Searches for Neutral Higgs Bosons in Extended Models
The DELPHI Collaboration, J. Abdallah
TL;DR
This study searches for neutral Higgs bosons in extended scalar sectors using DELPHI data from LEP1 and LEP2, covering production modes hZ, hA, and Yukawa processes with decays to $b\bar b$, $\tau^+\tau^-$, or $AA$. It employs a model-independent framework, expressing results as upper bounds on cross-section times branching ratios through $C^{2}$ factors, and combines multiple final states (four-$b$, four-$\tau$, six-$b$, and four-$\tau$) and selection streams to maximize sensitivity across the Higgs mass plane. No convincing signal is observed, and the paper provides comprehensive mass-dependent exclusions, translating into substantial constraints on two-Higgs-doublet and related models; an apparent excess in one LEP2 data set is not confirmed by other data. Overall, the work delivers a robust, model-agnostic set of limits that can reinterpret a wide class of electroweak-scalar theories.
Abstract
Searches for neutral Higgs bosons produced at LEP in association with Z bosons, in pairs and in the Yukawa process are presented in this paper. Higgs boson decays into b quarks, tau leptons, or other Higgs bosons are considered, giving rise to four-b, four-b+jets, six-b and four-tau final states, as well as mixed modes with b quarks and tau leptons. The whole mass domain kinematically accessible at LEP in these topologies is searched. The analysed data set covers both the LEP1 and LEP2 energy ranges and exploits most of the luminosity recorded by the DELPHI experiment. No convincing evidence for a signal is found, and results are presented in the form of mass-dependent upper bounds on coupling factors (in units of model-independent reference cross-sections) for all processes, allowing interpretation of the data in a large class of models.