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07 - Cherenkov and transition radiation detectors Jaroslav Adam Czech Technical University in Prague Version 2 Jaroslav Adam (CTU, Prague) DPD_07, Cherenkov and transition radiation Version 2 1 / 30

Transcript of Version 2 - physics.fjfi.cvut.cz · Layout of RICH1 in LHCb Cherenkov light emitted by Aerogel and...

Page 1: Version 2 - physics.fjfi.cvut.cz · Layout of RICH1 in LHCb Cherenkov light emitted by Aerogel and gaseous radiators Light reflected by flat and spherical mirrors outside the LHCb

07 - Cherenkov and transition radiation detectors

Jaroslav Adam

Czech Technical University in Prague

Version 2

Jaroslav Adam (CTU, Prague) DPD_07, Cherenkov and transition radiation Version 2 1 / 30

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Cherenkov radiation

Emitted by passage of charged particle in dielectricum at velocity greater than speed of lightin respective material

β > 1/n where n is refractive index

Dipole moment of polarized electrons, emission of electromagnetic field

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Angle of Cherenkov radiation emission

Light emitted into forward cone of aperture

cos θ =1βn

(1)

Threshold of Cherenkov light emission given by βthr ≥ 1n

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Yield of Cherenkov photons

Yield per unit length of track proportional to λ−2

Smaller than scintillation light

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Threshold Cherenkov detectors

Separation of particles with different masses at the same momentum

Set of Cherenkov radiators of different n, different threshold for each particle

Radiators of material of desired n or gaseous radiator at a given pressure

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Differential Cherenkov detectors

Tagging of particles in selected range of velocities

Light reflected by spherical mirror, aperture in front of PM provides velocity window

Particles parallel to optical axis (fixed-target experiments)

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Fitch-type differential Cherenkov detector

Upper limit on velocity by internal reflection

Light at higher angle does not escape into the light guide

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Ring imaging Cherenkov (RICH) detector

Particle identification by angle of Cherenkov radiation

Photons reflected by spherical mirror (SM) and focused onto spherical detector SD

Measured circle of Cherenkov photons to get particle velocity, together with particlemomentum provides the identification

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Detection of Cherenkov photons in RICH

Position sensitive detector of large surface

MWPC with photosensitive vapor in counter gas

Quartz entrance window for vapor of low ionization energy, UV transparent crystal otherwise

More intense rings by fast heavy ions (number of photons proportional to square of particlecharge)

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Cherenkov ring of relativistic heavy ion in RICH

Early measurement of heavy ion with RICH

Center of ring visible due to ionization loss in photon detector

Spurious signals by δ-rays of heavy ion

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Cherenkov rings by monoenergetic beam

100 events of collinear monoenergetic beam

Entrance windows by calcium-fluoride crystals

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Solid-state detectors in RICH

CsI photocathode as photoconverter

Single or multi-anode conventional photomultiplier or hybrid photomultiplier

Micropattern gaseous detector with CsI photocathode

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Cherenkov angle dependence on particle momentum

Cherenkov rings detected by system of multichannel photomultipliers

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Cherenkov rings in electromagnetic cascades

Secondary particles in cascade follows direction of initiating electron or photon

Also relativistic, emit overlapping Cherenkov rings, concentric with equal radii

Distortion of the ring (elliptic for inclined angle) gives direction of incidence - gamma-rayastronomy

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Detection of neutrino induced muons and electrons

Muon produced in interaction of atmospheric neutrino, detected by Cherenkov ring in heavywater

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Detection of neutrino induced muons and electrons

Cherenkov ring of electron from decay of muon which was produced by neutrino interaction

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Detector of Internally Reflected Cherenkov light (DIRC)

Based on internal reflection of Cherenkov radiation in quartz bars of rectangular cross section

Readout by system of PM tubes

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RICH of LHCb experimentDetectors RICH1 and RICH2

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Cherenkov radiators of RICH in LHCb

Different particle momenta covered by RICH1 (lower) and RICH2 (higher momentum)

Identification among several particle species

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Layout of RICH1 in LHCb

Cherenkov light emitted by Aerogel and gaseous radiators

Light reflected by flat and spherical mirrors outside the LHCb acceptance

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Layout of RICH1 in LHCbReflected Cherenkov light detected by the photon detectors

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Layout of RICH2 in LHCbSecond Cherenkov detector with different radiator

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Photon detector in RICH of LHCb

Hybrid photon detector HPD

Photon conversion at photocathode, photoelectron accelerated and detected by segmentedsilicon detector

Image of photocathode de-magnified onto the detector by the electrodes

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Transition radiation detectors (TRD)

Charged particle moving towards boundaty of materials of different dielectric properties

Time-dependent electromagnetic field of electric dipole of charged particle and it’s mirror atboundary

Emission of electromagnetic radiation

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Energy of transition-radiation photons

Average energy of TRD photons vs. electron momentum

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Arrangement of transition-radiation detector

Angle of emission of transition-radiation photons inversely proportional to Lorentz factor of theparticle

System of periodic foils and gaps as radiator

Photons detected by MWPC filled by Kr or Xe

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Energy loss distribution in TRD

Energy loss by relativistic electrons

(a) - radiator with gaps, (b) - radiator without gaps, no transition radiation in this case

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TRD of ALICE experiment

TRD located in the central barrel above TPC, provides electron identification

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Detector element of TRD in ALICE experiment

Radiator for transition radiation, gas drift volume of Xe/CO2 and MWPC

X-ray photons of transition radiation converted at the beginning of drift volume

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Electron identification by TRD in ALICE

Discrimination between electrons and pions

Increased specific energy loss by electrons at the same momentum

Signal at large drift times for electrons by conversion of transition radiation at the beginning ofdrift sector

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