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Register a new userVector Boson scattering at the LHC: counting experiments for unitarized models in a full six fermion approach
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Unitarization models describe phenomenologically the high energy behaviour of a strongly interacting symmetry breaking sector. In this work, predictions of some unitarized models in vector boson scattering at LHC are studied and compared with analogous studies in Equivalent Vector Boson Approximation and previous results for the benchmark no-Higgs scenario. To perform such studies, unitarized model amplitudes have been implemented in the PHANTOM Monte Carlo in a complete calculation with six fermions in the final state.
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In the present work we study the production of vector resonances at the LHC by means of the vector boson scattering $WZ to WZ$ and explore the sensitivities to these resonances for the expected future LHC luminosities. We are assuming that these vector resonances are generated dynamically from the self interactions of the longitudinal gauge bosons, $W_L$ and $Z_L$, and work under the framework of the electroweak chiral Lagrangian to describe in a model independent way the supposedly strong dynamics of these modes. The properties of the vector resonances, mass, width and couplings to the $W$ and $Z$ gauge bosons are derived from the inverse amplitude method approach. We implement all these features into a single model, the IAM-MC, adapted for MonteCarlo, built in a Lagrangian language in terms of the electroweak chiral Lagrangian and a chiral Lagrangian for the vector resonances, which mimics the resonant behavior of the IAM and provides unitary amplitudes. The model has been implemented in MadGraph, allowing us to perform a realistic study of the signal versus background events at the LHC. In particular, we have focused our study on the $ppto WZjj$ type of events, discussing first on the potential of the hadronic and semileptonic channels of the final $WZ$, and next exploring in more detail the clearest signals. These are provided by the leptonic decays of the gauge bosons, leading to a final state with $ell_1^+ell_1^-ell_2^+ u jj$, $ell=e,mu$, having a very distinctive signature, and showing clearly the emergence of the resonances with masses in the range of 1.5-2.5 TeV, which we have explored.
Vector-boson scattering into two Z bosons at the LHC is a key channel for the exploration of the electroweak sector of the Standard Model. It allows for the full reconstruction of the scattering process but at the price of a huge irreducible background. For the first time, we present full next-to-leading-order predictions for $pp to e^+e^-mu^+mu^-jj+X$ including all electroweak and QCD contributions for vector-boson scattering signal and irreducible background. The results are presented in the form of cross sections and differential distributions. A particular emphasis is put on the newly computed $O(alpha_s^2 alpha^5)$ corrections.
Vector-boson scattering (VBS) processes probe the innermost structure of electroweak interactions in the Standard Model, 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 summarise the details of the most relevant VBS signatures and review the related measurements available to date, along with their comparison with Standard-Model predictions. We conclude by discussing the perspective at the upcoming Large Hadron Collider runs and at future hadron facilities.
Boson-boson scattering and Higgs production in boson-boson fusion hold the key to electroweak symmetry breaking. In order to analyze these essential features of the Standard Model we have performed a partonic level study of all processes $q_1 q_2 to q_3 q_4 q_5 q_6 l u$ at the LHC using the exact matrix elements at $O(alpha_{em}^6)$ provided by Phase, a new MC generator. These processes include also three boson production and the purely electroweak contribution to toptop production as well as all irreducible backgrounds. Kinematical cuts have been studied in order to enhance the VV scattering signal over background. Phase has been compared with different Monte Carlos showing that a complete calculation is necessary for a correct description of the process.
Higgs Effective Field Theory (HEFT) is deployed to study elastic vector-boson scattering at the high LHC energies. The interaction is strong over most of the parameter space, with the minimal Standard Model being a remarkable exception. One-loop HEFT complemented with dispersion relations and the Equivalence Theorem leads to two different unitarization methods which produce analytical amplitudes corresponding to different approximate solutions to the dispersion relations: the Inverse Amplitude method (IAM) and the N/D method. The partial waves obtained can show poles in the second Riemann sheet whose natural interpretation is that of dynamical resonances with masses and widths depending on the starting HEFT parameters. Different unitarizations yield qualitatively, and in many cases quantitatively, very similar results. The amplitudes obtained provide realistic resonant and nonresonant cross sections to be compared with and to be used for a proper interpretation of the LHC data.
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