Forward Muon System for the D0 Experiment

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Forward Muon System for the D0 Experiment
D0 Note 4061 November 2002

• Presented by Dmitri Denisov
• Fermilab
• For the D0 Collaboration

644 members 73 institutions 18 countries
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Fermilab Tevatron Upgrade

• Tevatron Run 1 (1992-1996) produced reach harvest
  of interesting physics results, including top
  quark discovery
• In order to continue studies at the energy
  frontier Tevatron underwent serious upgrade in
  1997-2001
• factor of 10 higher luminosity
• factor of 10 smaller bunch spacing
• Physics goals for Tevatron Run 2
• precision studies of weak bosons, top, QCD,
  B-physics
• searches for Higgs, supersymmetry, extra
  dimensions, other new phenomena

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Challenges for the Tevatron Run 2 Detectors

• In order to fully exploit Tevatron capabilities
  in Run 2 D0 detector has been substantially
  upgraded
• smaller bunch crossing of 132ns (vs 3.1ms)
  required replacement of electronics as well as
  some of the slow detectors
• higher luminosity provides higher radiation
  fluxes and requires more radiation hard detectors
• higher event rate requires better trigger systems
  in order to select only 10-5 of the interactions
  which can be written to tapes
• new detectors have been added in order to improve
  detection of displaced vertices and provide
  momentum measurement in the central region
• Forward muon system of the D0 detector covers
  rapidity region between 1.0 and 2.0 and has been
  fully redesigned for Run 2
• separated functions of muon tracking and trigger
  detectors
• fast detectors with internal resolution time
  below 60ns
• radiation hard detectors
• detectors capable of operating in the magnetic
  field of the muon toroid and central solenoid
• time and coordinate resolution provide efficient
  muon detection and backgrounds suppression

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D0 Detector for Run II
Forward MDT Layers C B A
Pixel Counter Layers A B C
PDT Chambers C B A
Outer Counters
A-? Counters
Shielding
Shielding
Preshower
Silicon Tracker
New 2T Solenoid
Fiber Tracker
Electronics
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Forward Muon System

• Forward muon system consists of the following
  major elements
• shielding around Tevatron beam pipe
• provides factor of 100 reduction in backgrounds
• trigger system based on 3 layers of scintillation
  trigger counters
• 4608 scintillation counters with 1ns time
  resolution
• tracking system based on 3 layers of mini-drift
  tubes
• 50,000 wires assembled in 8 wires extrusion
  assemblies
• maximum drift time is 60ns
• coordinate resolution is 0.7mm

Forward scintillation counters
Shielding
Mini-drift tubes
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Shielding

• There are two major sources of backgrounds(non-muo
  n) hits in muon detectors at hadron colliders
• background particles coming from the accelerator
  tunnel
• background particles originated in interactions
  of p-pbar collision products propagating at
  small angles with accelerator and detector
  equipment
• Both of these backgrounds can be substantially
  reduced by placing shielding around beam pipe
• consists of 3 layers
• 50 cm of steel - absorb hadrons and e/gamma
• 12 cm of polyethylene - absorb neutrons
• 5 cm of lead - absorb gamma rays
• calculations based on GEANT/MARS codes
  demonstrate reduction in particle fluxes for
  shielded/unshielded detectors by a factor of
  50-100
• Run 1 muon detector occupancies have been in the
  5-10 level
• Run 2 muon detector occupancies are in the
  0.05-0.1 level in good agreement with
  calculations
• use of detectors less sensitive to backgrounds
  (high time resolution, small sensitive volume,
  etc.) provides advantages as well

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Shielding

• Effect of the shielding on background fluxes
• factor of 50-100 reduction

Hadron
e/gamma
Without Shielding
With Shielding
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Trigger Scintillation Counters

• 3 planes of 10x10m2 on both sides of the
  interaction region
• Counters arranged in R-f geometry matching
  central fiber tracker trigger
• Total number of counters 4608
• Major specifications
• fine segmentation
• time resolution of 1ns to separate tracks coming
  from interaction region from cosmic and
  accelerator tunnel
• low radiation aging
• operation in magnetic field up to 350Gs
• Simple and reliable design has been developed
• based on 12mm thick Bicron 404A scintillator
• light collection is performed using WLS bars
• fast 25mm diameter phototubes are used for light
  collection

10x10m2 plane of counters assembled in fish
scale design in the collision hall
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Trigger Scintillation Counters

• Cut to shape 404A scintillator with two Kumarin
  WLS bars attached
• collect light on the 25mm photocathode of 115M
  (MELZ)
• phototube
• Tyvek wrapping is used for better light
  collection
• Counters sizes are from 10x10cm2 to 1x1m2
• Average number of phe for large counters is 60
• Time resolution is 0.5-1ns depending on counter
  size
• limited by photoelectron statistics and amplitude
  fluctuations
• (single threshold discriminator)
• Amplitude response uniformity is 10

Counter Design
Radiation aging for 15fb-1 integrated
luminosity (Run II Tevatron goal) Pair
Kumarin(WLS)404A(Scintillator) demonstrates 10
light loss for 20krad irradiation. We expect
doses for the hottest regions to be well below
1krad (15fb-1) Phototube 115M losses 10 of
gain for anode accumulated charge of 100C
(15fb-1). This could be easily compensated by HV
adjustment
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Magnetic Shielding

• Magnetic shielding is provided with
• 1.2mm thick mu-metal
• 3mm or 6mm tick soft iron shield
• transverse to tube axis field has no effect up to
  700Gs
• field parallel to the tube affects phototubes
• 3mm iron shield (closed circles) 10 gain loss
  at 250Gs
• used in layers outside muon toroid
• 6mm iron shield (open circles) 10 gain loss at
  350Gs
• used in layer inside muon toroid
• LED tests with/without field
• less then 1-2 effect for all 4608 tubes

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Counters Performance During Data Taking

• During collider data collection performance of
  all counters is monitored
• efficiency of individual planes and counters
  based on reconstructed muon tracks
• stable above 99
• gain of all phototubes with respect to reference
  calibration set using LED system
• peak position stable within 2 over one year of
  operation
• typical variations in the gain do not exceed 5
• timing characteristics
• peak of LED pulse is stable within 0.5ns over a
  year of operation
• peak and width of the timing spectra for muon
  tracks
• Total number of dead counters after 1 year of
  operation is 5 (0.1)

1 year LED timing stability
Timing peak for muon tracks
s0.5ns
s1.8ns
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Forward Muon Tracking Detector

• Forward muon tracking detector is based on
  mini-drift tubes
• 1x1cm2 drift cell
• 8 cell aluminum extrusion comb with 0.7mm thick
  walls (to reduce dead zones)
• stainless steel cover and PVC sleeve provides
  electrical field configuration and gas tight
  volume

• Tubes length vary between 1m and 6m
• 50mm gold plated tungsten wire is supported every
  meter
• Total number of wires in the system is 50,000
• Tubes are assembled into 8 octants per layer with
  wires parallel to magnetic field lines
• There are 4 planes of wires in layer before
  toroid and 3 planes of wires in each of two
  layers after toroid
• muon has 10 hits on track average

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Working Gas for Mini-drift Tubes

• We are using CF4(90)CH4(10) gas mixture
• non-flammable
• very fast
• re-circulation with small losses (5) reduces
  gas cost
• no radiation aging
• wide 100 efficiency mip platou
• 2.9kV-3.4kV
• Time-to-distance dependence has been measured and
  simulated
• maximum drift time for tracks perpendicular to
  the plane is 40ns
• maximum dirft time for 45 degree tracks is 60ns
• Coordinate resolution of the mini-drift tube
  system is defined by electronics
• TDC bin is 19ns (cost driven)
• s0.7mm
• starts affect muon system only coordinate
  resolution for muon momentum above 50GeV/c

Accumulated charge for 15fb-1 is estimated at
30mC/cm Aging test with Sr90 r/a source
demonstrates no aging effects up to 2C/cm With
large safety factor mini-drift tubes radiation
aging is not an issue
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Mini-drift Tubes Performance

• During data collection many parameters of the
  mini-drift tubes are monitored
• gas flow
• 32 tubes are connected in serial with
  input/output flow monitoring
• high voltage values and currents
• all 50,000 wires operates at the same high
  voltage of 3.25kV
• individual planes efficiency using reconstructed
  muon segments
• typical efficiency is in the range above 99
• plane coordinate accuracy using reconstructed
  segments
• Reliability
• total number of disabled wires
• 0.3 after commissioning
• dead or noisy
• increase in number of disabled wires is less then
  0.1 per year of operation

RMS0.7mm
Coordinate resolution of mini-drift tube
plane based on local segment reconstruction
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Forward Muon System Performance

• Low occupancy of the forward muon detectors due
  to well designed shielding and use of fast
  detectors proved to be very low
• at the 0.05-0.1 level
• simple and reliable muon triggering
• after Level 1 trigger (scintillation counters
  only) 50 of events have good muon reconstructed
  off-line
• after Level 2 trigger (mini-drift tubes and
  scintillation counters) 80 of events have good
  track reconstructed off-line
• writing to tapes background free samples
• simple and background free muon off-line
  reconstruction
• High reliability of forward muon detectors
  provided above 99 up-time during physics data
  collection
• Based on efficient muon hits detection,
  triggering, and reconstruction D0 forward muon
  system is providing data for wide spectrum of
  physics studies at the energy frontier at the
  Tevatron
• Some important issues like alignment,
  electronics, triggering, reconstruction are not
  addressed due to limited talk time

Single Muon Event
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Summary D0 Forward Muon System

• D0 experiment developed and constructed
  multi-layer steelpolylead shielding which
  reduced background fluxes on the muon detectors
  by a factor of 50-100
• reduction in detectors aging, trigger rates, fake
  tracks
• Separation of triggering and tracking
  capabilities in the D0 forward muon system
  provides background free muon samples to be
  written to tapes
• Forward muon trigger system based on 4608
  scintillation counters
• simple and reliable counter design for counters
  from 10x10cm2 to 1x1m2
• time resolution of 1ns
• provides above 60 phe per mip
• radiation hard to well above 100kRad
• phototube magnetic shield provides reliable
  operation up to 350Gs
• Forward muon tracking system
• 50,000 wires of mini-drift tubes with 1x1cm2
  drift cells and length up to 6m
• modular extrusion based tube design
• CF4(90)CH4(10) gas mixture
• fast, 60ns max drift time
• non-flammable
• radiation hard above 2C/cm
• wide HV operating plateau of 0.5kV
• All system elements reached or exceeded Run II
  specifications and operate smoothly during over a
  year of data taking