AUTHOR
Türk, Christian

DATE
2003-10-30

DEPARTMENT
Applied Physics and Mechanical Engineering / Physics

SUMMARY
The theoretical framework for small scale phenomena is quantum physics, where the word "quantum" refers to the smallest possible package of a physical quantity. Especially, in this thesis, we consider the spin of elementary particles, a kind of "intrinsic" angular momentum. This property is peculiar to quantum theories and we first discuss how it is connected to non- relativistic low energy processes. In this approach the spin is not automatically contained in the theory. It is rather experimental evidence, such as the Stern-Gerlach experiment, which shows that spin must be introduced to fully explain all observations. We also look at the connection to spin in relativistic high energy theories. This requires a knowledge of the Poincaré group, as this group determines the structure of space-time to a large extent.

We also discuss the article by E. Wigner from 1939, where he classified the little group connected to the inhomogeneous Lorentz group, and all its fundamental representations. This allowed Wigner to classify fundamental particles according to their masses and spins. Spin is revealed to result from the symmetries of space-time.

Finally, we try to introduce a phenomenological "hybrid particle"-model, composed of quarks and gluons, of the proton in order to explain the infamous "Proton Spin Crisis" problem, the experimental observation that little or nothing of the spin of a proton seems to be carried by the quarks of which it consists. This was first observed by the European Muon Collaboration (EMC) at CERN in 1988.

The conclusions so far are that spin is a property not fully understood and that a better understanding is necessary for obtaining more accurate theories. It is also a powerful and sensitive "tool" to test different theories of nature.

ISSN 1402-1617 / ISRN LTU-EX--03/299--SE / NR 2003:299