The prototype for energy loss processes based on model approach V.Ivanchenko

Introduction EM physics is the key Geant4 physics domain The main goals of the presented work is to achieve better compatibility and flexibility of EM physics For several years lowenergy package have been developed in parallel to the standard package – alternative methods were investigated This work was done on base of many discussions with J.Apostolakis, M.Maire, M.G.Pia, and L.Urban V.Ivanchenko 01.10.2002

Problems of energy loss processes Extension to lower or higher energies needs creation of a new process Formulas for high energy processes are valid for ultra relativistic regime Low energy parameterizations becomes non precise at high energies Ionisation and Bremsstrahlung are coupled Fluctuations are the same for all particles Table builders are different for different process Many common peaces of software are repeated in different processes V.Ivanchenko 01.10.2002

Requirements for new design Model approach – different physical models for different materials and energy regions High energy and low energy models should work together for any particle Performance should be at least the same The same user interface as before should be available Physics should be unchanged Different models of energy loss fluctuations Different variants of subcutoff simulation V.Ivanchenko 01.10.2002

Prototype implementation HEP physics oriented The names of processes are not changed Old interfaces are kept The instantiation of a process in a physics list is the same Physics is transformed from processes to models The minimal set of models are implemented V.Ivanchenko 01.10.2002

Electron energy loss Two processes contribute to energy loss: ionisation and bremsstrahlung For both processes only one standard model for the energy region E>1keV Data from ICRU’37 V.Ivanchenko 01.10.2002

1 GeV electrons in silicon V.Ivanchenko 01.10.2002

Proton energy loss Only one process Two models – standard for E>2MeV and lowenergy below Other hadron ionisation are scaled from proton ionisation Data from ICRU’49 Bragg’s peak problem is fixed V.Ivanchenko 01.10.2002

Muon energy loss Three processes: ionisation, bremsstrahlung, and e+e- pair production Three models for ionisation: lowenergy below 200keV, standard from 200keV to 1GeV, relativistic above 1GeV V.Ivanchenko 01.10.2002

Performance test new/old 22.09.02 G4 4.1-ref-02 OS Em1 Em2 Em3 Em4 BTeV ATLAS ECAL E(GeV) 1 10 40 20 250 Linux egcs 0.67 0.89 0.94 0.88 - 0.64 0.68 Linux g++ 0.76 0.84 0.81 0.91 V.Ivanchenko 01.10.2002

Current status of the prototype The proof of the conception is achieved All standard energy loss processes are implemented except PAI model New physics available: Integral approach is implemented Fluctuations are defined for particles “Subcutoff processor” is defined for particles Number of loss and range tables can be decreased High and low energy models can be added easily Models are defined for particles – may be extended to definition per regions Optimized for standard - performance is improved V.Ivanchenko 01.10.2002

Integral approach The probability of EM process is exp(-sn) Step s is limited in order to keep (T) not changed significantly during the step Integral approach provides the probability exp(-nds) V.Ivanchenko 01.10.2002

What next ? The library can be delivered in the next reference tag as an alternative. In that case EM physics list should be modified: G4eIonisation -> G4eIonisationSTD G4hIonisation -> G4hIonisationSTD G4MultipleScattering -> G4MultipleScatteringSTD Modula PhysicsList can be delivered Presented results are preliminary Tests and reviews will follow before current energy loss processes will be substituted V.Ivanchenko 01.10.2002