Boosting probes of CP violation in the top Yukawa coupling with Deep Learning

TL;DR

This paper introduces a novel deep learning approach using conditional neural networks to efficiently analyze CP violation in the top-Higgs coupling, achieving high sensitivity with a single trained model across all CP phase values.

Contribution

The study develops and compares a conditional Graph Convolution Network and a Multi-Layer Perceptron for CP violation analysis, demonstrating the GCN's superior performance and enabling comprehensive phase sensitivity assessment with one training.

Findings

GCN outperforms MLP in CP phase sensitivity detection.

The method can exclude CP phases larger than 5° at 95.4% CL.

Approach surpasses traditional methods in sensitivity at HL-LHC.

Abstract

The precise measurement of the top-Higgs coupling is crucial in particle physics, offering insights into potential new physics Beyond the Standard Model (BSM) carrying {\cal CP} Violation (CPV) effects. In this paper, we explore the {\cal CP} properties of a Higgs boson coupling with a top quark pair, focusing on events where the Higgs state decays into a pair of $b$-quarks and the top-antitop system decays leptonically. The novelty of our analysis resides in the exploitation of two conditional Deep Learning (DL) networks: a Multi-Layer Perceptron (MLP) and a Graph Convolution Network (GCN). These models are trained for selected CPV phase values and then used to interpolate all possible values ranging from $0$ to $\pi/2$. This enables a comprehensive assessment of sensitivity across all {\cal CP} phase values, thereby streamlining the process as the models are trained only once. Notably, the conditional GCN exhibits superior performance over the conditional MLP, owing to the nature of graph-based Neural Network (NN) structures. Specifically, for Higgs top coupling modifier set to 1, with $\sqrt{s}= 13.6$ TeV and integrated luminosity of $3$ ab$^{-1}$ GCN excludes the {\cal CP} phase larger than $5^\circ$ at $95.4\%$ Confidence Level (C.L). Our Machine Learning (ML) informed findings indicate that assessment of the {\cal CP} properties of the Higgs coupling to the $t\bar t$ pair can be within reach of the High Luminosity Large Hadron Collider (HL-LHC), quantitatively surpassing the sensitivity of more traditional approaches.