Higgs-boson signals in superstring-inspired models at hadron supercolliders.

Abstract

In superstring-inspired ${\mathrm{E}}_{6}$ supergravity models, the mass of the lightest Higgs scalar (${H}_{L}$) is expected to be below \ensuremath{\sim}170 GeV if ${\mathrm{E}}_{6}$ is broken directly to a rank-5 subgroup and below \ensuremath{\sim}210 GeV if intermediate scales of \ensuremath{\sim}${10}^{10}$ GeV are allowed. We show that if the mass of the additional neutral gauge boson ${Z}^{0\mathcal{'}}$ is less than about 600 GeV, then \ensuremath{\sim}${10}^{4}$--${10}^{5}$ ${Z}^{0\mathcal{'}}$\ensuremath{\rightarrow}${Z}^{0}$${H}_{L}$ pairs may be expected per ${10}^{4}$ ${\mathrm{pb}}^{\mathrm{\ensuremath{-}}1}$, the annual integrated luminosity anticipated at the proposed 40-TeV pp supercollider. This large rate allows us to use the clean ${Z}^{0}$\ensuremath{\rightarrow}ll\ifmmode\bar\else\textasciimacron\fi{} decays as a trigger for the Higgs-boson search. We find that even if ${H}_{L}$\ensuremath{\rightarrow}tt\ifmmode\bar\else\textasciimacron\fi{} decays dominate, a signal-to-background ratio substantially exceeding unity is expected for reasonable experimental resolutions on the measurement of ${Z}^{0}$tt\ifmmode\bar\else\textasciimacron\fi{} and tt\ifmmode\bar\else\textasciimacron\fi{} invariant masses. We further show that for a wide range of parameters, ${H}_{L}$ can decay into chargino and neutralino pairs. These decays lead to hadron-free ${Z}^{0}$+missing ${p}_{T}$ (p${?}_{T}$) events which may stand out over the ${Z}^{0}$${Z}^{0}$ background and also to spectacular ${Z}^{0}$+n lepton+p${?}_{T}$ events (n\ensuremath{\le}4) which are almost free of standard-model backgrounds.