224 research outputs found
High Energy Resummation of Drell-Yan Processes
We present a computation of the inclusive Drell-Yan production cross-section
in perturbative QCD to all orders in the limit of high partonic centre-of-mass
energy. We compare our results to the fixed order NLO and NNLO results in MSbar
scheme, and provide predictions at NNNLO and beyond. Our expressions may be
used to obtain fully resummed results for the inclusive cross-section.Comment: 18 pages, 5 figures: version to be published in NP
BFKL at NNLO
We present a recent determination of an approximate expression for the
O(alpha_s^3) contribution chi_2 to the kernel of the BFKL equation. This
includes all collinear and anticollinear singular contributions and is derived
using duality relations between the GLAP and BFKL kernels.Comment: 8 pages. Talk presented at 12th International Conference on Elastic
and Diffractive Scattering: Forward Physics and QCD, Hamburg, DESY, Germany,
21-25 May 200
High energy resummation of direct photon production at hadronic colliders
Direct photon production is an important process at hadron colliders, being
relevant both for precision measurement of the gluon density, and as background
to Higgs and other new physics searches. Here we explore the implications of
recently derived results for high energy resummation of direct photon
production for the interpretation of measurements at the Tevatron and the LHC.
The effects of resummation are compared to various sources of theoretical
uncertainties like PDFs and scale variations. We show how the high--energy
resummation procedure stabilizes the logarithmic enhancement of the cross
section at high--energy which is present at any fixed order in the perturbative
expansion starting at NNLO. The effects of high--energy resummation are found
to be negligible at Tevatron, while they enhance the cross section by a few
percent for p_T \lsim 10 GeV at the LHC. Our results imply that the
discrepancy at small between fixed order NLO and Tevatron data cannot be
explained by unresummed high--energy contributions.Comment: 15 pages, 7 figure
Can we trust small x resummation?
We review the current status of small x resummation of evolution of parton
distributions and of deep-inelastic coefficient functions. We show that the
resummed perturbative expansion is stable, robust upon different treatments of
subleading terms, and that it matches smoothly to the unresummed perturbative
expansions, with corrections which are of the same order as the typical NNLO
ones in the HERA kinematic region. We discuss different approaches to small x
resummation: we show that the ambiguities in the resummation procedure are
small, provided all parametrically enhanced terms are included in the
resummation and properly matched.Comment: 12 pages, 12 figures; LaTeX with espcrc2.sty. Talk given at the 2008
Ringberg workshop "New Trends in HERA Physics
Finite-top-mass effects in NNLO Higgs production
We construct an accurate approximation to the exact NNLO cross section for
Higgs production in gluon-gluon fusion by matching the dominant finite top mass
corrections recently computed by us to the known result in the infinite mass
limit. The ensuing corrections to the partonic cross section are very large
when the center of mass energy of the partonic collision is much larger than
the Higgs mass, but lead to a moderate correction at the percent level to the
total Higgs production cross section at the LHC. Our computation thus reduces
the uncertainty related to these corrections at the LHC from the percent to the
per mille level.Comment: 4 pages, 4 figures; to be published in the proceedings of QCD2008.
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Boosted Top Quark Pair Production in Soft Collinear Effective Theory
We review a Soft Collinear Effective Theory approach to the study of
factorization and resummation of QCD effects in top-quark pair production. In
particular, we consider differential cross sections such as the top-quark pair
invariant mass distribution and the top-quark transverse momentum and rapidity
distributions. Furthermore, we focus our attention on the large invariant mass
and large transverse momentum kinematic regions, characteristic of boosted top
quarks. We discuss the factorization of the differential cross section in the
double soft gluon emission and small top-quark mass limit, both in Pair
Invariant Mass (PIM) and One Particle Inclusive (1PI) kinematics. The
factorization formulas can be employed in order to implement the simultaneous
resummation of soft emission and small mass effects up to
next-to-next-to-leading logarithmic accuracy. The results are also used to
construct improved next-to-next-to-leading order approximations for the
differential cross sections.Comment: 6 pages. Proceedings of the Second Annual Conference on Large Hadron
Collider Physics (LHCP 2014), Columbia University, New York, June 2-7, 201
Higgs production in gluon fusion at next-to-next-to-leading order QCD for finite top mass
The inclusive Higgs production cross section from gluon fusion is calculated
through NNLO QCD, including its top quark mass dependence. This is achieved
through a matching of the 1/mtop expansion of the partonic cross sections to
the exact large s-hat limits which are derived from k_T-factorization. The
accuracy of this procedure is estimated to be better than 1% for the hadronic
cross section. The final result is shown to be within 1% of the commonly used
effective theory approach, thus confirming earlier findings.Comment: 28 pages, 14 figure
Synthesis and biological evaluation of new natural phenolic (2E,4E,6E)-Octa-2,4,6-trienoic esters
In the present study the esterification of the OH groups of resveratrol, caffeic acid, ferulic acid, and -sitosterol with an antioxidant polyconjugated fatty acid, (2E,4E,6E)-octa-2,4,6-trienoic acid, was achieved. As the selective esterification of OH groups of natural compounds can affect their biological activity, a selective esterification of resveratrol and caffeic acid was performed by an enzymatic approach. The new resulting compounds were characterized spectroscopically (FT-IR, NMR mono, and bidimensional techniques); when necessary the experimental data were integrated by quantum chemical calculations. The antioxidant, anti-inflammatory and proliferative activity was evaluated. The good results encourage the use of these molecules as antioxidant and/or anti-inflammatory agents in dermocosmetic application
Parton distributions with threshold resummation
We construct a set of parton distribution functions (PDFs) in which
fixed-order NLO and NNLO calculations are supplemented with soft-gluon
(threshold) resummation up to NLL and NNLL accuracy respectively, suitable for
use in conjunction with any QCD calculation in which threshold resummation is
included at the level of partonic cross sections. These resummed PDF sets,
based on the NNPDF3.0 analysis, are extracted from deep-inelastic scattering,
Drell-Yan, and top quark pair production data, for which resummed calculations
can be consistently used. We find that, close to threshold, the inclusion of
resummed PDFs can partially compensate the enhancement in resummed matrix
elements, leading to resummed hadronic cross-sections closer to the fixed-order
calculation. On the other hand, far from threshold, resummed PDFs reduce to
their fixed-order counterparts. Our results demonstrate the need for a
consistent use of resummed PDFs in resummed calculations.Comment: 43 pages, 17 figures, accepted for publication in JHE
Proceedings of the workshop "Standard Model at the LHC" University College London 30 March - 1 April 2009
Proceedings from a 3-day discussion on Standard Model discoveries with the
first LHC dataComment: 9 contributions to the proceedings of the LHC Standard Model worksho
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