Скачать презентацию Photo Detectors in High Energy Physics Dieter Renker
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Photo Detectors in High Energy Physics Dieter Renker D. Renker, PSI International Workshop on new photon-detectors, Kobe, 6/27/2007
Outline Various detectors will be presented that involve photo sensors. The problems will be pointed out and the realized solutions which have been found, will be described. Calorimeters: PMT, PIN diode, APD, G-APD Ring image Čerenkov detectors: Gas detector, Multi anode PMT, Hybrid PMT Time of flight measurements: PMT, MCP, G-APD Tracker: Multi anode PMT, VLPC D. Renker, PSI International Workshop on new photon-detectors, Kobe, 6/27/2007
Photomultiplier tubes in calorimeters PMTs can be made to cover large areas with up to 20 inch diameter (Super. Kamiokande). Shown here is the crystal ball with 3 inch tubes for the measurement of + 0+e++ Challenges are: • large area • low light yield (pure Cs. I) • fast response D. Renker, PSI + International Workshop on new photon-detectors, Kobe, 6/27/2007
Photomultiplier tubes in calorimeters The amplification in the dynodes of a PMT has an extremely low level of noise. Summing over a large number of coincident PMT signals is therefore possible. Shown here is the 800 liter LXe calorimeter with 800 PMTs in the + e++ experiment. The deposited energy is derived from the sum of all PMT signals and the position of the conversion from the distribution of the individual amplitudes. 100 liter prototype D. Renker, PSI International Workshop on new photon-detectors, Kobe, 6/27/2007
PMT – some remarks PMT’s are a commercial product since 70 years. This is a long time for development and optimisation. Even so the progress during the last years is remarkable: the bulky shape turned into a flat design with very good effective area coverage and PMTs became position sensitive due to segmented (pixelised) anodes. Devices with segmented anodes with 256 pixels are available. In addition the prices came down considerably. Industry reduces the number of parts of the mechanically complicated dynode structure inside the vacuum container (some 40 pieces). To some extent the manual mounting of these parts is replaced by automated processes. The price per readout channel can be below 20 US$. The quantum efficiency is relative low (~25%) but new photo cathodes can reach 40 to 50% (Ga. As. P and Ultrabialkali). PMT’s with small transit time spread are available and allow a time resolution smaller than 100 ps. PMT’s are very sensitive to magnetic fields. Only some proximity focused types tolerate axial fields. D. Renker, PSI International Workshop on new photon-detectors, Kobe, 6/27/2007
PIN photodiodes General purpose detectors need magnetic fields for the measurement of the momentum of charged particles. The PMTs have to be replaced by solid state devices. CLEO pioneered the use of Cs. I(Tl) crystals and PIN photodiodes in an electromagnetic calorimeter (7800 Crystals and 4 diodes/crystal). The QE of PIN photodiodes matches the emission wavelength (550 nm) of Cs. I(Tl) better than PMT’s. It is ~80%. Consequently the energy resolution is very good: <2% for 1 Ge. V ’s. The PIN photodiode is a very successful device – all B-factories use them and L 3, GLAST … D. Renker, PSI International Workshop on new photon-detectors, Kobe, 6/27/2007
PIN photodiodes – problems • • D. Renker, PSI PIN photodiodes have no gain. The operation is very stable but they need a charge sensitive amplifier which makes the signal rise time slow and introduces noise to the system (CPIN ~80 p. F/cm 2). Calorimeters made of materials with low light yield (pure Cs. I in KTe. V and Čerenkov calorimeters with lead glass) cannot use PIN photodiodes. The full thickness of the PIN photodiodes (300 m) is sensitive. Charged particles (e. g. e+ and e-) which leak out at the rear end of the crystals and pass the diode produce an unwanted addition to the signal. A MIP creates some 100 electron-hole pairs per micron in silicon. This makes 30. 000 electron-hole pairs which fake ~6 Me. V additional energy in a Cs. I(Tl) calorimeter (Nuclear Counter Effect). International Workshop on new photon-detectors, Kobe, 6/27/2007
PIN photodiodes – nuclear counter effect High energy Low energy s Each dot stands for an energy deposition of more than 10 ke. V D. Renker, PSI 80 Ge. V e- beam in a 18 cm long Pb. WO 4 crystal International Workshop on new photon-detectors, Kobe, 6/27/2007
Basic APD Structure (CMS version) Photo-conversion electrons from the thin p-layer induce avalanche amplification at the p-n junction. Electrons created by ionising particles traversing the bulk are not amplified. deff ~ 6 m 50 times smaller than in a PIN diode. D. Renker, PSI International Workshop on new photon-detectors, Kobe, 6/27/2007
APDs in the CMS ECAL 36 supermodules with 1700 crystals each al 2 APD’s/crystal 122. 400 APD’s D. Renker, PSI t crys O 4 Pb. W In the endcaps vacuum phototriodes are used because of the very high radiation levels. International Workshop on new photon-detectors, Kobe, 6/27/2007
APD Impact on Energy Resolution ECAL energy resolution: CMS design goal : a ~ 3%, b ~ 0. 5%, c ~ 200 Me. V APD contributions to: a: photo statistics (area, QE) and avalanche fluctuations (excess noise factor) b: stability (gain sensitivity to voltage and temperature variation, aging and radiation damage) c: noise (low capacitance, serial resistance and dark current) D. Renker, PSI International Workshop on new photon-detectors, Kobe, 6/27/2007
Sampling Calorimeter of KLEO The KLEO calorimeter is made of 200 layers of scintillating fibers embedded in a lead absorber. For the readout fine mesh PMT’s are used on both ends of the 430 cm long fibers. An excellent energy resolution has been achieved: s/E = 5%/ E(Ge. V) The time resolution of allows the determination of K 0 0’s vertices from the photon arrival time. This is almost a homogeneous calorimeter because of the relative small amount of absorber material D. Renker, PSI International Workshop on new photon-detectors, Kobe, 6/27/2007
Sampling electromagnetic calorimeters – LHCb The Shashlik electromagnetic calorimeter of LHCb is a stack of scintillator- and lead tiles with wavelength shifting fibers perpendicular to the tiles and with PMT readout. • high radiation environment • good energy resolution • fast response • high dynamic range PMT: Hamamatsu R 7899 -20 D. Renker, PSI International Workshop on new photon-detectors, Kobe, 6/27/2007
Hadron Calorimeters Hadron calorimeters are almost always built as sampling devices because to some extent they allow to make the response to electrons equal to the response to hadrons (e/h=1, compensation) which is crucial for the energy resolution. The best example is the ZEUS calorimeter with uranium- and scintillator-plates. The energy sampled is typically a few percent of the total incident energy. A small number of photons have to be detected with good signal to noise ratio. Up to now all sampling hadron calorimeters which are based on the detection of light from plastic scintillators use PMT’s. D. Renker, PSI International Workshop on new photon-detectors, Kobe, 6/27/2007
Sampling Calorimeters – CMS HCAL with hybrid PMT’s CMS HCAL is made of brass, scintillator tiles, wavelength shifting fibers and proximity focused hybrid PMT’s. • needs to work in a 4 T magnetic field • with large dynamic range, • high position sensitivity and • low crosstalk CMS diode design 19 x 5. 4 mm D. Renker, PSI 73 x 2. 68 mm International Workshop on new photon-detectors, Kobe, 6/27/2007
Calorimeters with Si. PM readout for ILC and T 2 K Minical for the ILC: 11 layers of 3 x 3 plastic scintillator tiles (50 x 5 mm 3) with 2 mm Fe in between. Readout with WLS fibers and Si. PM’s. Calibration with light from a LED (shaded area) and with MIP’s from 90 Sr.
Ring Image Čerenkov counters RICH counter: measure photon impact point on the photon detector surface. Needed is detection of single photons with • large area coverage • good spatial resolution • high efficiency and good signal-to-noise ratio Special requirements depend on the specific features of individual RICH counter: • Operation in (high) magnetic field • High rate capability • Very high spatial resolution • Excellent timing (time-of-arrival information and background reduction) D. Renker, PSI International Workshop on new photon-detectors, Kobe, 6/27/2007
Rich in CLEO Rich – the classical example • Available space limited • Operation in a magnetic field • Low material budget – in front of the calorimeter 13% of a radiation length D. Renker, PSI Solution: The photon detector is a wire chamber filled with methan and TEA (triethylamine) which has a QE of 30% at 150 nm. International Workshop on new photon-detectors, Kobe, 6/27/2007
Gas Photo Multiplier with Cs. I photo-cathodes Alice: proximity focussing Cs. I RICH Hadron Blind Detector of PHENIX • liquid C 6 F 14 radiator • MWPC • cathode pads coated with Cs. I • total area 11 m 2 • triple Gas Electron Multiplier (GEM) • high QE • low sensitivity to charged particles • fast response (1. 6 ns for single photons) similar in HADES, COMPASS, J-LAB … No ion and photon feedback D. Renker, PSI International Workshop on new photon-detectors, Kobe, 6/27/2007
DIRC: Detection of Internally Reflected Čerenkov Light BABAR Rich requirements: Cs. I(Tl) needs to detect photons down to 20 Me. V small radiation length < 20% small radial size required /K separation at 4 Ge. V/c is 6. 5 mrad 3 separation requires 2. 2 mrad resolution PMT’s: ETL 9125 e+ e- Quartz Barbox Support tube (Al) Compensating coil Assembly flange Standoff box D. Renker, PSI International Workshop on new photon-detectors, Kobe, 6/27/2007
HERA-B RICH with multianode PMT’s Requirements: Rates ~1 MHz Long term stability High QE over ~3 m 2 Gas based detectors could not be used because of the high rate environment Multianode PMTs: R 5900 -M 16 and R 5900 -M 4 D. Renker, PSI International Workshop on new photon-detectors, Kobe, 6/27/2007
RICH for LHCb with hybrid PMT‘s • Large area (2. 8 m 2) with high active area fraction • Fast compared to the 25 ns bunch crossing time • Have to operate in a small magnetic field • Granularity 2. 5 x 2. 5 mm 2 hybrid PMT with 5 x demagnification the anode is a pixel detector with 8192 channels organized in 1024 super-pixels of 500 x 500 m 2 size. D. Renker, PSI International Workshop on new photon-detectors, Kobe, 6/27/2007
Time of flight for particle identification The plastic scintillators (3 m long, ~4 x 6 cm 2) with fine mesh PMT’s on both sides of the TOF detector provide a time resolution of 100 ps and allow a /K separation up to 1. 2 Ge. V. The Aerogel Cerenkov Counter (ACC) extends the /K separation to 3. 5 Ge. V. It also uses fine mesh PMT’s. D. Renker, PSI International Workshop on new photon-detectors, Kobe, 6/27/2007
Tracking with scintillating fibers and VLPC‘s in DØ • 80000 fibers 2. 5 and 1. 7 m long • single photon detection capability • 80% QE • operated at 6°K • gain ~50. 000 • position resolution 120 m D. Renker, PSI International Workshop on new photon-detectors, Kobe, 6/27/2007
Target Tracker of Opera locate the lead/emulsion brick where a neutrino interaction occurred Total area 3000 m 2 Few photo electrons: 6 to 7 p. e. per MIP 6700 x 2. 6 x 1 cm 3 64 -channel Hamamatsu H 7546 PMT D. Renker, PSI International Workshop on new photon-detectors, Kobe, 6/27/2007
Summary A large variety of techniques of photo sensors has been developed and realized in present detectors for high energy physics. There is an almost infinite number of alternative designs which have been proposed and partly tested in prototypes. The working horse is still the PMT when weak light flashes need to be detected. New types of photo sensors have always quickly been adopted in high energy physics experiments. The new Geiger-mode avalanche photodiodes will for sure have a heavy impact on the design of future detectors. D. Renker, PSI International Workshop on new photon-detectors, Kobe, 6/27/2007