StdHepC

1
StdHepC

• L. Garren
• Presented by M. Fischler
• Fermi National Accelerator Laboratory USA
• http//www-pat.fnal.gov/stdhep/c

2
What is StdHep?

• From event generators
• Lund, Pythia, Isajet, Herwig,
• Produce events in some form
• StdHep
• To simulation packages
• Consume events in some form
• Geant3, MCFast,
• Packages can conform to StdHep formats directly,
  but StdHep also has interfaces to package formats

3
What Does StdHep Do?

• Standardized Fortran Monte Carlo output
• HEPEVT common block
• PDG particle numbering scheme
• C requires a similar standard
• Analysis moving to C
• C Monte Carlo generators
• Events and particles are natural C objects
• StdHepC
• Initial interface much like HEPEVT common block
• Translation routines
• Major rewrite under way

4
5 Key Classes in StdHepC

• All classes are in StdHep namespace
• StdHepParticleData
• StdHepParticle
• StdHepCollision
• StdHepEvent
• StdHepRun

5

• Run is logically a sequence of
• Event is a set of
• Collision has a specially structured container of
  
• Particle has methods to refer to common
• ParticleData may come from standard
  reference or be application specific

6
StdHepParticle

• Volatile particle information
• Particle ID
• status code
• color
• generated mass
• helicity
• momentum (CLHEP LorentzVector)
• creation vertex (CLHEP LorentzVector)
• decay vertex (CLHEP LorentzVector)

7
(volatile Particle information continued)

• mother
• secondmother
• index to the first daughter
• index to the last daughter
• Method to access appropriate StdHepParticleData
• Mother and daughter entries deliberately designed
  to be compatible with HEPEVT common block
• Ideally, information about the particle tree
  should (will) be decoupled from the Particle class

8
StdHepCollision

• A Collision is a single beam interaction
• collision number
• input I/O stream
• for bookkeeping purposes
• number of Particles in the collision
• vector of pointers to Particles
• method to get Particle
• Conceptually, Collision is a special sort of
  container of Particles

9
StdHepEvent

• Each beam crossing may have several interactions.
  Therefore an Event is a collection of
  Collisions.
• event number
• number of Collisions
• vector of pointers to Collisions
• method to get Collision
• method to get Particle
• Conceptually, Event is special sort of container
  of Collisions

10
StdHepRun

• Collects event-independent informationLogically
  refers to a sequence of Events
• number of Events to generate
• number of Events generated
• number of Events written to I/O
• nominal center-of-mass energy
• cross section
• random number seeds
• I/O methods

11
Taking Advantage of C and O-O

• The classes described (particularly Particle)
  have some data which ought to be decoupled
• StdHepParticle
• mother
• secondmother
• index to the first daughter
• index to the last daughter
• These implement a type of aggregation, with
  special relationship properties
• The C std library defines semantics for
  containers - stick with those semantics!

12
A Collision is a DAG ltParticlegt

• Directed Acyclic Graph of Particles
• templated class, works as a stdcontainer
• but augmented with parent/child relations
• a parent may have any number of children
• a child may have more than one parent
• each parent or child (Particle) is a node on the
  graph
• Acyclic
• there is at most one relation between two nodes
• there cannot be a closed directed cycle

13
The DAG class

• Looks and feels like other container classes
• iterators same sorts of loop constructs
• Also embodies parent/child relationships
• Removes parent/child information from Particle
• Provides natural methods for traversing the
  particle tree in various ways
• Including the concept of two isomorphic graphs of
  different types of objects
• Allows for disconnected nodes

14
How DAG Will be Used

• class Particle
• class Collision public DAG ltParticlegt
• / plus any not-per-particle data and methods
  /
• DAG has methods to insert/delete a Particle,
  assign parent/child, and provide iterators
• dereferencing a DAGiterator gives you a
  Particle
• NodelistltParticlegt
• ordered list of some iterators associated with a
  DAG
• provides clean std syntax for loops over
  daughters, etc.

15
Some examples of DAG methods

• Constructors
• empty
• relations induce from another DAG
• fill from Nodelist in some other DAG
• itp dag.insert(p)
• itp dag.insertChild(p, itm)
• NodelistltTgt-returning methods
• NodelistltParticlegt children (itp)
• NodelistltParticlegt parents (itp)

16
Conclusion

• There is a strong need for C standard Monte
  Carlo generator interface.
• StdHepC is a natural object-oriented
  implementation of such an interface.
• At present we have working examples which
  integrate StdHepC with the Fortran versions of
  Herwig, Pythia, Isajet.
• On the other side, StdHepC provides event
  blocks readable by MCFast and Geant3, and will
  have an interface to Geant4.