PHOTOS - a universal Monte Carlo for QED radiative corrections: version 2.0

Abstract

This paper documents an update of the PHOTOS algorithm, by E. Barberio, B. van Eijk and Z. Was, for the Monte Carlo simulation of QED photon radiative corrections in decays. The algorithm is implemented as an independent package written in FORTRAN 77. The program is universal, i.e. it allows for easy interface 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, but it provides nal states with their full topology, including kinematical e ects due to massive particles. The proper soft photon behaviour is also reproduced. The algorithm is designed in such a w a y that the inclusion (if necessary) of the exact, process-dependent, matrix element subgenerator is possible and straightforward. This update of PHOTOS provides new options to improve the performances of the program in some speci c cases: the interference for two-body particle-antiparticle decays, the double bremsstrahlung, and re nements important for the decays into massive non-relativistic decay products. leptons, resonances, particle decays, Monte Carlo simulation, quantum electrodynamics, leading-log approximations. Nature of physical problem: Most of the decay modes of particles or resonances are accompanied by the QED real photon corrections. The presence of (a) hard photon(s) may a ect the shape of the measured distributions, detection e ciencies and/or experimental selection criteria. Method of solution: The Monte Carlo simulation is best suited for studying the combined process of production and decay of unstable particles, including QED corrections and detector e ciencies. Restrictions on the complexity of the problem: The QED O( ) and O( 2 ) corrections are implemented in the leading-logarithm approximation with the proper soft photon behaviour. Emission of non-collinear hard photons is simulated, but the validity of distribution may be restricted.Typical running time: 500 events/sec (VAX station 4000-90) for the Z ! + decay mode.

Measurements of the observed cross sections for e+e−→ exclusive light hadrons containing KS0 meson a

“…Final state radiation [31] decreases the detection efficiency not more than 0.5%. Detailed analysis based on Monte Carlo simulation for the BES-II detector [32] gives the detection efficiencies for each process at √ s = 3.773 and 3.650 GeV, which are summarized in the fifth columns of Tabs.…”

New hadronic currents in TAUOLA: for confrontation with the experimental data

“…That is why it is of importance to review the precision of this program as documented in Refs. [5,6,7]. For the C++ applications, the version of the program is available now.…”

“…The TAUOLA package [1,2,3,4] for simulation of τ-lepton decays and PHOTOS [5,6,7] for simulation of QED radiative corrections in decays, are computing projects with a rather long history. Written and maintained by well-defined (main) authors, they nonetheless migrated into a wide range of applications where they became ingredients of complicated simulation chains.…”

Why do we need higher-order fully exclusive Monte Carlo generator for Higgs boson production from heavy quark fusion at LHC?

“…Essential element consisted of simulating the decays of the τ -leptons. For that purpose TAUOLA [13,14,15] and PHOTOS [16,17] Monte Carlos were used. The three segments of the generation were combined using interface presented in [18].…”