2,547 research outputs found
Sudakov resummation of multiparton QCD cross sections
We present the general expressions for the resummation, up to next-to-leading
logarithmic accuracy, of Sudakov-type logarithms in processes with an
arbirtrary number of hard-scattering partons. These results document the
formulae used by the authors in several previous phenomenological studies. The
resummation formulae presented here, which are valid for phase-space
factorizable observables, determine the resummation correction in a
process-independent fashion. All process dependence is encoded in the colour
and flavour structure of the leading order and virtual one-loop amplitudes, and
in Sudakov weights associated to the cross section kinematics. We explicitly
illustrate the application to the case of Drell--Yan and prompt-photon
production.Comment: 13 pages, LaTe
Measurement of triple differential photon plus jet cross section by D0
We report on a new measurement of triple differential cross section for the
process ppbar -> photon + jet + X in ppbar collisions at sqrt(s)=1.96 TeV by
the D0 Collaboration at Fermilab based on a dataset corresponding to an
integrated luminosity of 1.1 fb-1.Comment: 3 pages, 1 figure, To appear in the Proceedings of the 2007
Europhysics Conference on High Energy Physics, Manchester, UK. Accepted for
publication in Journal of Physics : Conference Serie
Comment on Resummation of Mass Distribution for Jets Initiated by Massive Quarks
We compute in the heavy quark effective theory the soft coefficient D_2
entering the resummation of next-to-next-to-leading threshold logarithms for
jets initiated by a quark with a small mass compared to the hard scale of the
process. We find complete agreement with a previous computation in full QCD.
Contrary to our previous guess, this coefficient turns out to be different from
that one entering heavy flavor decay or heavy flavor fragmentation.Comment: 5 pages, no figures; minor changes, references added, version
accepted in Phys.Lett.
The Resummation of Soft Gluon in Hadronic Collisions
We compute the effects of soft gluon resummation for the production of high
mass systems in hadronic collisions. We carefully analyse the growth of the
perturbative expansion coefficients of the resummation formula. We propose an
expression consistent with the known leading and next-to-leading resummation
results, in which the coefficients grow much less than factorially. We apply
our formula to Drell--Yan pair production, heavy flavour production, and the
production of high invariant mass jet pairs in hadronic collisions. We find
that, with our formula, resummation effects become important only fairly close
to the threshold region. In the case of heavy flavour production we find that
resummation effects are small in the experimental configurations of practical
interest.Comment: 45 pages, Latex, epsfig, 10 figures. Minor corrections to text,
notation and references. The previously quoted HERAb NLO bottom production
cross section was wrong, and it has been fixed. Accepted for Publication on
Nucl. Phys.
Transverse Momentum Distributions in B-Decays
We consider transverse momentum distributions in B-decays. The O(alpha_S)
coefficients for soft and collinear logarithms are computed to next-to-leading
accuracy. Resummation of large logarithmic contributions is performed in impact
parameter space within the general formalism for transverese momentum
distributions. It is shown that the shape-function approach as used for the
threshold distribution case cannot be extended to the transverse momentum one.Comment: LaTex file, 8 pages, 1 postscript figur
QCD coherence in deep inelastic scattering at small x at HERA
QCD coherence effects in initial state radiation at small x in deep inelastic
scattering in HERA kinematics are studied with the help of the Monte Carlo
model SMALLX. Theoretical assumptions based on the CCFM evolution equation are
reviewed and the basic properties of the partonic final states are
investigated. The results are compared with those obtained in the conventional
DGLAP evolution scheme.Comment: 23 pages, latex, 9 ps figures included. One reference added and
citation in the paper improve
Vector boson production at hadron colliders: a fully exclusive QCD calculation at NNLO
We consider QCD radiative corrections to the production of W and Z bosons in
hadron collisions. We present a fully exclusive calculation up to
next-to-next-to-leading order (NNLO) in QCD perturbation theory. To perform
this NNLO computation, we use a recently proposed version of the subtraction
formalism. The calculation includes the gamma-Z interference, finite-width
effects, the leptonic decay of the vector bosons and the corresponding spin
correlations. Our calculation is implemented in a parton level Monte Carlo
program. The program allows the user to apply arbitrary kinematical cuts on the
final-state leptons and the associated jet activity, and to compute the
corresponding distributions in the form of bin histograms. We show selected
numerical results at the Tevatron and the LHC.Comment: 7 pages, 3 ps figure
Universality of transverse-momentum resummation and hard factors at the NNLO
We consider QCD radiative corrections to the production of colourless
high-mass systems in hadron collisions. The logarithmically-enhanced
contributions at small transverse momentum are treated to all perturbative
orders by a universal resummation formula that depends on a single
process-dependent hard factor. We show that the hard factor is directly related
to the all-order virtual amplitude of the corresponding partonic process. The
direct relation is universal (process independent), and it is expressed by an
all-order factorization formula that we explicitly evaluate up to the
next-to-next-to-leading order (NNLO) in QCD perturbation theory. Once the NNLO
scattering amplitude is available, the corresponding hard factor is directly
determined: it controls NNLO contributions in resummed calculations at full
next-to-next-to-leading logarithmic accuracy, and it can be used in
applications of the q_T subtraction formalism to perform fully-exclusive
perturbative calculations up to NNLO. The universality structure of the hard
factor and its explicit NNLO form are also extended to the related formalism of
threshold resummation.Comment: References added. Version accepted for publication on NP
Threshold resummation at NLL accuracy and soft-virtual cross sections at NLO
We consider QCD radiative corrections to the production of colourless
high-mass systems in hadron collisions. We show that the recent computation of
the soft-virtual corrections to Higgs boson production at NLO [1] together
with the universality structure of soft-gluon emission can be exploited to
extract the general expression of the hard-virtual coefficient that contributes
to threshold resummation at NLL accuracy. The hard-virtual coefficient is
directly related to the process-dependent virtual amplitude through a universal
(process-independent) factorization formula that we explicitly evaluate up to
three-loop order. As an application, we present the explicit expression of the
soft-virtual NLO corrections for the production of an arbitrary colourless
system. In the case of the Drell-Yan process, we confirm the recent result of
Ref.[2].Comment: Slightly expanded text, one reference added, version published on NP
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