Maria Grazia Pia, INFN Genova and CERN1 An OO model for intra-nuclear transport Maria Grazia Pia L. Bellagamba, A. Brunengo, E. Di Salvo for the Geant4 Collaboration

Maria Grazia Pia, INFN Genova and CERN2 Hadronic physics in Geant4 ] The most complete hadronic simulation kit on the market u data-driven, parameterisation-driven and theory- driven models u complementary and alternative models ] Common basic approach: expose the physics through OO design, to provide the transparency required for the validation of physics results

Maria Grazia Pia, INFN Genova and CERN3 A look at the past... Hadronic simulation was handled through packages u monolithic: either take all of a package or nothing u difficult to understand the physics approach u hard to disentangle the data, their use and the physics modeling...keeping in mind that this is complex physics, in some cases with poor support of experimental data

Maria Grazia Pia, INFN Genova and CERN4 Gheisha Fluka Calor Crystal Barrel and BaBar IFR An example: ( Geant3)

Maria Grazia Pia, INFN Genova and CERN5 Energy range of hadronic models ] Evaporation phase ] Pre-equilibrium: O(100 MeV) ] Intra-nuclear transport: ~100 MeV - 5 GeV (the resonance region) ] The high energy régime

Maria Grazia Pia, INFN Genova and CERN6 The context ] The Hadron Kinetic Model is situated in the context of Geant4 theory-driven hadronic models ] It covers the energy range of intra-nuclear transport in Geant4 ] It must satisfy the requirements u as a model for intra-nuclear transport to be used directly by the processes u as a back-end to higher energy models

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8 The physics idea ] Introduce the concept of time development into the traditional approach of intra-nuclear cascade ] Provides means to address interactions and transport with more sophisticated modeling, i.e. with greater precision

Maria Grazia Pia, INFN Genova and CERN9 Problem domain analysis ] Identify what the model should do (not how it should do it!) ] Decompose the domain into the basic physics concepts ] Further iteration of the decomposition within each sub-domain ] Close collaboration of OO experts with theoreticians

Maria Grazia Pia, INFN Genova and CERN10 Model domains Model-specific ] The time-development management ] The scattering of interacting particles ] The intra-nuclear transport Common to other theoretical models ] The 3D modeling of the nucleus ] The description of the interacting particles

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Maria Grazia Pia, INFN Genova and CERN12 Features of the OO design ] Mapping of physics onto OO design ] Openness to extension and evolution u new channels, new experimental data, new parameterisations, new theoretical models, new algorithms... ] Flexibility for reuse of components in other contexts u e.g. scattering component common to other models ] Extensive use of patterns u to cope with the physics complexity through common archetypes (Composite pattern) u to handle alternative algorithms or physics options (Strategy pattern)

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Maria Grazia Pia, INFN Genova and CERN15 The Kinetic Algorithm A step by step updating of a particle vector: ÊCreate a vector of particles, assign initial particle types, coordinates and momenta etc., assign initial value for the time evolution parameter ËFor a given step of the time evolution parameter find pairs of particles, according to a collision criterion, which are assumed to collide and particles which, according to their lifetimes, are assumed to decay ÌPerform particle collisions and particle decays, determining the generation of outgoing particles; during this step particle coordinates and momenta are updated (particle propagation) ÚStarting from, perform the next step (all this taking into account Pauli blocking)

Maria Grazia Pia, INFN Genova and CERN16 The Scatterer ] Two-body hadron elastic and inelastic scattering u including resonance excitation and deexcitation, particle absorption etc. ] Physics processes implemented: u baryon-baryon interactions (including interactions of baryon resonances) u baryon-antibaryon annihilation u meson-baryon interactions u meson-meson interactions ] Cross sections are calculated from: u tabulations of experimental data (by means of fits or interpolations) u parameterisations according to algebraic functions u from other cross sections via general principles ( detailed balance, AQM...) Yes, it is very complex indeed...

Maria Grazia Pia, INFN Genova and CERN17 The field transport ] At every step coordinates and momenta of all particles travelling through the nucleus are updated from the values at the time of previous interaction to the current time ] For transportation purpose particle-nucleus interaction is described through phenomenological potentials (optical potentials) ] The particle propagation can be operated u via a cascade approach, i.e. along a straight line trajectory – using potentials only to evaluate the final particle energy at the end of the step u via a numerical integration of the equations of motion –using the classical Runge-Kutta method (code reuse from Geant4 Geometry- Transportation)

Maria Grazia Pia, INFN Genova and CERN18 What is new in this model? In terms of physics... ] The kinetic algorithm ] The detailed and extensive scattering module ] The precise field transport ] The wealth of advanced theoretical modeling in each of its details and the thorough exploitation of existing experimental data è The combination of all the above ] The transparency of the physics

Maria Grazia Pia, INFN Genova and CERN19 What is new in this model? In terms of software... ] It fits into a general framework u easily interchangeable with other models at a fine granularity ] It is based on a solid OOAD u open to extension u open to evolution u capable to host alternative models/algorithms/data ] Ample code reuse u from the G4 Geometry/Transportation –fully exploits the knowledge of mathematical experts u by other models –powerful general components like the Scatterer ] OOAD contributes to make the physics transparent

Maria Grazia Pia, INFN Genova and CERN20 Conclusions ] Geant4 Hadron Kinetic Model represents a new approach to intra-nuclear transport ] OOAD has been the key to handle the underlying complex physics domain ] OOAD has allowed to clearly expose the physics, thus contributing to the validation of physics results ] The sound OOAD makes the model open to evolution and extension