Muon Detector Jiawen ZHANG

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Muon Detector Jiawen ZHANG

• Introduction
• The Detector Choices
• Simulation
• The structure and detector design
• The Expected performance
• Schedule

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BESII m detector

• Worked for 12 years
• Leakage problem
• Large size (56cm )
• Signal too slow
• Signal drift time is about 0 700ns, and the
  trigger signal delay is about 2.4ms
• Solid angle (63 )

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BESIII m Detector

• The m detector is the outmost subsystem of the
  BESIII detector. It includes detectors and hadron
  absorbers. Its main function is to identify
  muons from pions and other hadrons in the
  momentum range of 0.41.5GeV/c and to provide the
  solenoid flux return

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The Detector Choices

• Two possible kinds of detectors
• The Plastic Streamer Tubes (PST)
• The Resistive plate counters (RPC)
• RPC and PST are very similar, such as
  graphite painting, induced strips, gas mixture
  etc.

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The Resistive plate counters (RPC)

• Advantages
• Small dead region
• Fast response
• Lower cost
• No poisonous material in case of fire
• Shortcoming
• Very high voltage (8000V), easy to produce sparks
• No experience

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The Plastic Streamer Tubes (PST)

• Larger signal pulse, good signal noise ratio
• Taking ALEPH m detector as an example
• Typical strip signals around 6 mV (at BESIII m
  detector, the strips are shorter than ALEPH, so
  the signal maybe larger than 6 mV )
• Rise time 10 ns and width at the base 100ns
• Have a rather long plateau
• Stable operation , ALEPH has stop working,
  however the PST still works very stably
• More experience
• At IHEP, Beijing, some people ever made many
  PSTs for ALEPH

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Simulation

• Careful simulation studies were made for
  initial designing and optimizing
• Geant 3.21
• Condition
• 13 radiation lengths BGO,
• all of the other inner detectors equal to 6cm Fe
  plate

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m detection efficiency and p contamination
Increase the position pricisoin, considering
the p interaction with Fe which can produce
second class of particles, and, in turn, produce
more than one hit, the p contamination can be
reduced in the low momenta
Efficiency
Radial thickness of Fe (cm)
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m hits position distribution
Hits position s
The sigma of the hit position distribution of
moun will be about 4 to 8cm after mouns multiple
scatters in the absorber Fe. In this case,
improving the position distinguish will not help
the separation of moun and pion well but
increasing the electronic channels and cost.
Radial thickness of Fe (cm)
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The structure and detector design

• Requirements
• l High detection efficiency for muons.
• l Large solid angle coverage.
• l Wide momentum range (the minimum momentum
  400MeV).
• l High rejecting factor for other charged
  particles.
• l Suitable position precision.

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Structure of PST

• Similar to ALEPHs
• Each cell has an inner dimension of 0.90.9cm2,
  The internal surface of comb is painted with
  graphite .
• consists of plastic (PVC) comb profile having 9
  cells each
• Wires diameter 100 mm
• Strips on the two side of the streamer tubes
  (xstrips and ystrips) or one view only

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General structure

• Sandwiched structure with Fe as absorber material
  and PST
• The barrel counters are subdivided into 8
  sectors, and 12 layers
• inner radius is 1.5m and outer radius is about
  2.5m
• Length 3.6m
• 11 layers Fe 2, 2, 2, 3, 3, 4, 4, 6, 6, 8 and
  10cm (Total thickness 50cm)

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End cap m counter

• Each end cap m counter is divided 4 pieces
• Each end, the 4 pieces are separated to two
  parts and supported at left and right and each
  part has its own railway for moving
• 12 layers of PSTs

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Gas select

• ALEPH (12.5Ar 56.5 CO2 30 C4H10)
• Expensive and inflammable
• long plateau
• BESII ESC (40Ar 60CO2)
• cheap and safe
• short plateau
• Need some RD

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The Expected performance

• 0.4GeV/c may be the low momentum limit to
  identify m
• cos q 0.90
• efficiency gt95

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m detection efficiency and contamination from p
versus momentum
m Efficiency
Good m/p separation can be obtained with
momenta greater then 0.6GeV/c. With momenta
less then 0.5GeV/c, the separation becomes worse.
And with momenta less then 0.4GeV/c, the m
efficiency is rather lower. So 0.4GeV/c may be a
low momentum limit to identify m.
p contamination
Momentum GeV
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Read out channels

• Strips on the two side of the streamer tubes
  (xstrips and ystrips). Strips wide 3cm
• Barrel 1208125581211520528016800
• End cap 822421215744
• Total 1680015744 32500
• One side view only
• Barrel 558125280
• End cap 8224127872
• Total 52807872 13100
• Outer layers use wide strips, can reduce some
  channels

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Schedule

• 2001,Oct.2003,MayRD, Design and Lab.
  construction.
• 2003,Jun.2005,Oct.Chamber production and test.
• 2005,Nov.2006,MayInstallation.