arXiv subjects
Publications and source records attributed to D. Bardin.
Theoretical predictions for Bhabha scattering observables are presented including complete one-loop electroweak radiative corrections. A longitudinal polarization of the initial beams is taken into account. Numerical results for the asymmetry $A_{LR}$ and the relative correction $δ$ are given for the set of the energy $E_{cm}=250, 500, 1000$~GeV with various polarization degrees.
The implementation of the process $γγ\to ZZ$ at the one-loop level within {\tt SANC} system multi-channel approach is considered. The derived one-loop scalar form factors can be used for any cross channel after an appropriate permutation of their arguments -- Mandelstam variables $s,t,u$. To check of the correctness of the results we observe the independence of the scalar form factors on the gauge parameters and the validity of Ward identity (external photon transversality). We present the complete analytical results for the covariant and tensor structures and helicity amplitudes for this process. We make an extensive comparison of our analytical and numerical results with those existing in the literature.
This article presents new features of the MCSANC v.1.20 program, a Monte Carlo tool for calculation of the next-to-leading order electroweak and QCD corrections to various Standard Model processes. The extensions concern implementation of Drell--Yan-like processes and include a systematic treatment of the photon-induced contribution in proton--proton collisions and electroweak corrections beyond NLO approximation. There are also technical improvements such as calculation of the forward-backward asymmetry for the neutral current Drell--Yan process. The updated code is suitable for studies of the effects due to EW and QCD radiative corrections to Drell--Yan (and several other) processes at the LHC and for forthcoming high energy proton--proton colliders.
In this paper we present a description of the universal approach for analytic calculations for a certain class of $J$ functions for six topologies of the boxes for process $ud\rightarrow WA$. These functions $J$ arise at the reduction of infrared divergent box diagrams. The standard Passarino--Veltman reduction of four-point box diagram with an internal photon line connecting two external lines on the mass shell leads to infrared-divergent and mass-singular $D_0$ functions. In the system SANC a systematic procedure is adopted to separate both types of singularities into the simplest objects, namely $C_0$ functions. The functions $J$, in turn, are represented as certain linear combinations of the standard $D_0$ and $C_0$ functions. The subtracted $J$ functions are free of both types of singularities and are expressed as explicit and compact linear combinations of dilogarithm functions. We present extensive comparisons of numerical results of SANC with those obtained with the aid of the LoopTools package.
The {\tt SANC} computer system is aimed at support of analytic and numeric calculations for experiments at colliders. The system is reviewed briefly. Recent results on high-precision description of the Drell-Yan processes at the LHC are presented. Special attention is paid to the evaluation of higher order final-state QED corrections to the single $W$ and $Z$ boson production processes. A new Monte Carlo integrator {\tt mcsanc} suited for description of a series of high-energy physics processes at the one-loop precision level is presented.
In this paper we describe the analytic and numerical evaluation of the $γγ\to γZ$ process cross section and the $Z\to γγγ$ decay rate within the SANC system multi-channel approach at the one-loop accuracy level with all masses taking into account. The corresponding package for numeric calculations is presented. For checking of the results correctness we make a comparison with other independent calculations.
Modules and packages for the one-loop calculations at partonic level represent the first level of SANC output computer product. The next level represents Monte Carlo integrator mcsanc, realizing fully differential hadron level calculations (convolution with PDF) for the HEP processes at LHC. In this paper we describe the implementation into the framework mcsanc first set of processes: DY NC, DY CC, ff->HW(Z) and single top production. Both EW and QCD NLO corrections are taken into account. A comparison of SANC results with those existing in the world literature is given.
It this paper we present the results obtained with the newly created Standard SANC modules for calculation of the NLO QCD corrections to single top production processes in s and t channels at the partonic level, as well as top-decays. The main aim of these results is to prove the correct work of modules. A comprehensive comparison with results of the CompHEP system is given, where possible. These modules are intended to be used in Monte Carlo generators for single top production processes at the LHC. As in our recent paper, devoted to the electroweak corrections to these processes, we study the regularization of the top-legs associated infrared divergences with aid of the complex mass of the top quark. A comparison of QCD corrections with those computed by the conventional method is presented both for top production and decays. For s channel production we give an analytic proof of equivalence of the two methods in the limit of low top width.
Radiative corrections to the single top s and t channel production processes are revisited. Complete one-loop electroweak corrections are calculated within the SANC system. New is a study of the regularisation of the top-legs associated infrared divergences with aid of the complex mass of the top quark. A comparison of these electroweak corrections with those computed by the conventional method is presented both for top production and decays. Standard FORM and FORTRAN SANC modules are created. These modules are compiled into a package sanc_cc_v1.40, which may be downloaded from SANC project homepages. Many numerical results are presented at the partonic level with the aim to demonstrate the correct working of modules. These modules are intended to be used in Monte Carlo generators for single top production at the LHC. Where possible, we compare our results with those existing in the literature; in particular, a comprehensive comparison with results of the CompHEP system is given.
In this paper we continue to study a special class of Passarino-Veltman functions J arising at the reduction of infrared divergent box diagrams. We describe a procedure of separation of two types of singularities, infrared and mass singularities, which are absorbed in simple C0 functions. The infrared divergences of C0's can be regularized then by any method: photon mass, dimensionally or by the width of an unstable particle. Functions J, in turn, are represented as certain linear combinations of the standard D0 and C0 Passarino-Veltman functions. The former are free of both types of singularities and are expressed as explicit and compact linear combinations of logarithms and dilogarithm functions. We present extensive comparisons of numerical results with those obtained with the aid of the LoopTools package.
In this paper we describe the implementation of the SM process $γγ\toγγ$ through a fermion and boson loops into the framework of SANC system. The computations of this process takes into account non-zero mass of loop particles. We briefly describe additional precomputation modules used for calculation of massive box diagrams. We present the covariant and helicity amplitudes for this process, some particular cases of $D_0$ and $C_0$ Passarino--Veltman functions and also numerical results of corresponding SANC module evaluation. Whenever possible, we compare the results with those existing in the literature.
In this paper we present the results of the implementation of the decay t -> b f1 f1 into the SANC system (f1 is a massless fermion). The new aspect of the work is the combination of QCD and EW corrections. All calculations are done at the one-loop level in the Standard Model. We give a detailed account of the new procedure - the forming of a class of JAW,WA functions. These functions are related to the procedure of extraction of infra-red and mass-shell singular divergences. The emphasis of this paper is on the presentation of numerical results for various approaches: complete one-loop calculations and different versions of pole approximations.
In this note we summarize the status of the standard SANC modules (in the EW and QCD sectors of the Neutral Current branch - version 1.20 and the Charged Current branch - version 1.20). All versions of the codes are accessible from the SANC project servers at Dubna http://sanc.jinr.ru and CERN http://pcphsanc.cern.ch
In this paper we describe a check of the implementation of SANC system generated modules into the framework of the WINHAC Monte Carlo event generator. At this stage of work we limit ourselves to inclusion of complete one-loop electroweak corrections to the charged-current Drell--Yan process. We perform tuned comparisons of the results derived with the aid of two codes: 1) the standard SANC integrator with YFS-inspired treatment of the ISR QED corrections and 2) the WINHAC generator, upgraded with the SANC electroweak modules and downgraded to the O(α) QED corrections. The aim of these comparisons is to prove the correctness of implementation of the SANC electroweak modules into the WINHAC generator. This is achieved through the presented tuned comparisons.
This report summarizes the activity on comparisons of existings tools for the standard model and on issues in jet physics by the SMHC working group during and subsequent to the Workshop "Physics at TeV Colliders", Les Houches, France, 11-29 June, 2007.
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.
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.
In this paper we describe the implementation of processes f_1 bar-f_1 ZZ --> 0 and f_1 bar-f_1 HZ --> 0 into the framework of SANC system. The f_1 stands for a massless fermion f whose mass is kept non-zero only in arguments of ln functions and --> 0 means that all 4-momenta flow inwards. The derived 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 these processes: for the former only in the annihilation channel f_1 bar-f_1 --> ZZ, while for the latter in annihilation f_1 bar-f_1 --> HZ and decay H --> Z f_1 bar-f_1 channels. We briefly describe additional precomputation modules which were not covered in the previous paper. For the processes f_1 bar-f_1 --> HZ(ZZ) and decay H --> Z f_1 bar-f_1 we present compact results of calculation of the accompanying bremsstrahlung and discuss exhaustive numerical results. As applications there are two types of the Monte Carlo generators for the process H --> 4μ. The first one is the generator based on a single resonance approximation for one of the Z bosons. The second one, exploiting the double resonance approximation, is not described in this article. For the generator in the single approximation we present a short description. Whenever possible, we compare our results with those existing in the literature. For example, we present a comparison of the results for H --> 4 μdecay with those obtained by MC generator Prophecy4f.