Direct discovery of new light states at the FCCee

TL;DR

This paper explores the potential of the FCCee collider to directly discover light new particles, such as axion-like particles and heavy neutral leptons, which are common in theories addressing fundamental questions in particle physics.

Contribution

It provides a detailed analysis of the theory motivations and discovery prospects for light new states at the FCCee, emphasizing the importance of complementarity with other collider programs.

Findings

FCCee can probe light states between 1 and 100 GeV

Light states require embedding in larger theoretical frameworks

Complementarity with high energy colliders enhances discovery potential

Abstract

Light new states are ubiquitous in many models which address fundamental outstanding questions within the Standard Model (SM). The FCCee provides an excellent opportunity to probe these new particles with masses between $1$ and $100\,$GeV and their electroweak couplings. Here we discuss the theory motivations for axion-like particles and heavy neutral leptons and detail the potential of direct discovery at the FCCee. We highlight that our current understanding requires light new states to be embedded within a bigger theory framework and thus the complementarity of the precision frontier at the FCCee and the high energy frontier of the FCChh program.