AI 中文总结
针对LHC上不可区分的$tttW$与$tttt$过程，提出窗口去除方案实现NLO精度联合预言，其 inclusive 率比纯在壳$tttt$高10%以上，为实验测量提供了可靠的理论基础。
AI 中文摘要
在对四顶夸克产生（$tttt$）的测量中，大型强子对撞机（LHC）合作组观测到其与三顶夸克产生存在显著简并性。我们对主导的三顶夸克产生模式——即与W玻色子的伴随产生（$tttW$）进行了完整的次领头阶（NLO）计算，包含所有可能的量子色动力学（QCD）和电弱（EW）修正。超出领头阶（LO）后，伴随额外b味夸克辐射的$tttW$产生过程，与通过$t \to bW$衰变的$tttt$产生过程具有相同的末态。在离壳顶夸克极限下，非共振计算中共振贡献的常规重叠去除方法，要么会破坏规范不变性并产生幺正性违反，要么在所需的动量重排中存在显著的任意性。为克服这些问题，我们引入了一种新颖的窗口去除方案，为不可区分的$tttW+tttt$过程提供了一致的预言，且两个组分均以NLO精度描述。我们认为，在针对$tttt$产生的实验选择比较中应使用这种联合预言，因为在实践中无法将在壳$tttt$组分分离出来；该联合预言的 inclusive 率比纯在壳$tttt$的率高出10%以上。我们还研究了对额外硬且中心b喷注辐射的理想化 veto，它会压低共振$tttt$图的贡献及其与非共振$tttW$图的干涉，从而定义了一个相对纯净的类$tttW$信号区域。形式上的次领头耦合阶在LO时具有数值重要性，而对应的次领头NLO修正则在 inclusive 和微分层面均大幅抵消，因此完整NLO预言可通过保留前三个LO耦合阶加上领头QCD NLO修正来很好地近似。
英文摘要
In measurements of four-top-quark production ($tttt$), LHC collaborations observe a significant degeneracy with three-top-quark production. We compute the dominant three-top-production mode, namely associated production with a $W$ boson ($tttW$), at complete next-to-leading order (NLO), including all possible QCD and electroweak (EW) corrections. Beyond leading order (LO), $tttW$ production with the radiation of an additional $b$-flavoured quark contributes to the same final state as $tttt$ production with a $t \to bW$ decay. Away from the on-shell top-quark limit, the usual overlap removal of resonant contributions in the non-resonant computation either breaks gauge invariance and generates unitarity violation or involves a significant arbitrariness in the required reshuffling of momenta. To overcome these issues, we introduce a novel window-removal prescription that produces consistent predictions for the inseparable $tttW+tttt$ process, with both components described at NLO accuracy. We argue that such a joint prediction should be used in comparisons with experimental selections targeting $tttt$ production, since the on-shell $tttt$ component can not be isolated in practice. Such a joint prediction has an inclusive rate more than 10% higher than the purely on-shell $tttt$ one. We also study an idealised veto on additional hard and central $b$-jet radiation, which suppresses the contributions of resonant $tttt$ diagrams as well as their interference with non-resonant $tttW$ ones and therefore defines a relatively pure $tttW$-like signal region. Formally subleading coupling orders are numerically important at LO, while the corresponding subleading NLO corrections largely cancel both inclusively and differentially. Consequently, the complete-NLO prediction is well approximated by retaining the first three LO coupling orders together with the leading QCD NLO correction.
Comments23 pages, 14 figures, 1 table
