85 research outputs found
Tri-boson and WH production in the W+W+jj channel: predictions at full NLO accuracy and beyond
No full textAbstract
In this work, we present the first full NLO predictions for the process pp → μ+νμe+νejj at the LHC in a typical tri-boson phase space. The NLO corrections reach 50% at the level of the fiducial cross section and have a very different hierarchy with respect to vector-boson-scattering phase spaces. By comparing the cross section of the full off-shell process with the sum of contributing on-shell electroweak-boson production subchannels, we find that the process is dominated by WWW and WH production, while vector-boson-scattering topologies still play a non-negligible role. In addition, NLO QCD predictions matched to parton shower which are supplemented by approximate electroweak corrections are provided. For the fiducial cross section, the electroweak corrections turn out to be small but the QCD corrections reach 47%. For the inclusive cross section, matching to parton shower affects the predictions by 7%. However, for differential distributions corrections due to the parton shower can be much more sizeable, depending on the region of phase space
Fixed-order and merged parton-shower predictions for WW and WWj production at the LHC including NLO QCD and EW corrections
No full textAbstract: First, we present a combined analysis of pp →μ+vμe−v¯e and pp →μ+vμe−v¯ej at next-to-leading order, including both QCD and electroweak corrections. Second, we provide all-order predictions for pp →μ+vμe−v¯e+jets using merged parton-shower simulations that also include approximate EW effects. A fully inclusive sample for WW production is compared to the fixed-order computations for exclusive zero- and one-jet selections. The various higher-order effects are studied in detail at the level of cross sections and differential distributions for realistic experimental set-ups. Our study confirms that merged predictions are significantly more stable than the fixed-order ones in particular regarding ratios between the two processes
Vector-Boson scattering at the LHC: Unraveling the electroweak sector
No full textVector-boson scattering (VBS) processes probe the innermost structure of electroweak (EW) interactions in the Standard Model (SM), and provide a unique sensitivity for new physics phenomena affecting the gauge sector. In this review, we report on the salient aspects of this class of processes, both from the theory and experimental point of view. We start by discussing recent achievements relevant for their theoretical description, some of which have set important milestones in improving the precision and accuracy of the corresponding simulations. We continue by covering the development of experimental techniques aimed at detecting these rare processes and improving the signal sensitivity over large backgrounds. We then summarize the details of the most relevant VBS signatures and review the related measurements available to date, along with their comparison with SM predictions. We conclude by discussing the perspective at the upcoming Large Hadron Collider runs and at future hadron facilities
Automation of NLO QCD and EW corrections with Sherpa and Recola
No full textAbstract This publication presents the combination of the one-loop matrix-element generator Recola with the multipurpose Monte Carlo program Sherpa. Since both programs are highly automated, the resulting Sherpa +Recola framework allows for the computation of – in principle – any Standard Model process at both NLO QCD and EW accuracy. To illustrate this, three representative LHC processes have been computed at NLO QCD and EW: vector-boson production in association with jets, off-shell Z -boson pair production, and the production of a top-quark pair in association with a Higgs boson. In addition to fixed-order computations, when considering QCD corrections, all functionalities of Sherpa, i.e. particle decays, QCD parton showers, hadronisation, underlying events, etc. can be used in combination with Recola. This is demonstrated by the merging and matching of one-loop QCD matrix elements for Drell–Yan production in association with jets to the parton shower. The implementation is fully automatised, thus making it a perfect tool for both experimentalists and theorists who want to use state-of-the-art predictions at NLO accuracy
Quantum integration of elementary particle processes
No full textWe apply quantum integration to elementary particle-physics processes. In particular, we look at scattering processes such as e+e−→qq¯ and e+e−→qq¯′W. The corresponding probability distributions can be first appropriately loaded on a quantum computer using either quantum Generative Adversarial Networks or an exact method. The distributions are then integrated using the method of Quantum Amplitude Estimation which shows a quadratic speed-up with respect to classical techniques. In simulations of noiseless quantum computers, we obtain per-cent accurate results for one- and two-dimensional integration with up to six qubits. This work paves the way towards taking advantage of quantum algorithms for the integration of high-energy processes.We apply quantum integration to elementary particle-physics processes. In particular, we look at scattering processes such as and . The corresponding probability distributions can be first appropriately loaded on a quantum computer using either quantum Generative Adversarial Networks or an exact method. The distributions are then integrated sing the method of Quantum Amplitude Estimation which shows a quadratic speed-up with respect to classical techniques. In simulations of noiseless quantum computers, we obtain per-cent accurate results for one- and two-dimensional integration with up to six qubits. This work paves the way towards taking advantage of quantum algorithms for the integration of high-energy processes
Low-virtuality photon transitions gamma* -> f(f)over-bar and the photon-to-jet conversion fundtion [Low-virtuality photon transitions γ⁎→ff ̄ and the photon-to-jet conversion function]
No full textThe calculation of electroweak corrections to processes with jets in the final state involves contributions of low-virtuality photons leading to jets in the final state via the singular splitting γ⁎→qq ̄. These singularities can be absorbed into a photon-to-jet “fragmentation function”, better called “conversion function”, since the physical final state is any hadronic activity rather than an identified hadron. Using unitarity and a dispersion relation, we relate this γ⁎→qq ̄ conversion contribution to an integral over the imaginary part of the hadronic vacuum polarization and thus to the experimentally known quantity Δαhad(5)(MZ2). Therefore no unknown non-perturbative contribution remains that has to be taken from experiment. We also describe practical procedures following subtraction and phase-space-slicing approaches for isolating and cancelling the γ⁎→qq ̄ singularities against the photon-to-jet conversion function. The production of Z+jet at the LHC is considered as an example, where the photon-to-jet conversion is part of a correction of the order α2/αs relative to the leading-order cross section
Higher-order QCD predictions for dark matter production at the LHC in simplified models with s-channel mediators
No full textWeakly interacting dark matter particles can be pair-produced at colliders and detected through signatures featuring missing energy in association with either QCD/EW radiation or heavy quarks. In order to constrain the mass and the couplings to standard model particles, accurate and precise predictions for production cross sections and distributions are of prime importance. In this work, we consider various simplified models with s-channel mediators. We implement such models in the FeynRules/MadGraph5_aMC@NLO framework, which allows to include higher-order QCD corrections in realistic simulations and to study their effect systematically. As a first phenomenological application, we present predictions for dark matter production in association with jets and with a top-quark pair at the LHC, at next-to-leading order accuracy in QCD, including matching/merging to parton showers. Our study shows that higher-order QCD corrections to dark matter production via s-channel mediators have a significant impact not only on total production rates, but also on shapes of distributions. We also show that the inclusion of next-to-leading order effects results in a sizeable reduction of the theoretical uncertainties
La défaite électorale
No full textLa défaite électorale est un phénomène structurant de la vie politique démocratique. Rares sont les hommes politiques à ne jamais y avoir été confrontés, soit directement en tant que candidats, soit indirectement en tant que militants, collaborateurs ou membres d’un comité de campagne. Cet ouvrage propose une plongée du côté de ces battus des élections, qui, éclipsés par les glorieux vainqueurs, n’ont jusqu’à présent suscité qu’un intérêt de recherche réduit. En réunissant des contributions empiriquement fondées sur des expériences variées de défaites électorales, dans différents contextes historiques, géographiques et politiques, il se donne pour objectif de mieux saisir les enjeux symboliques et matériels de la défaite aux niveaux individuel et collectif. Trois angles d’analyse complémentaires sont plus particulièrement explorés par les auteurs : le premier centré sur la production du verdict de défaite, le deuxième sur les potentielles bifurcations biographiques des battus et enfin le troisième sur les appropriations partisanes de la défaite. Les études de la défaite « au concret » ici réunies ouvrent ainsi des pistes de recherche originales pour interroger de manière novatrice les processus de (dé)construction des carrières politiques, d’engagement et de désengagement politique, de transformation des milieux partisans ou encore de définition des règles de la compétition électorale
Exploring the scattering of vector bosons at LHCb
No full textIn this paper, I propose a strategy to measure vector-boson scattering (VBS) at the LHCb experiment. The typical VBS topology at hadron colliders features two energetic back-to-back jets with large rapidities and two gauge bosons produced centrally. In this article, I show that such a topology can actually be probed by the LHCb detector. In particular, tagging only one of the two jets in combination with two same-sign leptons allows for a measurement with upcoming luminosities. I present an illustrative event selection where cross sections and differential distributions are computed for VBS and its irreducible background.In this letter, I propose a strategy to measure vector-boson scattering (VBS) at the LHCb experiment. The typical VBS topology at hadron colliders features two energetic back-to-back jets with large rapidities and two gauge bosons produced centrally. In this article, I show that such a topology can actually be probed by the LHCb detector. In particular, tagging only one of the two jets in combination with two same-sign leptons allows for a measurement with upcoming luminosities. I present an illustrative event selection where cross sections and differential distributions are computed for VBS and its irreducible background
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