# Stefan Weinzierl's home page

** Current research interests: **
** Some previous research interests: **

** The walking path for pedestrians: **

### Through the looking glass ...

Let's start from the size of a crystal.
Increasing the resolution by ten million we are at the size of molecules.
Another factor of ten and we talk about atoms.
We increase the resolution further by a factor of one thousand
and we can see the atomic nucleus.
Another factor of ten and we can distinguish protons and neutrons.
And improving the resolution yet by another factor of one
thousand we are at the frontier of today: The world of elementary
particles like electrons and quarks...

### So here we are:

The elementary particles are split into two classes: One class makes up
the matter and particles in this class are also called fermions. The second
class consists of particles carrying the forces, like the photon which
is the carrier of the electromagnetic force. These particles are also
called bosons. Apart from the photon there are also the gluons as the
carrier of the strong force and the W- and Z-bosons as carrier of the weak
force.

The matter particles are further divided into three generations.
Particles of the second or third generation behave like the ones in the
first generation, except that they are heavier.
In the first generation we find two quarks, called the up- and the down-quark,
and two leptons: the well-known electron and the neutrino.

The particels can interact with each other. The theory which describes
the weak and electromagnetic interaction is called after the inventors
Glashow, Salam and Weinberg the GSW-model. The theory of the strong
interactions is called quantum chromodynamics.
Both theories in common is the underlying gauge principle. The GSW-model
is based on a SU(2)xU(1) gauge group, quantum chromodynamics or QCD for
short is based on a SU(3) gauge group.
Here high energy physics meets mathematics.

How do we know all this ? The answer is simple: from experiments.
Experiments in high energy physics usually accelerate two particles
before bringing them into collision. A detector around the collision
region analysis the outcome of the reaction.
The best-known laboratories where these experiments are done
are CERN at Geneva, FERMILAB close to Chicago and DESY at Hamburg.
Up to now no deviations of the experimental results from the theoretical
predictions have been seen.