PHOTOS Interface in C++; Technical and Physics Documentation

TL;DR

This paper documents the technical implementation, features, and validation of the PHOTOS Monte Carlo tool in C++, enhancing its physics precision and usability for particle decay simulations involving bremsstrahlung and lepton pairs.

Contribution

It introduces a C++ interface for PHOTOS with improved physics accuracy, detailed documentation, and new features like process-dependent kernels and exact phase space parametrization.

Findings

Physics precision surpasses the FORTRAN version.

Implementation of process-dependent photon emission kernels.

Validation with test results and examples.

Abstract

For five years now, PHOTOS Monte Carlo for bremsstrahlung in the decay of particles and resonances has been available with an interface to the C++ HepMC event record. The main purpose of the present paper is to document the technical aspects of the PHOTOS Monte Carlo installation and present version use. A multitude of test results and examples are distributed together with the program code. The PHOTOS C++ physics precision is better than its FORTRAN predecessor and more convenient steering options are also available. An algorithm for the event record interface necessary for process dependent photon emission kernel is implemented. It is used in Z and W decays for kernels of complete first order matrix elements of the decays. Additional emission of final state lepton pairs is also available. Physics assumptions used in the program and properties of the solution are reviewed. In particular, it is explained how the second order matrix elements were used in design and validation of the program iteration procedure. Also, it is explained that the phase space parametrization used in the program is exact.