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.
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.
Because of their narrow width, tau decays can be well separated from their production process. Only spin degrees of freedom connect these two parts of the physics process of interest for high energy ...collision experiments. In the following, we present a Monte Carlo algorithm which is based on that property. The interface supplements events generated by other programs, with tau decays. Effects of spin, genuine weak corrections or of new physics may be taken into account at the time when a tau decay is generated and written into an event record.
Eur.Phys.J.C52:83-92,2007 In this paper we describe the implementation of the processes f_1 bar-f_1 H A
--> 0 into the framework of SANC system. Here A stands for a photon and f_1 --
for a massless ...fermion whose mass is neglected everywhere besides arguments of
logarithmic functions. The symbol --> 0 means that all 4-momenta flow inwards.
The derived one-loop scalar form factors can be used for any cross channel
after an appropriate permutation of their arguments s,t,u. We present the
covariant and helicity amplitudes for all three possible cross channels. For
checking of the correctness of the results first of all we observe the
independence on the gauge parameters and the validity of Ward identity
(external photon transversality), and, secondly, we make an extensive
comparison with the other independent calculations.
Radiative corrections to the neutral current Drell--Yan-like processes are considered. Complete one-loop electroweak corrections are calculated within the SANC system. Theoretical uncertainties are ...discussed. Numerical results are presented for typical conditions of LHC experiments.
NLO QCD corrections to charged and neutral current Drell-Yan processes and their implementation in the computer system SANC are considered. On the partonic level both quark-antiquark and quark-gluon ...scattering channels are taken into account. Subtractions of the collinear singularities in the massive case are compared with ones in the MS-bar scheme. Results of SANC on the hadronic level are presented. Comparison with results of the MCFM package is shown.
We have calculated the electroweak radiative corrections at the O(alpha) level to the three channels of the process f_1 bar-f_1 Z A --> 0 and implemented them into the SANC system. Here A stands for ...the photon and f_1 for a first generation fermion whose mass is neglected everywhere except in arguments of logarithmic functions. The symbol --> 0 means that 4-momenta of all the external particles flow inwards. We present the complete analytical results for the covariant and helicity amplitudes for three cross channels: f_1 + bar-f_1 --> Z + gamma, Z --> f_1 + bar-f_1 + gamma and f_1 + gamma --> f_1 + Z. The one-loop scalar form factors of these channels are simply related by an appropriate permutation of their arguments s,t,u. To check the correctness of our results we first of all observe the independence of the scalar form factors on the gauge parameters and the validity of the Ward identity, i.e. external photon transversality, and, secondly, compare our numerical results with the other independent calculations available to us.
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.
In this paper we describe the implementation of the processes f_1 bar-f_1 H A --> 0 into the framework of SANC system. Here A stands for a photon and f_1 -- for a massless fermion whose mass is ...neglected everywhere besides arguments of logarithmic functions. The symbol --> 0 means that all 4-momenta flow inwards. The derived one-loop scalar form factors can be used for any cross channel after an appropriate permutation of their arguments s,t,u. We present the covariant and helicity amplitudes for all three possible cross channels. For checking of the correctness of the results first of all we observe the independence on the gauge parameters and the validity of Ward identity (external photon transversality), and, secondly, we make an extensive comparison with the other independent calculations.
Acta Phys.Polon. B34 (2003) 2665-2672 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.
