28,155 research outputs found
On parton distributions beyond the leading order
The importance of properly taking into account the factorization scheme
dependence of parton distribution functions is emphasized. A serious error in
the usual handling of this topic is pointed out and the correct procedure for
transforming parton distribution functions from one factorisation scheme to
another recalled. It is shown that the conventional and
DIS definitions thereof are ill-defined due to the lack of distinction between
the factorisation scheme dependence of parton distribution functions and
renormalisation scheme dependence of the strong coupling constant . A
novel definition of parton distribution functions is suggested and its role in
the construction of consistent next-to-leading order event generators briefly
outlined.Comment: PRA-HEP-93/05, Latex, 10 pages and 2 Postscript figures appended at
the end of this fil
Investigation of the factorization scheme dependence of finite order perturbative QCD calculations
The freedom associated with the definition of parton distribution functions
is analyzed and formulae governing the dependence of parton distribution
functions and hard scattering cross-sections on unphysical quantities
associated with the renormalization and factorization procedure are derived.
The issue of the specification of factorization schemes via the corresponding
higher order splitting functions is discussed in detail. A numerical analysis
of the practical applicability of the so called ZERO factorization scheme,
which could be useful for the construction of consistent NLO Monte Carlo event
generators, is presented.Comment: 44 pages, 6 figures, journal version of the text accepted for
publication in JHE
Geometry of gauge links in operator definitions of transverse-momentum dependent PDFs: A comparative view
Different approaches to the problem of a gauge-invariant operator definition
of transverse-momentum dependent parton densities (TMDs) are reviewed and
compared from the point of view of their compatibility with the operator
definition of collinear (integrated) parton distribution functions. In
particular, geometry of the longitudinal and transverse gauge links (Wilson
lines) both in unsubtracted quark TMDs and in the associate soft factors is
addressed. A possible connection between different operator definitions is also
discussed.Comment: 9 pages, 4 figures. Presented at the International Conference
"Photon-2011", 22-27 May 2011 Spa, Belgiu
Collinear factorization for deep inelastic scattering structure functions at large Bjorken xB
We examine the uncertainty of perturbative QCD factorization for hadron
structure functions in deep inelastic scattering at a large value of the
Bjorken variable xB. We analyze the target mass correction to the structure
functions by using the collinear factorization approach in the momentum space.
We express the long distance physics of structure functions and the leading
target mass corrections in terms of parton distribution functions with the
standard operator definition. We compare our result with existing work on the
target mass correction. We also discuss the impact of a final-state jet
function on the extraction of parton distributions at large fractional momentum
x.Comment: 18 pages, 10 figures; discussion on baryon number conservation
clarifie
A QCD Analysis of Double Parton Scattering: Color Correlations, Interference Effects and Evolution
We derive a factorization formula for the double Drell-Yan cross section in
terms of double parton distribution functions (dPDFs). Diparton flavor, spin
and color correlations and parton-exchange interference terms contribute, even
for unpolarized beams. Soft radiation effects are nontrivial for the color
correlation and interference contributions, and are described by
non-perturbative soft functions. We provide a field-theoretic definition of the
quark dPDFs and study some of their basic properties, including discrete
symmetries and their interpretation in a non-relativistic quark model. We
calculate the renormalization group evolution of the quark dPDFs and of the
soft functions. The evolution receives contributions from both ultraviolet and
rapidity divergences. We find that color correlation and interference effects
are Sudakov suppressed, greatly reducing the number of dPDFs needed to describe
double parton scattering at high energy experiments.Comment: 24 pages, 15 figures, v2: added WW cross section, additional spin
structures, finite terms of one-loop soft function, journal versio
Transverse parton distribution functions at next-to-next-to-leading order: the quark-to-quark case
We present a calculation of the perturbative quark-to-quark transverse parton
distribution function at next-to-next-to-leading order based on a gauge
invariant operator definition. We demonstrate for the first time that such a
definition works beyond the first non-trivial order. We extract from our
calculation the coefficient functions relevant for a
next-to-next-to-next-to-leading logarithmic resummation in a large class
of processes at hadron colliders.Comment: 4 pages, 1 figure, revised version, accepted for publication in PR
Calculation of the transverse parton distribution functions at next-to-next-to-leading order
We describe the perturbative calculation of the transverse parton distribution functions in all partonic channels up to next-to-next-to-leading order based on a gauge invariant operator definition. We demonstrate the cancellation of light-cone divergences and show that universal process-independent transverse parton distribution functions can be obtained through a refactorization. Our results serve as the first explicit higher-order calculation of these functions starting from first principles, and can be used to perform next-to-next-to-next-to-leading logarithmic q ( )T( ) resummation for a large class of processes at hadron colliders
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