1,679 research outputs found
A next-to-next-to-leading order calculation of soft-virtual cross sections
We compute the next-to-next-to-leading order (NNLO) soft and virtual QCD
corrections for the partonic cross section of colourless-final state processes
in hadronic collisions. The results are valid to all orders in the dimensional
regularization parameter \ep. The dependence of the results on a particular
process is given through finite contributions to the one and two-loop
amplitudes. To evaluate the accuracy of the soft-virtual approximation we
compare it with the full NNLO result for Drell-Yan and Higgs boson production
via gluon fusion. We also provide a universal expression for the hard
coefficient needed to perform threshold resummation up to
next-to-next-to-leading logarithmic (NNLL) accuracy.Comment: 25 pages, 4 figure
Subtraction terms at NNLO
Perturbative calculations at next-to-next-to-leading order for multi-particle
final states require a method to cancel infrared singularities. I discuss the
subtraction method at NNLO. As a concrete example I consider the leading-colour
contributions to e+ e- --> 2 jets. This is the simplest example which exhibits
all essential features. For this example, explicit subtraction terms are given,
which approximate the four-parton and three-parton final states in all double
and single unresolved limits, such that the subtracted matrix elements can be
integrated numerically.Comment: 41 page
Subtraction Terms for Hadronic Production Processes at Next-to-Next-to-Leading Order
I describe a subtraction scheme for the next-to-next-to-leading order
calculation of single inclusive production at hadron colliders. Such processes
include Drell-Yan, W^{+/-}, Z and Higgs Boson production. The key to such a
calculation is a treatment of initial state radiation which preserves the
production characteristics, such as the rapidity distribution, of the process
involved. The method builds upon the Dipole Formalism and, with proper
modifications, could be applied to deep inelastic scattering and e^+ e^-
annihilation to hadrons.Comment: 4 page
A simple shower and matching algorithm
We present a simple formalism for parton-shower Markov chains. As a first
step towards more complete uncertainty bands, we incorporate a comprehensive
exploration of the ambiguities inherent in such calculations. To reduce this
uncertainty, we then introduce a matching formalism which allows a generated
event sample to simultaneously reproduce any infrared safe distribution
calculated at leading or next-to-leading order in perturbation theory, up to
sub-leading corrections. To enable a more universal definition of perturbative
calculations, we also propose a more general definition of the hadronization
cutoff. Finally, we present an implementation of some of these ideas for
final-state gluon showers, in a code dubbed VINCIA.Comment: 32 pages, 6 figure
Observation of heteronuclear atomic Efimov resonances
The Efimov effect represents a cornerstone in few-body physics. Building on
the recent experimental observation with ultracold atoms, we report the first
experimental signature of Efimov physics in a heteronuclear system. A mixture
of K and Rb atoms was cooled to few hundred nanoKelvins and
stored in an optical dipole trap. Exploiting a broad interspecies Feshbach
resonance, the losses due to three-body collisions were studied as a function
of the interspecies scattering length. We observe an enhancement of the
three-body collisions for three distinct values of the interspecies scattering
lengths, both positive and negative. We attribute the two features at negative
scattering length to the existence of two kind of Efimov trimers, namely KKRb
and KRbRb.Comment: 4 pages, 4 figure
Latest measurements of beauty quark production at HERA
The latest results of beauty quark production measurements at HERA are
presented. New measurements have been obtained both in the photoproduction and
the deep inelastic scattering regimes. The results were compared with the NLO
QCD calculations.Comment: 3 pages, 2 figures. Talk presented at the 31st International
Conference on High Energy Physics (ICHEP02), Amsterdam, The Netherlands, July
24-31, 200
Molecular Research on Platelet Activity in Health and Disease 2.0
Hsia and collaborators [...
Nuclear charm and bottom production: a comparison among high energy approaches
We calculate the nucleon and nuclear photoproduction cross sections for heavy
quarks within the -factorization formalism, considering the current
high energy approaches which include nuclear and saturation effects. Our
results demonstrate that a future experimental analysis of this process would
allow to constraint the QCD dynamics at high energies.Comment: 10 pages, 2 figures. Version to be published in Eur. Phys. J.
Jet measurements at DO using a KT algorithm
DO has implemented and calibrated a KT jet algorithm for the first time in a
ppbar collider. We present two results based on 1992-1996 data which were
recently published: the subjet multiplicity in quark and gluon jets and the
central inclusive jet cross section. The measured ratio between subjet
multiplicities in gluon and quark jets is consistent with theoretical
predictions and previous experimental values. NLO pQCD predictions of the KT
inclusive jet cross section agree with the DO measurement, although marginally
in the low pT range. We also present a preliminary measurement of thrust cross
sections, which indicates the need to include higher than alpha_s^3 terms and
resumation in the theoretical calculations.Comment: 8 pages, 10 figures, presented at the High-Energy Physics
International Conference in Quantum Chromodynamics, Montpellier, France, July
2-9th 2002. To be published in Nuclear Physics
Next-to-leading order jet distributions for Higgs boson production via weak-boson fusion
The weak-boson fusion process is expected to provide crucial information on
Higgs boson couplings at the Large Hadron Collider at CERN. The achievable
statistical accuracy demands comparison with next-to-leading order QCD
calculations, which are presented here in the form of a fully flexible parton
Monte Carlo program. QCD corrections are determined for jet distributions and
are shown to be modest, of order 5 to 10% in most cases, but reaching 30%
occasionally. Remaining scale uncertainties range from order 5% or less for
distributions to below +-2% for the Higgs boson cross section in typical
weak-boson fusion search regions.Comment: 19 pages, 8 figure
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