185 research outputs found
Non-perturbative bottom PDF and its possible impact on new physics searches
Heavy quark parton distribution functions (PDFs) play an important role in
several Standard Model and New Physics processes. Most PDF analyses rely on the
assumption that the charm and bottom PDFs are generated perturbatively by gluon
splitting and do not include any non-perturbative degrees of freedom. However,
a non-perturbative, intrinsic heavy quark PDFs have been predicted in the
literature. We demonstrate that to a very good approximation the
scale-evolution of the intrinsic heavy quark content of the nucleon is governed
by non-singlet evolution equations, and use this approximation to model the
intrinsic bottom distribution and its impact on parton-parton luminosities at
the LHC.Comment: Presented at the Cracow Epiphany Conference, 7-9 January 2016,
Krakow, Polan
Transverse momentum dependent splitting functions at work: quark-to-gluon splitting
Using the recently obtained Pgq splitting function we extend the low x
evolution equation for gluons to account for contributions originating from
quark-to-gluon splitting. In order to write down a consistent equation we resum
virtual corrections coming from the gluon channel and demonstrate that this
implies a suitable regularization of the Pgq singularity, corresponding to a
soft emitted quark. We also note that the obtained equation is in a
straightforward manner generalized to a nonlinear evolution equation which
takes into account effects due to the presence of high gluon densities.Comment: 13 pages, 3 figures, published 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
TMD splitting functions in kT factorization: the real contribution to the gluon-to-gluon splitting
We calculate the transverse momentum dependent gluon-to-gluon splitting
function within -factorization, generalizing the framework employed in the
calculation of the quark splitting functions in [1-3] and demonstrate at the
same time the consistency of the extended formalism with previous results.
While existing versions of factorized evolution equations contain already
a gluon-to-gluon splitting function i.e. the leading order
Balitsky-Fadin-Kuraev-Lipatov (BFKL) kernel or the
Ciafaloni-Catani-Fiore-Marchesini (CCFM) kernel, the obtained splitting
function has the important property that it reduces both to the leading order
BFKL kernel in the high energy limit, to the
Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) gluon-to-gluon splitting
function in the collinear limit as well as to the CCFM kernel in the soft
limit. At the same time we demonstrate that this splitting kernel can be
obtained from a direct calculation of the QCD Feynman diagrams, based on a
combined implementation of the Curci-Furmanski-Petronzio formalism for the
calculation of the collinear splitting functions and the framework of high
energy factorization.Comment: 29 pages, 5 figures, published versio
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