ALP-ine quests at the LHC: hunting axion-like particles via peaks and dips in $t \bar{t}$ production

TL;DR

This paper analyzes the sensitivity of LHC searches for axion-like particles in top-antitop final states, deriving new limits, distinguishing production mechanisms, and exploring future prospects with detailed kinematic and angular analyses.

Contribution

It introduces new constraints on ALP couplings from LHC data and proposes methods to differentiate ALP production modes using invariant mass and angular correlations.

Findings

Current LHC data constrains ALP couplings to top quarks and gluons.

Angular and mass distributions can distinguish ALP production mechanisms.

High-luminosity LHC data enhances sensitivity to ALP properties.

Abstract

We present an analysis of the sensitivity of current and future LHC searches for new spin-0 particles in top-anti-top-quark ($t\bar{t}$) final states, focusing on generic axion-like particles (ALPs) that are coupled to top quarks and gluons. As a first step, we derive new limits on the effective ALP Lagrangian in terms of the Wilson coefficients $c_t$ and $c_{\tilde{G}}$ based on the results of the CMS search using $35.9$ fb$^{-1}$ of data, collected at $\sqrt{s} = 13$ TeV. We then investigate how the production of an ALP with generic couplings to gluons and top quarks can be distinguished from the production of a pseudoscalar which couples to gluons exclusively via a top-quark loop. To this end, we make use of the invariant $t\bar{t}$ mass distribution and angular correlations that are sensitive to the $t\bar{t}$ spin correlation. Using a mass of 400 GeV as an example, we find that already the data collected during Run 2 and Run 3 of the LHC provides an interesting sensitivity to the underlying nature of a possible new particle. We also analyze the prospects for data anticipated to be collected during the high-luminosity phase of the LHC. Finally, we compare the limits obtained from the $t \bar t$ searches to existing experimental bounds from LHC searches for narrow di-photon resonances, from measurements of the production of four top quarks, and from global analyses of ALP-SMEFT interference effects.