87 research outputs found
The role of output and feedback in second language acquisition: a classroom-based study of grammar acquisition by adult English language learners
Second language acquisition (SLA) has been a concern of many teachers and researchers since the early 1960s. One of the issues related to SLA has been finding the techniques which effectively focus the learners’ attention on the target form. A number of theories and methods have been advocated for this purpose, ranging from implicit options to more explicit ones. Although each of the suggested methods has its own advantages, they have, so far, proved insufficient to get learners to be able to notice the gap between their own interlanguage forms and the target language forms. Swain (1995, 1998) has argued that a part from providing the learners with comprehensible input, comprehensible output also plays a beneficial role in L2 acquisition. By encouraging the learners to speak or write in the L2 and providing them with the opportunities to do so, the learners can notice that they are not able to say what they want to say in the target language. On the basis of Swain’s output hypothesis, we assumed that encouraging adult learners (university students) to produce target-like output would promote their achievement of the grammatical competence necessary for producing academic tests. The purpose of this article is to present the evidence from a class-room-based, small-scale study of the effect of output on learner acquisition of L2 modal verbs, adjectives and adverbs conveying the meanings of uncertainty, all of which are parts of speech that are important metadiscourse items. The results of the present study suggest that an approach in which students are encouraged to produce comprehensible output, combined with their being provided with learning reinforcement ensured by appropriate feedback, can be an effective source of establishing long-lasting grammatical accuracy in the students’ target languag
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
An NLO+PS generator for t¯t and Wt production and decay including non-resonant and interference effects
We present a Monte Carlo generator that implements significant theoretical
improvements in the simulation of top-quark pair production and decay at the
LHC. Spin correlations and off-shell effects in top-decay chains are described
in terms of exact matrix elements for at NLO QCD, where the leptons and belong to different
families, and quarks are massive. Thus, the contributions from
and single-top production as well as their quantum interference are fully
included. Matrix elements are matched to the Pythia8 parton shower using a
recently proposed method that allows for a consistent treatment of resonances
in the POWHEG framework. These theoretical improvements are especially
important for the interpretation of precision measurements of the top-quark
mass, for single-top analyses in the channel, and for and
backgrounds in the presence of jet vetoes or cuts that enhance off-shell
effects. The new generator is based on a process-independent interface of the
OpenLoops amplitude generator with the POWHEGBOX framework.Comment: 49 pages, 22 figure
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
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