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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

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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

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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

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

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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

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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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Maria Grazia Pia, INFN Genova and CERN7

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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

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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

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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)

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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...

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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)

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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

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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

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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

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