Precision Validation of Geant4 Electromagnetic Physics Geant4 DNA Project Meeting 26 July 2004, CERN Michela Piergentili INFN Genova, Italy S. Guatelli (INFN Genova), V. Ivanchenko (Budker), M. Maire (LAPP), A. Mantero (INFN Genova), B. Mascialino (INFN Genova), P. Nieminen (ESA), L. Pandola (INFN LNGS), S. Parlati (INFN LNGS), A. Pfeiffer (CERN), M.G. Pia (INFN Genova), M. Piergentili (INFN Genova), L. Urban (Budapest)

Geant4 Electromagnetic Physics  Alternative models for the same physics process  High energy models –fundamental for LHC experiments, cosmic ray experiments etc.  Low energy models –fundamental for space and medical applications, neutrino experiments, antimatter spectroscopy etc. It handles electrons and positrons gamma, X-ray and optical photons muons charged hadrons ions multiple scattering Bremsstrahlung ionisation annihilation photoelectric effect Compton scattering Rayleigh effect gamma conversion e+e- pair production synchrotron radiation transition radiation Cherenkov refraction reflection absorption scintillation fluorescence Auger Geant4 e.m. package Standard Package LowEnergy Package Muon Package Optical photon Package

Standard electromagnetic processes Photons –Compton scattering  conversion –photoelectric effect Electrons and positrons –Bremsstrahlung –Ionisation  ray production –positron annihilation –synchrotron radiation Charged hadrons Variety of models Variety of models for ionisation and energy loss 1 keV up to 100 TeV Shower shapes Courtesy of D. Wright (Babar)

Geant4 Low Energy Package Geant4 Low Energy Package is fundamental for –Biomedical applications –Space Science –Neutrino and dark matter experiments Geant4 Low Energy Package describes the interactions of photons, electrons, positrons, hadrons and ions with matter down to low energies. Extensions of the physics models 250 eV / 100 eV –down to 250 eV / 100 eV for electrons and photons < 1 keV –down to < 1 keV for protons, antiprotons, ions Two models available: –based on evaluated data libraries –based on Penelope analytical models

Low energy e.m. extensions Fundamental for neutrino/dark matter experiments, space and medical applications, antimatter spectroscopy etc. e,  down to 250 eV Based on EPDL97, EEDL and EADL evaluated data libraries shell effects Photon attenuation Hadron and ion models based on Ziegler and ICRU data and parameterisations Bragg peak ions antiprotons protons

Processes à la Penelope The whole physics content of the Penelope Monte Carlo code has been re-engineered into Geant4 (except for multiple scattering) –for photons, electrons, positrons F. Salvat Physics models by F. Salvat (University of Barcelona, Spain), J.M. Fernandez-Varea J.M. Fernandez-Varea (University of Barcelona, Spain), E. Acosta J. Sempau (University of Cordoba, Argentina), J. Sempau (University of Catalonia, Spain) Power of the OO technology: –extending the software system is easy –all processes obey to the same abstract interfaces –using new implementations in application code is simple x-ray attenuation coeff in Al Attenuation coeff. (cm 2 /g) NIST data Penelope

E.M. Physics Validation Validation is fundamental in Geant4 Validations at different levels Comparisons to experimental measurements and recognised standard references Unit, integration, system testing Microscopic physics validation Macroscopic validation experimental use cases

Microscopic validation Validation of Geant4 electromagnetic physics models Attenuation coefficients, CSDA ranges, Stopping Power, distributions of physics quantities Quantitative comparisons to experimental data and recognised standard references

G4Standard G4 LowE NIST Photon mass attenuation coefficient Photon beam (I o ) Transmitted photons (I)  2 N-L =13.1 – =20 - p=0.87  2 N-S =23.2 – =15 - p=0.08 x-ray attenuation coeff in U NIST data Penelope  2 =19.3 =22 p=0.63 Absorber Materials Absorber Materials : Be, Al, Si, Ge, Fe, Cs, Au, Pb, U

Electron stopping power and CSDA range G4 Standard G4 LowE-EPDL NIST CSDA range : particle range without energy loss fluctuations and multiple scattering centre Experimental set-up Absorber Materials Absorber Materials : Be, Al, Si, Ge, Fe, Cs, Au, Pb, U  2 N-S =0.267 =28 p=1  2 N-L =1.315 =28 p=1 G4 Standard G4 LowE-EPDL NIST

Transmission tests e - beam Experimental set-up

Backscattering coefficient – E=100keV Angle of incidence (with respect to the normal to the sample surface) = 0° G4 LowE Lockwood et al. (1981) Incident e - beam Experimental set-up Backscattered e-

The problem of validation: finding reliable data Note: Geant4 validation is not always easy experimental data often exhibit large differences! Backscattering low energies - Au

Conclusions Geant4 electromagnetic package encompasses an ample set of physics models, specialised for particle type, energy range and detector applications Exploitation of OO technology and sound architectural design make it possible to extend the Geant4 physics capabilities –LowE / Livermore extensions –LowE / Penelope –LowE/ hadrons and ions Geant4 e.m. physics is subject to a rigorous testing and validation process Geant4 e.m. physics validation is in progress with Geant4 6.2 –IEEE TNS paper to be submitted in October

Geant4 Physics Book A project has been launched for a Geant4 Physics Book To have a solid and comprehensive reference on Geant4 physics Wide effort involving Geant4 Collaboration Main focus of the project is Geant4 physics models validation