Geant 4 Electromagnetic Processes 2 Geant 4 cuts

Geant 4: Electromagnetic Processes 2 ¬Geant 4 cuts ¬Stopping powers and ranges ¬Fluctuations ¬Multiple scattering V. Ivanchenko 16. 07. 02 Salamanca 1

Electromagnetic processes ¬ Energy spectrum of electrons 1/T 2 ¬ Energy spectrum of Bremsstahlung 1/ ¬ Huge number of low energy e- and gammas cannot be tracked by any Monte Carlo ¬ Cuts should be used V. Ivanchenko 16. 07. 02 Salamanca 2

Geant 4 cuts No tracking cuts, only production thresholds Cuts can be established to any particle but mandatory cuts on gamma and electrons Thresholds for production secondaries are expressed in range, universal for all media, Range 10 ke. V gamma in Si 2 cm Range of 10 ke. V electron in Si 2 microns Energy thresholds for a material is calculated from this cut in range. In 2002 a possibility to set a cut by logical volume will be implemented V. Ivanchenko 16. 07. 02 Salamanca 3

G 4 cuts § Production cuts for a typical G 4 Ionisation Tc subdivides continues and discrete part: § Energy loss § -electron production § Energy loss can be used for generation of -electrons under the threshold (subcutoff) and for fluorescence and Auger –electrons emission V. Ivanchenko 16. 07. 02 Salamanca 4

G 3/G 4 cuts in Pb/Ar calorimeter Protons 500 Me. V G 3 Cut 450 ke. V Ar Pb Ar G 4 1. 5 mm - 450 ke. V LAr 2 Me. V Pb V. Ivanchenko 16. 07. 02 Salamanca 5

Geant 4 validation ¬ Everyday task for Geant 4 team is the validation of the toolkit ¬ Comparison with data ¬ G 3/G 4 comparisons ¬ Comparison experiments (Ba. Bar, SLAC, Stanford; ATLAS, CERN, Geneve; others) ¬ Testing procedures V. Ivanchenko 16. 07. 02 Salamanca 6

G 3/G 4/Data comparison V. Ivanchenko 16. 07. 02 Salamanca 7

Remarks about G 4 cuts ¬ The use of production threshold is mandatory only for ionisation and bremsstahlung process ¬ Other processes can use or ignore G 4 cuts ¬ Alternative mechanism is User. Limits, which can be defined in a given G 4 Logical. Volume: – – Maximum step size; Maximum track length; Maximum track time; Minimun kinetic energy; – Minimum range; V. Ivanchenko 16. 07. 02 Salamanca 8

Stopping powers and ranges ¬ At initialization stage d. E/dx, R(E), and E(R) tables are calculated for all materials and basic particles e-, e+, -, +, p, pbar ¬ At run time d. E/dx, R(T), T(R) for hadrons and ions are calculated using scaling Tp=T·mp/m V. Ivanchenko 16. 07. 02 Salamanca Deuterons 9

Stopping powers and ranges ¬ Scaling is applicable to all types of ions ¬ Initialization should be redone if run conditions are changed: • New basic particle • New material • New cut V. Ivanchenko 16. 07. 02 Salamanca 10

Straggling ¬ At each step of charged particle after calculation of average energy deposition the sampling of energy is performed ¬ Three fluctuation models are used • Bohr fluctuations • Vavilov fluctuations • Landau fluctuations V. Ivanchenko 16. 07. 02 Salamanca 11

Multiple Scattering ¬ Provides step limit ¬ Sample transverse displacement at end point of the step ¬ Sample scattering angle ¬ Model is used in which scattering angles are not small V. Ivanchenko 16. 07. 02 Salamanca 12

Conclusion remarks ¬ Geant 4 electromagnetic model based on new conception: universal cut in range ¬ Geant 4 is not a frozen program – it is a free toolkit, which allows to implement any variant of cuts and thresholds ¬ Geant 4 electromagnetic physics is well tested and demonstrates a good quality for HEP applications ¬ In some cases Geant 4 provide physics which is absent in Geant 3, in others – more precise models V. Ivanchenko 16. 07. 02 Salamanca 13