Putting it all together - Particle Detectors. Writeup for 3 rd section: http://yeti.phy.bris.ac.uk/Level3/phys30800/CourseMaterials/Part_3.pdf. Measurements. Destructive Initial particle absorbed or significantly scattered
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Writeup for 3rd section:
Time of flight
Radius of curvature in a magnetic field gives the momentum
Pattern recognition can be tricky….
Rate of energy loss – dE/dx
Total energy - Calorimetry
Deflection of a charged particle by large numbers of small angle scatters.
ds/dW 1/q4 ds/dq 1/q3
Most probable scatter is at small angle
Efficiency of detector reduced by (1- e-n)
Response of PbWO4 calo
to 120GeV e-
Often a detector has to cope with many different types of particle of many different energies.
Construct a system of detectors allowing measurement of different aspects of different particles.The “General Purpose” Detector
Tracking (charged particles, magnetic field)
Calorimeter (electrons, photons, hadrons)
Muon tracking (generally only muons get this far)The “General Purpose” Detector
Tracking parts: - will generally cross the tracking detector without leaving a signal.
Desirable – don’t want to scatter the photon or convert to charged particles. minimize material.
But, some will pair convert.
Calorimeter -will produce an EM shower.
Length scale X0.
Contained in EM portion of calo.
Muon tracking – won’t reachGeneral Purpose Detector: Photons
Tracking parts: – will leave a trail of ionization.
Measure curvature to measure momentum.
Some will undergo Bremsstrahlung.
Calorimeter -will produce an EM shower.
Same as for photons.
Muon tracking – won’t reachGeneral Purpose Detector: Electrons
Tracking parts: – charged hadrons will leave a trail of ionization.
Calorimeter -will produce an hadronic shower.
Length scale l0
Energy in both EM and hadronic parts of calo.
Muon tracking – won’t reachGeneral Purpose Detector: Hadrons
Tracking parts: –will leave a trail of ionization.
Bremsstrahlung not a problem.
Calorimeter –X0for muons so long that no shower takes place.
Still deposits energy by ionization.
Muon tracking – crosses, leaving track of ionizationGeneral Purpose Detector: Muons
Tracking parts: – Decay close to interaction point. If daughters are charged may be able to reconstruct decay vertex.
Calorimeter, Muon tracking- primary particle never reaches, but daughters may.General Purpose Detector: Tau, B-mesons, D-mesons
Produce visible light parts:
Transport to a light detector
Total internal reflection
Wavelength shifting fibres.
Convert to an electrical signal
Total Internal Reflection
(solid-angle, qi>qc)/(total solid-angle)
Typically only get a few photons at light detector due to passage of particle
Need a detector sensitive at the single-photon level.
Hybrid photodiodeLight Detectors
Light falls on a photocathode in an evacuated tube and electrons emitted (photoelectric effect)
Quantum Efficiency depends on cathode material and wavelength ( QE ~ 25% )
Photoelectrons focused and accelerated towards the first dynode by electric field.Photomultiplier Tube
When photoelectron strikes dynode several electrons emitted (on average) n ~ 5
Several dynodes ( ~ 10 ) give high gain ( 107)
PMT sensitive to magnetic field – need screening in many applicationsPhotomultiplier Tube
Scintillator transparent to the light it produces (but usually put in a wavelength-shifter to move out of UV)
Plastic wavelength shifter
~ 10 photons per keV deposited ( ~ 1% of energy deposited, or about 10,000 photons/cm for MIP)
Conduction (on average) n ~ 5
Gas ionization chambers.
- (on average) n ~ 5
This matrix of silicon microstrip detectors was at the heart of the ALEPH detector at LEP
event observed in the Delphi Vertex detector
event observed in the SLD detector
DELPHI at LEP features extensive particle identification capability from its TPC and RICH counters