arXiv subjects

Jonas M. Lindert

Publications and source records attributed to Jonas M. Lindert.

At least 37 records · Page 2Linked to original sources

arXiv2017

Electroweak Higgs production with HiggsPO at NLO QCD

We present the HiggsPO UFO model for Monte Carlo event generation of electroweak $VH$ and VBF Higgs production processes at NLO in QCD in the formalism of Higgs pseudo-observables (PO). We illustrate the use of this tool by studying the QCD corrections, matched to a parton shower, for several benchmark points in the Higgs PO parameter space. We find that, while being sizable and thus important to be considered in realistic experimental analyses, the QCD higher-order corrections largely factorize. As an additional finding, based on the NLO results, we advocate to consider 2D distributions of the two-jet azimuthal-angle difference and the leading jet $p_T$ for new physics searches in VBF Higgs production. The HiggsPO UFO model is publicly available.

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arXiv2017

NLO QCD+EW predictions for HV and HV+jet production including parton-shower effects

We present the first NLO QCD+EW predictions for Higgs boson production in association with a l nu or l+ l- pair plus zero or one jets at the LHC. Fixed-order NLO QCD+EW calculations are combined with a QCD+QED parton shower using the recently developed resonance-aware method in the POWHEG framework. Moreover, applying the improved MINLO technique to H l nu and H l+ l- production at NLO QCD+EW, we obtain predictions that are NLO accurate for observables with both zero or one resolved jet. This approach permits also to capture higher-order effects associated with the interplay of EW corrections and QCD radiation. The behavior of EW corrections is studied for various kinematic distributions, relevant for experimental analyses of Higgsstrahlung processes at the 13 TeV LHC. Exact NLO EW corrections are complemented with approximate analytic formulae that account for the leading and next-to-leading Sudakov logarithms in the high-energy regime. In the tails of transverse-momentum distributions, relevant for analyses in the boosted Higgs regime, the Sudakov approximation works well, and NLO EW effects can largely exceed the ten percent level. Our predictions are based on the POWHEX BOX RES + OpenLoops framework in combination with the Pythia 8.1 parton shower.

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arXiv2017

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+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 top-mediated Higgs production cross section. We also observe a significant reduction in the mass-renormalization scheme uncertainty, once the NLO QCD prediction for the interference is employed.

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arXiv2016

NLO QCD Predictions for off-shell $t \bar t$ and $t \bar t H$ Production and Decay at a Linear Collider

We present predictions for $t \bar t$ and $t \bar t H$ production and decay at future lepton colliders including non-resonant and interference contributions up to next-to-leading order (NLO) in perturbative QCD. The obtained precision predictions are necessary for a future precise determination of the top-quark Yukawa coupling, and allow for top-quark phenomenology in the continuum at an unprecedented level of accuracy. Simulations are performed with the automated NLO Monte-Carlo framework WHIZARD interfaced to the OpenLoops matrix element generator.

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arXiv2016

NLO QCD+EW for V+jets

In this contribution recent results regarding the NLO electroweak corrections for vector boson production in association with jets are presented. Besides discussing the phenomenology of the fixed-order results, their corporation in existing NLO QCD parton shower matched and merged calculations, which can directly be used in experimental analyses, will be shown.

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arXiv2016

An NLO+PS generator for $t\bar{t}$ 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 $p p \to \ell^+ν_{\scriptscriptstyle\ell}\, l^-\barν_{\scriptscriptstyle l} b \bar{b}$ at NLO QCD, where the leptons $\ell$ and $l$ belong to different families, and $b$ quarks are massive. Thus, the contributions from $t\bar{t}$ and $Wt$ 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 $Wt$ channel, and for $t\bar{t}$ and $Wt$ 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.

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arXiv2016

Differential Higgs Boson Pair Production at Next-to-Next-to-Leading Order in QCD

We report on the first fully differential calculation for double Higgs boson production through gluon fusion in hadron collisions up to next-to-next-to-leading order (NNLO) in QCD perturbation theory. The calculation is performed in the heavy-top limit of the Standard Model, and in the phenomenological results we focus on pp collisions at 14 TeV. We present differential distributions through NNLO for various observables including the transverse-momentum and rapidity distributions of the two Higgs bosons. NNLO corrections are at the level of 10%-25% with respect to the next-to-leading order (NLO) prediction with a residual scale uncertainty of 5%-15% and an overall mild phase-space dependence. Only at NNLO the perturbative expansion starts to converge yielding overlapping scale uncertainty bands between NNLO and NLO in most of the phase-space. The calculation includes NLO predictions for pp -> HH+jet+X. Corrections to the corresponding distributions exceed 50% with a residual scale dependence of 20%-30%.

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arXiv2016

NLO QCD+EW predictions for V+jets including off-shell vector-boson decays and multijet merging

We present next-to-leading order (NLO) predictions including QCD and electroweak (EW) corrections for the production and decay of off-shell electroweak vector bosons in association with up to two jets at the 13 TeV LHC. All possible dilepton final states with zero, one or two charged leptons that can arise from off-shell W and Z bosons or photons are considered. All predictions are obtained using the automated implementation of NLO QCD+EW corrections in the OpenLoops matrix-element generator combined with the Munich and Sherpa Monte Carlo frameworks. Electroweak corrections play an especially important role in the context of BSM searches, due to the presence of large EW Sudakov logarithms at the TeV scale. In this kinematic regime, important observables such as the jet transverse momentum or the total transverse energy are strongly sensitive to multijet emissions. As a result, fixed-order NLO QCD+EW predictions are plagued by huge QCD corrections and poor theoretical precision. To remedy this problem we present an approximate method that allows for a simple and reliable implementation of NLO EW corrections in the MEPS@NLO multijet merging framework. Using this general approach we present an inclusive simulation of vector-boson production in association with jets that guarantees NLO QCD+EW accuracy in all phase space regions involving up to two resolved jets.

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arXiv2015

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.

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arXiv2015

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.

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arXiv2015

NLO QCD+EW automation and precise predictions for V+multijet production

In this talk we present a fully automated implementation of next-to-leading order electroweak (NLO EW) corrections in OpenLoops together with Sherpa and Munich. As a first application, we present NLO QCD+EW predictions for the production of positively charged W bosons in association with up to three jets and for the production of a Z boson or photon in association with one jet.

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arXiv2015

NLO electroweak automation and precise predictions for W+multijet production at the LHC

We present a fully automated implementation of next-to-leading order electroweak (NLO EW) corrections in the OpenLoops matrix-element generator combined with the Sherpa and Munich Monte Carlo frameworks. The process-independent character of the implemented algorithms opens the door to NLO QCD+EW simulations for a vast range of Standard Model processes, up to high particle multiplicity, at current and future colliders. As a first application, we present NLO QCD+EW predictions for the production of positively charged on-shell W bosons in association with up to three jets at the Large Hadron Collider. At the TeV energy scale, due to the presence of large Sudakov logarithms, EW corrections reach the 20-40% level and play an important role for searches of physics beyond the Standard Model. The dependence of NLO EW effects on the jet multiplicity is investigated in detail, and we find that W+multijet final states feature genuinely different EW effects as compared to the case of W+1jet.

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arXiv2014

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 $μ$ 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.

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arXiv2014

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 $25 - 30\%$ compared to the leading-order prediction. Besides corrections to inclusive cross sections also important kinematic distributions are investigated.

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arXiv2014

A lower bound on light neutralino dark matter from LHC data

Under the hypothesis that the MSSM neutralino accounts for the observed dark matter density, we investigate how light this particle is still allowed to be after the latest LHC data. In particular, we discuss the impact of searches for events with multiple taus and missing transverse momentum, which are a generic prediction of the light neutralino scenario.

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arXiv2013

Cornering light Neutralino Dark Matter at the LHC

We investigate the current status of the light neutralino dark matter scenario within the minimal supersymmetric standard model (MSSM) taking into account latest results from the LHC. A discussion of the relevant constraints, in particular from the dark matter relic abundance, leads us to a manageable simplified model defined by a subset of MSSM parameters. Within this simplified model we reinterpret a recent search for electroweak supersymmetric particle production based on a signature including multi-taus plus missing transverse momentum performed by the ATLAS collaboration. In this way we derive stringent constraints on the light neutralino parameter space. In combination with further experimental information from the LHC, such as dark matter searches in the monojet channel and constraints on invisible Higgs decays, we obtain a lower bound on the lightest neutralino mass of about 24 GeV. This limit is stronger than any current limit set by underground direct dark matter searches or indirect detection experiments. With a mild improvement of the sensitivity of the multi-tau search, light neutralino dark matter can be fully tested up to about 30 GeV.

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arXiv2013

NLO corrections to squark-squark production and decay at the LHC

We present the analysis of the signature 2j + ETmiss (+X) via squark-squark production and direct decay into the lightest neutralino, pp -> squark squark -> j j chi_1^0 chi_1^0 (+X), in next-to-leading order QCD within the framework of the minimal supersymmetric standard model. In our approximation the produced squarks are treated on shell. Thus, the calculation of production and decay factorizes. In this way, we provide a consistent, fully differential calculation of NLO QCD factorizable corrections to the given processes. Clustering final states into partonic jets, we investigate the experimental inclusive signature 2j + ETmiss for several benchmark scenarios. We compare resulting differential distributions with leading-order approximations rescaled by a flat K-factor and examine a possible impact for cut-and-count searches for supersymmetry at the LHC.

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arXiv2013

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.

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