P. Bartalini / IPHE LausannePhysics meeting - LHCb week - Milano, 28 september Status of Physics generators n QCD Models, Decay Models and Interfaces n What is already available o Fortran packages o Status of Pythia 6.1 n What will be available in “few” years from now o Transition to C++ o Development guidelines n Prospects for integration in GAUDI n Primary generation in GEANT 4 n Status of the BPACK project o What has been done in the 1999 o Y2K and future

P. Bartalini / IPHE LausannePhysics meeting - LHCb week - Milano, 28 september Requirements n Well assessed general purpose Q.C.D. models  Description of the event in terms of d  /dp T, d  /d  of pions, kaons, D hadrons, B hadrons etc. HNeed tuning on data o B production asymmetries (?) n Dedicated physics generators to simulate decays  Inclusive models (B semileptionic decays, B-->KX, B-->  X) HNeed tuning on data  Exclusive models (ex. B-->J/  K s ) o Take into account interference terms HHelicity approach HAmplitude approach o Knowledge of the probability density functions o Oscillations (?), CP violation (?) n Event Generator interfaces o Common physics inputs HMasses, charges, spins, branching ratios o Event record HModularization of the physics generators HInput for the simulation step HInformation for the analysis step

P. Bartalini / IPHE LausannePhysics meeting - LHCb week - Milano, 28 september Available (Fortran) Packages n Pythia 6.1 (T. Sjöstrand); Herwig 6.1 (P. Marchesini, B. Webber) o Meet most of the physics and requirements for QCD models o Work is in progress (Lund, Cabridge, Milano) o Well maintained and available at CERN (SGI, OSF, AIX, SunOS, HPUX, Linux, WNT) n QQ 9.2 (D. Jaffe, L. Garren) o Meet most of the physics requirements for decay packages o Work is in progress, short term plans (CLEO, Fermilab) o LHCb maintains a frozen version running on AIX, HPUX, Linux, WNT n StdHep 4.06 (L. Garren) o Meet the standardization, modularization and analysis requirements for the physics generators listed above o Version frozen, further developments foreseen in C++ o Well maintained and available at CERN (SGI, OSF, AIX, SunOS, Linux) o LHCb maintains a frozen version running on the missing platforms (HPUX and WNT)

P. Bartalini / IPHE LausannePhysics meeting - LHCb week - Milano, 28 september Status of Pythia 6.1 n Currently available Pythia (17 August 2000) o LHCb uses Pythia (10 October 1999) n Pythia 6.1 main news (from 4 March 1997) o Jetset+Pythia fusion o Double precision o Matching of initial and final state shower to matrix elements o New parton distribution functions o Energy dependent P T min. in multiple interactions HPublished proceedings of the LHC Standard Model Workshop, B production [hep-ph ] o Popcorn baryon production (optional) o Charm & Bottom asymmetries (from Pythia 6.135) H[E. Norrbin et. Al, Phys. Lett. B442 (1998) 407] HTo be studied by LHCb. HInteresting physics topic by itself HNeed validation for most recent Pythia versions o Forced Fragmentation (not available in official package) HRecently implemented by LHCb H[Presentation at the May 2000 LHCb week] o New entries in Susy, Higgs, Technicolour, Color Reconnection and  Physics.

P. Bartalini / IPHE LausannePhysics meeting - LHCb week - Milano, 28 september C++ Generators n Pythia 7.0 (L. Lönnblad) o First version released on June [hep-ph/ ] H not recommended for scientific studies o Guaranteed on Linux with GNU GCC compiler version o Next versions aim to be fully ANSI/ISO C++ compliant o Dependencies: CLHEP o Milestones Hhaving something of production quality within a year from now H“several years” needed to declare obsolete Pythia 6 n Herwig++ (M. Seymour, B. Webber) o Stuck at the design phase; no preliminary version available o Dedicated workshop held in UK in April 2000 o Now 2 post-docs working full time (time scale 3 years) n EvtGen 1.0 (A. Ryd) o Decay framework that meet most of the physics requirements o Lack of B s mesons and B barions decay models o Currently used and maintained by BABAR (OSF, AIX, SunOS, HPUX, Linux) o Unofficial LHC version now maintained by ATLAS at CERN HATLAS/BABAR/CDF EvtGen meeting recently held in Berkeley

P. Bartalini / IPHE LausannePhysics meeting - LHCb week - Milano, 28 september C++ Interfaces n StdHep 4.09 (L. Garren) o Extends the functionalities of StdHep 4.06 providing event record classes that are basically a translation from the /HEPEVT/ common block o Included in CLHEP 1.5 o Will evolve in parallel with Pythia 7 n HepMC 0.91 (M. A. Dobbs, J. B. Hansen) o Particles and Vertices in a graph structure o Meet all the modularization requirements (spin density matrix) o Coding conventions are GAUDI compliant o Pursued for inclusion in CLHEP o Suggested as standard event generator interface for GEANT 4 n StdHep and HepMC have been invited to merge in a single package o CLHEP Workshop recently held at Fermilab (30 june 2000)

P. Bartalini / IPHE LausannePhysics meeting - LHCb week - Milano, 28 september Prospects for integration in the GAUDI framework n All the physics generators, including those that will not migrate to C++ are of interest for LHCb o Communications with the StdHEP common block will be in any case essential (not only in a short time scale) n All the physics generator information has to be accessible at the analysis step o GEANT 4 will be fed by GIGA (subset of generator information) o HepMC will probably be the standard for all the C++ physics event generators. it is also a good candidate to preserve the full generator information for the analysis step n As far as it is possible, physics generator and simulation packages should have some consistency in the physics inputs n Milestones o Preliminary Integration (by end of 2001) HStdHep still needed to drive the fortran based generators HHepMC adopted as standard event record HFirst production tests with Pythia 7 o End of integration (by end of 2002) HThe framework will support all the physics generators and will allow for generator level validation tests (Pythia 7 vs Pythia 6, EvtGen vs QQ)

P. Bartalini / IPHE LausannePhysics meeting - LHCb week - Milano, 28 september Primary generation in GEANT 4 n (Achieved by GIGA) n Full primary decay chains can be specified in the generator step o GEANT 4 will only simulate the transport of particles defined as G4ParticleDefinition class objects o GEANT 4 will respect the decay channels and the center of mass kinematics simulated by the physics generator (forced decay channel) n Possible sources of problems o Tracking of particles which are not defined as G4ParticleDefinition class objects HB hits in VELO detector can happen! o Forced decay channel HOscillations (is proper decay time preserved ?) HRegeneration in material n Direct interface to physics event generators o StdHep interface option ruled out o Adopt HepMC event record ? o Direct link to Pythia 7 ?

P. Bartalini / IPHE LausannePhysics meeting - LHCb week - Milano, 28 september BPACK (1999) n Some activity at the end of the year o Workshop on Standard Model Physics at the LHC o Informal meeting with Marjorie Shapiro (CDF) to discuss plans for QQ maintenance o Idea of a common effort on a B decay package o Proposal of ATLAS to collaborate also with BABAR HAccess to EvtGen HAccess to recent data for tuning purposes n Further meetings at CERN and in Video-conference with Fermilab and LBL o Organizational issues o Collection of physics and software requirements HEvtGen seems to be the best candidate to start with HIdentification of specific tasks n Discussion in LHCb at the December 1999 LHCb week and at the physics generator mini-Workshop held in Clermont Ferrnand o From January 2000 LHCb and CMS contribute to the project just as OBSERVER

P. Bartalini / IPHE LausannePhysics meeting - LHCb week - Milano, 28 september BPACK (Y2K and future) n From 2000 the BPACK acronym indicates the ideal decay package LHCb wants to have… n ATLAS, CDF and BABAR decide to concentrate on EvtGen o Meeting in Berkley in the context of the summer ATLAS week o Recent Progresses on the following subjects HTreatment of B s Mixing HImplementation of B s and  b decays (ex. B s --> VV) HImplementation of spin 3/2 particles HIntegration with Pythia 6, StdHep and HepMC interface n LHCb strategy for BPACK (What do the LHCb physics requirements imply ?) o Join ATLAS/CDF/BABAR collaboration and stay with EvtGen ? HLimited manpower needed (at least one software coordinator and one physics coordinator) HFor now It may be worth to become EvtGen users o Have our own project ? HNeed to start as soon as possible to be ready by 2005 HNeed allocation of reasonable resources and manpower o Physicists will spontaneously contribute to the channel of their interest ? n Next end of the year physics generator mini- Workshop to be held in Lausanne or at CERN o Further news as soon as possible