Status of physics generators
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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 Primary generation in GEANT 4

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Status of Physics generators

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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

  • Primary generation in GEANT 4

  • Status of the BPACK project

    • What has been done in the 1999

    • Y2K and future


Requirements

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

    • B production asymmetries (?)

  • 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


Available fortran packages

Available (Fortran) Packages

  • Pythia 6.1 (T. Sjöstrand); Herwig 6.1 (P. Marchesini, B. Webber)

    • Meet most of the physics and requirements for QCD models

    • Work is in progress (Lund, Cabridge, 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

  • StdHep 4.06 (L. Garren)

    • Meet the standardization, modularization and analysis requirements for the physics generators listed above

    • Version frozen, further developments foreseen 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)


Status of pythia 6 1

Status of Pythia 6.1

  • Currently available Pythia 6.152 (17 August 2000)

    • LHCb uses Pythia 6.134 (10 October 1999)

  • Pythia 6.1 main news (from 4 March 1997)

    • Jetset+Pythia 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)

    • Charm & Bottom asymmetries (from Pythia 6.135)

      • [E. Norrbin et. Al, Phys. Lett. B442 (1998) 407]

      • To be studied by LHCb.

        • Interesting physics topic by itself

        • Need validation for most recent Pythia versions

    • 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.


C generators

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 within a year from now

      • “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)

    • Unofficial LHC version now maintained by ATLAS at CERN

      • ATLAS/BABAR/CDF EvtGen meeting recently held in Berkeley


C interfaces

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 1.5

    • Will evolve in parallel with Pythia 7

  • HepMC 0.91 (M. A. Dobbs, J. B. Hansen)

    • Particles and Vertices in a graph structure

    • Meet all the modularization requirements (spin density matrix)

    • Coding conventions are GAUDI compliant

    • Pursued for inclusion in CLHEP

    • Suggested as standard event generator interface for GEANT 4

  • StdHep and HepMC have been invited to merge in a single package

    • CLHEP Workshop recently held at Fermilab (30 june 2000)


Prospects for integration in the gaudi framework

Prospects for integration in the GAUDI framework

  • All the physics generators, including those that will not migrate to C++ are of interest for LHCb

    • Communications with the StdHEP common block will be in any case essential (not only in a short time scale)

  • All the physics generator information has to be accessible at the analysis step

    • GEANT 4 will be fed by GIGA (subset of generator information)

    • 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

  • As far as it is possible, physics generator and simulation packages should have some consistency in the physics inputs

  • Milestones

    • Preliminary Integration (by end of 2001)

      • StdHep still needed to drive the fortran based generators

      • HepMC adopted as standard event record

      • First production tests with Pythia 7

    • End of integration (by end of 2002)

      • The framework will support all the physics generators and will allow for generator level validation tests (Pythia 7 vs Pythia 6, EvtGen vs QQ)


Primary generation in geant 4

Primary generation in GEANT 4

  • (Achieved by GIGA)

  • 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 ?)

      • Regeneration in material

  • Direct interface to physics event generators

    • StdHep interface option ruled out

    • Adopt HepMC event record ?

    • Direct link to Pythia 7 ?


Bpack 1999

BPACK (1999)

  • Some activity at the end of the year

    • 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


Bpack y2k and future

BPACK (Y2K and future)

  • 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

  • LHCb strategy for BPACK (What do the LHCb physics requirements imply ?)

    • Join ATLAS/CDF/BABAR collaboration and stay with EvtGen ?

      • Limited manpower needed (at least one software coordinator and one physics coordinator)

      • For now It may be worth to become 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 ?

  • Next end of the year physics generator mini-Workshop to be held in Lausanne or at CERN

    • Further news as soon as possible


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