particle identification @ star
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g.j.kunde@yale.edu Pylos June 2002 1
Particle Identification @ STAR Gerd J. Kunde, Yale
TPC EMC Future RPC
Summary
g.j.kunde@yale.edu Pylos June 2002 3
420 CM
TPC 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
Self supporting Inner Field Cage: Al on Kapton using Nomex honeycomb; 0.5% rad length
g.j.kunde@yale.edu Pylos June 2002 4
Solenoidal Magnetic Field
• Magnetic Field
0.0 G
2.5 kG
5.0 kG
• Radial Uniformity
40 gauss
• Phi Uniformity
1 gauss
g.j.kunde@yale.edu Pylos June 2002 5
Outer and Inner Sectors of the Pad Plane
60 cm
190 cmOuter sector6.2 × 19.5 mm pads
3940 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
g.j.kunde@yale.edu Pylos June 2002 6
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
g.j.kunde@yale.edu Pylos June 2002 7
Drift Velocity Control Using Lasers and Tracks
Pressure (mbar)
5.44
5.45
Drif
t ve
loci
ty (
cm/
s)
1010 1020
• Lasers for coarse value
• Fine adjustment from tracking matching both side of the TPC
g.j.kunde@yale.edu Pylos June 2002 8
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 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)
g.j.kunde@yale.edu Pylos June 2002 9
Many 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
g.j.kunde@yale.edu Pylos June 2002 10
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 …
g.j.kunde@yale.edu Pylos June 2002 11
Offline Particle Identification by dE/dx
6.7%Design
7.5%With calibration
9 %No calibration
12
Kp
d
ed
E/d
x (k
eV
/cm
)
0
8
4
Anti - 3He
dE/dx PID range:
~ 0.7 GeV/c for K/
~ 1.0 GeV/c for K/p
g.j.kunde@yale.edu Pylos June 2002 12
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 +
g.j.kunde@yale.edu Pylos June 2002 13
STRANGENESS! (Preliminary)
K0
s
K+
bar
g.j.kunde@yale.edu Pylos June 2002 14
Two Photon Decays
0 Branching Ratio 98.80 % Z Z ee++ e e-- Z Z Conversion Probability ~ 1%• ee++ and and ee-- Tracking Efficiency 60 - 90% • Overall 0 Reconstruction probability ~ 10-4
0
e+
e- e+
e-
Z Z ee++ e e-- Z Z
g.j.kunde@yale.edu Pylos June 2002 15
Pizero Reconstruction
r (c
m)
100
z (cm)0-100-200 1000
TPC
TPC
4 Primary Photon Candidates
Primary Vertex
e-
e+
Z
Z Z ee++ e e-- Z
Detected energy
loss in the TPC
B.
Note: Most tracks are not shown
g.j.kunde@yale.edu Pylos June 2002 16
xy distance of closest approach (cm)
z distance of closest approach (cm)
• Opposite charged tracks• Small distance of closest
approach• Small opening Anglee-
e+
e+
e-
coun
ts
Topological Selection
B.
positron – electron
g.j.kunde@yale.edu Pylos June 2002 17
Primary Photon Selection
p = pe+ + pe-
Primary Vertex
Photon Momentum Vector
e+
e-
Photon Conversion Vector
Angular Difference
coun
ts
Angular Difference (Degrees)
4000
2000
6000
2100
g.j.kunde@yale.edu Pylos June 2002 18
Photon Purity: via positron dE/dx
photon pt (Gev/c)
Pur
ity69%
-4 0 -4
1
0e+ dE/dx deviant
p (GeV/c)10.1
dE/d
x
dE/d
x
5
2electron p(GeV/c)10
Conversion products
Minimum biasCentral
>95% below
1Gev/c
-bin the deviant in photon pt
-fit with a Gaussian+exp.
Applyphoton
cuts
g.j.kunde@yale.edu Pylos June 2002 19
Extracting YieldsOne photon
rotated by in ,2nd order
polynomial
Two photon invariant mass spectrum,
Gaussian + Nbg*(2nd poly)
After background subtraction,Gaussian
0
g.j.kunde@yale.edu Pylos June 2002 20
x-ray like images
• Photon conversion points– Conversion probability, (lZ2)
• A tool not ‘just’ physics– map the detector material– improve the material layout in
Geant
Inner Field Cage
SVTGlue joints
Mc data
Real data
g.j.kunde@yale.edu Pylos June 2002 21
STAR Barrel Electromagnetic Calorimeter (BEMC)
• Full barrel EMC– -1.0 < < 1.0– Full azimutal coverage– 120 modules
• ()module ~ (1.0, 0.1)• 40 towers/module
– 21 X0
– ()tower ~ (0.05, 0.05)– E/E ~ 14%/√E
• Shower max detector– Positioned at ~ 5 X0
– Larger spatial resolution – () ~ (0.007, 0.007)
• Pre-shower detector– 2 X0
– not avaliable this year
g.j.kunde@yale.edu Pylos June 2002 22
BEMC patch for next run
• Full West side– 60 modules
• 2400 towers• 18 K SMD channels
• Huge impact on physics
– High-pt 0
– electrons– Jets– J/
g.j.kunde@yale.edu Pylos June 2002 23
BEMC calibration – MIP peak
• Select MIP candidate– Low multiplicity event– Vertex cut to keep tower
projective characteristics– Track momentum > 1.2
GeV/c– The projection of the track in
the inner and outer EMC radius must be in the same tower
– All adjacent towers shall not have any projected tracks
• Peak + background fit• Mean ADC gain from MIP peak
position– 8 MeV/ADC count
220 k minibias AuAu events|zvertex| < 40 cmpMIP > 1.2 GeV/c
g.j.kunde@yale.edu Pylos June 2002 24
BEMC High tower trigger performance
• Threshold set at 2 GeV – Big enhancement at
high pt tracks (~30 at 6-7 GeV/c)
– Enhancement at way side tracks (back-to-back jets?)
g.j.kunde@yale.edu Pylos June 2002 25
0 reconstruction with BEMC
• 0 in AuAu events– 200 k minibias events– No SMD present
• Only towers• Larger background• Small shift on mass
value
STAR preliminary
g.j.kunde@yale.edu Pylos June 2002 26
e/h discrimination with BEMC
• Neural network software under development
• 5 parameters– Etower/ptrack
– EPSD
– ESMD
– Width of point ()– Separation between point
and projected track ()• Hadronic suppression
becomes worse without PSD – Simulations are under
way
g.j.kunde@yale.edu Pylos June 2002 29
Ranges of Particle Identification
g.j.kunde@yale.edu Pylos June 2002 30
Resistive Plate Chambers
• Narrow single gaps don’t work well in avalanche mode • Wider single gaps?
– enhanced streamer-free range of operating voltage • but time resolution suffers...
– primary ionziation is a stochastic process!• timing jitter from location of ionization in RPC
– avalanches from single primary clusters tend to merge• fluctuations in avalanche development dominate
• Many narrow gaps!– characteristic distance for primary ionization decreased
• decreased timing jitter from primary ionization step– N-independent avalanches, hence an averaging
• decreased timing jitter from avalanche fluctuations
g.j.kunde@yale.edu Pylos June 2002 31
Comparison
g.j.kunde@yale.edu Pylos June 2002 32
Alice Prototype
g.j.kunde@yale.edu Pylos June 2002 33
Rice Final Prototype
g.j.kunde@yale.edu Pylos June 2002 34
rpc
g.j.kunde@yale.edu Pylos June 2002 35
Proposal to install 60 m2 in STAR
g.j.kunde@yale.edu Pylos June 2002 36
Production of RPC at Rice
g.j.kunde@yale.edu Pylos June 2002 37
FEE Breakthrough
g.j.kunde@yale.edu Pylos June 2002 38
RPC Performance
Voltage (kv) Voltage (kv)
TimeEff.
Eff.
Time
cell 5 cell 11 (final)
g.j.kunde@yale.edu Pylos June 2002 39
RPC Summary
• TOF remains a viable technique for Particle Identification in modern experiments...
• MGRPC detectors are inexpensive and appear to outperform the conventional technology...
• Recent Major Successes a specific fishing line is a great choice for the 220 µm spacer...
• Detector module design (Rice v.11) is now final for STAR... <60ps stop-resolution is typical...
• Maxim 3760 preamp & other standard components is an adequate approach to the FEE...
• Collaboration of US and Chinese institutions developed...
g.j.kunde@yale.edu Pylos June 2002 40
Summary
• TPC– Identification via dE/dx
– Topological Methods/Combinatorical Methods
– Pizero
– Baryons up to 5 GeV/c
• EMC– Pizero
– Hadron Suppression
• RPC– Prototype with <60ps Stop Resolution
– Proposal for 60 m2
g.j.kunde@yale.edu Pylos June 2002 41
STAR Collaborators/Institutions
Brazil: Universidade de Sao Paolo
China: IHEP - Beijing, IPP - Wuhan
England:
University of Birmingham
France:
Institut de Recherches Subatomiques Strasbourg, SUBATECH - Nantes
Germany:
Max Planck Institute Munich, University of Frankfurt
India: Institute of Physics - Bhubaneswar, VECC
Calcutta, Panjab University - Chandrigrarh, University of Rajasthan - Jaipur, Jammu University, IIT -Bombay
Poland:
Warsaw University, Warsaw University of Technology
Russia:
MEPHI – Moscow, LPP/LHE JINR – Dubna, IHEP - Protvinoh
U.S. Universities:
Arkansas, UC Berkeley, UC Davis, UCLA,
Carnegie Mellon, Creighton, Indiana, Kent
State, MSU, CCNY, Ohio State, Penn State,
Purdue, Rice, Texas A&M, UT Austin,
Washington, Wayne State, Yale
U.S. Labs:
Argonne, Berkeley, and Brookhaven
National Laboratories
~400
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