Observability of a heavy Higgs boson at hadron supercolliders

We present a coherent analysis of Higgs-boson production in the channels $\mathrm{pp}\to \mathrm{ZZX}\to l^{+}{l}^{-}{l}^{\prime +}{l}^{\prime -}X(l, l^{\prime }=e, \mu )$ and $\mathrm{pp}\to \mathrm{ZZX}\to l^{+}{l}^{-}\nu \overline{\nu }X(\nu ={\nu }_e, {\nu }_{\mu }, {\nu }_{\tau })$ for $m_H\ge 600$ GeV at hadron supercolliders, using the exact matrix elements for $\mathrm{gg}\to \mathrm{ZZ}$ and $\mathrm{qq}\to \mathrm{qqZZ}$. The importance of a complete understanding of the shape of the perturbative $\mathrm{pp}\to \mathrm{ZZX}$ background from nonresonant diagrams is emphasized. We find that for the CERN Large Hadron Collider (LHC) to have a Higgs-boson discovery potential comparable to that of the Superconducting Super Collider (SSC) requires at least a factor of 10 times more integrated luminosity. In particular, assuming an integrated luminosity of ${10}^4$ ${\mathrm{pb}}^{-1\mathrm{}}$ and perfect lepton identification efficiency, the LHC (SSC) can identify Higgs bosons as resonances with mass up to 600 (800) GeV in $\mathrm{pp}\to \mathrm{ZZX}\to l^{+}{l}^{-}{l}^{\prime +}{l}^{\prime -}X$. To extend the discovery range of the LHC to $m_H=800\mathrm{}$ GeV in this channel requires an integrated luminosity of at least ${10}^5$ ${\mathrm{pb}}^{-1\mathrm{}}$. For $m_H>800\mathrm{}$ GeV, a clear resonance structure is missing; however, one can still discriminate between a heavy Higgs boson with $m_H\sim 1$ TeV and a light Higgs boson ($m_H\lesssim 2M_z$) at the SSC.