The principal objective in High Energy Physics is to understand experimentally the ultimate "view" of the matter and the interactions holding it together. We are asking ourselves: In order to look into the matter at small distances, the research usually requires high-resolution "microscopes" which are the gigantic particles accelerators ! The current world's highest energy accelerator, Fermilab Tevatron Collider, can see the matter constituents at the distance of 10^(-19)m, 1/10000 of the size of a hydrogen nucleus (remember Heisenberg's Uncertainty Principle). Also we require bright microscopes, accelerators with high luminosity, to look into the details of matter constituents and rare interactions.

Although the idea (theory) of classifying the world into more fundamental elements can be traced back to the Greek era, the modern particle physics has started in 1897 when J.J. Thomson extracted experimentally electrons as cathode rays. Experimental and theoretical knowledges accumulated since then have beared fruit of "Standard Model of Elementary Particles" in late 1970's. Important experimental milestones that led us to this Model could be listed as follows:

  • discovery of top quark (heaviest matter constituent) at Fermilab in 1994-95
  • a series of precision validations by LEP experiments at CERN
  • discovery of W and Z particles (weak force carriers) at CERN in 1983-85*
  • observation of three jets events (gluon) at DESY in 1979
  • discovery of bottom quark (2nd heaviest quark) at Fermilab in 1977
  • discovery of tau (heaviest lepton) at SLAC in 1975*
  • discovery of charm quark at SLAC and Brookhaven in 1974*
  • discovery of the neutrino interaction via Z particle at CERN in 1973-74
  • discovery of proton substructure (scale invariance) at SLAC in early 1960's*
  • discovery of CP violation in K-decay at BNL in 1964*
  • discovery of parity violation in weak decay in 1957*
  • observation of "V" events (strange quark) in 1950's and quark model in 1964*
  • discovery of pi and K mesons in cosmic rays in 1947*
  • discovery of mu lepton in cosmic rays in 1947*
  • discovery of positron (anti-electron) in cosmic rays in 1933*
  • discovery of electron in 1897 and atomic models since 1903*
    *Nobel prize awarded

    Is that all ? The answer is no. The Standard Model is merely a model which can describe the present observations. We know for sure that there are missing stories. The followings are a part of questions which we address:

  • "Symmetry breaking" - Why W/Z are heavy unlike photons ?
  • "Supersymmetry (SUSY)" - Isn't the world symmetric in fermion-boson (SUSY) ?
  • "Origin of the mass" - Why quarks have masses ? Why the top is so heavy ?
  • "Grand unification" - Can protons decay ? (Is there a quark-to-lepton transition ?)
  • "Compositness" - Are the quarks elementary ?
  • "Neutrino mass" - Are neutrinos massless ?
  • "5th force" - Can CP-violation be explained by the Standard Model?
  • ...
    You can see the details of how we obtained the Standard Model and what are beyond it in the item, "High Energy Physics (way to and beyond the Standard Model)" .

    K. Hara (Webmaster of HEP Lab) on Nov. 28, 1997