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J.P. Wellisch CERN/EP/SFT

Physics of Hadronic Showers at LHC HEP 2003, Europhysics conference, Aachen, Germany. J.P. Wellisch CERN/EP/SFT. Overview. Introducing a system for classification of modeling approaches. Two novel theoretical approaches: Chiral invariant phase-space decay Binary cascade

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J.P. Wellisch CERN/EP/SFT

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  1. Physics of Hadronic Showers at LHCHEP 2003, Europhysics conference, Aachen, Germany. J.P. Wellisch CERN/EP/SFT

  2. Overview • Introducing a system for classification of modeling approaches. • Two novel theoretical approaches: • Chiral invariant phase-space decay • Binary cascade • Summary

  3. Three categories of modeling approaches • Data driven modeling • Parametrization driven modeling • Theory driven modeling

  4. Parameterisation driven models • Total cross-sections. • Final state generators - two domains: • high energy inelastic (Aachen, CMS) • low energy inelastic, elastic, fission, capture (TRIUMF, UBC, CERN) • Stopping particles • base line (TRIUMF, CHAOS) • mu- (TRIUMF, FIDUNA) • pi- (INFN, CERN, TRIUMF) • K- (Crystal Barrel, TRIUMF) • anti-protons (JLAB, CERN) • Electromagnetic transitions of the exotic atom prior to capture; effects of atomic binding. (Novosibirsk, ESA)

  5. Example:Proton cross-sections

  6. Data driven models: • Radioactive decay, photon evaporation, internal conversion (ENSDF), elastic scattering (SAID), etc.. • Low energy neutron • Based on evaluated data: G4NDN, derived from • ENDF, Jef, JENDL, CENDL, ENSDF, Brond, IRDF, FENDL, MENDL,... • Sampling codes for ENDF-B VI derived data formats • Use the file-system to ensure granular and transparent access/usage of data sets • Doppler broadening not static on input data, but on the fly from 0K data.

  7. Example of data driven modeling: neutron capture, and isotope production

  8. Theory driven models • Ultra-high energy models • Parton transport model (in discussion) • High energy models • ‘Fritjof’ type string model (CERN) • Quark gluon String (CERN) • Pythia(7) interface (Lund, CERN) • Intra-nuclear transport models (or replacements) • Bertini cascade (HIP, CERN) • Binary cascades (CERN, U.Frankfurt) • QMD (CERN, Inst.Th.Phys. Frankfurt) • Chiral invariant phase-space decay (JLAB, CERN, ITEP) • Partial Mars rewrite (Kyoto, in collaboration with UVic. and FNAL) • De-excitation • Evaporation, fission, multi-fragmentation, fermi-break-up (Valencia)

  9. Example of a theoretical final state generator: quark gluon string model

  10. Novel theoretical approaches • Chiral invariant phase-space decay • A quark level 3-dimensional event generator for fragmentation of excited hadronic systems (quasmons) into hadrons. • Binary cascade • In between Bertini’s cascade and quantuum molecular dynamics.

  11. Binary cascading • Some characteristics of binary cascading: • In binary cascading, like in QMD, each nucleon participant is described by • And the total wave function is assumed to be the direct product of these (no antisymmetrization). • The equations of motion for this wave-form are identical in structure to the classical Hamilton equations, and can be solved by numerical integration. • Nuclear Hamiltonian is calculated from optical potentials based on the information on all hadrons in the system

  12. The imaginary part of the G-matrix • Acts like a scattering term • Described as 2-body, point-like collisions • Collision assumption of black disk cross-section

  13. The nuclear model • The nuclear density distributions used are the Saxon-Woods form for high A • And the harmonic oscillator form for light nuclei (A<17) • The nucleon momenta are randomly selected between zero and the Fermi momentum at a chosen location in configuration space.

  14. Why binary cascade? • The name binary cascade comes from the fact that only binary collisions (and decay) are considered, like • No further details on the mathematics, but the nucleon and delta resonances taken into consideration are these • D1232, D1600, D1620, D1700, D1900, D1905, D1910, D1920, D1930, D1950 • N1400, N1520, N1535, N1650, N1675, N1680, N1700, N1710, N1720, N1900, N1990, N2090, N2190, N2220, N2250

  15. Binary cascadeprediction Sample the Impact parameter over A large area. Make the ratio of ‘hits’ To trials, times the area sampled

  16. Lead Forward peaks in proton scattering (256 MeV) Beryllium Iron Aluminum

  17. Chiral Invariant Phase-space Decay. • A quark level 3-dimensional event generator for fragmentation of excited hadronic systems (quasmons) into hadrons. • Based on the QCD idea of asymptotic freedom • Local chiral invariance restoration lets us consider quark partons massless, and we can integrate the invariant phase-space distribution of quark partons and quark exchange (fusion) mechanism of hadronization • The only non-kinematical concept used is that of a temperature of the quasmon.

  18. Vacuum CHIPS • This allows to calculate the decay of free excited hadronic systems: • In an finite thermalized system of N partons with total mass M, the invariant phase-space integral is proportional to , and the statistical density of states is proportional to . Hence we can write the probability to find N partons with temperature T in a state with mass M as • Note that for this distribution, the mean mass square is

  19. Vacuum CHIPS • We use this formula to calculate the number of partons in the quasmon, and obtain the parton spectrum • To obtain the probability for quark fusion into hadrons, we can compute the probability to find two partons with momenta q and k with the invariant mass m.

  20. Vacuum CHIPS • Using the delta function to perform the integration and the mass constraint, we find the total kinematical probability of hadronization of a parton with momentum k into a hadron with mass m: • Accounting for spin and quark content of the final state hadron adds (2s+1) and a combinatorial factor. • At this level of the language, CHIPS can be applied to p-pbar annihilation

  21. Anti proton annihilation

  22. Anti proton annihilation

  23. Nuclear CHIPS • In order to apply CHIPS for an excited hadronic system within nuclei, we have to add parton exchange with nuclear clusters to the model • The kinematical picture is, that a color neutral quasmon emits a parton, which is absorbed by a nucleon or a nuclear cluster. This results in a colored residual quasmon, and a colored compound. • The colored compound then decays into an outgoing nuclear fragment and a ‘recoil’ quark that is incorporated by the colored quasmon.

  24. The parton exchange diagram

  25. A few results: For more information see:Eur.Phys.Journal A9,411(2000) and Eur.Phys.Journal A9,421(2000)

  26. Conclusions • Established UML and OO design as technique for pooling expertise. • Established categorization of physics modeling. • Binary cascade has significant predictive power, also in the giant resonance regime, providing an alternative for the ‘classical’ cascade models. • Chiral invariant phase-space decay allows to use partonic concepts at energies far below 1 GeV.

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