epgen — Monte Carlo Generator for Scalar Meson Photoproduction

A C++ Monte Carlo event generator for simulating scalar meson production in electron-positron annihilation (e⁺e⁻ → scalar meson + photon).

Features

• Two integration methods available:
  • TFoam — adaptive Monte Carlo integrator from ROOT
  • von Neumann — rejection sampling
• Comparative cross-section scan over a configurable energy range
• Output as ROOT TTrees (.root) and tables (.csv)
• MPI-parallelised event generation (mpi.cpp) for distributed runs

Dependencies

• ROOT (CERN data analysis framework)
• CLHEP (C++ class library for HEP)
• MPI (for the parallel build target, e.g. OpenMPI or MPICH)
• g++ with C++11 support

Build

# Default build
make spectre.out

# Parallelised MPI build
make mpi.out

# Validation executable
make validation.out

# Clean all build artefacts
make clean

Usage

Run the energy-scan executable:

./spectre.out [nEvents]

• nEvents — optional number of Monte Carlo events per energy point (default: 10 000 000)
• Energy range and step are configured inside spectre.cpp (default: 500–1500 MeV, step 10 MeV)

Output files produced:

• treeTFoam.root — ROOT TTree with TFoam-generated four-momenta
• treeNeum.root — ROOT TTree with Neumann-generated four-momenta
• integrals.csv — energy vs. cross-section integral for both methods

For the MPI parallel run:

mpirun -np <N> ./mpi.out