How to use SANC to improve the PHOTOS Monte Carlo simulation of bremsstrahlung in leptonic W-Boson decays

Using the SANC system we study the one-loop electroweak standard model predictions, including virtual and real photon emission, for the decays of the on-shell vector boson, W --> L ANTI-NU (GAMMA). The complete one-loop corrections and exact photon emission matrix element are taken into account. For the phase-space integration, the Monte Carlo technique is used. This provides a useful element, first for the evaluation of the theoretical uncertainty of PHOTOS. Later we analyse the source of the differences between SANC and PHOTOS and we calculate the additional weight, which once installed, improves predictions of PHOTOS simulations. We can conclude that, after the correction of the weight is implemented, the theoretical uncertainty of PHOTOS simulations due to an incomplete first-order matrix element is reduced to below alpha/pi, for observables not tagging the photon in a direct way, and to 10% otherwise. This is interesting for applications in the phenomenology of the ongoing LEP2 and future LC and LHC experimental studies.Comment: Submitted to Acta Physica Polonica. 8 pages, 5 figure

News on PHOTOS Monte Carlo: gamma^* -> pi^+ pi^-(gamma) and K^\pm -> pi^+ pi^- e^\pm nu (gamma)

PHOTOS Monte Carlo is widely used for simulating QED effects in decay of intermediate particles and resonances. It can be easily connected to other main process generators. In this paper we consider decaying processes gamma^* -> pi^+ pi^-(gamma) and K^\pm -> pi^+ pi^- e^\pm nu (gamma) in the framework of Scalar QED. These two processes are interesting not only for the technical aspect of PHOTOS Monte Carlo, but also for precision measurement of alpha_{QED}(M_Z), g-2, as well as pi pi scattering lengths.Comment: 6 pages, 11 figures, proceedings of the PhiPsi09, Oct. 13-16, 2009, Beijing, Chin

An electroweak library for the calculation of EWRC to e+ e- --> f fbar within the CalcPHEP project

We present a description of calculations of the electroweak amplitude for e+ e- --> f fbar process. The calculations are done within the OMS (on-mass-shell) renormalization scheme in two gauges: in Rxi, which allows an explicit control of gauge invariance by examining cancellation of gauge parameters and search for gauge-invariant subsets of diagrams, and in the unitary gauge as a cross-check. The formulae we derived are realized in a FORTRAN code eeffLib, which is being created within the framework of the project CalcPHEP. We present a comprehensive comparison between eeffLib results for the light top with corresponding results of the well-known program ZFITTER for the u ubar channel, as well as a preliminary comparison with results existing in the world literature.Comment: Revised version, 47 Latex, including 14 figures (2 eps figures), 5 table

PHOTOS Monte Carlo for precision simulation of QED in decays - History and properties of the project

Because of properties of QED, the bremsstrahlung corrections to decays of particles or resonances can be calculated, with a good precision, separately from other effects. Thanks to the widespread use of event records such calculations can be embodied into a separate module of Monte Carlo simulation chains, as used in High Energy Experiments of today. The PHOTOS Monte Carlo program is used for this purpose since nearly 20 years now. In the following talk let us review the main ideas and constraints which shaped the program version of today and enabled it widespread use. We will concentrate specially on conflicting requirements originating from the properties of QED matrix elements on one side and degrading (evolving) with time standards of event record(s). These issues, quite common in other modular software applications, become more and more difficult to handle as precision requirements become higher.Comment: Prepared for XI International Workshop on Advanced Computing and Analysis Techniques in Physics Research, Amsterdam, the Netherlands, April 23 200

Comparison of SANC with KORALZ and PHOTOS

Using the SANC system we study the one-loop electroweak standard model prediction, including virtual and real photon emissions, for the decays of on-shell vector and scalar bosons B --> f anti-f (gamma), where B is a vector boson, Z or W, or a Standard Model Higgs. The complete one-loop corrections and exact photon emission matrix element are taken into account. For the phase-space integration, the Monte Carlo technique is used. For Z decay the QED part of the calculation is first cross-checked with the exact one-loop QED prediction of KORALZ. For Higgs boson and W decays, a comparison is made with the approximate QED calculation of PHOTOS Monte Carlo. This provides a useful element for the evaluation of the theoretical uncertainty of PHOTOS, very interesting for its application in ongoing LEP2 and future LC and LHC phenomenology.Comment: Submitted to Acta Physica Polonica. 9 pages, 6 figure

Scalar QED, NLO and PHOTOS Monte Carlo

Recently, due to improvement at experiments, QED bremsstrahlung in B meson decays into pair of scalars (\pi's and/or K's) is of phenomenological interest. In practical application where experimental acceptance must be taken into account, PHOTOS Monte Carlo is often used for simulation of these QED effects. Phenomenologically sound predictions, valid over all phase space can not be obtained for complex objects, with the scalar QED alone. We will nonetheless use scalar QED to test the performance of PHOTOS. We present the analytical form of the kernel used in the older versions of PHOTOS, and the exact one with respect to first order scalar QED. Matrix element and phase space jacobians are factorized in the final weight. In this paper we also present aspects of program design, that are related to phase space generation, especially when mass terms become significant. The discussed effects are way beyond the direct phenomenological interest of today. We use this opportunity to present some foundations of the program organization that assure its precision, which may be useful for future extensions. An agreement of better than 0.01% with independent calculations of scalar QED is demonstrated

PHOTOS Monte Carlo for precision simulation of QED in decays

Because of properties of QED, the bremsstrahlung corrections to decays of particles or resonances can be calculated, with a good precision, separately from other effects. Thanks to the widespread use of event records such calculations can be embodied into a separate module of Monte Carlo simulation chains, as used in High Energy Experiments of today. The PHOTOS Monte Carlo program is used for this purpose since nearly 20 years now. In the following talk let us review the main ideas and constraints which shaped the program version of today and enabled it widespread use. We will concentrate specially on conflicting requirements originating from the properties of QED matrix elements on one side and degrading (evolving) with time standards of event record(s). These issues, quite common in other modular software applications, become more and more difficult to handle as precision requirements become higher