gem r&d for tpc readout - university of victoriakarlen/talks/tpc/bnl01.pdf14 november 2001 dean...
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GEM R&D for TPC Readout
RHIC Detector WorkshopBNL, November 14, 2001
Dean KarlenCarleton University
Carleton GEM/TPC group: Bob Carnegie, Jacques Dubeau, Madhu Dixit, D.K., Hans Mes
http://www.physics.carleton.ca/~karlen/gem
14 November 2001 Dean Karlen / Carleton University 2
Outline
Brief summary of LC tracking issuesTPC readout with GEMsGEM R&D studies at Carleton
space point resolution (x-rays)tracking resolution (cosmics)
Summary
14 November 2001 Dean Karlen / Carleton University 3
LC tracking systems
Tracking requirements:good momentum resolution for high energy isolated charged particles
recoil mass resolution for dileptons in HZend-point resolution for leptonic susy decays
reconstruction of hadron jetsgood two-track separationenergy flow requires good absolute position resolution with minimal mass
15 (GeV/c) 105)/1( −−×≈∆ tp
14 November 2001 Dean Karlen / Carleton University 4
LC tracking systems
To achieve these requirements:High magnetic fields (~ 4 T)Large tracking volume3D space point measurements
less sensitive to accelerator backgrounds
European and US baselineLC detector designs include alarge Time Projection Chamber
14 November 2001 Dean Karlen / Carleton University 5
TPC tracker for a future LC
European design:
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LC TPC R&D underway
International collaboration formed:Aachen, Carleton, CERN, DESY, Hamburg, Karlsruhe, Krakow, LBNL, Orsay, Saclay, MIT, NIKHEF, Novosibirsk, MPI Munich, RostockSeveral issues:
gas choicereadout technology (emphasis of R&D):
Gas Electron Multiplier (GEM)Micromesh Gaseous Structure (micromegas)conventional pads or siliconconventional wire chamber
pad geometryelectronics
goal: complete R&D and prototype: 2-3 years
see: DESY-PRC R&D 01/03October 4, 2001
14 November 2001 Dean Karlen / Carleton University 7
Outline
Brief summary of LC tracking issuesTPC readout with GEMsGEM R&D studies at Carleton
space point resolution (x-rays)tracking resolution (cosmics)
Summary
14 November 2001 Dean Karlen / Carleton University 8
Gas Electron Multiplier (GEM)
Edrift = 0.2 – 1.0 kV/cm
∆V ≅ 400 V
∆V ≅ 400 V
Etransfer ≅ 3 kV/cm
Einduction ≅ 3.5 kV/cm
Readout pads
14 November 2001 Dean Karlen / Carleton University 9
Using a GEM for TPC readout
Conventional TPCreadout
GEM TPCreadout
Induced signals (motion of positive ions) spread over large area.
Direct signals (electrons on pads) spread over smaller area. Induced signals (e- motion) also present.
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Potential advantages for GEM readout
Improved space point resolutionE×B and track angle systematics suppressed
Improved two particle separation powerr -φ : signals distributed over smaller areaz : faster pulses (ve > vion)
Natural ion feedback suppressionno gating required (non-triggered expt.)
Less mass in TPC endcapno wires held under tension
present focus
14 November 2001 Dean Karlen / Carleton University 11
Outline
Brief summary of LC tracking issuesTPC readout with GEMsGEM R&D studies at Carleton
space point resolution (x-rays)tracking resolution (cosmics)
Summary
14 November 2001 Dean Karlen / Carleton University 12
Point resolution studies at Carleton
x-ray tube
2D micrometerstage
pin holeGEM cell
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GEM foils and pads for this study
fabricated at the CERN PCB workshop
GEM foil
140 µm
50 µm
GEM pads
2.5 mm pitchhexagons
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Details
x-ray mean energy: 4.5 keVpinhole diameter: ~50 µmGas: Ar CO2 (~90:10) / P10 : Ar CH4 (90:10)pre-amps:
fast Lecroy HQV 810 with Ar CO2
slower ALEPH TPC pre-amp with P10
readout:two 4-channel digital scopes (9 bit ADC)
500 MHz sampling for HQV 810125 MHz sampling for ALEPH preamps
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An event
1
2
3
4 6
7
8
-0.2
-0.15
-0.1
-0.05
0
0 0.02 0.04 0.06 0.08 0.1x 10 -5
-0.2
-0.1
0
0 0.02 0.04 0.06 0.08 0.1x 10 -5
-0.02
-0.01
0
0 0.02 0.04 0.06 0.08 0.1 x 10-5
-0.015
-0.01
-0.005
0
0 0.02 0.04 0.06 0.08 0.1x 10
-5 -0.015
-0.01
-0.005
0
0 0.02 0.04 0.06 0.08 0.1x 10 -5
-0.02
-0.01
0
0 0.02 0.04 0.06 0.08 0.1x 10 -5
-0.1
-0.075
-0.05
-0.025
0
0 0.02 0.04 0.06 0.08 0.1x 10 -5
Ar CO2 (90:10)HQV810 preamps
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Localization from charge sharing
1
2 8
-0.2
-0.15
-0.1
-0.05
0
0 0.02 0.04 0.06 0.08 0.1x 10
-5
-0.2
-0.1
0
0 0.02 0.04 0.06 0.08 0.1x 10-5
-0.1
-0.075
-0.05
-0.025
0
0 0.02 0.04 0.06 0.08 0.1x 10
-5
x
y
v
PAD 2 PAD 8
PAD 10.6
0.8
1
1.2
1.4
1.6
1.8
2
2.2
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8
10
10
20
20
30
30
40
40
50
50
60
60
70
70
80
80
90
90Pad 1 fraction
Pad 8 fraction
x coordinate (mm)
y co
ordi
nate
(mm
)
2D Gaussian model
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Charge sharing result – P10
(x,y)col = (0.4,1.243) mm y = 1.265 mmσy = 0.064 mm
x = 0.408 mmσx = 0.066 mm
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Scan over entire pad
100 µm circles centred at pin hole locations during scan
With P10 gas:cloud size 550 µmx,y standard deviations: ~70 µm
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Localization from charge sharing
Method works only in regions where significant charge is deposited on 3 pads
P10Ar CO2
Chargesharingregions
Chargesharingregion
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Localization from induced signals
3
4 6
7
-0.02
-0.01
0
0 0.02 0.04 0.06 0.08 0.1 x 10-5
-0.015
-0.01
-0.005
0
0 0.02 0.04 0.06 0.08 0.1x 10
-5
-0.015
-0.01
-0.005
0
0 0.02 0.04 0.06 0.08 0.1x 10
-5
-0.02
-0.01
0
0 0.02 0.04 0.06 0.08 0.1x 10 -5
1.75
2
2.25
2.5
2.75
3
3.25
3.5
3.75
4
0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1 0.11dist
ance
fro
m p
ad c
entr
e (m
m)
-3
-2
-1
0
1
2
3
-3 -2 -1 0 1 2 3
-5
-
-
rel. signal amplitude
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Scan over entire pad
With P10 gas:x,y standard deviations: ~80 µmnote: systematics in x clearly seen
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Strip geometry – charge sharing
strip 1
frac
tion
of c
harg
e co
llect
ed b
y st
rip 1
With P10 gas:x standard deviation: ~70 µm
strip 1 strip 2
Gaussian model
Linear model
x
strip 2
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Strip geometry – induced signals
2
2.5
3
3.5
4
4.5
5
5.5
6
0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
dist
ance
fro
m s
trip
cen
tre
Strip geometry has larger induced signals by factor of 2 – 3
x standard deviation: ~70 µm
strips
pads
rel. signal amplitude
14 November 2001 Dean Karlen / Carleton University 24
Outline
Brief summary of LC tracking issuesTPC readout with GEMsGEM R&D studies at Carleton
space point resolution (x-rays)tracking resolution (cosmics)
Summary
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Tracking studies
Mini-TPC constructed
15 c
m
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Tracking studies
Cosmic ray telescope Readout pad layout
5 m
m
2.5 mm
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Details – cosmic data taking
Gas: Ar CH4 (90:10)Drift field: 135 V/cmpre-amps: ALEPH TPC pre-ampreadout: 32 channel custom FADC
200 MHz sampling8 bit
trigger rates:cosmic telescope: 0.4 Hzrequire at least one pad hit: 0.04 Hz
Data:6 days of running (end of October, 2001)
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First event
BOTTOMTOP
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Gain stability
Charge per row Charge vs time
Stable within 5%
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Tracking studies
Fit x-y and y-z separately
y-z fit:for each row form weighted average of pulse arrival timeperform unweighted linear fit of the 5 rowy-coordinates vs row timespulse arrival time (50% rise) dependant on pulse amplitude
needs further study
14 November 2001 Dean Karlen / Carleton University 31
y-z fit results
Not diffusion limitedpulse arrival time definition needs improving
800 micron resolution independent of drift length
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x-y fit
use model of uniform line of charge, with Gaussian transverse spread, σ
charge fractions given by integral over pad
fit uses observed charge fractions within each row
min χ2 with x0, φ and σ free
ionization fluctuationsnot included in modelunimportant for φ = 0leads to track angle effect on resolution
14 November 2001 Dean Karlen / Carleton University 33
Transverse width of line charge
Results from fit of data: diffusion apparent
σ(m
m)
σ2(m
m2 )
drift time (ns) drift time (ns)
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Track x0 resolution
x0 resolution from single row:
do fit excluding the row: x0, φ, σfreedo fit for single row: only x0freecompare 1 row x0 to 4 row x0
σx = 220 ± 20 µm σx = 320 ± 10 µm
σx = 420 ± 8 µm σx = 560 ± 8 µm
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Centroid finding
Linear weighted x0 coordinate less accurate
linear weightingGaussian modelσx = 220 ± 20 µm σx = 290 ± 20 µm
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Track angle effect
Appears to be significant, but small statistics
σx = 110 ± 15 µm σx = 280 ± 50 µm
05.0<φ 15.005.0 <φ<mm 10<z mm 10<z
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Sample events (z < 10 mm, |φ| < 0.05)
14 November 2001 Dean Karlen / Carleton University 38
Sample events (z < 10 mm, |φ| < 0.05)
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Sample events (z < 10 mm, |φ| < 0.05)
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Sample events (z < 10 mm, |φ| < 0.05)
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Sample events (z < 10 mm, |φ| < 0.05)
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Sample events (z < 10 mm, |φ| < 0.05)
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Future plans for Carleton studies
Continue cosmic tracking studiesalternative gases (lower diffusion)include calibration constants (none so far!)alternative readout pad geometriesQ: can direct charge signals alone provide optimal resolution and two particle separation?Q: are the small induced signals helpful?
Try new ideas for spreading signal over more pads
resistive layer above pads that absorbs charge and leave only induced signals
14 November 2001 Dean Karlen / Carleton University 44
Summary
TPC is the leading candidate for a future linear collider
Coordinated international effort for R&D for a LC TPCemphasis is on new readout methods involving micro-pattern gas detectors
Findings from Carleton GEM/TPC R&D:Good space point resolution and tracking resolution achieved with relatively large pads
pad diameter ~ 4 x transverse diffusion is ok
GEM readout for TPCs looks promising