Sparticle and Higgs-boson production and detection at CERN LEP II in two supergravity models

We study the most promising signals for supersymmetry at CERN LEP II in the context of two well-motivated supergravity models: (i) the minimal SU(5) supergravity model including the stringent constraints from proton stability and a not too young universe and (ii) a recently proposed string-inspired no-scale flipped SU(5) supergravity model. Our computations span the neutralino, chargino, slepton, and Higgs sectors together with their interconnections in this class of models. We find that the number of ‘‘mixed’’ (1-lepton+2-jets+p/) events occurring in the decay of pair-produced charginos (${\mathrm{\chi }}_1^{\pm }$) is generally significant (per scrL=100 ${\mathrm{pb}}^{\mathrm{-}1}$) for both models and that these predictions do not overlap. That is, if ${\mathit{m}}_{\mathrm{\chi }1}^{\pm }$<100 GeV then LEP II should be able to exclude at least one of the two models. In the no-scale flipped SU(5) model we find that the number of acoplanar dielectron events from selectron pair production should allow for exploration of selectron masses up to the kinematical limit and chargino masses indirectly as high as 150 GeV. We find that the cross section ${\mathit{e}}^{+}$ ${\mathit{e}}^{\mathrm{-}}$→${\mathit{Z}}^{\mathrm{*}}$h deviates negligibly from the SM result in the minimal model, whereas it can be as much as 1/3 lower in the flipped model. The usually neglected invisible mode h→${\mathrm{\chi }}_1^0$ ${\mathrm{\chi }}_1^0$ can erode the preferred h→2 jets signal by as much as 40% in these models. We conclude that the charged slepton sector is a deeper probe than the chargino, neutralino, or Higgs sectors of the flipped SU(5) model at LEP II, while the opposite is true for the minimal SU(5) model where the slepton sector is no probe at all.