MC-tester as tool for transition from F77 HEPEVT to C++ HepMC Nadia Davidson

Who am I? PhD Student from the University of Melbourne, working on ATLAS Will be in Krakow for 4 months Working on transition of HEPTOOLS to HepMC

What is HEPEVT? What is HepMC? Event Records for Monte Carlo Generators Makes the interfacing of different event generators simpler However, there will always be ambiguities and limitations to the way the event information is stored. HEPEVENT is the Fortran HEP standard HepMC is a C++ container

What is HEPEVT? Defined by a Fortran common block Also a 2 nd block for spin information

What is HepMC? A package of C++ classes Events are represented as graphs

Event contains a list of vertices Vertices have pointers to their incoming and outgoing particles Spin density matrices can be stored + Flow information (such as colour)

Motivation to move to HepMC High Energy Particle Physics tools are becoming Object Orientated Frameworks for running MC-generators E.g. Athena (ATLAS software) is written in C++ and python Monte-Carlo Generators E.g. Pythia 8, Hergwig++ HepMC is becoming a standard container for event records

Step One: MC-tester Gain experience using HepMC Demonstrates general event record interface for HEPEVT and HepMC Great testing tool for checking new C++ Monte-Carlo generators against their older Fortran version.

What is MC-TESTER? Written by Piotr Golonka, Tomasz Pierzchala, Zbigniew Was. C++ Program from around 2003 Automates the comparison of intermediate state decays for different Monte-Carlo generators. Produces a list comparing branching ratios and invariant mass distributions for the decay modes found.

Table of decay modes: ● Decay channel ● Branching ratio for generator #1 and #2 ● Rough statistical errors of branching ratios ● Maximal “Shape Difference Parameter” ● Similarity Coefficients (combined: for all decay modes) Slide from one of Piotr’s Talk!

● Histogrammes of invariant mass from generator #1 and #2 ● Ratio of the two histogrammes ● Shape Difference Parameter value Example of histogrammes: Slide from one of Piotr’s Talk!

Directory Structure Example Added Interface Extended to HepMC

Event data access: HEPEvent library Now added

Two classes added HepMCEvent (Inherits from the HepEvent and HepMC::GenEvent classes) Has a list of HepMCParticles Implemented some basic method to access these HepMCParticle (Inherits from the HepParticle and HepMC::GenParticle classes) Implemented methods to access GenParticle properties Also methods to getList of Mother/Daughter Particles is needed by MC-Tester Other methods left as stub as not needed by MC- tester

C++ example added Example of use in main method for the pythia 8 event generatior … //Initialize MC-TESTER MC_Initialize(); … + Some configuration In event loop { … // Fill phythia event // to HepMC format ToHepMC.fill_next_event( event, HepMCEvt ); //Make new MC-TESTER // HepMCEvent event and // pass to the tester HepMCEvent * temp_event = new HepMCEvent(*HepMCEvt); MC_Analyze(temp_event); } //Finalise MC-TESTER MC_Finalize(); …

Example: Comparision of pythia 6.4 (Fortran) to pythia 8.1 (C++) Is now possible to compare the output of Fortran and C++ monte-carlo generators. Example: tau decay in e+e  Z0 events

Plans Some more debugging and clean up of MC-Tester HepMC example needed (will not take long) But successful first step done Move to looking at tauola interface?