Optimized Probes of the CP Nature of the Top Quark Yukawa Coupling at Hadron Colliders

Darius A Faroughy,Blaž Bortolato,Aleks Smolkovič,Nejc Košnik,Jernej F Kamenik

doi:10.3390/sym13071129

Darius A Faroughy, Blaž Bortolato + Show 3 more

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https://doi.org/10.3390/sym13071129

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Abstract

We summarize our recent proposals for probing the CP-odd iκ˜t¯γ5th interaction at the LHC and its projected upgrades directly using associated on-shell Higgs boson and top quark or top quark pair production. We first recount how to construct a CP-odd observable based on top quark polarization in Wb→th scattering with optimal linear sensitivity to κ˜. For the corresponding hadronic process pp→thj we then present a method of extracting the phase-space dependent weight function that allows to retain close to optimal sensitivity to κ˜. For the case of top quark pair production in association with the Higgs boson, pp→tt¯h, with semileptonically decaying tops, we instead show how one can construct manifestly CP-odd observables that rely solely on measuring the momenta of the Higgs boson and the leptons and b-jets from the decaying tops without having to distinguish the charge of the b-jets. Finally, we introduce machine learning (ML) and non-ML techniques to study the phase-space optimization of such CP-odd observables. We emphasize a simple optimized linear combination α·ω that gives similar sensitivity as the studied fully fledged ML models. Using α·ω we review sensitivity projections to κ˜ at HL-LHC, HE-LHC, and FCC-hh.

Highlights

We have recently addressed this challenge by identifying observables with optimal sensitivity to a single CP-odd parameter in both th and tth associated production at the LHC, which can be realistically measured and exhibit close to optimal sensitivity to CP-odd interactions between the Higgs boson and the top quark [24]
We present the bounds for HL- and HE-LHC, FCC-hh by using the optimal observable (60) with the weights shown in the upper plot of Figure 8
Directly and with minimal additional assumptions, the presence of a CP-odd component of the top quark Yukawa (κ), we have studied manifestly CP-odd observables in th and tth production at the LHC and its prospective upgrades

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Due to the high dimensionality and complexity of the phase-space in this process with top quarks decaying semileptonically, using the complete kinematical information accessible experimentally to construct an optimal CP-odd observable is challenging To this end we have employed neural networks (NN) trained on Monte-Carlo generated samples to efficiently parametrize the weight function of events across the multi-dimensional phasespace in order to maximize the statistical sensitivity to κ [27]. CP-odd observables in the process pp → tth in which both top quarks decays semileptonically: t → b l + ν and t → b l − ν This process has a higher S/B ratio compared to pp → thj and has been measured by the LHC collaborations [45,46] Section on manifestly CP-odd observables, directly sensitive to κand accessible by measurements of final-state momenta in the lab frame

Laboratory Frame CP-Odd Observables in tth Production

NN-Based Optimized CP-Odd Observables

Phase-Space Optimization of a Single ω

Neural Network as a CP-Odd Observable

Findings

Conclusions