit resolution capability of the gas detector
2) The width of the induced charge distribution depends on the separation between the anode and pad planes
--- STAR inner sectors 2 mm gap outer sectors 4 mm gap
3) Mechanical stability and wire plane accuracy limit the gap separation
4) In high multiplicity environment the anode wire readout is not very useful
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Hit Position from Pad Readout
Ideally the induced signal should be distributed across three pads with amplitudes h1, h2 and h3.
)/ln(2
)/ln(
13
2
3122
22
hhw
x
hhh
w
Pad Plane
0 x
h1 h2 h3
Induce charge distribution
Non-Gaussian shape better use weighted average --- Laser signals --- Drift direction
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STAR TPC Characteristics
P10 Gas
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Electrons Transport in Gas Electron clouds from primary ionization drift towards the anode and undergo diffusionD – diffusion coefficientUnder magnetic field (parallel to Electric Field E) the transverse diffusion coefficient --
2)(1)(
T
T
DBD
P10 Gas – ~ 2.30 at 0.5 T DT(0.5T) = 230 m/sqrt(cm) DL = 360 m/sqrt(cm)Diffusion Contribution ~ D*sqrt(L) For L=200 cm drift in STAR TPC T ~ 3.3 mm; L ~ 5.1 mm-- Anode Wire – Pad Plane two-hit resolution does not match the diffusion limit – motivation for GEM read-out !!
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Two-Hit Resolutions
Inner Sector Pads – 2.85 x 11.5 mmOuter Sector Pads – 6.20 x 19.5 mm
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Laser System for Drift Velocity
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TPC Laser Tracks
Laser System -- 500 laser triggers every a few hours ! -- drift velocity ~ 0.02%
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What Happens to Positive Ions?
Gate open Gate closed
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Large Data Set is needed for correction studies !
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2
2ln
14 2
222
2222
I
cm
A
ZzcmrN
dx
dE eeeA
Ionization Energy
Bethe-Bloch Formula
density effect
ionization constant
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STAR TPC: Ar-CH4 (90-10) Atmosphere Pressure45 max samples
Particle Identification Using dE/dx
Kp
d
e
Inner Sector pads smaller – not as good as outer pads for dE/dx
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Momentum Resolution: the STAR Magnet+TPC
• Momentum resolution is only limited by the strength of the magnetic field and is independent of the mass of the particle at high PT
• Momentum resolution at low PT is determined by multiple coulomb scattering (MCS)
MCS Contribution
B Field limited
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Reconstruct Ks, and
KS π+π- (i/ 69%), c = 2.69cm
Λ pπ- (i/ 64%), c = 7.89cm
- Λπ- (i/ 99.9%), c =4.91cm
(Ks)
p(+)
Decay vertex-
Primary Vertex
p
-
Primary Vertex
-
-
STARSTAR
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STAR TPCThe STAR TPC has performed as designed -- unexpected space-charge problem due to higher RHIC luminosity ~ 6 x design luminosity some charge leakage in the gating grid boundary can be corrected for reliably so far
STAR benefited from 1) better than design spec on construction and E and B
alignment 2) TPC has two almost independent halves
(central membrane) 3) many monitor systems and lots of data
STAR TPC upgrade – FEE and DAQSTAR TPC is expected to perform at RHICII @40 x design L
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Multi-Gap Resistive Plate Chamber
E. Gorini et al. Nucl. Instr. Meth. A 396(1997)93
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Good time resolution (<100ps), high detection efficiency(>95%),high granularity, robustious, low cost ($2M +electronic).
USTC and Tsinghua
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Chinese MRPC Works
TOF “alone” PID pT range:
/K ~1.6GeV/c,
(,K )/p ~ 3.0GeV/c
Chinese STAR Groups – Shanghai Institute of Applied Physics, University of ScienceAnd Technology of China, Tsinghua University, Hua Zhong Normal University and Institute of Modern Physics at LanZhou
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The End
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The sagitta is determined by 3 measurements with error (x):
( N > 10 )
L
s
B
y
x
qBpBvq
mvT )(
2
23
223.
3.0
8)()()(
BL
px
s
x
s
s
p
p T
meas
T
T
)( 3121
2 xxxs
m)(T3.0)cGeV( BpT
Tp
BLL
3.022sin
2
Tp
BLs
22
8
3.0
82cos1
Momentum Measurement in a Uniform Field
)4/(720
3.0
)(2
.
NBL
px
p
p T
meas
T
T
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TRANSITION AVALANCHE TO STREAMER