1. P. Bartalini / IPHE LausanneLHCb physics generator workshop - Lausanne, 2 march 2001 1 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 o Prospects for integration in GAUDI HNext talk (Gloria Corti)

2. P. Bartalini / IPHE LausanneLHCb physics generator workshop - Lausanne, 2 march 2001 2 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 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

3. P. Bartalini / IPHE LausanneLHCb physics generator workshop - Lausanne, 2 march 2001 3 Available (Fortran) Packages n Pythia 6.1 (T. Sjöstrand); Herwig 6.1 (P. Marchesini, B. Webber) o Meet most of the physics requirements for QCD models o Work is in progress (Lund, Cambridge, 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 HDoes LHCb want to follow the Fermilab upgrade plans ? 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 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)

4. P. Bartalini / IPHE LausanneLHCb physics generator workshop - Lausanne, 2 march 2001 4 Status of Pythia 6.1 n Currently available Pythia 6.157 (5 february 2001) o LHCb uses Pythia 6.134 (10 October 1999) HPlans to switch soon to a more recent version n Pythia 6.1 main news (from 4 March 1997) o Jetset+Pythia+SPythia 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 0003142] o Popcorn baryon production (optional) o Improvement of c & b prod. asymmetries (from Pythia 6.135) HCurrently studied in LHCb (N.Brook, this workshop). HInteresting physics topic by itself HNeed validation for most recent Pythia versions o c & b flavour excitation in mult. Int. (from Pythia 6.138) o new treatment of c & b radiation (from Pythia 6.154) 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. o Documentation H[hep-ph 0010017] (Pythia 6.154) HJ.P.Guillaud (LAPP) “Pythia Mini-Guide”

5. P. Bartalini / IPHE LausanneLHCb physics generator workshop - Lausanne, 2 march 2001 5 C++ Generators n Pythia 7.0 (L. Lönnblad) o First version released on June 14 2000 [hep-ph/0006152] H not recommended for scientific studies o Guaranteed on Linux with GNU GCC compiler version 2.95.2 o Next versions aim to be fully ANSI/ISO C++ compliant o Dependencies: CLHEP o Milestones Hhaving something of production quality in 2002 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 ATLAS/BABAR/CDF EvtGen meeting held at Berkeley in summer 2000

6. P. Bartalini / IPHE LausanneLHCb physics generator workshop - Lausanne, 2 march 2001 6 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 from version 1.5 o HepPDT sub-package to handle decay tables HPythia 7, EvtGen, QQ (not yet) n HepMC 1.01 (M. A. Dobbs, J. B. Hansen) o Documentation [Comput. Phys. Commun. 134 (2001) 41] o Particles and Vertices in a graph structure o Meet all the modularization requirements (spin density matrix) o Coding conventions are GAUDI compliant n StdHep and HepMC are currently being merged in a single package o Event Generation in ATLAS-Gaudi will make use of both StdHep and HEPMC HUp-to-date news in next talk (Gloria Corti)

7. P. Bartalini / IPHE LausanneLHCb physics generator workshop - Lausanne, 2 march 2001 7 Primary generation in GEANT 4 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 ?)

8. P. Bartalini / IPHE LausanneLHCb physics generator workshop - Lausanne, 2 march 2001 8 BPACK (1999-2000) n Some activity at the end of 1999 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

9. P. Bartalini / IPHE LausanneLHCb physics generator workshop - Lausanne, 2 march 2001 9 BPACK (future steps) 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 o Further news ??? n LHCb strategy for BPACK (What do the LHCb physics requirements imply ?) o Join ATLAS/CDF/BABAR collaboration and stay with EvtGen ? HFor now It may be worth to become at least 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 ?