Geant 4 Electromagnetic Physics 1 V Ivanchenko BINP

Geant 4: Electromagnetic Physics 1 V. Ivanchenko, BINP & CERN ¬Process interface ¬Physics categories ¬Electromagnetic physics ¬Physics. List V. Ivanchenko 01. 09. 03 EM processes 1

Introduction ¬It a short course on Geant 4 electromagnetic physics consist of 4 lectures ¬It is personal view on Geant 4 physics ¬This course includes the material and slides from lectures and presentations of P. Gumplinger, M. Maire, P. Nieminen, M. G. Pia, M. Verderi, and L. Urban. V. Ivanchenko 01. 09. 03 EM processes 2

Geant 4 physics processes Physics is described via abstract interface called process associated with particles Process provides Interaction Lenths, Step. Limits, and Do. It methods Process active Along. Step, Post. Step, At. Rest Distinction between process and model – one process may includes many models Generation of final state is independent from the access and use of cross sections and from tracking V. Ivanchenko 01. 09. 03 EM processes 3

What is tracked in Geant 4 ? G 4 Track • Propagated by the tracking, • Snapshot of the particle state. G 4 Dynamic. Particle • Momentum, pre-assigned decay… • The « particle type » : G 4 Particle. Definition § G 4 Electron, § G 4 Pion. Plus… G 4 Process. Manager • « Hangs » the physics sensitivity; Physics. List class is used for instanciation of processes V. Ivanchenko Process_1 Process_2 • The physics processes; Process_3 01. 09. 03 EM processes 4

G 4 VProcess interface ¬ G 4 VProcess defines 6 pure virtual methods: – – – At. Rest. Get. Physical. Interaction. Length(…. ) At. Rest. Do. It(…) Along. Step. Get. Physical. Interaction. Length(…) Along. Step. Do. It(…) Post. Step. Get. Physical. Interaction. Length(…) Post. Step. Do. It(…) ¬ There also other virtual methods: – Is. Applicable( const G 4 Particle. Definition&) – Build. Physics. Table( const G 4 Particle. Definition&) – …. ¬ G 4 VProcess defined in source/processes/management V. Ivanchenko 01. 09. 03 EM processes 5

G 4 VProcess actions ¬ Abstract class defining the common interface of all processes in GEANT 4 ¬ At. Rest – decay at rest, annihilation at rest, … At. Rest Along. Step ¬ Along. Step – continuous energy losses, multiple scattering, … Post. Step ¬ Post. Step – decay in flight, hardron elastic and inelastic, … V. Ivanchenko 01. 09. 03 EM processes 6

Geant 4 physics categories There are following categories: Electromagnetic Hadronic Decay Optical Transportation Parameterisation V. Ivanchenko Subcategories of Electromagnetic domain: 01. 09. 03 EM processes Muons Lowenergy Standard Xrays Utils 7

Electromagnetic Physics ¬Processes of gamma, electron, and positron interactions with media was traditionally called “Electromagnetic Processes” (EM) ¬Hadron interaction with atomic electrons are also EM ¬Hadron photo- and electro- production are simulated in framework of G 4 hadronic physics V. Ivanchenko 01. 09. 03 EM processes 8

EM packages ¬ Standard – basic set of processes for HEP ¬ Muons – basic set of muon processes for HEP ¬ Xrays – xray and optical proton production ¬ Lowenergy – alternative set of processes with low energy extension of gamma, electron, and hadron EM physics V. Ivanchenko ¬ Utils – common classes and interfaces for other EM packages: – interfaces – energy loss tables builders – fluctuations of energy losses – multiple scattering 01. 09. 03 EM processes 9

Standard EM Physics ¬The projectile is assumed to have the energy Ekin > 1 ke. V ¬The atomic electrons are quasi-free – their binding energies neglected (except some corrections at low energies) ¬The atomic nucleus are fixed – no recoil ¬The matter is described as homogeneous, isotropic, amorphous V. Ivanchenko 01. 09. 03 EM processes 10

Standard EM Processes ¬ Gamma – – ¬ Muons Photo-electric effect Compton scattering e+e- pair production + - pair production ¬ Electron and positron – Ionization – Bremsstrahlung – Positron annihilation V. Ivanchenko – Ionization – Bremsstrahlung – e+e- pair production ¬ Hadrons – Ionization ¬ Ions – Ionization ¬ Multiple scattering 01. 09. 03 EM processes 11

Standard EM Physics (Michel Maire and Laszlo Urban) ¬ Standard G 4 physics was based on G 3 knowledge/experience ¬ Review of G 3 models have been done ¬ More precise theories were used if possible/ necessary ¬ Extension to highest energies in progress V. Ivanchenko Landau-Pomeranchuk-Migdal Effect for bremsstrahlung 01. 09. 03 EM processes 12

Physics. List ¬ It is one of the « mandatory user classes » ; – Defined in source/run ¬ Defines the three pure virtual methods: – Construct. Particle() – Construct. Processe() – Set. Cuts() ¬ Concrete Physics. List needs to inherit from G 4 VUser. Physics. List or G 4 VModular. Physics. List ¬ For interactivity G 4 User. Physics. List. Messenger can be used to handle Physics. List parameters V. Ivanchenko 01. 09. 03 EM processes 13

Example: Add. Transportation void G 4 VUser. Physics. List: : Add. Transportation() { G 4 Transportation* the. Transportation. Process= new G 4 Transportation(); // loop over all particles in G 4 Particle. Table the. Particle. Iterator->reset(); while( (*the. Particle. Iterator)() ){ G 4 Particle. Definition* particle = the. Particle. Iterator->value(); G 4 Process. Manager* pmanager = particle->Get. Process. Manager(); if (!particle->Is. Short. Lived()) { if ( pmanager == 0) { G 4 Exception("G 4 VUser. Physics. List: : Add. Transportation : no process manager!"); } else { // add transportation with ordering = ( -1, "first" ) pmanager->Add. Process(the. Transportation. Process); pmanager->Set. Process. Ordering. To. First(the. Transportation. Process, idx. Along. Step) pmanager->Set. Process. Ordering. To. First(the. Transportation. Process, idx. Post. Step); } } } V. Ivanchenko 01. 09. 03 EM processes 14

Processes ordering ¬ Ordering of following processes is critical: – Assuming n processes, the ordering of the Along. Get. Physical. Interaction. Length should be: [n-2] … [n-1] multiple scattering [n] transportation ¬ Why ? – Processes return a « true path length » ; – The multiple scattering convers it into a shorter « geometrical » path length; – Based on this new length, the transportation can geometrically limits the step. ¬ Other processes ordering usually do not matter. V. Ivanchenko 01. 09. 03 EM processes 15

Example: Gamma processes ¬ Discrete processes - only Post. Step actions; – Use function Add. Discrete. Process; – pmanager is the G 4 Process. Manager of the gamma; – Assume the transportation has been set by Add. Transportation; ¬ Code sample: // Construct processes for gamma: pmanager->Add. Discrete. Process(new G 4 Gamma. Conversion()); pmanager->Add. Discrete. Process(new G 4 Compton. Scattering()); pmanager->Add. Discrete. Process(new G 4 Photo. Electric. Effect()); V. Ivanchenko 01. 09. 03 EM processes 16

Example: Electron processes // Construct processes for positron G 4 VProcess* the. Multiple. Scattering = new G 4 Multiple. Scattering(); G 4 VProcess* e. Ionisation = new G 4 e. Ionisation(); G 4 VProcess* e. Bremsstrahlung = new G 4 e. Bremsstrahlung(); // add processes pmanager->Add. Process(the. Multiple. Scattering); pmanager->Add. Process(e. Ionisation); pmanager->Add. Process(e. Bremsstrahlung); // set ordering for Along. Step. Do. It pmanager->Set. Process. Ordering(the. Multiple. Scattering, idx. Along. Step, 1); pmanager->Set. Process. Ordering(e. Ionisation, idx. Along. Step, 2); // set ordering for Post. Step. Do. It pmanager->Set. Process. Ordering(the. Multiple. Scattering, idx. Post. Step, 1); pmanager->Set. Process. Ordering(e. Ionisation, idx. Post. Step, 2); pmanager->Set. Process. Ordering(e. Bremsstrahlung, idx. Post. Step, 3); V. Ivanchenko 01. 09. 03 EM processes 17

Example: Positrons processes G 4 VProcess* theeplus. Multiple. Scattering = new G 4 Multiple. Scattering(); G 4 VProcess* theeplus. Ionisation = new G 4 e. Ionisation(); G 4 VProcess* theeplus. Bremsstrahlung = new G 4 e. Bremsstrahlung(); G 4 VProcess* theeplus. Annihilation = new G 4 eplus. Annihilation(); pmanager->Add. Process(theeplus. Multiple. Scattering); pmanager->Add. Process(theeplus. Ionisation); pmanager->Add. Process(theeplus. Bremsstrahlung); pmanager->Add. Process(theeplus. Annihilation); pmanager->Set. Process. Ordering. To. First(theeplus. Annihilation, idx. At. Rest); pmanager->Set. Process. Ordering(theeplus. Multiple. Scattering, idx. Along. Step, 1); pmanager->Set. Process. Ordering(theeplus. Ionisation, idx. Along. Step, 2); pmanager->Set. Process. Ordering(theeplus. Multiple. Scattering, idx. Post. Step, 1); pmanager->Set. Process. Ordering(theeplus. Ionisation, idx. Post. Step, 2); pmanager->Set. Process. Ordering(theeplus. Bremsstrahlung, idx. Post. Step, 3); pmanager->Set. Process. Ordering(theeplus. Annihilation, idx. Post. Step, 4); V. Ivanchenko 01. 09. 03 EM processes 18

Hadrons EM processes ¬ Hadrons (pions, kaons, proton, …) ¬ Light ions (deuteron, triton, alpha) ¬ Heavy ions (Generic. Ion) ¬ Example: G 4 VProcess* the. Multiple. Scattering = new G 4 Multiple. Scattering(); G 4 VProcess* h. Ionisation = new G 4 h. Ionisation(); pmanager->Add. Process(the. Multiple. Scattering); pmanager->Add. Process(h. Ionisation); pmanager->Set. Process. Ordering(the. Multiple. Scattering, idx. Along. Step, 1); pmanager->Set. Process. Ordering(h. Ionisation, idx. Along. Step, 2); pmanager->Set. Process. Ordering(the. Multiple. Scattering, idx. Post. Step, 1); pmanager->Set. Process. Ordering(h. Ionisation, idx. Post. Step, 2); V. Ivanchenko 01. 09. 03 EM processes 19

How to build Physics. List? ¬ Physics. List can be build by experience user ¬ Physics. List can be taken from G 4 examples or from the web page: – http: //geant 4. web. cern. ch/geant 4/organisation/ /working_groups. html#vg. Had ¬ Novice examples – N 02: Simplified tracker geometry with uniform magnetic field – N 03: Simplified calorimeter geometry – N 04: Simplified collider detector with a readout geometry ¬ Extended and advanced examples V. Ivanchenko 01. 09. 03 EM processes 20

Conclusion remarks ¬ Using Geant 4 examples novice user can design his/her Physics. List with EM physics processes without detailed studying of interaction of particles with matter ¬ Default values of internal model parameters are reasonably defined ¬ To estimate the accuracy of simulation results indeed one have to study Geant 4 in more details ¬ It is true for any simulation software! V. Ivanchenko 01. 09. 03 EM processes 21