112 research outputs found
Top-Quark Physics at the LHC
We report on the precision determination of the top-quark mass to
next-to-next-to-leading order in QCD in well-defined renormalization schemes
using data from the Large Hadron Collider for single-top and top-quark pair
production. We also discuss the calibration of the so-called Monte Carlo
top-quark mass parameter which is determined from a comparison to events with
top-quark decay products. The implications of the measured value of the
top-quark mass for conclusions about the stability of the electroweak vacuum
state of our Universe are illustrated. At future lepton colliders, we provide
for the first time matched exclusive calculations valid both at the top
threshold and in the continuum, also fully differentially. In addition, we
calculate fully off-shell top-pair production (also with an associated Higgs
boson) at next-to-leading order in QCD, which allows to extract the top-Yukawa
coupling with an unprecedented precision.Comment: 15 pages, 8 figures. Part of the final report of the Collaborative
Research Center 676 "Particles, Strings and the Early Universe" 2006 - 201
Top-quark pair production at hadron colliders: differential cross section and phenomenological applications with DiffTop
The results of phenomenological studies of top-quark pair production in
proton-proton collisions are presented. Differential cross sections are
calculated in perturbative QCD at approximate next-to-next-to-leading order
by using methods of threshold resummation beyond the
leading logarithmic accuracy. Predictions for the single-particle inclusive
kinematics are presented for transverse momentum and rapidity distributions of
final-state top quarks. Uncertainties related to the description of proton
structure, top-quark mass and strong coupling constant are investigated in
detail. The results are compared to the recent measurements by the ATLAS and
CMS collaborations at the LHC at the center of mass energy of 7 TeV. The
calculation presented here is implemented in the computer code \textsc{Difftop}
and can be applied to the general case of heavy-quark pair production at
hadron-hadron colliders. For the first time, a fit of parton distribution
functions at NNLO is performed by using the differential cross sections of
top-quark pair production together with other data sets. The impact of the
top-pair production on the precision of the gluon distribution at high scales
is illustrated.Comment: 30 pages, 12 figures, 2 tables, regular article. Version accepted for
a publication on JHE
Threshold and jet radius joint resummation for single-inclusive jet production
We present the first threshold and jet radius jointly resummed cross section
for single-inclusive hadronic jet production. We work at next-to-leading
logarithmic accuracy and our framework allows for a systematic extension beyond
the currently achieved precision. Longstanding numerical issues are overcome by
performing the resummation directly in momentum space within Soft Collinear
Effective Theory. We present the first numerical results for the LHC and
observe an improved description of the available data. Our results are of
immediate relevance for LHC precision phenomenology including the extraction of
parton distribution functions and the QCD strong coupling constant.Comment: 5 pages, 3 figures, minor text changes, PDF uncertainties included
and more references added. Replaced to match the published versio
Differential cross sections for top pair production at the LHC
We present results of phenomenological studies for top-quark pair production
at the LHC at the center of mass energy TeV. The transverse
momentum and rapidity distributions for final-state top quarks are calculated
in perturbative QCD at approximate next-to-next-to-leading order by using methods of threshold resummation beyond the leading
logarithmic accuracy. The theoretical predictions are obtained by using the
computer code \textsc{DiffTop} and are compared to recent measurements by the
ATLAS and CMS collaborations. \textsc{Difftop} can be employed in the general
case of heavy-quark pair production at hadron-hadron colliders and provides a
basis for applications in QCD analyses for parton distribution functions
determination.Comment: 6 pages, 2 figures, Conference proceedings for DIS2014, XXII
International Workshop on Deep-Inelastic Scattering and Related Subjects, 28
April - 2 May 2014, Warsaw, Poland, and ICHEP 2014, 37 International
Conference on High Energy Physics, 2-9 July 2014, Valencia, Spai
Top-quark production at the LHC: differential cross section and phenomenological applications
We discuss top-quark pair production at hadron colliders and review available
calculations of differential top-pair production cross section in perturbative
QCD at approximate next-to-next-to-leading order (NNLO) within the threshold
resummation formalism. These calculations are implemented into an open source
program under development. We present phenomenological studies at the LHC that
include transverse momentum and rapidity distribution of the top quarks at a
center-of-mass energy of 7 TeV. Preliminary results obtained with this program
are in very good agreement with the recent LHC measurements.Comment: 5 pages, 2 Figures, conference proceeding, DIS2013: XXI International
Workshop on Deep-Inelastic Scattering and Related Subjects 22-26 April 2013,
Marseilles, Franc
On evolution kernels of twist-two operators
The evolution kernels that govern the scale dependence of the generalized
parton distributions are invariant under transformations of the
collinear subgroup of the conformal group. Beyond
one loop the symmetry generators, due to quantum effects, differ from the
canonical ones. We construct the transformation which brings the {\it full}
symmetry generators back to their canonical form and show that the eigenvalues
(anomalous dimensions) of the new, canonically invariant, evolution kernel
coincide with the so-called parity respecting anomalous dimensions. We develop
an efficient method that allows one to restore an invariant kernel from the
corresponding anomalous dimensions. As an example, the explicit expressions for
NNLO invariant kernels for the twist two flavor-nonsinglet operators in QCD and
for the planar part of the universal anomalous dimension in SYM are
presented.Comment: 12 pages, two figures; The three-loop QCD kernel in electronic form
is given in the ancillary fil
QCD threshold corrections for gluino pair production at hadron colliders
We present the complete threshold enhanced predictions in QCD for the total cross section of gluino pair production at hadron colliders at next-to-next-to-leading order. Thanks to the computation of the required one-loop hard matching coefficients our results are accurate to the next-to-next-to-leading logarithm. In a brief phenomenological study we provide predictions for the total hadronic cross sections at the LHC and we discuss the uncertainties arising from scale variations and the parton distribution functions
Anti- jet function at next-to-next-to-leading order
Jets constructed via clustering algorithms (e.g., anti-, soft-drop) have
been proposed for many precision measurements, such as the strong coupling
and the nucleon intrinsic dynamics. However, the theoretical
accuracy is affected by missing QCD corrections at higher orders for the jet
functions in the associated factorization theorems. Their calculation is
complicated by the jet clustering procedure. In this work, we propose a method
to evaluate jet functions at higher orders in QCD. The calculation involves the
phase space sector decomposition with suitable soft subtractions. As a concrete
example, we present the quark-jet function using the anti- algorithm with
E-scheme recombination at next-to-next-to-leading order.Comment: 12 pages, update the references, add a plot to demonstrate the fully
differential nature of the calculated jet function, match the punished
versio
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