Higgs sector in aU(1)′extension of the minimal supersymmetric standard model

We consider the Higgs sector in an extension of the minimal supersymmetric standard model (MSSM) with extra SM singlets, involving an extra $U(1{)}^{\prime }$ gauge symmetry, in which the domain-wall problem is avoided and the effective $\mu$ parameter is decoupled from the new gauge boson $Z^{\prime }$ mass. The model involves a rich Higgs structure very different from that of the MSSM. In particular, there are large mixings between Higgs doublets and the SM singlets, significantly affecting the Higgs spectrum, production cross sections, decay modes, existing exclusion limits, and allowed parameter range. Scalars considerably lighter than the CERN LEP2 bound (114 GeV) are allowed, and the range $\tan \beta \sim 1$ is both allowed and theoretically favored. Phenomenologically, we concentrate our study on the lighter (least model-dependent, yet characteristic) Higgs particles with significant $SU(2)$-doublet components to their wave functions, for the case of no explicit $CP$ violation in the Higgs sector. We consider their spectra, including the dominant radiative corrections to their masses from the top/stop loop. We computed their production cross sections and reexamine the existing exclusion limits at LEP2. We outline the searching strategy for some representative scenarios at a future linear collider. We emphasize that gaugino, Higgsino, and singlino decay modes are indicative of extended models and have been given little attention. We present a comprehensive list of model scenarios in the Appendices.