Artikel über N.Tesla

III-1
1 Introduction
1.1 Particle Physics Today
The Standard Model of particle physics was built up through decades of intensive
dialogue between theory and experiments at both hadron and electron machines. It
has become increasingly coherent as experimental analyses have established the basic
physical concepts. Leptons and quarks were discovered as the fundamental constituents
of matter. The photon, the W and Z bosons, and the gluons were identified as the
carriers of the electromagnetic, weak and strong forces. Electromagnetic and weak
forces have been unified within the electroweak gauge field theory. The QCD gauge
field theory has been confirmed as the theory of strong interactions.
In the last few years many aspects of the model have been stringently tested, some
to the per-mille level, with e + e − , ep and p¯p machines making complementary contributions,
especially to the determination of the electroweak parameters. With the e + e −
data from LEP1 and SLC measurements of the lineshape and couplings of the Z boson
became so precise that the mass of the top quark was already tightly constrained
by quantum level calculations before it was directly measured in p¯p at the Tevatron.
Since then LEP2 and the Tevatron have extended the precision measurements to the
properties of the W bosons. Combining these results with neutrino scattering data and
low energy measurements, the experimental analysis is in excellent concordance with
the electroweak part of the Standard Model.
At the same time the predictions of QCD have also been thoroughly tested. Notable
among the QCD results from LEP1 and SLC were precise measurements of the strong
coupling α s . At HERA the proton structure is being probed to the shortest accessible
distances. HERA and the Tevatron have been able to explore a wide range of QCD
phenomena at small and large distances involving both the proton and the photon,
supplemented by data on the photon from γγ studies at LEP.
Despite these great successes there are many gaps in our understanding. The clearest
gap of all is the present lack of any direct evidence for the microscopic dynamics
of electroweak symmetry breaking and the generation of the masses of gauge bosons
and fermions. These masses are generated in the Standard Model by the Higgs mechanism.
A fundamental field is introduced, the Higgs boson field, whose non–zero vacuum
expectation value breaks the electroweak symmetry spontaneously. Interaction with
this field generates the W and Z boson masses while leaving the photon massless; the
masses of the quarks and leptons are generated by the same mechanism. The precision
electroweak analysis favours a Higgs boson mass which is in the region of the limit
which has been reached in searches at LEP2. The LEP experiments have reported a