Round tour of Physics



Our present knowledge of elementary particles physics is based on the so-called "Standard Model", which has been verified with unprecedented precision by the LEP experiments. The purpose of this "Round tour of Physics with DELPHI" is to provide an overview of the main results obtained at LEP and will be largely, but not exclusively, illustrated (for reasons of convenience) by pictures from the Delphi experiment. World averages will also be included whenever possible.
Although the Standard Model has proven a very successful description of existing data, most people believe that it can only be an effective low energy theory. The status of the search for new particles, either foreseen by the Standard Model (Higgs) or beyond the Standard Model is also reviewed.

Constituents of matter :
Matter is made from quarks and leptons, held together and transforming into each other by means of gauge bosons: the photon, gluons and weak bosons. This chapter provides a rather elementary introduction to basic concepts of elementary particle physics and our "best theory today", the Standard Model.

LEP Accelerator and Experiments :
The study of elementary particles requires large accelerators and very sophisticated detectors. This gives an illustrated description of the LEP accelerator, the principles of particle detection and their application to actual detectors.

e+ e- Scattering reactions :
Overview of the various kinds of events observed in e+ e- interactions, illustrated with pictures from the DELPHI experiment.

Z0 properties :
The study of the properties of the Z0 gauge boson made at LEP and of the resulting stringent tests of the Standard Model.

Tau decays :
The Tau lepton is a rather young particle, as it was discovered in 1975 by M.Perl and collaborators at SLAC. An impressive progress was made recently in our knowledge of its properties. This was largely contributed to by the LEP experiments.

Jets and Gluons :
Quarks are not observed directly ...

Heavy quark physics :

Above the Z0 :
Since end 1995, LEP started to increase the energy above the Z0, hoping to reach its maximum close to 200 GeV in 1998. This opens a new era with precision measurements above the WW threshold and a new impetus for the search of new particles (see below).

A window into extremely high energies :
The high precision obtained in the knowledge of the strengths of the interactions allows them to be extrapolated to very high energies, where they are believed to join together into a "Grand Unified Theory".

Search for new particles :
The energy increase of LEP will hopefully allow to discover the long awaited Higgs boson, the only undiscovered buiding block of the Standard Model. But it could also lead to new particles beyond the Standard Model, in particular Supersymmetric particles, among which some are expected to be rather light and possibly in the reach of LEP experiments.

Elementary Particles and Cosmology :
There exists a close link between the particles produced at the very high energies reached by accelerators and the state through which the matter of the Universe went at very early times.