Monte Carlo Event Generator for High Energy Diffraction

Installation

This has been tested on a standalone Ubuntu 24.04 and CERN lxplus. To compile with ROOT libraries, see the docs and README.

First run

Will print out instructions. See also ./docs/FAQ.md

Physics simulation, synthesis and event generation

• pp: Central exclusive Pomeron-Pomeron, Gamma-Pomeron, Gamma-Gamma (kt-EPA), Durham QCD/KMR (gg) processes
• UPC initial states (eA,pA,AA) and their forward processes
• Forward proton excitation (N*)
• A user extendable set of scattering amplitudes with helicity amplitudes e.g. from MadGraph
• Differential eikonal event-by-event Pomeron loop integral screening (absorption) with numerical Fourier-Bessel transform
• Durham QCD loop framework with spin-parity projection and a generalized gluon pdf transformation (Shuvaev transform+Sudakov suppression)
• Tensor Pomeron model scattering amplitudes for continuum + resonances
• Arbitrary Jacob-Wick helicity decay 1 → 2 amplitudes with any spin and cascade spin correlations, polarization parametrized via spin density matrices and 'Glueball filter dynamics'



• Exact 2 → N relativistic kinematics with different phase space composition options, automated Lorentz scalars and 4-momenta for arbitrary amplitudes
• Arbitrary wide/deep decay chains according to the phase space with interpreter syntax
• Elastic scattering through the eikonal screening amplitude
• Single and Double Diffraction (triple Pomeron) and soft Non-Diffractive (with a 'Retro style' KISS fragmentation) - as a simple reference
  

Spin-2 couplings (left), central exclusive production pp → p + X + p spectrums (right)

Physics analysis, inference and inversion

• Ultrafast and automated fiducial observable studies (tracking cuts, forward vetos) - physics in 5 minutes
• Spin studies: 2-body final state angular distribution Laplace's spherical harmonics expansion (to arbitrary order in LM) and inversion via an extended Maximum Likelihood fit and closed-form algebraic inversion - including multistep factorization of fiducial acceptance and efficiency via moment mixing matrices (1. detector, 2. fiducial and 3. flat phase space)

Spherical moments in fidual phase space (left) vs after inversion in flat phase space (right)

• HPC-distributable automated parameter inference using arbitrary differential distributions with icetune
• Automated fiducial cross-section comparisons with icepacks against HEPData
• Output to Rivet via HepMC - robust check of the generator output, measurement definition and projections against existing fiducial measurements

Decay angles in Collins-Soper, Helicity, Lab, Gottfried, Pseudo-Gottfried, Non-rotated rest frame

Technology

• Fully multithreaded (max CPU) VEGAS importance sampling Monte Carlo engine; weighted and unweighted event generation
• NEUROJAC neural importance sampling with spline-coupling normalizing flows
• JSON object file (partial JSON5) and commandline control
• HepMC3, HepMC2 and HEPEVT event record output, HepMC3 to LHE converter
• Autotesting and comparison with LHC/Tevatron/RHIC measurements
• Automatic version update notifications
• Based on modern C++20 language

Inline References

The source code includes inline references to the relevant papers - not only as a technical/academic reference, but also to avoid 'black-boxification' and improve code quality. These can be printed by running:

Compatible HEP software

• HepMC 3: New rewrite of HepMC event record
• LHAPDF 6: Standard for evaluating parton densities from discretised data files
• ROOT: Standard analysis tool framework in HEP
• MadGraph 5_aMC@NLO: Amplitude generator
• Pythia 8: For fragmenting partonic final states or forward systems, for example
• Delphes 3: Fast detector simulation framework
• Rivet: Robust Independent Validation of Experiment and Theory toolkit

License