Collider searches of scalar singlets across lifetimes

TL;DR

This paper explores collider search strategies for scalar singlets with varying lifetimes, analyzing different decay signatures and comparing models like the generic scalar singlet and relaxion to identify natural parameter spaces and experimental bounds.

Contribution

It provides a comprehensive analysis of collider signatures for scalar singlets across lifetimes, including bounds from Higgs decays and coupling fits, highlighting differences between models.

Findings

Bounds from Higgs decays constrain singlet parameters

Displaced and delayed jets are key signatures for long-lived singlets

Distinct features differentiate the generic scalar singlet from the relaxion

Abstract

Spin-0 singlets arise in well-motivated extensions of the Standard Model. Their lifetime determines the best search strategies at hadron and lepton colliders. To cover a large range of singlet decay lengths, we investigate bounds from Higgs decays into a pair of singlets, considering signatures of invisible decays, displaced and delayed jets, and coupling fits of untagged decays. We examine the generic scalar singlet and the relaxion, and derive a matching as well as qualitative differences between them. For each model, we discuss its natural parameter space and the searches probing it.