2,342 research outputs found
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.Comment: Contribution to Cracow Epiphany Conference 201
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 ( 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.Comment: Contribution RADCOR 2009 Int. Symposiu
Inclusion of the QCD next-to-leading order corrections in the quark-gluon Monte Carlo shower
Methodology of including QCD NLO corrections in the quark--gluon Monte Carlo
shower is outlined. The work concentrates on two issues: (i) constructing
leading order (LO) parton shower Monte Carlo from scratch, such that it
rigorously extends collinear factorization into the exclusive (fully
unintegrated) one which we call the Monte Carlo factorization scheme; (ii)
introducing next-to-leading-order (NLO) corrections to the hard process in this
new environment. The presented solution is designed to be extended to the full
NLO level Monte Carlo, including NLO corrections not only in the hard process
but in the whole shower. The issue of the difference between the factorization
scheme implemented in the Monte Carlo (MC) solution and the standard MSbar
scheme is addressed. The principal MC implementation is designed for the
electroweak boson production process at the LHC, but in order to discuss
universality -- process independence, the deep inelastic lepton--hadron
scaterring is also brought into the MC framework.Comment: 28 pages, 6 figures, updated to match journal versio
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.Comment: 9 pages, 6 figure
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.Comment: Contribution to the XXXV International Conference of Theoretical
Physics "Matter to the Deepest", Ustron, Poland, September 12-18, 201
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