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Status of Physics generators

Status of Physics generators. QCD Models, Decay Models and Interfaces What is already available Fortran packages Status of Pythia 6.1 What will be available in “few” years from now Transition to C++ Development guidelines Prospects for integration in GAUDI Next talk (Gloria Corti).

theophilus-stavros
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Status of Physics generators

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  1. Status of Physics generators • QCD Models, Decay Models and Interfaces • What is already available • Fortran packages • Status of Pythia 6.1 • What will be available in “few” years from now • Transition to C++ • Development guidelines • Prospects for integration in GAUDI • Next talk (Gloria Corti)

  2. Requirements • Well assessed general purpose Q.C.D. models • Description of the event in terms of ds/dpT, ds/dh of pions, kaons, D hadrons, B hadrons etc. • Need tuning on data • Dedicated physics generators to simulate decays • Inclusive models (B semileptionic decays, B-->KX, B-->pX) • Need tuning on data • Exclusive models (ex. B-->J/yKs) • Take into account interference terms • Helicity approach • Amplitude approach • Knowledge of the probability density functions • Oscillations (?), CP violation (?) • Event Generator interfaces • Common physics inputs • Masses, charges, spins, branching ratios • Event record • Modularization of the physics generators • Input for the simulation step • Information for the analysis step

  3. Available (Fortran) Packages • Pythia 6.1 (T. Sjöstrand); Herwig 6.1 (P. Marchesini, B. Webber) • Meet most of the physics requirements for QCD models • Work is in progress (Lund, Cambridge, Milano) • Well maintained and available at CERN (SGI, OSF, AIX, SunOS, HPUX, Linux, WNT) • QQ 9.2 (D. Jaffe, L. Garren) • Meet most of the physics requirements for decay packages • Work is in progress, short term plans (CLEO, Fermilab) • LHCb maintains a frozen version running on AIX, HPUX, Linux, WNT • Does LHCb want to follow the Fermilab upgrade plans ? • StdHep 4.06 (L. Garren) • Meet the standardization, modularization and analysis requirements for the physics generators listed above • Version frozen, further developments in C++ • Well maintained and available at CERN (SGI, OSF, AIX, SunOS, Linux) • LHCb maintains a frozen version running on the missing platforms (HPUX and WNT)

  4. Status of Pythia 6.1 • Currently available Pythia 6.157 (5 february 2001) • LHCb uses Pythia 6.134 (10 October 1999) • Plans to switch soon to a more recent version • Pythia 6.1 main news (from 4 March 1997) • Jetset+Pythia+SPythia fusion • Double precision • Matching of initial and final state shower to matrix elements • New parton distribution functions • Energy dependent PT min. in multiple interactions • Published proceedings of the LHC Standard Model Workshop, B production [hep-ph 0003142] • Popcorn baryon production (optional) • Improvement of c & b prod. asymmetries (from Pythia 6.135) • Currently studied in LHCb (N.Brook, this workshop). • Interesting physics topic by itself • Need validation for most recent Pythia versions • c & b flavour excitation in mult. Int. (from Pythia 6.138) • new treatment of c & b radiation (from Pythia 6.154) • Forced Fragmentation (not available in official package) • Recently implemented by LHCb • [Presentation at the May 2000 LHCb week] • New entries in Susy, Higgs, Technicolour, Color Reconnection and  Physics. • Documentation • [hep-ph 0010017] (Pythia 6.154) • J.P.Guillaud (LAPP) “Pythia Mini-Guide”

  5. C++ Generators • Pythia 7.0 (L. Lönnblad) • First version released on June 14 2000 [hep-ph/0006152] • not recommended for scientific studies • Guaranteed on Linux with GNU GCC compiler version 2.95.2 • Next versions aim to be fully ANSI/ISO C++ compliant • Dependencies: CLHEP • Milestones • having something of production quality in 2002 • “several years” needed to declare obsolete Pythia 6 • Herwig++ (M. Seymour, B. Webber) • Stuck at the design phase; no preliminary version available • Dedicated workshop held in UK in April 2000 • Now 2 post-docs working full time (time scale 3 years) • EvtGen 1.0 (A. Ryd) • Decay framework that meet most of the physics requirements • Lack of Bs mesons and B barions decay models • Currently used and maintained by BABAR (OSF, AIX, SunOS, HPUX, Linux) • ATLAS/BABAR/CDF EvtGen meeting held at Berkeley in summer 2000

  6. C++ Interfaces • StdHep 4.09 (L. Garren) • Extends the functionalities of StdHep 4.06 providing event record classes that are basically a translation from the /HEPEVT/ common block • Included in CLHEP from version 1.5 • HepPDT sub-package to handle decay tables • Pythia 7, EvtGen, QQ (not yet) • HepMC 1.01 (M. A. Dobbs, J. B. Hansen) • Documentation [Comput. Phys. Commun. 134 (2001) 41] • Particles and Vertices in a graph structure • Meet all the modularization requirements (spin density matrix) • Coding conventions are GAUDI compliant • StdHep and HepMC are currently being merged in a single package • Event Generation in ATLAS-Gaudi will make use of both StdHep and HEPMC • Up-to-date news in next talk (Gloria Corti)

  7. Primary generation in GEANT 4 • Full primary decay chains can be specified in the generator step • GEANT 4 will only simulate the transport of particles defined as G4ParticleDefinition class objects • GEANT 4 will respect the decay channels and the center of mass kinematics simulated by the physics generator (forced decay channel) • Possible sources of problems • Tracking of particles which are not defined as G4ParticleDefinition class objects • B hits in VELO detector can happen! • Forced decay channel • Oscillations (is proper decay time preserved ?)

  8. BPACK (1999-2000) • Some activity at the end of 1999 • Workshop on Standard Model Physics at the LHC • Informal meeting with Marjorie Shapiro (CDF) to discuss plans for QQ maintenance • Idea of a common effort on a B decay package • Proposal of ATLAS to collaborate also with BABAR • Access to EvtGen • Access to recent data for tuning purposes • Further meetings at CERN and in Video-conference with Fermilab and LBL • Organizational issues • Collection of physics and software requirements • EvtGen seems to be the best candidate to start with • Identification of specific tasks • Discussion in LHCb at the December 1999 LHCb week and at the physics generator mini-Workshop held in Clermont Ferrnand • From January 2000 LHCb and CMS contribute to the project just as OBSERVER

  9. BPACK (future steps) • From 2000 the BPACK acronym indicates the ideal decay package LHCb wants to have… • ATLAS, CDF and BABAR decide to concentrate on EvtGen • Meeting in Berkley in the context of the summer ATLAS week • Recent Progresses on the following subjects • Treatment of Bs Mixing • Implementation of Bs and b decays (ex. Bs --> VV) • Implementation of spin 3/2 particles • Integration with Pythia 6, StdHep and HepMC interface • Further news ??? • LHCb strategy for BPACK (What do the LHCb physics requirements imply ?) • Join ATLAS/CDF/BABAR collaboration and stay with EvtGen ? • For now It may be worth to become at least EvtGen users • Have our own project ? • Need to start as soon as possible to be ready by 2005 • Need allocation of reasonable resources and manpower • Physicists will spontaneously contribute to the channel of their interest ?

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