76 research outputs found
On cascade decays of squarks at the LHC in NLO QCD
In this paper we present an analysis at NLO of the contribution from
squark-squark production to the experimental signature 2j + 2l + missing E_T
(+X) with opposite-sign same flavor leptons, taking into account decays and
experimental cuts. We consider the case in which one squark decays directly
into the lightest neutralino chi^0_1 and the other one into the second lightest
neutralino and subsequently into l^+l^-chi^0_1 via an intermediate slepton. On
one hand we study effects of the NLO corrections on invariant mass
distributions which can be used for future parameter determination. On the
other hand we analyze the impact on predictions for cut-and-count searches
using this experimental signature.Comment: 21 pages, 10 figure
LHC Tests of Light Neutralino Dark Matter without Light Sfermions
We address the question how light the lightest MSSM neutralino can be as dark
matter candidate in a scenario where all supersymmetric scalar particles are
heavy. The hypothesis that the neutralino accounts for the observed dark matter
density sets strong requirements on the supersymmetric spectrum, thus providing
an handle for collider tests. In particular for a lightest neutralino below 100
GeV the relic density constraint translates into an upper bound on the Higgsino
mass parameter in case all supersymmetric scalar particles are heavy. One
can define a simplified model that highlights only the necessary features of
the spectrum and their observable consequences at the LHC. Reinterpreting
recent searches at the LHC we derive limits on the mass of the lightest
neutralino that, in many cases, prove to be more constraining than dark matter
experiments themselves.Comment: 22 pages, 8 figure
Electroweak corrections to squark-antisquark production at the LHC
We present the calculation of the electroweak corrections for
squark-antisquark pair production at the LHC within the Minimal Supersymmetric
Standard Model. Taking into account all possible chirality and light-flavor
configurations, we evaluate the NLO EW corrections, which are of O(a_s^2 a), as
well as the subleading tree-level contributions of O(a_s a) and O(a^2).
Numerical results are presented for several scans in the SUSY parameter space
and relevant differential distributions are investigated. The impact of the
electroweak corrections is nonnegligible and strongly depends on the chirality
configuration of the produced squarks. Our analysis includes a discussion of
photon-gluon initiated processes with a focus on the impact of the
corresponding large PDF uncertainties.Comment: 33 pages, 12 figures; V2: Original results unchanged. Various minor
modifications. Matches version published in JHE
Pseudo-observables in electroweak Higgs production
We discuss how the leading electroweak Higgs production processes at the LHC,
namely vector-boson fusion and Higgs+W/Z associated production, can be
characterized in generic extensions of the Standard Model by a proper set of
pseudo-observables (PO). We analyze the symmetry properties of these PO and
their relation with the PO set appearing in Higgs decays. We discuss in detail
the kinematical studies necessary to extract the production PO from data, and
present a first estimate of the LHC sensitivity on these observables in the
high-luminosity phase. The impact of QCD corrections and the kinematical
studies necessary to test the validity of the momentum expansion at the basis
of the PO decomposition are also discussed.Comment: 34 pages, 12 figures, 1 tabl
Top-squark pair production at the LHC: a complete analysis at next-to-leading order
We present a complete next-to-leading order study of top-squark pair
production at the LHC, including QCD and EW corrections. The calculation is
performed within the Minimal Supersymmetric Standard Model and numerical
results are presented for parameter regions compatible with the observed Higgs
boson. We employ the most recent parton distribution functions including QED
corrections and we find NLO EW corrections to the inclusive stop-pair
production cross section up to compared to the leading-order
prediction. Besides corrections to inclusive cross sections also important
kinematic distributions are investigated.Comment: 27 pages, 10 figures. Version published in JHEP. The numerical
discussion in Section 3 has been extended. References have been adde
Resonance-aware NLOPS matching for off-shell production with semileptonic decays
The increasingly high accuracy of top-quark studies at the LHC calls for a
theoretical description of production and decay in terms of exact
matrix elements for the full process that includes the off-shell
production and the chain decays of and intermediate states,
together with their quantum interference. Corresponding NLO QCD calculations
matched to parton showers are available for the case of dileptonic channels and
are implemented in the bb4l Monte Carlo generator, which is based on the
resonance-aware POWHEG method. In this paper, we present the first NLOPS
predictions of this kind for the case of semileptonic channels. In this
context, the interplay of off-shell production with various other
QCD and electroweak subprocesses that yield the same semileptonic final state
is discussed in detail. On the technical side, we improve the resonance-aware
POWHEG procedure by means of new resonance histories based on matrix elements,
which enable a realistic separation of and contributions.
Moreover, we introduce a general approach which makes it possible to avoid
certain spurious terms that arise from the perturbative expansion of decay
widths in any off-shell higher-order calculation, and which are large enough to
jeopardise physical finite-width effects. These methods are implemented in a
new version of the bb4l Monte Carlo generator, which is applicable to all
dileptonic and semileptonic channels, and can be extended to fully hadronic
channels. The presented results include a NLOPS comparison of off-shell against
on-shell production and decay, where we highlight various
non-trivial aspects related to NLO and parton-shower radiation in leptonic and
hadronic top decays.Comment: 78 pages, 20 figures, 6 table
Top-Bottom Interference Effects in Higgs Plus Jet Production at the LHC
We compute next-to-leading order QCD corrections to the top-bottom interference contribution to H þ j production at the LHC. To achieve this, we combine the recent computation of the two-loop amplitudes for gg → Hg and qg → Hq, performed in the approximation of a small b-quark mass, and the numerical calculation of the squared one-loop amplitudes for gg → Hgg and qg → Hqg, performed within OPENLOOPS. We find that QCD corrections to the interference are large and similar to the QCD corrections to the topmediated Higgs production cross section. We also observe a significant reduction in the mass-renormalization scheme uncertainty once the next-to-leading order QCD prediction for the interference is employed
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