In an effective operator approach, the full set of leading contributions to anomalous top couplings comprises various new trilinear as well as higher interaction vertices, some of which are related to one another by gauge symmetry or equations of motion. In order to study trilinear top couplings to Standard Model gauge bosons such as tt, ttZ, tbW and ttg, the operator set can be restricted accordingly. However, the complete basis cannot be mapped onto an on-shell parametrization of the trilinear vertices alone. Four-fermion contact terms qqtt and udtb must be included if the relation to the operator basis is to be retained. In this paper, we point out how these interactions contribute to the single top search channels for anomalous trilinear tbW couplings at the LHC and Tevatron, thus affecting the corresponding bounds. All results are based on full leading-order partonic matrix elements, thus automatically accounting for off-shell and interference effects as well as irreducible backgrounds. A discussion of the quantitative effects of going from on-shell tops to full matrix elements including acceptance cuts is also provided.
We present an approach to predict exclusive W + bW −b production at lepton colliders that correctly describes the top-anti-top threshold as well as the continuum region. We incorporate tt form factors for the NLL threshold resummation derived in NRQCD into a factorized relativistic cross section using an extended double-pole approximation, which accounts for fixed-order QCD corrections to the top decays at NLO. This is combined with the full fixed-order QCD result at NLO for W + bW −b production to obtain predictions that are not only valid at threshold but smoothly transition to the continuum region. Our implementation is based on the Monte Carlo event generator Whizard and the code Toppik and allows to compute fully-differential threshold-resummed cross sections including the interference with non-resonant background processes. For the first time it is now possible to systematically study general differential observables at future lepton colliders involving the decay products of the top quarks at energies close to the pair production threshold and beyond.
The article discusses various approaches to statistical disclosure control based on random noise that are currently being discussed for official population statistics and censuses. A particular focus is on a stringent delineation between different concepts influencing the discussion: we separate clearly between risk measures, noise distributions, and output mechanisms—putting these concepts into scope and into relation with each other. The article also remarks on utility and risk aspects of some specific output mechanisms and parameter setups, with special attention on static outputs that are rather typical in official population statistics. In particular, it is argued that unbounded noise distributions, such as plain Laplace, may jeopardize key unique census features without a clear need from a risk perspective. On the other hand, bounded noise distributions, such as the truncated Laplace or the cell key method, can contribute effectively to safeguarding these unique census features while controlling disclosure risks in census-like outputs. Finally, the article analyses some typical attack scenarios to constrain generic noise parameter ranges that suggest a good risk/utility compromise for the 2021 EU census output scenario. The analysis also shows that strictly differentially private mechanisms would be severely constrained in this scenario.
In an effective theory approach, the full minimal set of leading contributions to anomalous charged-current top couplings comprises various new trilinear tbW as well as quartic tbff interaction vertices, some of which are related to one another by equations of motion. While much effort in earlier work has gone into the extraction of the trilinear couplings from single top measurements, we argue in this article that these structures can be assessed independently by other observables, while single top production forms a unique window to the four-fermion sector. An effective theory approach is employed to infer and classify the minimal set of such couplings from dimension six operators in the minimal flavor violation scheme. In the phenomenological analysis, we present a Monte Carlo study at detector level to quantify the expected performance of the next LHC run to bound as well as distinguish the various contact couplings. Special attention is directed toward differential final state distributions including detector effects as a means to optimize the signal sensitivity as well as the discriminative power with respect to the possible coupling structures.
We describe the multi-purpose Monte-Carlo event generator WHIZARD for the simulation of high-energy particle physics experiments. Besides the presentation of the general features of the program like SM physics, BSM physics, and QCD effects, special emphasis will be given to the support of the most accurate simulation of the collider environments at hadron colliders and especially at future linear lepton colliders. On the more technical side, the very recent code refactoring towards a completely object-oriented software package to improve maintainability, flexibility and code development will be discussed. Finally, we present ongoing work and future plans regarding higher-order corrections, more general model support including the setup to search for new physics in vector boson scattering at the LHC, as well as several lines of performance improvements.
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