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Karol Kolodziej

Publications and source records attributed to Karol Kolodziej.

At least 19 recordsLinked to original sources
arXiv2025

Monte Carlo phase space integration of multiparticle cross sections with carlomat_4.5

Multidimensional phase space integrals must be calculated in order to obtain predictions for total or differential cross sections, or to simulate unweighted events of multiparticle reactions. The corresponding matrix elements, already in the leading order, receive contributions typically from dozens of thousands of the Feynman diagrams, many of which often involve strong peaks due to denominators of some Feynman propagators approaching their minima. As the number of peaks exceeds by far the number of integration variables, such integrals can practically be performed within the multichannel Monte Carlo approach, with different phase space parameterizations, each designed to smooth possibly a few peaks at a time. This obviously requires a lot different phase space parameterizations which, if possible, should be generated and combined in a single multichannel Monte Carlo procedure in a fully automatic way.A few different approaches to the calculation of the multidimensional phase space integrals have been incorporated in version 4.5 of the multipurpose Monte Carlo program carlomat. The present work illustrates how carlomat_4.5 can facilitate the challenging task of calculating the multidimensional phase space integrals.

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arXiv2023

PSGen, a generator of phase space parameterizations for the multichannel Monte Carlo integration

PSGen is a new general purpose Fortran program which has been written to facilitate the Monte Carlo phase space integration of the S matrix element of any 2 -> n scattering process, with n=2,...,9, provided by the user. The program is written in Fortran 90/95. It uses a new very fast algorithm that automatically generates calls to Fortran subroutines containing different phase space parameterizations of the considered class of processes.The parameterizations take into account mappings of poles due to the Feynman propagators of unstable heavy particles decaying into 2 or 3 on shell final state particles according to predefined patterns, possible single or double $t$-channel poles and peaks due to one on shell photon or gluon radiation. The individual subroutines are organized in a single multichannel kinematics subroutine which can be easily called while computing the phase space integral of the S matrix element as a function of generated particle four momenta, in either the leading or higher orders of the perturbation series. The particle four momenta can be used in a quadruple precision version, if necessary.

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arXiv2017

Photon radiation in $e^+e^-\to$ hadrons at low energies with CARLOMAT 3.1

We present a sample of results for the cross sections of several processes of low energetic $e^+e^-$ annihilation into final states containing pions accompanied by one or two photons, or a light lepton pair. The results, which have been obtained with a new version of a multipurpose Monte Carlo program CARLOMAT, labelled 3.1, demonstrate new capabilities of the program which, among others, include a possibility of taking into account either the initial or final state radiation separately, or both at a time, and a possibility of inclusion of the electromagnetic charged pion form factor for processes with charged pion pairs. We also discuss some problems related to the $U(1)$ electromagnetic gauge invariance.

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arXiv2015

Probing the top-Higgs coupling through the secondary lepton distributions in the associated production of the top-quark pair and Higgs boson at the LHC

We complement the analysis of the anomalous top-Higgs coupling effects on the secondary lepton distributions in the associated production of the top-quark pair and Higgs boson in proton-proton collisions at the LHC of the former work by one of the present authors by taking into account the quark-antiquark production mechanism. We also present simple arguments which explain why the effects of the scalar and pseudoscalar anomalous couplings on the unpolarized cross section of the process are completely insensitive to the sign of either of them.

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arXiv2015

CARLOMAT_3.0, an automatic tool for the electron-positron annihilation into hadrons at low energies

A new version of CARLOMAT that allows to generate automatically the Monte Carlo programs dedicated to the description of the processes e+e- -> hadrons at low center-of-mass energies is presented. The program has been substantially modified in order to incorporate the photon-vector meson mixing terms and to make possible computation of the helicity amplitudes nvolving the Feynman interaction vertices of new tensor structures, like those predicted by the Resonance Chiral Theory or Hidden Local Symmetry model, and the effective Lagrangian of the electromagnetic interaction of the nucleons. Moreover, a number of new options have been introduced in the program in order to enable a better control over the effective models implemented. In particular, they offer a possibility to determine the dominant production mechanisms of the final state chosen by the user.

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arXiv2014

New applications of CARLOMAT

Modifications of CARLOMAT, a program for automatic computation of the lowest order cross sections of multiparticle reactions, that include an abridgement of the phase space integration routine, an interface to parton density functions, improvement of the color matrix computation, supplementation of the Cabibbo-Kobayashi-Maskawa mixing in the quark sector, implementation of effective models such as scalar electrodynamics, the $Wtb$ interaction with operators of dimension up to 5 and a general top--Higgs coupling, are discussed. The modifications, together with recent developments concerning mainly description of the $e^+e^-$ annihilation into hadrons at low energies, broaden the spectrum of possible applications of the program.

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arXiv2013

The top--Higgs coupling at the LHC

The factorization scale dependence of the anomalous top-Higgs coupling effects in the leading order differential cross sections and distributions of the secondary lepton in the process of associated production of the top quark pair and the Higgs boson at the LHC is discussed. It is also shown that the differential cross section as a function of the rapidity of the secondary lepton in the process is practically not sensitive to a sign of the anomalous pseudoscalar coupling.

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arXiv2013

'carlomat', version 2 of the program for automatic computation of lowest order cross sections

Version 2 of 'carlomat', a program for automatic computation of the lowest order cross sections of multiparticle reactions, is described. The substantial modifications with respect to version 1 of the program include: generation of a single phase space parametrization for the Feynman diagrams of the same topology, an interface to parton density functions, improvement of the color matrix computation, the Cabibbo-Kobayashi-Maskawa mixing in the quark sector, the effective models including scalar electrodynamics, the Wtb interaction with operators of dimension up to 5 and a general top-higgs coupling. Moreover, some minor modifications have been made and several bugs in the program have been corrected.

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arXiv2013

Secondary lepton distributions as a probe of the top--higgs coupling at the LHC

The differential distributions in rapidity and angles of the secondary lepton in the associated production of the top quark pair and higgs boson in proton-proton collisions at the LHC are quite sensitive to the top-higgs coupling. However, the effects of anomalous couplings of the most general t anti-t h interaction with operators of dimension-six that are clearly visible in the signal of the associated production of the top quark pair and higgs boson are to large extent obscured by the background sub-processes with the same final state. This means that analyses of such effects, in addition to higher order corrections that are usually calculated for the on-shell top quarks and higgs boson, should include their decays and possibly complete off resonance background contributions to the corresponding exclusive reactions.

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arXiv2009

Signal and Background in e+e- ->t anti-t H

We discuss the reaction of associated production of a top quark pair and a Higgs boson at the future e+e- linear collider that can be used to determine the top-Higgs Yukawa coupling. Taking into account decays of the top quarks and the light Higgs boson leads to reactions with 8 fermions in the final state which, in the framework of the standard model, receive contributions typically from many thousands Feynman diagrams. An overwhelming majority of the diagrams comprises the off resonance background to the resonant signal of associated production and decay of the top quark pair and Higgs boson. We address the signal and background issue by comparing cross sections calculated with the signal diagrams only and with the complete sets of the diagrams.

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arXiv2009

e+ e- -> t anti-t H including decays: on the size of background contributions

We present results for the lowest order cross sections, calculated with the complete set of the standard model Feynman diagrams, of all possible detection channels of the associated production of the top quark pair and the light Higgs boson, which may be used for determination of the top-Higgs Yukawa coupling at the future e+e- linear collider. We show that, for typical particle identification cuts, the background contributions are large. In particular, the QCD background contributions are much bigger than could be expected when taking into account a possibly low virtuality of exchanged gluons. Moreover, we include the initial state radiation effects and discuss the dependence of the cross sections on the Higgs boson and top quark masses.

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arXiv2008

Off resonance background effects in e+e- -> t anti-t H

The top quark Yukawa coupling to the intermediate mass Higgs boson can be determined in the reaction e+e- -> t anti-t H that, after taking into account decays, will be detected at the International Linear Collider through reactions with 8 particles in the final state. Such 2 -> 8 reactions receive contributions from tens thousands of Feynman diagrams, already in the lowest order of Standard Model, most of which comprise background to resonant associated production and decay of the top quark pair and Higgs boson. We illustrate the background effects by comparing cross sections of three reactions, which represent different detection channels of e+e- -> t anti-t H, calculated with the complete sets of the lowest order Feynman diagrams with the corresponding signal cross sections calculated with the diagrams of associated production and decay of off mass shell top quark pair and Higgs boson only. The comparison that is performed with different selections of cuts shows that the background effects are sizeable, but they can be reduced by appropriate choice of cuts.

hep-ph↗
arXiv2007

Off mass shell effects in associated production of the top quark pair and Higgs boson at a linear collider

We discuss effects related to the fact that the final state particles of a reaction e+ e- -> t \bar{t} H are actually produced and they decay off mass shell. For the intermediate mass Higgs boson, which decays preferably into a b\bar{b}-quark pair, the reaction will be observed through reactions with 8 fermions in the final state. Such reactions, already in the lowest order of the standard model, receive contributions typically from a few dozen thousands of the Feynman diagrams, the vast majority of which constitute background to the signal of associated production of the top quark pair and Higgs boson. In order to illustrate pure off mass shell effects we neglect the background contributions and compare the `signal' cross section with the cross section in the narrow width approximation for e+ e- -> b u \bar{d} \bar{b} mu- \bar{nu}_mu b \bar{b}, which is one of possible detection channels of the associated production of the top quark pair and Higgs boson at a linear collider.

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arXiv2006

Factorizable electroweak O(alpha) corrections for top quark pair production and decay at a linear e+e- collider

We calculate the standard model predictions for top quark pair production and decay into six fermions at a linear e+ e- collider. We include the factorizable electroweak O(alpha) corrections in the pole approximation and QED corrections due to the initial state radiation in the structure function approach. The effects of the radiative corrections on the predictions are illustrated by showing numerical results for two selected six-fermion reactions e+ e- -> b nu_mu mu+ bar{b} mu- bar{nu_mu} and e+ e- -> b nu_mu mu+ bar{b} d bar{u}.

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arXiv2005

Factorizable corrections to e+e- -> mu+ mu- b bar_b at a linear collider

We discuss the standard model factorizable radiative corrections to e+e- -> mu+ mu- b bar_b, which is one of the best detection channels of the low mass Higgs boson produced through the Higgsstrahlung mechanism at a linear collider. The discussion includes the leading virtual and real quantum electrodynamics corrections due to the initial state radiation, the one-loop electroweak factorizable corrections to the on-shell Higgsstrahlung reaction and to subsequent decays of the Z and Higgs boson, and the quantum chromodynamics corrections to the Higgs boson decay width into a b bar_b-quark pair.

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arXiv2005

Towards high precision predictions for top quark pair production and decay at a linear collider

We report on the progress in work on improving precision of the standard model theoretical predictions for the top quark pair production and decay into six fermions at a linear collider. Two programs have been combined into a single Monte Carlo program: 'eett6f', a MC program for e+e- -> 6f, and 'topfit', a program for electroweak radiative corrections to e+e- -> t\bar t. The MC program is described and preliminary numerical results are shown.

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