Precise theoretical predictions are vital for the interpretation of Standard Model measurements and facilitate conclusive searches for New Physics phenomena at the LHC. In this contribution I highlight some of the ongoing efforts in the framework of the Sherpa event generator to provide accurate and realistic simulations of Standard Model production processes. This includes the automated evaluation of NLO QCD and NLO EW corrections and their consistent consideration in the parton-shower evolution of scattering events. Particular emphasis is given to examples and applications involving the production of top quarks.
Automated computations of electroweak corrections using Sherpa+Recola
考虑到实验精度和LHC可以测量的众多过程，电弱（EW）校正变得越来越重要。这就要求EW校正的自动化，特别是在多用途蒙特卡罗发生器中实现，以便对这些贡献进行系统研究。在这些程序中，我介绍了Sherpa Monte Carlo中矩阵元素生成器Recola的实现。Sherpa+Recola的组合允许在原则上以NLO QCD和EW精度计算标准模型中的任何过程。除了固定阶NLO计算，Sherpa的所有功能，如部分子簇射或强子化仍然可用。
We present an automated implementation for the calculation of one-loop double and single Sudakov logarithms stemming from electroweak radiative corrections within the Sherpa event generation framework, based on the derivation in[1]. At high energies, these logarithms constitute the leading contributions to the full NLO electroweak corrections. As examples, we show applications for relevant processes at both the LHC and future hadron colliders, namely on-shell W boson pair production, EW-induced dijet production and electron-positron production in association with four jets, providing the first…
Comparing different ansatzes to describe electroweak radiative corrections to exclusive semileptonic B meson decays into (pseudo)scalar final state mesons using Monte-Carlo techniques
The analysis of hadronic vector boson decays at LHC does not normally allow for interference with QCD production. These effects are studied here using the Sherpa package and can move by several GeV/c 2 the peak positions experiments would reconstruct. However, their impact depends strongly on the kinematics involved. The shifts expected in boosted W and Z bosons, which have been the subject of experimental study, are explored for the first time. The effects in the channels examined are all very small or negligible, but this may not true if lower transverse momenta are analysed, for example in …
The aim of this thesis is the completion of the NLO automated framework of the MC program WHIZARD, accounting for NLO corrections in the full SM for cross sections and distributions of processes at hadron and lepton colliders. Specifically, it builds on the implemented FKS subtraction scheme for NLO QCD calculations, and extends it to automated NLO EW and QCD-EW mixed corrections. To that end, the implemented FKS scheme is generalised to systematically subtract QED and QCD infrared (IR) divergences in mixed coupling expansions. The automated computation of NLO contributions is validated for a …
In this work we revisit the algorithm of Denner and Pozzorini for the calculation of one-loop electroweak Sudakov logarithms and we automate it in the MadGraph5_aMC@NLO framework. We adapt the formulas for modern calculations, keeping light-quarks and photons strictly massless and dealing with infrared divergences via dimensional regularisation. We improve the approximation by taking into account additional logarithms that are angular dependent. We prove that an imaginary term has been previously omitted and we show that it cannot be in general neglected for $2\rightarrow n$ processes with $n>…
We present results on NLO electroweak (EW) corrections to multiple massive boson production processes at a future muon collider. Inclusive cross sections with $\mathcal{O}(α)$ corrections for processes for up to four bosons in the final state as well as differential distributions for $HZ$ production are computed for $\sqrt{s}=3$, $10$ and $14$ TeV by using FKS subtraction in the NLO EW automated Monte-Carlo framework WHIZARD+RECOLA. Large logarithmic effects due to collinear ISR and EW virtual correction factors as well as the impacts of an energy cut on hard photons are discussed with an emph…
We present the key features relevant to the automated computation of all the leading- and next-to-leading order contributions to short-distance cross sections in a mixed-coupling expansion, with special emphasis on the first subleading NLO term in the QCD+EW scenario, commonly referred to as NLO EW corrections. We discuss, in particular, the FKS subtraction in the context of a mixed-coupling expansion; the extension of the FKS subtraction to processes that include final-state tagged particles, defined by means of fragmentation functions; and some properties of the complex mass scheme. We combi…
We have developed a framework for automated transverse momentum resummation for arbitrary electroweak final states based on reweighting tree-level events. It is fully differential in the kinematics of the electroweak final states, which facilitates a straightforward analysis of arbitrary observables in the small transverse momentum region. We have implemented the resummation at next-to-next-to-leading logarithmic accuracy and match to next-to-leading fixed-order results using the event generator MadGraph5_aMC@NLO. Results for $Z$ and $W$ boson production with leptonic decay as well as $WZ$ pro…
EW corrections and Heavy Boson Radiation at a high-energy muon collider
INFN, Sezione di Bologna（意大利国家核物理研究所博洛尼亚分部）；Center for Cosmology, Particle Physics and Phenomenology, Université catholique de Louvain（鲁汶天主教大学宇宙学、粒子物理与现象学中心）；TIFLab, Università degli Studi di Milano & INFN, Sezione di Milano（米兰大学理论物理实验室及意大利国家核物理研究所米兰分部）
UFO Sightings with Matchete: Connecting BSM Lagrangians with Event Generators
RWTH Aachen University（亚琛工业大学）；PSI Center for Neutron and Muon Sciences（瑞士保罗谢尔研究所中子与μ子科学中心）；Albert Einstein Center for Fundamental Physics, Institute for Theoretical Physics, University of Bern（伯尔尼大学爱因斯坦基础物理中心理论物理研究所）
QCD NLO with Powheg matching and top threshold matching in WHIZARD
我们目前的状态的自动化NLO过程中的事件发生器WHIZARD。该程序提供了一个自动的FKS减法和相空间积分的FKS区域，而（QCD）NLO矩阵元素是通过访问Binoth Les Houches接口从外部链接的一个循环程序。无质量和大规模的测试案例和验证显示了几个e+e-过程。此外，我们还讨论了正在进行的工作和未来的计划。第二部分讨论了NRQCD预言与NLL阈值重算对轻子对撞机上NLO连续谱顶对产生的匹配。在重算中考虑了顶对的S波和P波产生。列入WHIZARD允许研究更多的排他性的观测值，而不仅仅是总截面，并自动占重要的电弱和相对论性的修正在阈值区域。
