PSGen, a generator of phase space parameterizations for the multichannel Monte Carlo integration

Abstract

PSGen is a new general purpose Fortran program which has been written to facilitate the Monte Carlo phase space integration of the S matrix element of any 2→n scattering process, with n=2,...,9, provided by the user. The program is written in Fortran 90/95. It uses a new very fast algorithm that automatically generates calls to Fortran subroutines containing different phase space parameterizations of the considered class of processes. The parameterizations take into account mappings of poles due to the Feynman propagators of unstable heavy particles decaying into 2 or 3 on shell final state particles according to predefined patterns, possible single or double t-channel poles and peaks due to one on shell photon or gluon radiation. The individual subroutines are organized in a single multichannel kinematics subroutine which can be easily called while computing the phase space integral of the S matrix element as a function of generated particle four momenta, in either the leading or higher orders of the perturbation series. The particle four momenta can be used in a quadruple precision version, if necessary. Program summaryProgram Title:PSGenCPC Library link to program files:https://doi.org/10.17632/y7nprysy8g.1Developer's repository link:https://www.kk.us.edu.pl/psgen.htmlLicensing provisions: GPLv3Programming language: Fortran 90/95Nature of problem: Automatic generation of Fortran routines which allow for the multichannel Monte Carlo integration of user's provided S matrix element as a function of generated particle four momenta of any 2→n, with n=2,...,9, scattering process. The S matrix can be defined in either the leading or higher orders.Solution method: A new very fast algorithm written in Fortran 90/95 generates calls to different handwritten subroutines containing phase space parameterizations which, among others, take into account poles due to the Feynman propagators of unstable heavy particles decaying into 2 or 3 on shell final state particles according to predefined patterns, possible single or double t-channel poles and peaks due to one on shell photon or gluon radiation. The generated routines are moved to a directory, where they are combined in a single properly normalized multichannel phase space parameterization. The corresponding kinematics subroutine is self-consistent and can be readily combined with any program which calculates the S matrix element in either the leading or higher orders of the perturbation series. The particle four momenta can be generated in a quadruple precision version, if necessary. The automatically generated subroutine containing calls to different kinematics subroutines can be easily supplemented with calls to user's own made kinematics subroutines.