Electromagnetic Physics

Budker Inst. of Physics IHEP Protvino MEPHI Moscow Pittsburg University Electromagnetic Physics Authors: P. Gumplinger, M. Maire, P. Nieminen, M.G. Pia, L. Urban Extended introduction

It handles electrons and positrons g, X-ray and optical photons muons charged hadrons ions Comparable to Geant3 already in the 1st a release (1997) High energy extensions fundamental for LHC experiments, cosmic ray experiments etc. Low energy extensions fundamental for space and medical applications, neutrino experiments, antimatter spectroscopy etc. Alternative models for the same physics process Electromagnetic physics • multiple scattering • Cherenkov • transition radiation • ionisation • Bremsstrahlung • annihilation • photoelectric effect • Compton scattering • Rayleigh effect • g conversion • e+e- pair production • refraction • reflection • absorption • scintillation • synchrotron radiation • fluorescence • Augereffect(in progress) energy loss

OO design Top level class diagram of electromagnetic physics Alternative models, obeying the same abstract interface, are provided for the same physics interaction

OO design of Low Energy e.m. processes: general

OO design of Low Energy e.m. processes: photons

OO design of Low Energy e.m. processes: electrons

OO design of Low Energy e.m. processes: hadrons

Production thresholds • No tracking cuts, only production thresholds • thresholds for producing secondaries are expressed in range, universal for all media • converted into energy for each particle and material • It makes better sense to use the range cut-off • Range of 10 keV gamma in Si ~ a few cm • Range of 10 keV electron in Si ~ a few micron

Liquid Ar Liquid Ar Pb Pb Effect of production thresholds DCUTE= 455 keV In Geant3 500 MeV incident proton one must set the cut for delta-rays (DCUTE) either to the Liquid Argon value, thus producing many small unnecessary d-rays in Pb, or to the Pb value, thus killing the d-rays production everywhere Threshold in range: 1.5 mm 455 keV electron energy in liquid Ar 2 MeV electron energy in Pb DCUTE= 2 MeV

An example how to set cut values void ExN03PhysicsList::SetCuts() { if (verboseLevel >1) G4cout << "ExN03PhysicsList::SetCuts:"; // Set cut values for gamma at first and for e- second and next for e+, // because some processes for e+/e- need cut values for gamma SetCutValue(cutForGamma, "gamma"); SetCutValue(cutForElectron, "e-"); SetCutValue(cutForElectron, "e+"); // Set cut values for proton and anti_proton before all other hadrons // because some processes for hadrons need cut values for proton/anti_proton SetCutValue(cutForProton, "proton"); SetCutValue(cutForProton, "anti_proton"); SetCutValueForOthers(defaultCutValue) if (verboseLevel>1) DumpCutValuesTable(); }

Standard electromagnetic processes Shower profile, 1 GeV e- in water • Photons • Compton scattering • g conversion • photoelectric effect • Electrons and positrons • Bremsstrahlung • ionisation • continuous energy loss from Bremsstrahlung and ionisation • d ray production • positron annihilation • synchrotron radiation • Charged hadrons J&H Crannel - Phys. Rev. 184-2 August69

Features of Standard e.m. processes Multiple scattering 6.56 MeV proton , 92.6 mm Si • Multiple scattering • new model • computes mean free path length and lateral displacement • Ionisation features • optimize the generation of d rays near boundaries • Variety of models for ionisation and energy loss • including the PhotoAbsorption Interaction model • Differential and Integral approach • for ionisation, Bremsstrahlung, positron annihilation, energy loss and multiple scattering J.Vincour and P.Bem Nucl.Instr.Meth. 148. (1978) 399

Ionisation energy loss produced by charged particles in thin layers of absorbers Photo Absorption Ionisation Model 3 GeV/c p in 1.5 cm Ar+CH4 5 GeV/c p in 20.5 mm Si Ionisation energy loss distribution produced by pions, PAI model

Low energy e.m. extensions Fundamental for space and medical applications, neutrino experiments, antimatter spectroscopy etc. Low energy hadrons and ions models based on Ziegler and ICRU data and parameterisations Barkas effect: models for antiprotons e,down to 250 eV Geant3 down to 10 keV (positrons in progress) Photon transmissionon 1 mm Al

Based on EPDL97, EEDL and EADL evaluated data libraries cross sections sampling of the final state Photoelectric effect Compton scattering Rayleigh scattering Bremsstrahlung Ionisation Fluorescence Geant3.21 Geant4 C, N, O line emissions included Low energy extensions: e-, g 250 eV up to 100 GeV 10 keV limit 250 eV limit

Example of application of Geant4 Low Energy e.m. processes water Fe Photon attenuation coefficient Comparison of Geant4 electromagnetic processes with NIST data : Standard and Low Energy processes

Low energy extensions: hadrons and ions Various models, depending on the energy range and the charge • E > 2 MeV Bethe-Bloch • 1 keV < E < 2 MeV  parameterizations • Ziegler 1977, 1985 • ICRU 1993 • corrections due to chemical formulae of materials • nuclear stopping power • E < 1 keV  free electron gas model • Barkas effect taken into account • quantum harmonic oscillator model

Muon processes Validity range: 1 keV up to 1000 PeV scale • High energy extensions based on theoretical models • Bremsstrahlung • Ionisation and d ray production • e+e- Pair production  simulation of ultra-high energy and cosmic ray physics

Processes for optical photons • Optical photon its wavelength is much greater than the typical atomic spacing • Production of optical photons in HEP detectors is mainly due to Cherenkov effect and scintillation • Optical properties, e.g. dielectric coefficient, surface smoothness, can be set to a G4LogicalVolume • Processes in Geant4 • in-flight absorption • Rayleigh scattering • reflection and refraction on medium boundaries Track of a photon entering a light concentrator CTF-Borexino

Examples of application of Geant4 e.m. physics The plot is the visible energy in silicon as a function of the energy of the incident electron The experimental results are from: Sicapo Collaboration, NIM A332 (85-90) 1993 Sampling calorimeter

Standard electromagnetic process classes (1) • Photon processes • Compton scattering (class G4ComptonScattering) • Gamma conversion (class G4GammaConversion) • Photo-electric effect (class G4PhotoElectricEffect) • Electron/positron processes • Bremsstrahlung (class G4eBremsstrahlung) • Ionisation and delta ray production (class G4eIonisation) • Positron annihilation (class G4eplusAnnihilation) • Synchrotron radiation (class G4SynchrotronRadiation) • Hadron (e.m.) processes • Ionisation (class G4hIonisation) • All charged particles • Multiple scattering (class G4MultipleScattering) • The ionisation/energy loss of the hadrons can be simulated optionally using the G4PAIonisation/G4PAIenergyLoss classes

Standard electromagnetic process classes (2) • The (e)ionisation, bremsstrahlung, positron annihilation, energy loss, and multiple scattering processes have been implemented in the so-called “integral approach” as well • The corresponding classes are: • G4IeBremsstrahlung • G4IeIonisation • G4IeplusAnnihilation • G4IeEnergyLoss • G4IMultipleScattering

Low Energy electromagnetic process classes • Photon processes • Compton scattering (class G4LowEnergyCompton) • Rayleigh scattering (class G4LowEnergyRayleigh) • Gamma conversion (class G4LowEnergyGammaConversion) • Photoelectric effect (class G4LowEnergyPhotoElectric) • Electron processes • Bremsstrahlung (class G4LowEnergyBremsstrahlung) • Ionisation and delta ray production (class G4LowEnergyIonisation) • Hadron and ion (e.m.) processes • Ionisation and delta ray production (class G4hLowEnergyIonisation)

Muon process classes • Bremsstrahlung (class G4MuBremsstrahlung) • Ionisation and delta ray/knock on electron production (G4MuIonisation) • Nuclear interaction (class G4MuNuclearInteraction) • Direct pair production (class G4MuPairProduction) X-ray production process classes • Cerenkov process (class G4Cerenkov) • Transition radiation (classes G4TransitionRadiation and G4ForwardXrayTR) • The Low Energy electromagnetic processes also produce X-rays through fluorescence

Other practical details • Data files for the low energy electromagnetic processes are available from the Geant4 Download web page • To use the Low Energy electron and photon processes, the user must set the environment variable $G4LEDATA as the path to the external data set above

If you want to learn more... • Low Energy Electromagnetic Physics homepage • http://www.ge.infn.it/geant4/lowE/index.html • Gallery of electromagnetic physics documentation and results • http://wwwinfo.cern.ch/asd/geant4/reports/gallery/ • User's Guide: For Application Developers • http://wwwinfo.cern.ch/asd/geant4/G4UsersDocuments/UsersGuides/ForApplicationDeveloper/html/index.html • User's Guide: For Toolkit Developers • http://wwwinfo.cern.ch/asd/geant4/G4UsersDocuments/UsersGuides/ForToolkitDeveloper/html/index.html • Physics Reference Manual • http://wwwinfo.cern.ch/asd/geant4/G4UsersDocuments/UsersGuides/PhysicsReferenceManual/html/PhysicsReferenceManual.html

Geant4 examples illustrating electromagnetic physics Novice examples • N02: Simplified tracker geometry with uniform magnetic field • N03: Simplified calorimeter geometry • N04: Simplified collider detector with a readout geometry Advanced examples • xray_telescope: Typical X-ray telescope • gammaray_telescope: Typical g ray telescope • brachytherapy: Medical physics application

Electromagnetic Physics