arXiv subjects

A. Kusina

Publications and source records attributed to A. Kusina.

83 records · Page 5Linked to original sources

arXiv2012

Strange Quark PDFs and Implications for Drell-Yan Boson Production at the LHC

Global analyses of Parton Distribution Functions (PDFs) have provided incisive constraints on the up and down quark components of the proton, but constraining the other flavor degrees of freedom is more challenging. Higher-order theory predictions and new data sets have contributed to recent improvements. Despite these efforts, the strange quark PDF has a sizable uncertainty, particularly in the small x region. We examine the constraints from experiment and theory, and investigate the impact of this uncertainty on LHC observables. In particular, we study W/Z production to see how the s-quark uncertainty propagates to these observables, and examine the extent to which precise measurements at the LHC can provide additional information on the proton flavor structure.

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arXiv2012

A Survey of Heavy Quark Theory for PDF Analyses

We survey some of the recent developments in the extraction and application of heavy quark Parton Distribution Functions (PDFs). We also highlight some of the key HERA measurements which have contributed to these advances.

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arXiv2011

Fully NLO Parton Shower in QCD

The project of constructing a complete NLO-level Parton Shower Monte Carlo for the QCD processes developed in IFJ PAN in Krakow is reviewed. Four issues are discussed: (1) the extension of the standard inclusive collinear factorization into a new, fully exclusive scheme; (2) reconstruction of the LO Parton Shower in the new scheme; (3) inclusion of the exclusive NLO corrections into the hard process and (4) inclusion of the exclusive NLO corrections into the evolution (ladder) part.

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arXiv2011

Colour coherence of soft gluons in the fully unintegrated NLO singlet kernels

Feynman diagrams with two real partons contributing to the next-to-leading-order singlet gluon-quark DGLAP kernel are analysed. The infra-red singularities of unintegrated distributions are examined numerically. The analytical formulae are also given in some cases. The role of the colour coherence effects is found to be crucial for cancellations of the double- and single-logarithmic infra-red singularities.

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arXiv2011

Two real parton contributions to non-singlet kernels for exclusive QCD DGLAP evolution

Results for the two real parton differential distributions needed for implementing a next-to-leading order (NLO) parton shower Monte Carlo are presented. They are also integrated over the phase space in order to provide solid numerical control of the MC codes and for the discussion of the differences between the standard $\bar{MS}$ factorization and Monte Carlo implementation at the level of inclusive NLO evolution kernels. Presented results cover the class of non-singlet diagrams entering into NLO kernels. The classic work of Curci-Furmanski-Pertonzio was used as a guide in the calculations.

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arXiv2011

NLO evolution kernels: Monte Carlo versus MSbar

We investigate the differences between the NLO evolution kernels in the Curci-Furmanski-Petronzio (CFP) and Monte Carlo (MC) factorization schemes for the non-singlet case. We show the origin of these differences and present them explicitly. We examine the influence of the choice of the factorization scale in the MC scheme (given by the upper phase space limit) on the evolution kernels in this scheme.

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arXiv2010

Monte Carlo modelling of NLO DGLAP QCD Evolution in the fully unintegrated form

Presently available perturbative QCD calculations combining hard process matrix element with the Parton Shower Monte Carlo programs feature hard process matrix element calculated often beyond the leading order (LO), that is including complete next-to-leading-order (NLO), or even next-to-next-to-leading-order (NNLO) corrections, while Parton Shower is only at the leading order (LO). We report here on a work in progress which demonstrate feasibility of constructing Parton Shower Monte Carlo (PSMC) featuring complete NLO corrections to QCD evolution with respect to the logarithm of the factorization scale. This effort presently covers non-singlet subset of Feynman diagrams contributing to the above QCD evolution. It should be stressed that our approach to the NLO QCD evolution is exclusive, that is giving insight into the fully unintegrated phase space. However, at the inclusive level our implementation agrees exactly with the standard inclusive picture of the NLO DGLAP evolution. Our new approach (after including NLO singlet diagrams) provides a complete method of combining the resummed and fixed order perturbative QCD calculations beyond the LO in a form suitable for the MC implementation, an alternative to the existing ones. First practical applications will include Monte Carlo generators for W/Z production processes in hadron-hadron colliders and lepton-hadron colliders.

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arXiv2010

Monte Carlo modelling of NLO DGLAP QCD evolution in the fully unintegrated form

We are reporting on the ongoing effort of the Monte Carlo (MC) modelling of NLO DGLAP QCD evolution in the fully unintegrated form. The resulting parton shower MC is performing on its own the NLO QCD evolution, contrary to all known programs of this kind which are limited to LO level only. We overview this new MC scheme, for the non-singlet subset of the gluonstrahlung diagrams. Precision numerical tests of this new scheme are also shown.

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arXiv2010

Properties of inclusive versus exclusive QCD evolution kernels

We investigate the role of the choice of the upper phase space limit Q in the Curci-Furmanski-Petronzio (CFP) factorization scheme, which exploits dimensional regularization MS scheme. We examine how the choice of Q influences the evaluation of the standard DGLAP (inclusive) evolution kernels, gaining experience needed in the construction of the exclusive Monte Carlo modelling of the NLO DGLAP evolution. In particular, we uncover three types of mechanisms which assure the independence on Q of the inclusive DGLAP kernels calculated in the CFP scheme. We use the examples of three types of the Feynman diagrams to illustrate our analysis.

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arXiv2010

Exclusive Monte Carlo modelling of NLO DGLAP evolution

The next-to-leading order (NLO) evolution of the parton distribution functions (PDFs) in QCD is a common tool in the lepton-hadron and hadron-hadron collider data analysis. The standard NLO DGLAP evolution is formulated for inclusive (integrated) PDFs and done using inclusive NLO kernels. We report here on the ongoing project, called KRKMC, in which NLO DGLAP evolution is performed for the exclusive multiparton (fully unintegrated) distributions (ePDFs) with the help of the exclusive kernels. These kernels are calculated within the two-parton phase space for the non-singlet evolution, using Curci-Furmanski-Petronzio factorization scheme. The multiparton distribution, with multiple use of the exclusive NLO kernels, is implemented in the Monte Carlo program simulating multi-gluon emission from single quark emitter. High statistics tests ($\sim 10^{10}$ events) show that the new scheme works perfectly well in practice and, at the inclusive (integrated) level, is equivalent with the traditional inclusive NLO DGLAP evolution. Once completed, this new technique is aimed as a building block for the new more precise NLO parton shower Monte Carlo, for W/Z production at LHC and for ep scattering, as well as a starting point for other perturbative QCD based Monte Carlo projects.

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arXiv2008

Hierarchical Markovian algorithm in QCD evolution

A general formalism was introduced for reorganization of QCD evolution equations and derivation of hierarchical solution to DGLAP equation. The hierarchical solution separates two types of parton emissions: the flavour changing emissions and the diagonal ones (bremsstrahlung). It has been shown that both of the achieved processes are of the Markovian type, what gives a nice possibility of Monte Carlo implementation. Hierarchical algorithm has been implemented and crosschecked with standard Markovian algorithm implemented in program EvolFMC.

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