用超图神经网络提升顶夸克四重产生产物的探测能力,增强对新物理的敏感度。
Probing SMEFT Operators through $t\bar{t}t\bar{t}$ Production with Hyper-Graph Neural Networks at the LHC
- 构建超图神经网络,捕捉多体末态的高阶关联结构。
- 在140 fb⁻¹数据下达到9.11σ显著性,优于现有方法。
- 可精确约束新物理的威尔逊系数,适用于未来高亮度对撞机研究。
我们在√s = 13 TeV质子-质子碰撞中,研究t̄tt̄t产生过程,采用超图神经网络(H-GNN)区分多轻子信号与主导的标准模型背景,包括t̄tW、t̄tZ、t̄tH、t̄tVV、单顶伴随产生及双/三玻色子过程。H-GNN将每个事件表示为超图,节点对应重建喷注和轻子,超边编码任意子集间的高阶关联,从而学习t̄tt̄t末态的多体动量结构。结合同号双轻子、三轻子与四轻子通道(类CMS选型),H-GNN在受控条件下实现0.951的ROC曲线下面积,统计显著性达Z = 9.11(140 fb⁻¹),优于SPANet(Z = 8.62)、Particle Transformer(Z = 7.37)及ATLAS分析(Z = 5.13)。利用优化信号提取能力,推导出维度六算符ΩΦu、Ω(1)tt、Ω(1)qq、Ω(1)qt、Ω(8)qt的95%置信区间限值,并投影至HL-LHC 1000 fb⁻¹与3000 fb⁻¹下,假设背景估计有50%不确定性。
原文摘要 · Abstract (English)
We present a phenomenological study of $t\bar{t}t\bar{t}$ production in proton-proton collisions at $\sqrt{s} = 13$~TeV, using a Hyper-Graph Neural Network (H-GNN) to discriminate multilepton signal events from the dominant SM backgrounds, namely $t\bar{t}W$, $t\bar{t}Z$, $t\bar{t}H$, $t\bar{t}VV$, single-top associated production, and diboson and triboson processes. In the H-GNN architecture each event is represented as a hypergraph whose nodes correspond to reconstructed jets and leptons and whose hyperedges encode higher-order correlations among arbitrary subsets of these objects, allowing the network to learn the many-body kinematic structures that characterize the $t\bar{t}t\bar{t}$ final state. Combining same-sign di-lepton, tri-lepton, and four-lepton channels following a CMS-like event selection, the H-GNN attains an area under the ROC curve of $0.951$ for the $t\bar{t}t\bar{t}$ signal and yields a statistical significance of $Z = 9.11$ at an integrated luminosity of $\mathcal{L} = 140~\mathrm{fb}^{-1}$, to be compared with $Z = 8.62$ for a SPANet baseline, $Z = 7.37$ for a Particle Transformer baseline, and $Z = 5.13$ obtained by the ATLAS analysis, evaluated under identical event selection. We exploit the improved signal extraction to derive one- and two-parameter $95\%$ confidence level limits on the Wilson coefficients of the dimension-six operators $\mathcal{O}_{Φu}$, $\mathcal{O}^{(1)}_{tt}$, $\mathcal{O}^{(1)}_{qq}$, $\mathcal{O}^{(1)}_{qt}$, and $\mathcal{O}^{(8)}_{qt}$, and we project the expected sensitivity at the HL-LHC integrated luminosities of $1000~\mathrm{fb}^{-1}$ and $3000~\mathrm{fb}^{-1}$ with $50\%$ uncertainty on the background estimation.
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