Nonresonant Searches for Axion-Like Particles in Vector Boson Scattering Processes at the LHC

TL;DR

This paper introduces a novel nonresonant search method for Axion-Like Particles at the LHC using vector boson scattering processes, providing competitive constraints on ALP couplings up to 100 GeV.

Contribution

It develops a gauge-invariant framework for nonresonant ALP searches in VBS, reinterprets existing CMS data, and projects future sensitivities at the LHC.

Findings

Constraints on ALP couplings to electroweak bosons are competitive up to 100 GeV.

Constraints are independent of ALP gluon couplings and decay width.

Future analyses at LHC Run 3 and HL-LHC can significantly improve sensitivity.

Abstract

We propose a new search for Axion-Like Particles (ALPs), targeting Vector Boson Scattering (VBS) processes at the LHC. We consider nonresonant ALP-mediated VBS, where the ALP participates as an off-shell mediator. This process occurs whenever the ALP is too light to be produced resonantly, and it takes advantage of the derivative nature of ALP interactions with the electroweak Standard Model bosons. We study the production of $ZZ$, $Z\gamma$, $W^\pm \gamma$, $W^\pm Z$ and $W^\pm W^\pm$ pairs with large diboson invariant masses in association with two jets. Working in a gauge-invariant framework, upper limits on ALP couplings to electroweak bosons are obtained from a reinterpretation of Run 2 public CMS VBS analyses. The constraints inferred on ALP couplings to $ZZ$, $Z\gamma$ and $W^\pm W^\pm$ pairs are very competitive for ALP masses up to 100 GeV. They have the advantage of being independent of the ALP coupling to gluons and of the ALP decay width. Simple projections for LHC Run 3 and HL-LHC are also calculated, demonstrating the power of future dedicated analyses at ATLAS and CMS.