Prospects for integration of physics event
generators
P. Bartalini
OUTLINE
•
Event generators
•
Event generation in GEANT 4
•
Event generator interfaces
•
The BPACK project
P.Bartalini - software week - 25 nov. 1999 1
C++ Event generators
•
Pythia 7
- Pythia is a Monte Carlo package for simulating multi-
particle production in collisions between elementary parti-
cles (T.Sj¨
ostrand et. al.).
- C++ version, contact person: Leif L¨
onnblad (Lund)
- Work is in progress (almost finished)
•
Herwig++
- HERWIG is a Monte Carlo package for simulat-
ing hadron emission reactions with interfering gluons
(P.Marchesini et. al.).
- C++ version, contact persons: M. Seymour (RAL) and
B. Webber (Cambridge/CERN)
- Work is in progress (just started)
•
EvtGen 1
- EvtGen is a Monte Carlo package dedicated to
B
me-
son decays that follows the amplitude approach (A.Ryd)
- C++ version, contact person: A.Ryd (Caltech)
- The first version is ready (tested on OSF, AIX, SunOS,
HPUX, Linux)
- Not yet amenable for LHC
→
BPACK project
P.Bartalini - software week - 25 nov. 1999 2
Pythia 7 overview
•
Event
list of Collision
list of ParticleData
•
Collision
list of Step
initial colliding particles
initial collision vertex
•
Step
list of Particles
list of intermediate particles
P.Bartalini - software week - 25 nov. 1999 3
Pythia 7 overview
•
Particle
ParticleData
pointers to decay products (Particles)
color connections
pointers to modifications of this particle
spin
4-momentum
generated mass
vertex (space & time)
decay (space & time)
proper lifetime
resolution scale
pointer to creation step
P.Bartalini - software week - 25 nov. 1999 4
Pythia 7 overview
•
ParticleData
PDG number
name as character string
mass
ParticleMass
width
lifetime
charge
spin
color
stable flag
anti-particle pointer
flag about how to treat anti-particle
decay table
P.Bartalini - software week - 25 nov. 1999 5
Event generation in GEANT 4
contact person Makoto Asai (Hiroshima)
•
Actual generation of primary particles is done by con-
crete classes of G4VPrimaryGenerator derived from
G4VuserPrimaryGeneratorAction; for now GEANT 4 pro-
vides a couple of G4VPrimaryGenerator concrete classes
- G4ParticleGun
- G4HEPEvtInterface
→
reads an ASCII file produced
by an event generator and reproduces G4PrimaryParticle
objects associated with a G4PrimaryVertex object
- once Pythia 7 version is ready GEANT 4 will provide
a direct interface
•
Present scenario
→
disentangle generation and simulation
•
Future scenario
→
just Pythia ? More sophisticated gen-
erator interfaces (StdHepC++) ?
P.Bartalini - software week - 25 nov. 1999 6
B decay in GEANT ?
B interaction in the VELO detector and material can happen!
P.Bartalini - software week - 25 nov. 1999 7
particle genaration, tracking, decays
•
A concrete class of G4VPrimaryGenerator,
the G4PrimaryParticle object is constructed with either a
pointer to G4ParticleDefinition or an integer number which
represents P.D.G. particle code.
•
GEANT 4 will simulate only the particles which are de-
fined as G4ParticleDefinition class objects. Other primary
particles will be simply ignored by G4EventManager. But
it may still be useful to construct such “intermediate” par-
ticles for recording the origin of the primary event
•
The G4PrimaryParticle class object can have a list of its
daughter particles. If the parent particle is an “intermedi-
ate” particle, which Geant4 does not have a corresponding
G4ParticleDefinition, this parent particle is ignored and
daughters are assumed to start from the vertex with which
their parent is associated
•
GEANT 4 is able to perform decay in flight of particle
that have a corresponding G4ParticleDefinition, however
the priority is given to the physics generator
P.Bartalini - software week - 25 nov. 1999 8
StdHep
•
The SICb simulation currently uses the public version of
StdHep
, the generator and analysis framework built by
the Fermilab simulation group; also maintained at CERN
•
PDG compliant particle data base
•
Translation routines
- Generator commons
→
/HEPEVT/
- /HEPEVT/
→
generator commons, Geant 3 (KINE
and VERT).
•
Utility routines:
- QQ related (decay particles and update /HEPEVT/)
- Quark contents; mother/daughter operations
•
Tools (not used in SICb):
- Machine independent I/O streams
- Generator event display
P.Bartalini - software week - 25 nov. 1999 9
StdHepC++
contact person: Lyn Garren (Fermilab)
•
The first version (StdHep 4.07) is available and it is tested
on the Fermilab supported platforms
•
It is consistent with the Pythia 7 strategies
•
For backward compatibility it provides interfaces to the
existing fortran /HEPEVT/ common block
•
It will implement all functions currently in the fortran Std-
Hep implementation
•
It will iterface EvtGen !
•
XDR, LHC++ and root I/O will be supported
•
It is identified as being pursued for inclusion in CLHEP
or enchancements of a CLHEP package; contact person:
Andreas Pfeiffer (CERN)
•
The spinoff on GEANT 4 have to be discussed; CLHEP–
GEANT 4 contact person: Gabriele Cosmo (CERN)
P.Bartalini - software week - 25 nov. 1999 10
The BPACK project
•
Joint effort for a common development od a
B
decay
package (collaborators from ATLAS, CMS, LHCb, BaBar,
CDF, Theory)
•
first meeting of CMS, LHCb and ATLAS Friday November
12 at 9:00-12:30 in room 40-4d-08
•
first video conference meeting of BaBar, CDF, CMS, LHCb
and ATLAS; Wednesday November 17 at 17:00-19:30 in
room 40-4-C01
•
second meeting of CMS, LHCb and ATLAS Friday Decem-
ber 3 at 14:00-18:00 in room 32-S-C22
•
http://home.cern.ch/ msmizans/production/Bpack
•
physics requirements
→
EvtGen
•
software requirements
→
StdHepC++, Decay data base
•
organisation requrements
→
officialisation, LoI
- Olivier Schneider presentation at the LHCb week
- END OF THE YEAR LHCb GENERATOR MINI–
WORKSHOP IN CLERMONT FERRAND
P.Bartalini - software week - 25 nov. 1999 11
