116 research outputs found
Electroweak gauge boson polarisation at the LHC
We study the polarisation of gauge bosons produced at the LHC. Polarisation
effects for W bosons manifest themselves in the angular distributions of the
lepton and in the distributions of lepton transverse momentum and missing
transverse energy. The distributions also depend on the selection cuts, with
kinematic effects competing with polarisation effects. The polarisation is
discussed for a range of different processes producing W bosons: W+jets, W from
top (single and pair) production, W pair production and W production in
association with a Z or Higgs boson. The relative contributions of the
different polarisation states varies from process to process, reflecting the
dynamics of the underlying hard-scattering process. We also present results for
the polarisation of the Z boson produced in association with QCD jets at the
LHC, and comment on the differences between W and Z production.Comment: 27 pages, 25 figure
Top-quark mass effects in double and triple Higgs production in gluon-gluon fusion at NLO
The observation of double and triple scalar boson production at hadron
colliders could provide key information on the Higgs self couplings and the
potential. As for single Higgs production the largest rates for multiple Higgs
production come from gluon-gluon fusion processes mediated by a top-quark loop.
However, at variance with single Higgs production, top-quark mass and width
effects from the loops cannot be neglected. Computations including the exact
top-quark mass dependence are only available at the leading order, and
currently predictions at higher orders are obtained by means of approximations
based on the Higgs-gluon effective field theory (HEFT). In this work we present
a reweighting technique that, starting from events obtained via the MC@NLO
method in the HEFT, allows to exactly include the top-quark mass and width
effects coming from one- and two-loop amplitudes. We describe our approach and
apply it to double Higgs production at NLO in QCD, computing the needed
one-loop amplitudes and using approximations for the unknown two-loop ones. The
results are compared to other approaches used in the literature, arguing that
they provide more accurate predictions for distributions and for total rates as
well. As a novel application of our procedure we present predictions at NLO in
QCD for triple Higgs production at hadron colliders.Comment: 24 pages, 8 figure
Higgs and Z boson associated production via gluon fusion in the SM and the 2HDM
We analyse the associated production of Higgs and boson via heavy-quark
loops at the LHC in the Standard Model and beyond. We first review the main
features of the Born production, and in particular discuss the
high-energy behaviour, angular distributions and boson polarisation. We
then consider the effects of extra QCD radiation as described by the
loop matrix elements, and find that they dominate at high Higgs transverse
momentum. We show how merged samples of 0-- and 1--jet multiplicities, matched
to a parton shower can provide a reliable description of differential
distributions in production. In addition to the Standard Model study,
results in a generic two-Higgs-doublet-model are obtained and presented for a
set of representative and experimentally viable benchmarks for ,
and production. We observe that various interesting features appear
either due to the resonant enhancement of the cross-section or to interference
patterns between resonant and non-resonant contributions.Comment: 29 pages, 12 figure
NLO predictions for Higgs boson pair production with full top quark mass dependence matched to parton showers
We present the first combination of NLO QCD matrix elements for di-Higgs
production, retaining the full top quark mass dependence, with a parton shower.
Results are provided within both the POWHEG-BOX and MadGraph5_aMC@NLO Monte
Carlo frameworks. We assess in detail the theoretical uncertainties and provide
differential results. We find that, as expected, the shower effects are
relatively large for observables like the transverse momentum of the Higgs
boson pair, which are sensitive to extra radiation. However, these shower
effects are still much smaller than the differences between the Born-improved
HEFT approximation and the full NLO calculation in the tails of the
distributions.Comment: replaced by published version; in addition typos corrected in
definition of pole coefficients below Eq.(2.4
Higgs pair production at the LHC with NLO and parton-shower effects
We present predictions for the SM-Higgs-pair production channels of relevance
at the LHC: gluon-gluon fusion, VBF, and top-pair, W, Z and single-top
associated production. All these results are at the NLO accuracy in QCD, and
matched to parton showers by means of the MC@NLO method; hence, they are fully
differential. With the exception of the gluon-gluon fusion process, for which a
special treatment is needed in order to improve upon the infinite-top-mass
limit, our predictions are obtained in a fully automatic way within the
publicly available MadGraph5_aMC@NLO framework. We show that for all channels
in general, and for gluon-gluon fusion and top-pair associated production in
particular, NLO corrections reduce the theoretical uncertainties, and are
needed in order to arrive at reliable predictions for total rates as well as
for distributions.Comment: 11 pages, 7 figures, version accepted for publication on PL
Hypokalemia: A clinical update
Hypokalemia is a common electrolyte disturbance, especially in hospitalized patients. It can have various causes, including endocrine ones. Sometimes, hypokalemia requires urgent medical attention. The aim of this review is to present updated information regarding: (1) the definition and prevalence of hypokalemia, (2) the physiology of potassium homeostasis, (3) the various causes leading to hypokalemia, (4) the diagnostic steps for the assessment of hypokalemia and (5) the appropriate treatment of hypokalemia depending on the cause. Practical algorithms for the optimal diagnostic, treatment and follow-up strategy are presented, while an individualized approach is emphasized
Truncation, validity, uncertainties
The truncation of the standard-model effective field theory, its validity andthe associated uncertainties have been discussed in meetings of the LHC EFT WG.Proposals were made by participants to address these issues. No consensus wasreached and no formal recommendation is therefore put forward at this time.None of the proposals has been approved or validated and further work is neededto establish a prescription. This note aims at summarizing the proposals andpoints of debate.<br
Truncation, validity, uncertainties
The truncation of the standard-model effective field theory, its validity andthe associated uncertainties have been discussed in meetings of the LHC EFT WG.Proposals were made by participants to address these issues. No consensus wasreached and no formal recommendation is therefore put forward at this time.None of the proposals has been approved or validated and further work is neededto establish a prescription. This note aims at summarizing the proposals andpoints of debate.<br
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