craig woody bnl rhic detector advisory committee review december 19, 2002 a fast, compact tpc for...
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Craig Woody BNL
RHIC Detector Advisory Committee ReviewDecember 19, 2002
A Fast, Compact TPC for Dalitz Rejection and Inner Tracking in PHENIX
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Physics goals Description of the combined TPC/HBD detector Main R&D Issues Goals, milestones, funding
Outline
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• Low mass lepton pairs and vector mesons
• Charm and B physics with resolved secondary verticies - low mass tracking just outside vertex detector - allows measurement in both heavy ion and pp running
• Improved inner tracking for PHENIX - increased h and f coverage (needed for jet and g-jet physics) - tracking through the magnetic field (improves momentum resolution, the ability to measure real low pT tracks, and to reject high pT background tracks)
Physics measurements addressed by this detector
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e+
e-
TPC / HBD e-
e+
p
p
p
V0
measured in outer PHENIX
detectors(Pe > 200 MeV/c)
• Operate PHENIX with low inner B field to optimize measurement of low momentum tracks
• Identify signal electrons (low mass pairs, r,w,f, …) with p>200 MeV in outer PHENIX detectors
• Identify low momentum electrons (p<200 MeV) using Cherenkov light from HBD and/or dE/dx from TPC
• Calculate effective mass between all opposite sign tracks identified as electrons (eelectron > 0.9, prej > 1:200)
• Reject pair if mass < 130 MeV
Must provide sufficient Dalitz rejection (>90%) while preserving the true signal
Strategy for Low Mass Pair Measurement
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Dalitz Rejection and Vector Meson Survival Probability
K. Ozawa
Survival probability of is ~85% for Dalitz rejection ratio of 90%.
Central Au+Au collisionsee = 100%, prej = 1:200 (HBD,RICH)
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PHENIX Tracking
a
decays
conversionsB
DC
- DC only- PC1-PC3 matching- Random background
PT distribution of charged tracks
Drift Chamber
Momentum determined by measuring a angle
Tracking through the magnetic fieldwill help eliminate backgroundsfrom decays and conversion whichare problematic at high PT
PHENIX presently has no tracking inside magnetic field
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PHENIX Inner Magnetic Field
± Configuration
BR
BZz=20cm
field from CDR scaled to 0.78 Tm
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 50 100 150 200 250 300 350
R (cm)
Bz
(Tm
)
++ 1.25 Tm
+ 0.73 Tm
+- 0.22 Tm
DC at 220 cm
B dl to drift chamber
Field Integrals Inner Coil creates a “field free” (∫Bdl=0) region inside the Central Magnet
Inner field itself is non-uniform
Tracking with TPC will aid in electron
id in HBD
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Tracking at High Field and Vertex Resolution
Momentum resolution Impact parameter resolution
V. Rykov ++ Configuration B = 9 KG
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TPC/HBD Detector
• Fast, compact TPC R<70 cm, L< 80 cm, Tdrift 4 msec
• Serves as an inner tracking detector in both HI and pp, providing tracking through the central magnetic field Df = 2p, |h| 1.0 Dp/p ~ .02p
• Provides electron id by dE/dx e/p separation below 200 MeV
• HBD is a proximity focused Cherenkov detector with a ~ 50 cm radiator length
• Provides electron id with minimal signals for charged particles
“Hadron Blind Detector”
GEMs are used for both TPC and HBD
TPC ReadoutPlane
CsI Readout Plane
Drift regions
Readout Pads
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Rates and Occupancy
100 MeV e-
C.Aidala
35 pad rows, 80K channels DR ~ 1 cm, RDf ~ 2 mm DZ ~ 2.5 mm (140 samples)
11M voxels
Innermost pad row ~ 3% occupancy
Requirement: The TPC should work at the highest HI and pp luminosities
Au-Au : L ~ 8 x 1027 cm-2s-1
L x s = 8 x 1027 x 7.2 b = 58 kHz dNch/dy = 150 (min.bias) ~ 250 trks/evt, 15 trks/msec Nhits/evt ~ 100K occupancy ~ 1%
p-p : L ~ 2 x 1032 cm-2s-1
L x s = 2 x 1032 x 60 mb (Ss = 500 GeV) = 12MHz ~ 50 events in 4 msec drift time dNch/dy = 2.6 ~ 5 trks/evt, 52 trks/msec
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R & D Issues for the TPC
Performance of GEM detectors• Stability, gain uniformity, aging• Studies of fast drift gases (CF4, CH4, mixtures…)
- Drift velocities, drift lengths, diffusion parameters, dE/dx, ion feedback,… - Optical transmission into the VUV for use with HBD
• Optimize spatial resolution
Detector component design• Readout plane • Field cage • Understand E x B effects for drifting charge in non-uniform magnetic field• Understand space charge effects (do we need gating ?)
Electronics
Infrastructure issues • Requires engineering and integration study (additional manpower needed)
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GEM Detectors at BNL
Several multistage GEM detectors have been obtained from Sauli’s group at CERN and are currently being used for detector studies at
BNL
B. YuHigh precision (100 mm) scanning x-ray source
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Double GEM Gas Gain Uniformity
5.4keV collimated x-rays (~1mm2) scanned with a 1mmx1mm grid over 9cmx9cm area.
90 100 110 120 130 140 150
Relative Amplitude
Good gain uniformity and energy resolution is important for particle id using dE/dx
p
k
pe
0.2 1.0 P (GeV/c)
miniTPC35 pad rows CH4
dE/d
x (k
eV/c
m)
e/p separation below 200 MeV
N. SmirnovB. Yu
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GEM Spatial Resolution
J.Va’vra et.al., NIM A324 (1993) 113-126
Diffusion LimitsL~ 80 mm/35cm ~ 500 mm
GEM’s produce inherently good spatial resolution due to direct collection of electron signal
Must keep channel count low
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Interpolating Pad ReadoutTwo Intermediate Strips
Single Intermediate Zigzag
-100
-80
-60
-40
-20
0
20
40
60
80
100
3000 3500 4000 4500 5000 5500 6000 6500 7000
Reconstructed Position [µm]P
os
itio
n E
rro
r [µ
m]
Overall position error: 93µm rms Including ~ 100µm fwhm x-ray p.e. range,
100µm beam width, alignment errors
Fine “Zigzag” pattern
B. Yu
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Test Drift Cell
Drift Stack E-Field calculation
C. Thorn
Joint R&D with LEGS
Will be used to study
• Drift velocities• Drift lengths• Diffusion parameters• Energy loss (dE/dx)• Study impurities• Readout structures• Field cage design
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TPC Readout
Readout Pads 35 pad rows, 5K ch/planeDR ~ 1 cm, RDf ~ 2 mm
Number of pads 80KPad size 2x10 mm2
Drift time 3.5 msecSampling rate 40 MHz (25 ns)Sampling resolution 2.5 mm, 8 bits Number of samples 140Unsuppressed data volume 11 MBSuppressed data volume (~1/10) 1 MBActual data volume 100 KBBuffer latency 4 msecReadout time 40 msecData transmission rate 200 Gbit/secPower per channel 100 mWTotal power 8 KW
200 ch readout card
15 cm
5 cm
R&D Issues
• Need to minimize power• Distribution of analog and digital signals• Low noise, zero suppression• Data volume (triggering)
Readout features
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TPC Readout Electronics
Options• Commercial ADC + FPGA
• ALICE ALTRO chip
• Custom ASIC (may only need for preamp/shaper)
Considerations• Speed (need ~ 40 Mhz)
• Power (< 100 mW/ch total)
• Compatibility w/PHENIX readout
• Cost and availability
AD9289 Serial ADC4 ch / 65MHz / 8 bit
ADC each channel
AMU/ADC
C-Y. Chi
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HBD Readout Electronics
Options• Separate (slow) ADC + TDC
• Fast ADC used to extrapolate T0 measurement
Considerations• Low noise (signal ~ 40 p.e.’s)
• Low mass (inside PHENIX accept.) (signals brought to edge of detector)
• ~ 5K channels - too few for ASIC
• Needs time measurement ~ few nsC-Y. Chi
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FY03 R&D Goals
• Complete TPC test cell• Carry out gas studies of TPC with GEM readout• Preliminary design of TPC field cage & readout plane• Carry out CsI photocathode studies with GEMs• Measure CF4 scintillation (NSLS Feb ’03)• Carry out aging studies (GEMs, CsI, CF4)• Measure HBD response to hadrons and electrons• Define HBD detector configuration• Preliminary engineering design and integration study• Preliminary design of TPC and HBD electronics• Build test setup for TPC and HBD electronic components• Improved Monte Carlo simulations
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• Demonstrate proof of principle of TPC with GEM readout
• Demonstrate proof of principle of CsI + GEM operation
• Determine feasibility of operation in pure CF4 (or choose alternative gas)
• Demonstrate feasibility of combined TPC/HBD detector concept
• Decide on ALICE ALTRO chip, commercial ADC+FPGA or ASIC for TPC
• Decide on slow ADC+ TDC or fast ADC for HBD readout
FY03 R&D Milestones
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R&D Goals & Milestones for FY04 & FY05
FY2004
• Construct TPC/HBD prototype detectors• Construct gas system for prototype detectors• Build prototype HBD and TPC electronics• Build test setup for TPC and HBD electronics• Carry out detailed engineering design and integration study• Carry out further detailed Monte Carlo simulations
FY2005• Complete engineering and integration design• Complete TPC detector design • Complete design of TPC readout electronics
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R&D Budget RequestCategory Description FY03 ($K) FY04($K) FY05($K)
Salaries Post Doc 45 45 45(incl. fringe) Electrical Engineer (1.0-1.25 FTE) 100 125 125
Electrical Tech (0.25 FTE) 20 20 20Mechanical Engineer (0.25 FTE) 25 25 25Mechanical Designer (0.25 FTE) 20 20 20Mechanical Tech (0.25 FTE) 20 20 20
Supplies Lab equipment 30 20 15Electronics ASIC fabrication 30 60 75
Test equipment 15 25 15Total 305 360 360Total (incl 40% overhead) 427 504 504
Related R&D Efforts
• Joint effort with STAR (includes additional equipment costs)• LEGS TPC• Detector R&D at FIT*• TPC w/GEM readout for NLC/TESLA
Additional institutional manpower contributions
*Florida Institute of Technology - 2 physicists, 1 student interested
BNL Weizmann Stony Brook Columbia TokyoPhysicists 1.50 1.50 0.25 0.25 0.25Physics Associates 0.50Post docs 0.25 0.5Students 1.00 1.00 0.5Technicians 0.25Electrical Engineers 0.25 0.25Mechanical Engineers 0.25Mechanical DesignersFTEs 2.50 2.75 1.50 0.50 1.25Total FTEs 8.50
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20 cm
55 cm
70 cm
CsI Photocathode
C.Aidala
Single 100 MeV/c electron track
GEANT Simulation of TPC/HBD
TPC/HBD detector in PHENIX PISA simulation package
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Fast drift gases - CH4 and CF4
10 cm /ms
12 cm /ms
40 cm drift ~ 3-4 ms Requires high drift field
1 V / cm / Torr
CF4 -Ar
1 KV / cm
C2 H6
CH4
C2 H2 P10
CF4
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Ion Feedback in GEMs
ElectronsIons
F.Sauli
B.YuTriple GEM
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Space Charge Distortions
Emax ~ 1.7V/cmEmax ~ 1.4V/cm
Distortion field components in TPC volume.
Radial Axial
200 GeV Au+Au Ion feedback 10%
q ~ 2.5 x 10-3 radDx ~ 0.5 mm for 40 cm drift
G ~ 103
r ~ 10-8 C/m3
B. Yu
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GEM Aging and Discharge Rates
Experience from COMPASS
• Triple GEM greatly reduces discharge probability rate• no discharges over months of operation• no loss of gain or resolution due to aging
S.Kappler, 2001 International Workshop on Aging Phenomena in Gaseous Detectors http://www.desy.agingworkshop
S.Bachmann et.al., NIM A479 (2002) 294
Triple GEM
Aging rate at RHIC
• Min bias 1.3 x 107 trks/sec• dE/dx = 80 ion pairs/cm (CH4)• Gain = 2 x 103
• dQ/dt = 64 C/yr, A= 8247 cm2
dQ/dA = 0.08 mC/mm2/yr
Triple GEMArCO2, G~8.5x103
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Used for measurements of VUV gastransmission and CsI quantum efficiency
VUV Spectrometer
Ratio of Quantum Efficiencies Before and After Exposure to Gas
0
20
40
60
80
100
120
140
1150 1250 1350 1450 1550 1650 1750
Wavelength [Angstroms]
QE
(Aft
.)/Q
E(B
ef.)
[%
]
1. Ar (1 min.)
2. Ar (5 min.)
3. Ar (10 min.)
4. CF4 (1 min.)
5. CF4 (5 min.)
6. CF4 (10 min.)
(Au-Ni-Cu-G-10 Substrate)
B.Azmoun
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Use of ALTRO Chip in PHENIX
Backend of the ALTRO chip15 write clocks
signalL1 trigger
(write to buffer)
L1 (W)L1 (W)
L1 (W)L1 (W)
L1 (W)L1 (W)
L2 trigger
(keep the buffer)
Read or drop L2 events
L1 (W)L2 (keep)
L1 (W)L2 (keep)
L1 (W)L2 (keep)
ALTRO’s event buffer could be divided to
8 * 512 word blocks or
4 * 1024 words blocksTime
C-Y. Chi
Problem for PHENIX a) no overlapping event buffers (space between L1 triggers could be as short as 4 beam clocks) b) L1 trigger delay is too short (i.e., 15*25 ns = 375 ns)
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• We need to generate a fake L1 trigger every 512*25ns = 12.8s. ( used as L1 delay buffer)
• Our L1 trigger will become ALTRO chip’s L2 trigger.• We read the L1 data buffers to a FPGA/ASIC. We will parse our
data blocks from ALTRO data buffers
Two overlapping TPC data block
ALTRO 512 words buffers
TPC data block PHENIX L1 Two PHENIX L1
Use of ALTRO Chip in PHENIX
C-Y. Chi
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Implementation Plan
Construction (2 years)
• Detector: $250K• Gas System: $250 K• Detector mounted electronics: $4.0M (80K Readout Channels @ $50/ch)• Other readout electronics: $500K
Total: $5.0 M
FY 2003
FY 2004
FY 2005
FY 2006
FY 2007
FY 2008
HBD TPC
R&D
Operation
Construction
R&D
Construction
Operation
R&D (3 years)
Total: $1.4M
(LDRD for $100K in FY 2001 & FY 2002)