INTERMEDIATE-HIGGS-BOSON AND HEAVY-HIGGS-BOSON PHYSICS AT A 0.5 TEV E+E- COLLIDER

We explore the potential of a future e+e- collider in the 0.5 TeV center-of-mass energy range to detect intermediate or heavy Higgs bosons in the standard model. We first briefly assess the logistics for finding a Higgs boson of intermediate mass, with M(Z) < m(H) < 2M(W). We then study in detail the possibility of detecting a heavy Higgs boson, with m(H) > 2M(W), through the production of pairs of weak bosons. We quantitatively analyze the sensitivity of the process e+e- --> nunuBARW+W-(ZZ) to the presence of a heavy-Higgs-boson resonance in the standard model. We compare this signal to various backgrounds and to the smaller signal from e+e- --> ZH --> mu+mu-W+W-(ZZ), assuming the weak-boson pairs to be detected and measured in their dominant hadronic decay modes W+W-(ZZ) --> 4 jets. A related Higgs-boson signal in 6-jet final states is also estimated. We show how the main backgrounds from e+e-W+W- (ZZ), enuWZ, and ttBAR production can be reduced by suitable acceptance cuts. Bremsstrahlung and typical beamstrahlung corrections are calculated. These corrections reduce Higgs-boson production by scattering mechanisms but increase production by annihilation mechanisms; they also smear out some dynamical features such as Jacobian peaks in p(T)(H). With all these corrections included, we conclude that it should be possible to detect a heavy-Higgs-boson signal in the nunuBARW+W-(ZZ) channels up to mass m(H) = 350 GeV.