Linear Collider TPC R&D in Canada Madhu Dixit Carleton University

Linear Collider TPC R&D in Canada

Madhu Dixit

Carleton University

Stanford 25/9/2003 M. Dixit




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)





TPC read out with a Gas Electron Multiplier (GEM*)

How to find charge centroid in a GEM? – Zigzag shape makes chevrons share charge between pads to

facilitate centroid finding– Optimize readout geometry and diffusion to do the best with

rectangular pads– Where is the induced signal on the neighboring pads?

* F. Sauli, NIM A386,531 (1997)•GEM spatial resolution ~ 40 µm

with 200 µm pitch anodes•Impractical for a TPC•TPC pad widths ~ mm•All charge on a single pad for a TPC in high B field•Difficult centroid finding•Resolution ~ Pad width/√12


MPGD-TPC R&D in Canada - Goals• New ideas to get good space-point resolution from ~ mm wide pads

– Studies with a GEM & Micromegas test cells using collimated x-rays

• Limits to achievable resolution by with conventional techniques by optimizing geometry and gas diffusion– 15 cm drift TPC with GEM readout– Operating parameters– Cosmic ray tracking studies

• Assess the performance of MPGD-TPC in a test beam and in a high magnetic field

(r-) ~ 70 µm within reach with R&D,





Pads centroid from induced signals in a GEM

GEM Proportional wire

Cathode padsAnode pads

• Short ~ 200 ns signal•Wire/pad readout electronics won’t work!•Need fast high frequency pulse shape sampling electronics



Resistive anode GEM test cell setup





Outlook & summary

• Consensus for a 500 GeV e+ e- linear collider within this decade - proposals in Europe & in the US & Japan

• A micro-pattern detector (MPGD) readout TPC is being be developed for the LC detector with resolution and 2 track resolving power approaching diffusion limits

• Better MPGD-TPC resolution has a significant impact on the design of the LC detector design and its physics reach

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Linear Collider TPC R&D in Canada Madhu Dixit Carleton University