41 research outputs found
Electroweak top-quark pair production at the LHC with bosons to NLO QCD in POWHEG
We present the calculation of the NLO QCD corrections to the electroweak
production of top-antitop pairs at the CERN LHC in the presence of a new
neutral gauge boson. The corrections are implemented in the parton shower Monte
Carlo program POWHEG. Standard Model (SM) and new physics interference effects
are properly taken into account. QED singularities, first appearing at this
order, are consistently subtracted. Numerical results are presented for SM and
total cross sections and distributions in invariant mass, transverse
momentum, azimuthal angle and rapidity of the top-quark pair. The remaining
theoretical uncertainty from scale and PDF variations is estimated, and the
potential of the charge asymmetry to distinguish between new physics models is
investigated for the Sequential SM and a leptophobic topcolor model.Comment: 33 pages, 15 figures, 1 table. Discussion added on uncertainties from
parton showers and NLL contribution
Update on nCTEQ PDFs: nuclear PDF uncertainties and LHC applications
We present updated nCTEQ nuclear parton distribution functions with errors
including pion production data from RHIC. We compare them with the results of
other groups and present selected LHC applications.Comment: Presented at DIS2014, 28 April - 2 May 2014, Warsaw, Poland.
PoS(DIS2014)04
CTEQ nuclear parton distribution functions
We show for the first time preliminary results of nuclear parton distribution
function analysis of charged lepton DIS and Drell-Yan data within the CTEQ
framework including error PDFs. We compare our error estimates to estimates of
different nPDF groups.Comment: 5 pages, to appear in the proceedings of XXI International Workshop
on Deep-Inelastic Scattering and Related Subjects, Marseilles, Franc
A Hybrid Scheme for Heavy Flavors: Merging the FFNS and VFNS
We introduce a Hybrid Variable Flavor Number Scheme for heavy flavors,
denoted H-VFNS, which incorporates the advantages of both the traditional
Variable Flavor Number Scheme (VFNS) as well as the Fixed Flavor Number Scheme
(FFNS). By including an explicit -dependence in both the Parton
Distribution Functions (PDFs) and the strong coupling constant , we
generate coexisting sets of PDFs and for at any
scale , that are related analytically by the
matching conditions. The H-VFNS resums the heavy quark contributions and
provides the freedom to choose the optimal for each particular data set.
Thus, we can fit selected HERA data in a FFNS framework, while retaining the
benefits of the VFNS to analyze LHC data at high scales. We illustrate how such
a fit can be implemented for the case of both HERA and LHC data.Comment: 15 pages, 11 figures, updated to match journa
Heavy Quark Production in the ACOT Scheme Beyond NLO
We analyze the properties of the ACOT scheme for heavy quark production and
make use of the MS-Bar massless results at NNLO and N3LO for the structure
functions F2 and FL in neutral current deep-inelastic scattering to estimate
the higher order corrections. The dominant heavy quark mass effects at higher
orders can be taken into account using the massless Wilson coefficients
together with an appropriate slow-rescaling prescription implementing the phase
space constraints. Combining the exact ACOT scheme at NLO with these
expressions should provide a good approximation to the full calculation in the
ACOT scheme at NNLO and N3LO.Comment: 4 pages, 2 figures. Presented at DIS12, March 2012, Bonn, German
NLO+NLL limits on W' and Z' gauge boson masses in general extensions of the Standard Model
QCD resummation predictions for the production of charged (W') and neutral
(Z') heavy gauge bosons decaying leptonically are presented. The results of our
resummation code at next-to-leading order and next-to-leading logarithmic
(NLO+NLL) accuracy are compared to Monte Carlo predictions obtained with PYTHIA
at leading order (LO) supplemented with parton showers (PS) and FEWZ at NLO and
next-to-next-to-leading order (NNLO) for the -differential and total cross
sections in the Sequential Standard Model (SSM) and general SU(2)xSU(2)xU(1)
models. The LO+PS Monte Carlo and NNLO fixed-order predictions are shown to
agree approximately with those at NLO+NLL at small and intermediate ,
respectively, and the importance of resummation for total cross sections is
shown to increase with the gauge boson mass. The theoretical uncertainties are
estimated by variations of the renormalisation/factorisation scales and of the
parton densities, the former being significantly reduced by the resummation
procedure. New limits at NLO+NLL on W' and Z' boson masses are obtained by
reinterpreting the latest ATLAS and CMS results in general extensions of the
Standard Model.Comment: 26 pages, 10 figures, 6 table
nCTEQ15 - Global analysis of nuclear parton distributions with uncertainties in the CTEQ framework
We present the new nCTEQ15 set of nuclear parton distribution functions with
uncertainties. This fit extends the CTEQ proton PDFs to include the nuclear
dependence using data on nuclei all the way up to 208^Pb. The uncertainties are
determined using the Hessian method with an optimal rescaling of the
eigenvectors to accurately represent the uncertainties for the chosen tolerance
criteria. In addition to the Deep Inelastic Scattering (DIS) and Drell-Yan (DY)
processes, we also include inclusive pion production data from RHIC to help
constrain the nuclear gluon PDF. Furthermore, we investigate the correlation of
the data sets with specific nPDF flavor components, and asses the impact of
individual experiments. We also provide comparisons of the nCTEQ15 set with
recent fits from other groups.Comment: 35 page
NLO QCD corrections to tW' and tZ' production in forward-backward asymmetry models
We consider Z' and W' models recently proposed to explain the top
forward-backward asymmetry at the Tevatron. We present the next-to-leading
order QCD corrections to associated production of such vector bosons together
with top quarks at the Large Hadron Collider, for centre-of-mass energies of 7
and 8 TeV. The corrections are significant, modifying the total production
cross-section by 30-50%. We consider the effects of the corrections on the top
and vector-boson kinematics. The results are directly applicable to current
experimental searches, for both the ATLAS and CMS collaborations.Comment: 62 pages, 13 figures, 36 tables. v3 Updated to correspond to Journal
version and incorporate supplementary materia