Micromegas TPC Beam Test Result

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Micromegas TPC Beam Test Result

• H.Kuroiwa (Hiroshima Univ.)
• Collaboration with
• Saclay, Orsay, Carlton, MPI, DESY, MSU, KEK,
  Tsukuba U, TUAT, Kogakuin U, Kinki U, Saga U

Motivation Micromegas TPC Setup Preliminary
Results Summary
The 8th ACFA Workshop on Physics and Detector at
the Linear Collider Jul. 12, 2005, EXCO, Daegu,
Korea
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Motivation

• Comparison of several sensors using same Field
  Cage, Electronics, analysis
• MWPC Beam test in Jun, 2004
• GEM Beam test in Apr, 2005
• Micromegas

Previous talk
Beam test in Jun. 22Jul. 1, 2005 We try to
understand Micromegas TPC performance
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Micromegas
50µm

• Micromesh supported by 50-100µm - high insulating
  pillars
• Multiplication takes place between the anode and
  the mesh
• One stage
• Direct detection of avalanche electrons
• Small EB effect
• Fast signals
• Self-suppression of positive ion feedback
• the ions return to the grid
• Better spatial resolution
• No wire angular effect

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TPC

• Length of FC 26 cm
• Pad
• 26 mm, 0.3mm gap
• 32 pads12 pad rows
• ? 384 readout channels
• Non-staggered
• Pad plane 1010cm
• Readout
• ALEPH TPC electronics
• 24 amplifiers, 16 channels each
• 500ns shaping time, charge sensitive
• sampled every 80 ns
• digitized by 6 TPDs

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Mesh Signals

• There is a 55Fe source attached on the back of
  the cathode plane to monitor Micromegas stability
  by looking at mesh signals
• (Readout by a multi channel analyzer MCA 8000
  from Amptek)

Ar 5isobutane
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Experimental Setup

• KEK-PS p2 beam line
• 4GeV p-
• Super conducting magnet (JACEE)
• B 0, 0.5 and 1T
• Gas
• Ar isobutane (955) vd 4.18cm/µsec at
  220V/cm

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Preliminary Results

• Charge Distribution
• Pad Response
• X Resolution
• Z Resolution

• Analysis
• Double fit (developed at DESY)

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Charge Distribution
charge distribution at Row6 as a function of Z

• Charge distribution (B 1T)
• For 12 rows

Edge effect
Edge effect
We saw no significant attenuation
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Pad Response Function

• is evaluated by a normalized charge (NQi Qi/?Q)
  on pad i, as a function of (Xpad - Xtrack)

Charge width for different drift regions (B 0T)
anode
Z ?
cathode
Distribution becomes wider at longer drift
distance
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Width of PRF as a function of Z
B 0T
Preliminary results
B 0.5T
B 1T
Measured CD in good agreement with Mag. Simulation
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X Resolution as a function of Z
Row6 Row7 Cd Cd(PRF)
Cd fixed for each B
Preliminary results
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X Resolution (How to Fit?)
s0 resolution w/o diffusionCd diffusion
constant Neff effective number of electrons
Diffusion
Other
1- fix Cd from PRF 2- fit sx f(z) with s0 and
Neff free 3- Plot Magboltz curve with s0
obtained from the fit (2)Cd is known
Neff from (2)
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Z Resolution as a function of Z
B 0T
Preliminary results
B 0.5T

• sz ? 500µm at 0.5T

B 1T
Unlike sX, sZ has no significant B-dependence
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Summary

• To measure Micromegas TPC performance
• We did the beam test at KEK-PS p2 beam line using
  4GeV neg. pions in magnetic field
• Micromegas in TPC worked stably
• Measured diffusion constants are consistent
  with Mag. simulation
• sx ? 200µm , sz ? 800µm at 1T
• But these results are still very preliminary