Non-Minimal Supersymmetric Higgs Bosons at LEP2

TL;DR

The paper investigates LEP2’s sensitivity to a non-minimal Higgs sector extended by a gauge singlet, where a new quartic coupling $\lambda$ and singlet-doublet mixing can raise CP-even Higgs masses and dilute $Z$ couplings. It derives an absolute bound $m_{h_1}^2\le\Lambda^2$ with $\Lambda^2$ given by the rotated mass matrix $M'^2$ and computes the maximal bound $\Lambda_{\max}\approx136-146$ GeV (for $m_t\in[150,195]$ GeV$)$. The analysis develops strategies to exclude values of $\Lambda$ (i.e., $\Lambda_{\min}$) using LEP2 via CP-even $Z\to Zh_i$, CP-odd/charged channels, and $Z\to hA$, including a practical “worst-case” scanning approach and a simplified bound method; it shows that LEP2 can exclude $\Lambda_{\min}\approx81-105$ GeV depending on machine energy and luminosity, while the MSSM limit serves as a reference. The results reveal that singlet mixing complicates searches—reducing $Zh$ reach, while charged-Higgs channels can gain importance when $\lambda$ is sizable—and that, despite these challenges, a substantial region of parameter space remains accessible to LEP2, with potential for discovery under favorable mixings. The findings provide a concrete framework for translating collider non-observations into bounds on the non-minimal Higgs sector, and they extend the LEP2 reach to (M+$n$)SSM scenarios with $R^2=1/(2+n)$ couplings.

Abstract

We discuss the discovery reach of LEP2 for the Higgs sector of a general extension of the MSSM including a single gauge singlet field. This change introduces a new quartic Higgs boson self-coupling which can increase the masses of the CP-even states, and also allows mixing between singlet and non-singlet states which can reduce the couplings of the mass eigenstates to the $Z$. The lightest CP-even Higgs boson is bounded by a parameter $Λ$ which takes a maximum value $Λ_{max}\approx 136-146$ GeV for top mass $150-195$ GeV. We generalise the discussion of the bound to include the entire CP-even spectrum and show how experiment may exclude values of $Λ$ smaller than some $Λ_{min}$. CP-even Higgs boson searches at LEP2 will be able to exclude $Λ_{min}\approx 81-105$ GeV, depending on the machine parameters. We also present exclusion plots in the $m_A-\tanβ$ plane, based on an analysis of CP-even, CP-odd and charged Higgs production processes at LEP2.