collider could make a “ no - lose ” search for MSSM Higgs bosons ?

The lightest CP-even Higgs boson h in the minimum supersymmetric standard model (MSSM) has a mass upper bound depending on the top quark and squark masses. An ee collider with enough energy and luminosity to produce h + Z at measurable rates up to the maximum h mass would cover the entire MSSM parameter space, if h+A production was also searched for. We explore the energy and/or luminosity needed for various top quark and squark masses. For mt = 150GeV and 1TeV SUSY mass scale, a 230GeV collider with 10 fb −1 luminosity would suffice. The theoretical appeal of supersymmetry (SUSY) is that it solves the problem of large radiative corrections in the scalar sector, associated with the grand unification scale. The minimal supersymmetric extension of the Standard Model (MSSM) [1] has five Higgs bosons, one of which (h) is necessarily relatively light; their discovery could contribute the first direct evidence both for SUSY and for the Higgs mechanism. These Higgs bosons are therefore the object of intense experimental investigation; a lower limit mh > ∼ 40GeV has already been set by ee experiments at LEP I [2–5] and the range of search will be extended at LEP II with CM energy √ s = 190GeV to 240GeV possible [6]. In this letter we address the question: what is the lowest energy ee collider that could completely cover the MSSM parameter space [7–11] and thereby independently guarantee discovery or rejection of the MSSM? This question is relevant because LEP I, LEP II, SSC and LHC will not fully cover all MSSM parameters [7,10,11], and the possibilities of higher energy ee linear colliders are being examined [12]. The Higgs sector of the minimum supersymmetric standard model (MSSM) has three neutral and two charged Higgs bosons, h, H, A, H of which h and H are CP-even and mh < mH ; a mixing angle α appears in the h and H couplings. At tree level all their masses and couplings are controlled by two parameters, that may be taken to be mA and the ratio tan β = v2/v1 of vacuum expectation values giving masses to up-type quarks (v2) and down-type quarks (v1) respectively; renormalization group arguments in no-scale models [13] suggest that 1 < tan β < mt/mb but mA is unconstrained. At one-loop level, however, there are significant radiative corrections [14], that depend on several other parameters but especially on the top quark and squark masses; as a result the h mass has an upper bound m2h < ∼ M Z cos β + 6GF π √ 2 m4t ln ( m̃ mt )