Exotic decays of the 125 GeV Higgs boson at future e+e− colliders**Supported by Fermi Research Alliance, LLC (DE-AC02-07CH11359) with the U.S. Department of Energy, DOE (DE-SC0013642), IHEP(Y6515580U1), and IHEP Innovation (Y4545171Y2)

Zhen Liu,Hao Zhang,Lian-Tao Wang

doi:10.1088/1674-1137/41/6/063102

Abstract

The discovery of unexpected properties of the Higgs boson would offer an intriguing opportunity to shed light on some of the most profound puzzles in particle physics. Beyond Standard Model (BSM) decays of the Higgs boson could reveal new physics in a direct manner. Future electron-positron lepton colliders operating as Higgs factories, including CEPC, FCC-ee and ILC, with the advantages of a clean collider environment and large statistics, could greatly enhance sensitivity in searching for these BSM decays. In this work, we perform a general study of Higgs exotic decays at future e+e- lepton colliders, focusing on the Higgs decays with hadronic final states and/or missing energy, which are very challenging for the High-Luminosity program of the Large Hadron Collider (HL-LHC). We show that with simple selection cuts, (10-3-10-5) limits on the Higgs exotic decay branching fractions can be achieved using the leptonic decaying spectator Z boson in the associated production mode e+e-→ ZH. We further discuss the interplay between detector performance and Higgs exotic decays, and other possibilities of exotic decays. Our work is a first step in a comprehensive study of Higgs exotic decays at future lepton colliders, which is a key area of Higgs physics that deserves further investigation.

Highlights

The recent discovery of the Higgs boson by the ATLAS and CMS experiments at the Large Hadron Collider (LHC) opened a new era of particle physics [1, 2]
The future lepton colliders operating as Higgs factories, with their clean collider environment and large statistics, would measure the Higgs boson couplings to a relative precision of O(0.1% ∼ 1%) [16,17,18]
New physics could manifest itself through Higgs exotic decays if some new light degrees of freedom are present, which are not described by the Standard Model (SM) effective field theory (EFT)

Summary

Introduction

The recent discovery of the Higgs boson by the ATLAS and CMS experiments at the Large Hadron Collider (LHC) opened a new era of particle physics [1, 2]. The precise measurements of the properties of this Higgs boson have great potential to shed light on BSM physics. The HL-LHC will measure many SM model decay modes of the Higgs boson to a relative precision of O(10%) [11,12,13,14,15]. Many discussions about the physics potential of future lepton colliders focus on the precision measurement of the Higgs properties in the effective field theory (EFT) framework [19,20,21,22,23,24]. Systematically searching for Higgs exotic decays would be an important physics component of the future lepton collider programs. We discuss many important future directions for the Higgs exotic decay programs

Higgs exotic decay modes considered in this work

Higgsstrahlung process

Phenomenological analysis

Summary and outlook