Linear Collider TPC R&D in Canada Bob Carnegie, Madhu Dixit , Dean Karlen, Steve Kennedy, Jean- Pierre Martin, Hans Mes, Ernie Neuheimer, Alasdair Rankin, & Kirsten Sachs Carleton University, University of Montreal, TRIUMF, & University of Victoria ECFA/DESY Prague - November 16, 2002
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Linear Collider TPC R&D in Canada Bob Carnegie, Madhu Dixit, Dean Karlen, Steve Kennedy, Jean-Pierre Martin, Hans Mes, Ernie Neuheimer, Alasdair Rankin,
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Linear Collider TPC R&D in Canada
Bob Carnegie, Madhu Dixit, Dean Karlen, Steve Kennedy, Jean-Pierre
Martin, Hans Mes, Ernie Neuheimer, Alasdair Rankin, & Kirsten Sachs
Carleton University, University of Montreal, TRIUMF, & University of Victoria
ECFA/DESY Prague - November 16, 2002
•16/11/02 •M. Dixit •2
AbstractIn an ideal TPC, the limit to achievable spatial resolution comes only from diffusion. The traditional wire/pad TPC fails to meet this goal due to large ExB and track angle effects. While not hampered by such systematics, an MPGD readout TPC will achieve the ultimate diffusion limit of resolution if only the electron avalanche position could be accurately measured. We describe below our recent work on: i) measuring the limits to achievable GEM-TPC spatial resolution from gas diffusion by optimizing readout geometry; & ii) GEM test cell results on the possibility of improving position sensing in an MPGD from charge dispersion of avalanche charge on a resistive anode.
•16/11/02 •M. Dixit •3
ExB cancels track angle effect
TPC wire/pad readout
100 µm
•Average Aleph resolution ~ 150 µm•About 100 µm best for all drift distances• Limit from diffusion (10 cm drift) ~ 15 µm; (2 m drift) ~ 60 µm•100 µm limit for all drift distances comes from wide pad response
ExB & track angle systematics in a TPC(Aleph TPC example)
•16/11/02 •M. Dixit •4
An MPGD Readout TPC for the LC
• ExB and track angle systematic effects cannot be avoided in a wire/pad TPC
• Even when systematics cancel, the resolution is determined by the width of the pad response function (PRF) & not by physics of diffusion
• Large (PRF) further limits the TPC 2 track resolving power
• Positive ion space-charge effects - additional complication• A micro-pattern gas detector ( MPGD* ) readout TPC has
- Negligible ExB (no preferred angles in an MPGD)- Natural suppression of positive ion space charge effects- Resolution and 2-track resolving power approaching diffusion limit
Such as Gas Electron Multiplier (GEM), Micromegas
•16/11/02 •M. Dixit •5
MPGD-TPC R&D in Canada
• Study of limits to achievable diffusion limited resolution by optimizing readout geometry– 15 cm drift TPC with GEM readout– Cosmic ray tracking studies
• The possibility of improving position sensing from charge dispersion in an MPGD with a resistive anode – GEM test cell results using collimated x-rays
•16/11/02 •M. Dixit •6
GEM-TPC studies
15 cm max. drift distanceGases: Ar CO2 ; P10TPC wire preamplifiers salvaged from Aleph64 channels of 200 MHz FADCs built by U of Montreal
New readout pad layouts:•Trigger & veto + 174 pads with 3 fold multiplexingTracking study:• diffusion effects• pad width effects on resolution •track angle effect
•16/11/02 •M. Dixit •7
Cosmic ray test GEM-TPC
•16/11/02 •M. Dixit •8
New TPC pad layout for increased acceptance
amplitudes color coded:
2 trigger + 4 veto
Resolution study for central 2 & 3 mm wide pad rows
100 80 60 40 25 15
Track fit 3 top + 3 bottom 2.5 mm wide pad rows 3-fold multiplexed
•Measure signal amplitudes for remaining 500 events
•Compute 3 pad centre of gravity for each event
•Correct for bias in CG determination
•16/11/02 •M. Dixit •23
Polynomial fits define pulse shapes
Use 500 events to define standardized pulse shapes for early charge pulse (left), and delayed charge dispersion pulse (right)
•16/11/02 •M. Dixit •24
Bias correction to centre of gravity
•16/11/02 •M. Dixit •25
Resolution near a strip edge
= 78 µm
•16/11/02 •M. Dixit •26
Resolution near the centre of a strip
= 61 µm
•16/11/02 •M. Dixit •27
Resolution between edge & centre
= 67 µm
•16/11/02 •M. Dixit •28
Resolution scan - summary
Spatial resolution
Position residuals
X-ray spot position (mm)
•16/11/02 •M. Dixit •29
Outlook & summary• Diffusion limited resolution ~ 140 µm in GEM readout
TPC with 2mm wide pads (charge cloud width ~ 700 µm) for short distances
• Promising preliminary results for localization from charge dispersion – further tests with GEM test cell planned– Optimize parameters– Incorporate in the mini-TPC readout