PHOTOS - A UNIVERSAL MONTE-CARLO FOR QED RADIATIVE-CORRECTIONS IN DECAYS

In this paper we present an algorithm for the Monte Carlo simulation of QED single-photon radiative corrections in decays. The algorithm is implemented in an independent package written in FORTRAN 77. The program is universal, i.e. it allows for easy interfacing with "any" program generating decays of "any" particle. The program can be used to estimate the size of the QED bremsstrahlung in the leading-logarithmic (collinear) approximation. The proper soft-photon behavior is also reproduced. The program is designed such that the inclusion (if necessary) of the exact, process dependent, O(alpha) matrix element is possible and straightforward. The program provides final states with their full topology, including kinematical effects due to massive particles. For Z decays into pairs of light fermions, an extensive comparison of our algorithm with programs based on exact O(alpha) matrix elements was performed.