Dark Higgs in Hidden Sector as a Probe for Dark Matter

TL;DR

This paper analyzes the potential of the FCC-ee collider to detect long-lived scalar particles from exotic Higgs decays, demonstrating sensitivity to decay lengths from millimeters to meters through displaced vertex reconstruction.

Contribution

It presents a detailed sensitivity analysis for detecting long-lived scalars in Higgs decays at FCC-ee, using advanced simulation and vertex reconstruction techniques.

Findings

FCC-ee can detect long-lived scalars with decay lengths from 1 mm to 10 m.

The analysis shows high sensitivity for scalar masses of 20 and 60 GeV.

Displaced vertex reconstruction effectively suppresses Standard Model backgrounds.

Abstract

This study presents a sensitivity analysis of exotic Higgs boson decays at the electron--positron stage of the Future Circular Collider (FCC-ee), performed within the FCCAnalyses framework. The analysis investigates Higgs boson production in association with a Z boson in electron--positron collisions at a center-of-mass energy of 240~GeV. The Higgs boson is assumed to decay into a pair of long-lived scalar particles, while the Z boson decays leptonically. A hadronic final state is considered, in which the long-lived scalars subsequently decay into bottom--antibottom quark pairs. The simulation chain is implemented using the FCCAnalyses framework, with event generation performed using \textsc{MadGraph} and \textsc{Pythia}, and detector effects modeled with \textsc{Delphes}. Displaced vertices arising from the decays of long-lived particles are reconstructed using the FCCAnalyses implementation of the \textsc{LCFIPlus} secondary vertex finding algorithm, enhanced with extended features such as customized track selection. The final event selection requires the reconstruction of a Z boson together with at least two displaced vertices. This strategy efficiently suppresses Standard Model backgrounds while retaining at least three expected signal events, including statistical uncertainties, over most of the explored parameter space. The study considers scalar masses of 20~GeV and 60~GeV and mixing angles of $10^{-5}$, $10^{-6}$, and $10^{-7}$. The results demonstrate that FCC-ee will be sensitive to long-lived scalars with decay lengths ranging from approximately 1~mm to 10~m, with optimal sensitivity around a decay length of 0.3~m.