GRANIITTI: A Monte Carlo Event Generator for High Energy Diffraction

Abstract

We describe the physics and computational power of GRANIITTI Monte Carlo event generator, a new fully multithreaded engine designed for high energy diffraction, written in modern C++. The emphasis is especially on the low-mass domain of central exclusive processes of the S-matrix, where exotic QCD phenomena such as glueballs are expected and holographic dualities with gravity may be tested. The generator includes photon-photon, photon-pomeron, pomeron-pomeron, Durham QCD model and Tensor pomeron model type scattering amplitudes and advanced spin analysis tools. The generator combines a full parametric resonance spectrum with continuum interference and forward + central spin correlations together with event-by-event eikonal screening loop and forward proton excitation kinematics. We demonstrate the state-of-the-art capabilities and show how the enigmatic `glueball filter' observable is driven by spin polarization.