116 research outputs found
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
On the dependence of QCD splitting functions on the choice of the evolution variable
We show that already at the NLO level the DGLAP evolution kernel Pqq starts
to depend on the choice of the evolution variable. We give an explicit example
of such a variable, namely the maximum of transverse momenta of emitted partons
and we identify a class of evolution variables that leave the NLO Pqq kernel
unchanged with respect to the known standard MS-bar results. The kernels are
calculated using a modified Curci-Furmanski-Petronzio method which is based on
a direct Feynman-graphs calculation.Comment: 16 pages, 4 figure
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
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
Calculation of QCD NLO Splitting Functions in the light-cone gauge: a new regularization prescription
We report on the progress in calculating NLO DGLAP splitting functions for
using the New Principal Value prescription, which is a modification of
the standard Principal Value approach proposed by Curci, Furmanski and
Petronzio in 1980. The new prescription reproduces the standard results on the
inclusive (integrated) level, but simplifies individual contributions and
restricts the cancellations between real and virtual diagrams which makes it
useful for Monte Carlo simulations.Comment: Presented by O.Gituliar at XX Cracow Epiphany Conference, Cracow
(Poland), 8--10 Jan 201
Evolution kernels for parton shower Monte Carlo
We report on re-calculation of the next-to-leading order DGLAP evolution
kernels performed in a scheme suited for Monte Carlo simulations of parton
cascades (parton showers).Comment: Presented at Cracow Epiphany Conference, 8-10 January 201
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