With an expected rate of about one event per 100,000 top-quark pairs, four top-quark final states very rarely arise at the LHC. Though scarce, they offer a unique window onto top-quark compositeness, self-interactions and more generically, onto any top-philic new physics. By employing simplified models featuring heavy resonances, we study the range of validity of effective theory interpretations of current four top-quark analyses at the LHC and establish their future reach at the HL-LHC. We find that for the class of models under consideration, the effective field theory interpretations are not applicable. We therefore present the most up-to-date limits obtained from public CMS analyses using simplified models. Finally, we put forward a novel recasting strategy for the experimental results based on the production of top quarks with large transverse momentum.
We explore constraints on various new physics resonances from four top-quark production based on current experimental data. Both light and heavy resonances are studied in the work. A comparison of full width effect and narrow width approximation is also made.
We investigate the phenomenology of a scalar top-philic dark matter candidate when adding a dimension-five contact interaction term, as motivated by possible underlying extensions of the Standard Model such as composite Higgs models. We show that the presence of contact interactions can have a major impact on the dark matter relic density as well as on its direct and indirect detection prospects, while the collider phenomenology of the model is unaffected. This underlines the complementarity of collider and cosmological constraints on dark matter models.
Sizeable exotic Higgs boson production through gluon fusion via top quark loops is correlated with large Higgs decay probabilities into top quark final states, if these are kinematically accessible. It is known that $gg\to S \to t\bar t$ is particularly susceptible to signal-background interference effects that can significantly impact discovery sensitivities. In such an instance, identifying more robust signatures to enhance the discovery sensitivity becomes necessary, shifting phenomenological focus to final states that show a reduced destructive signal-background interference. In this work,…
我们研究了LHC中的四顶末态，作为新物理（NP）效应的探针，由于新粒子主要与顶夸克耦合，其质量低于顶夸克对产生阈值。我们考虑简单的NP模型包含一个新的粒子与自旋0，自旋1，或自旋2，并找到与目前的实验结果兼容的基准点。我们发现，NP和QED振幅之间的干扰效应可以很大，指出NLO贡献的必要性，明确计算和考虑NP时，是本。我们研究这些模型和标准模型（SM）在部分子水平和重建水平之间的运动学差异。在后一种情况下，我们专注于选择需要两个相同符号的轻子和多个喷流的事件。我们调查如何不同的洛伦兹结构的光NP影响的运动硬度，偏振，自旋相关性，和角分布的部分子级和/或最终状态的粒子。我们发现自旋为2的轻NP比SM更难被运动学识别。我们还表明，相同符号的轻子之间的角间距是一个敏感的观察自旋0 NP。自旋为0和自旋为2的NP情况也会在$t\bar t γγ$中产生一个信号，光子的不变质量指示新粒子的质量。自旋为1的NP可以通过四顶信号的过量和其他可观测量的轻微或无修改来识别，例如由于朗道-杨定理，$t\bar t γγ$中缺少信号。我们评论的机会，将打开从运动学重建的一些顶夸克在四顶态。我们的研究结果提供了新的手柄，以探测轻亲顶NP作为正在进行的实验计划的一部分，在大型强子对撞机运行2及以后的四顶生产搜索。
Measurements carried out or reinterpreted within the framework of effective field theory (EFT) will constitute a key component of the LHC legacy in the quest towards physics beyond the standard model. Numerous EFT measurements were already published by the CMS Collaboration. In the top quark sector, four distinct approaches to EFT have been identified, each successfully applied in several analyses. We review the pros and cons of each approach, while illustrating them with recent analyses in which they were adopted.
With the absence of the direct detection of new physics and the large data set collected at the LHC, the search for indirect effects in precision measurements became popular. Effective field theories enable to interpret these effects that originate from physics manifested at currently unreachable energy scales in a model independent framework. In this report, an overview of new analyses performed by the ATLAS and CMS Collaborations in the field of top quark physics is given.
The study of the processes with the production of top quarks represents a unique possibility to test the standard model (SM) predictions and probe the new physics effects. Potential deviations from the SM expectations are parametrized within the framework of the Effective Field Theory (EFT). The latest EFT results from ATLAS and CMS experiments are presented. Dedicated studies of processes with flavour-changing neutral currents are also discussed.
The LHC effective field theory working group gathers members of the LHC experiments and the theory community to provide a framework for the interpretation of LHC data in the context of EFT. In this note we discuss experimental observables and corresponding measurements in analysis of the Higgs, top, and electroweak data at the LHC. We review the relationship between operators and measurements relevant for the interpretation of experimental data in the context of a global SMEFT analysis. One of the goals of ongoing effort is bridging the gap between theory and experimental communities working o…
我们设计了一个在LHC上产生标准模型$t\bar t t \bar t$的同号双轻子和三轻子通道的搜索策略。我们研究不同的信号功能，并鉴于预期的信号事件的数量少，我们详细审查所有可还原和不可还原的背景。我们的分析表明，通过施加一组基本的喷流和轻子选择标准，SM $pp \to t\bar t t \bar t$过程可以证明在不久的将来，在运行II，当结合两个多轻子搜索通道。我们认为，这种搜索策略也应该被用来作为一个指导方针，以测试新物理耦合为主的顶夸克。特别是，我们表明，在四顶最终状态的非共振新物理增强将通过这种搜索策略检测。我们研究了两个{ \it top-philic}简化模型，一个中性标量玻色子和一个$Z^\prime$，目前和未来的排斥限制，他们的质量和耦合。
We present a global interpretation of Higgs, diboson, and top quark production and decay measurements from the LHC in the framework of the Standard Model Effective Field Theory (SMEFT) at dimension six. We constrain simultaneously 36 independent directions in its parameter space, and compare the outcome of the global analysis with that from individual and two-parameter fits. Our results are obtained by means of state-of-the-art theoretical calculations for the SM and the EFT cross-sections, and account for both linear and quadratic corrections in the $1/Λ^2$ expansion. We demonstrate how the i…
Effective Field Theories are an established framework to bridge the gap between UV and low energy theories. In the context of the Standard Model, the bottom-up approach extends its operator set and thus equips us to astutely probe its observables while encapsulating indirect evidence of unknown high scale theories. While the top-down approach, on the other hand, employs functional techniques to integrate out the heavy fields from a BSM Lagrangian leading to a set of SMEFT operators. An intricate interplay of the two approaches enhances the efficacy of the SMEFT in making meaningful predictions…
