J. H. D. Jensen og H. Øverås Die Polarisation eines Müonenstrahles beim Pionenzerfall im Fluge

Abstract

The paper presents a calculation of the polarization of a muon which is created by the disintegration of a pion in flight. The muon is an elementary particle, similar to the electron, but heavier and short lived. The pion is a particle that is created in cosmic rays and it disintegrates into a muon and a neutrino. Elementary particles have spin. It is a nonclassical property but it appears as if the particle rotates. The direction of the rotation axis is called the direction of polarization. When a pion in flight disintegrates in a muon and a neutrino the muon will be polarized. The polarization is calculated by theory in the paper.

The disintegration of the pion is generated by the weak nuclear force. In 1958 the main features of the theory had just been established and B. Stech and Jensen had in 1955 given an important contribution to the theory. In the paper of 1958 Jensen and Øverås calculated the angle between the muon spin and the direction of the motion of the muon.

J. H. D. Jensen (1907-1973) was born in Hamburg. He studied science at the universities in Hamburg and Freiburg and started work as an assistant in theoretical physics in Hamburg in 1932. Han got his doctorate there in 1936 and became dosent in 1937. He worked for the weather service 1939-1940 before he got a professorship at the Technische Hochschule in Hannover, 1941-1948. Later he became professor in Heidelberg and he also was professor emeritus there, 1969-1973. Jensen got the Nobel Prize in 1963.

Jensen had wide interests but his main activity soon was nuclear physics, and it was for his work on the so called shell model that he got the Nobel Prize. He shared the one half with Maria Goeppert Mayer who developed similar ideas in Chicago.

After the discovery of the neutron in 1932 it became clear that the atomic nucleus is a bound state of protons and neutrons, caused by the strong nuclear force. Since the strong forces have short range the liquid drop model or the «compound nucleus» of Bohr was the dominant model for a long time. As the measurements of nuclear properties improved Haxel, Suess and Jensen studied the so called «magic numbers», numbers of protons and neutrons that led to very stable nuclei. In analogy with atomic physics the idea of nucleons moving on shells became promoted again. This shell model was a great step forward for the understanding of nuclei. Jensen published papers about this model from 1949.

Helge Øverås (1928- ) the coauthor of the 1958 paper was at that time a young technical physicist from NTH employed at CERN. He worked first with theoretical particle physics but soon changed to more technical problems concerning accelerators at CERN, in particular applications of computers. He stayed at CERN until he retired.