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Particle Detectors for Colliders Ionization & Tracking Detectors
Robert S. Orr University of Toronto
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R.S. Orr 2009 TRIUMF Summer Institute
Generic Detector Layers of Detector Systems around Collision Point R.S. Orr 2009 TRIUMF Summer Institute
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Tracking Detectors Observe particle trajectories in space with as little disturbance as possible use a thin ( ) detector Scintillators Scintillating fibres Gas trackers Solid state trackers Gas Based Detectors Multiwire proportional chamber Drift Chamber Time projection chamber Gas microstrip GEM (gas electron multiplier)
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R.S. Orr 2009 TRIUMF Summer Institute
Generic Detector R.S. Orr 2009 TRIUMF Summer Institute small – amplification?
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R.S. Orr 2009 TRIUMF Summer Institute
Multiwire Proportional Chamber wire spacing = resolution cathode anode wires cathode Drift Chamber – measure arrival time of charge = spatial resolution R.S. Orr 2009 TRIUMF Summer Institute
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R.S. Orr 2009 TRIUMF Summer Institute
Schematic of Wire Chamber Cell anode wire field shaping cathode wire mesh pc board collects signal envelope to contain gas gas should not absorb electrons Repeat “n” times R.S. Orr 2009 TRIUMF Summer Institute
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R.S. Orr 2009 TRIUMF Summer Institute
3 stages in signal generation 1) Ionization by track passing through cell 2) Ionization drifts in E field time 3) In high E field region near wire, primary ionization electrons gain enough energy to start ionizing the gas Avalanche More charges Charge amplification Noise free amplifier microvolt signal if no amplification R.S. Orr 2009 TRIUMF Summer Institute
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R.S. Orr 2009 TRIUMF Summer Institute
Gas Amplification R.S. Orr 2009 TRIUMF Summer Institute
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R.S. Orr 2009 TRIUMF Summer Institute
Behaviour as Voltage Increased Collection – Recombination dominated All charge collected Amplification by gas multiplication Still proportional – particle ident Saturation Breakdown – Geiger/Mueller Volts R.S. Orr 2009 TRIUMF Summer Institute
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R.S. Orr 2009 TRIUMF Summer Institute
Diffusion Ions & electrons diffuse in space E field determines average direction Collisions limit velocity Maximum average velocity =Drift velocity R.S. Orr 2009 TRIUMF Summer Institute
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Diffusion Ions and electrons diffuse under influence of electric field
Maxwell velocity distribution From Kinetic theory , after t, linear distribution due to diffusion number of particles Diffusion coefficient 2-d RMS Spread 3-d about 1mm after 1 sec in air
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Mobility For a classical gas In argon
ion charge and mass p gas pressure ion scattering cross section In argon Electrons collected quickly compared to +ve ions drift velocity electric field
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Diffusion and Drift Chamber Accuracy
Diffusion coefficient from kinetic theory Mean free path In argon Diffusion gives limit on spatial accuracy drift chamber To reduce D Lower temperature Raise pressure (reduce mobility)
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Working Gas Argon Noble gases give multiplication at lowest electric field Polyatomic gases have non-ionization energy loss mechanisms Choose cheap noble gas with low ionization potential Krypton X Xenon X Argon OK Cheap, safe, non-reactive remove electro-negative contaminants Pure argon limited to gain Many excited ions produced during avalanche Absorb - quenchers rare, expensive absorbed on cathode cheap – welding etc returns to anode - breakdown
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Quenchers Polymerization Organic quenchers polymerize Absorb
Deposits on cathodes Absorb non-radiative high resistance ion buildup – discharge sparks, broken wires Rotational vibrational modes Poly-atomic gas e.g. Methane Add non-polymerizing agent – water methylal Typical gases Magic Gas or add electronegative gas (a bit of poison) Typical
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R.S. Orr 2009 TRIUMF Summer Institute
Gas Admixtures R.S. Orr 2009 TRIUMF Summer Institute
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R.S. Orr 2009 TRIUMF Summer Institute
Signal from Gas Counter electrostatic energy of field potential energy of q Anode Cathode charge q moved by dr potential length of counter capacitance/unit length Electrons produced in avalanche close to anode wire Small dr – small signal +ve ions drift across whole radius Large dr – large signal Typically 1% R.S. Orr 2009 TRIUMF Summer Institute
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R.S. Orr 2009 TRIUMF Summer Institute
Time Development of Signal Assume All signal comes from ions Start from a Typically get 50% of signal in T ~700ns RC differentiation for fast signal R.S. Orr 2009 TRIUMF Summer Institute
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Different Realizations of Ionization Trackers
Drift Chamber MWPC Time Projection Chamber Jet Chamber R.S. Orr 2009 TRIUMF Summer Institute
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R.S. Orr 2009 TRIUMF Summer Institute
Drift Chamber Cell potential shaping wires sense wire drift time Carefully shape potential (field lines) Optimize drift time – space relation R.S. Orr 2009 TRIUMF Summer Institute
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R.S. Orr 2009 TRIUMF Summer Institute
Left-Right Ambiguity Resolution 2 anode wires staggered anode wires ghost track inclined anode plane good for high magnetic field R.S. Orr 2009 TRIUMF Summer Institute
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R.S. Orr 2009 TRIUMF Summer Institute
Jet Chamber annihilation at 30 GeV R.S. Orr 2009 TRIUMF Summer Institute
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Lorentz Angle – Drift Chamber in Magnetic Field
mean time between collisions Drifting electron will see Electric Field Magnetic Field Will also see stochastic force due to collisions with gas molecules solution: (1) (2) (3) Assume over time stochastic retardation electron mobility acceleration constant cyclotron frequency
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Lorentz Angle – Drift Chamber in Magnetic Field
solution: (1) (2) (3) Drift velocity has three components parallel to perp to plane of If perpendicular
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R.S. Orr 2009 TRIUMF Summer Institute
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Compensate for Lorentz angle by tilting electric field in drift cells
1kV 2kV 3kV equipotential sense wires field wires next cell Compensate for Lorentz angle by tilting electric field in drift cells
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R.S. Orr 2009 TRIUMF Summer Institute
Structure of ZEUS DC 120 micron space resolution 2.5mm 2 track resolution 500 ns max drift time Total wire tension 12 tons 4608 W sense wires (30 micron) 19584 CuBe field wires R.S. Orr 2009 TRIUMF Summer Institute
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R.S. Orr 2009 TRIUMF Summer Institute
Tilted E Field – R-L ambiguity resolution real track segments reflected ghost segments R.S. Orr 2009 TRIUMF Summer Institute
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R.S. Orr 2009 TRIUMF Summer Institute
Spatial Resolution Variation in drift time – space relation Smearing Small number of primary electrons reach sense wire Statistics R.S. Orr 2009 TRIUMF Summer Institute
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R.S. Orr 2009 TRIUMF Summer Institute
Stereo Wires – 3-d Reconstruction stereo wires stereo cameras – 3-d pictures paraxial wires r,x r’,x’ R.S. Orr 2009 TRIUMF Summer Institute
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R.S. Orr 2009 TRIUMF Summer Institute
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R.S. Orr 2009 TRIUMF Summer Institute
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R.S. Orr 2009 TRIUMF Summer Institute
Layers of Detector Systems around Collision Point R.S. Orr 2009 TRIUMF Summer Institute
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R.S. Orr 2009 TRIUMF Summer Institute
Square Drift Cells - ARGUS isochrones Precision High Density of Information Pattern recognition complex R-L ambiguity resolved by trying all possible combinations R.S. Orr 2009 TRIUMF Summer Institute
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R.S. Orr 2009 TRIUMF Summer Institute
ARGUS Events R.S. Orr 2009 TRIUMF Summer Institute
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R.S. Orr 2009 TRIUMF Summer Institute
dE/dx Particle Identification R.S. Orr 2009 TRIUMF Summer Institute
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BaBar Drift Chamber constructed at TRIUMF
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Time Projection Chamber
Only two drift cells parallel to , so no Lorentz angle measure z, from drift time measure r,Φ from pads and wires on endplates Good pattern recognition and precision in medium multiplicity environment space charge limitation R.S. Orr 2009 TRIUMF Summer Institute
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pad – position on the wire
wire – drift time pad – position on the wire R.S. Orr 2009 TRIUMF Summer Institute
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Diffusion in TPC Why does diffusion not ruin resolution?
transverse diffusion Diffusion limits spatial resolution drift length mean free path mean electron velocity R.S. Orr 2009 TRIUMF Summer Institute
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R.S. Orr 2009 TRIUMF Summer Institute
Diffusion in TPC Compare this to previous plot with B=0 reduces diffusion if particles drift along tight helices transverse diffusion reduced by R.S. Orr 2009 TRIUMF Summer Institute
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R.S. Orr 2009 TRIUMF Summer Institute
ATLAS Tracker R.S. Orr 2009 TRIUMF Summer Institute
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R.S. Orr 2009 TRIUMF Summer Institute
ATLAS Straw Tracker Radiator Straws End-cap straw Straws R.S. Orr 2009 TRIUMF Summer Institute
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R.S. Orr 2009 TRIUMF Summer Institute
Straw tracker test beam module R.S. Orr 2009 TRIUMF Summer Institute
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R.S. Orr 2009 TRIUMF Summer Institute
Assembly of straw tracker R.S. Orr 2009 TRIUMF Summer Institute
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Inner Detector (ID) The Inner Detector (ID) comprises four sub-systems: Pixels ( channels) Silicon Tracker (SCT) (6 106 channels) Transition Radiation Tracker (TRT) (4 105 channels) Common ID items
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