How do we detect particles? - PowerPoint Presentation

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How do we detect particles?

HSSIP-Project presentation: Elias

Kunze

& Julia

Nehlin

Electromagnetic interactions:

E

lectron-positron scattering

Electron-electron scattering Photon-electron scattering Photon emission in deceleration or acceleration  Bremsstrahlung Annihilation  e+ + e- Pair creation  e+ + e-

 radiation of a charged particle due to its deceleration caused by an electric field of another charged particle

Electromagnetic showers:

Cascade of

secondary particles

is produced by interacting with dense matterE as starting point  cascade of positrons & photons  acceleration  e. m. radiation!More photons  more e+ e- pairs! energy loss of e- dominates  number decays exponentially!

Electromagnetic showers:

Characterization:

Number

of p.Location Longitudinal distribution Transverse distribution If material has a high atomic number  greater nuclear charges  greater acceleration!  We need material with high atomic number!

How can we analyze particle showers?

Detector construction:

Tracking chamber

 sensing devices determine particles trajectoriesElectromagnetic calorimeters  we’ll come back to this one…Hadronic calorimeter  measures total energy of hadronsMuon chamber  muons are detected.

Electromagnetic calorimeters:

ECAL

measures:

the total energy of electrons, e+, photons  total absorptionspatial location of energy depositdirectionShowers of e+, e- pairs in the material e- are deflected by electric fields  radiate photonsPhotons make e-/e+ pairs  cycleFinal number: proportional to energy of first p.

Homogeneous calorimeter

:



Full volume detectors (sensitive)  medium for energy and signal to cause shower development + detect particles Types:Liquid scintillatorsLead loaded glassDense crystal scintillators: PbWO4 (+others)  CMS!

Sampling calorimeter

:

 Liquid-Argon calorimeter (ATLAS)

Layers of steel + liquid argon  interspaced Lead gives shower development  Ionisation  gaps of liquid argon Inductive signal registered by copper electrodesAccordion shaped absorbers and electrodes

Geant4:

Toolkit to simulate interactions of particles with matter

 electromagnetic and nuclear passages

Geometry & TrackingPhysics processes and modelsGraphics etc.Fundamental for understanding detector performance

Geant4:

Applications:

High energy & nuclear physics detectors (ATLAS, CMS,

LHCb, HARP “…”)Accelerators and ShieldingMedicine Radiotherapy (particle beams) Simulation & scanners (PET scan)Space Satellites Space-environment

Using Geant4:

Using Geant4:

Using Geant4:

Comparison of material at 100 MeV for ECAL

Using Geant4:

Comparison of particles at 50 GeV

ECAL Comparison:

PbWO4 Crystals

Energy can be measured more precisely

Quite compactNot able to measure and compare initial/final energyLead-Tungstate looses property with time  less transparentLiquid-Argon/LeadLiquid-Argon is resistant to radiationAbility to measure where the majority of a particles energy was submitted Energy that is submitted in lead must be estimatedLarge size, compared to CMS

Thank you!