status of physics generators

P. Bartalini / IPHE Lausanne Physics meeting - LHCb week - Milano, 28 september 2000 1

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 d/dpT, d/d 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-->X)

Need tuning on data Exclusive models (ex. B-->J/Ks) 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 6.1Status 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 itselfNeed 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++ GeneratorsC++ 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++ InterfacesC++ 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)




(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 withIdentification 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

status of physics generators

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