Pursuing the origin of electroweak symmetry breaking: a 'Bayesian   Physics' argument for a 600 GeV e+e- collider
  High-energy data has been accumulating over the last ten years, and it should not be ignored when making decisions about the future experimental program. In particular, we argue that the electroweak data collected at LEP, SLC and Tevatron indicate a light scalar particle with mass less than 500 GeV. This result is based on considering a wide variety of theories including the Standard Model, supersymmetry, large extra dimensions, and composite models. We argue that a high luminosity, 600 GeV e+e- collider would then be the natural choice to feel confident about finding and studying states connected to electroweak symmetry breaking. We also argue from the data that worrying about resonances at multi-TeV energies as the only signal for electroweak symmetry breaking is not as important a discovery issue for the next generation of colliders. Such concerns should perhaps be replaced with more relevant discovery issues such as a Higgs boson that decays invisibly, and ``new physics'' that could conspire with a heavier Higgs boson to accommodate precision electroweak data. An e+e- collider with energy less than about 600 GeV is ideally suited to cover these possibilities. 
G.L. Kane, James D. Wells