Differential cross sections have been measured for nucleon-isobar production and elastic scattering in p -p interactions from 6.2 to 29.7 GeV/c in the laboratory angle range 8 < O , ,

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Electrons of two million volts energy from an electrostatic generator were used to investigate the properties of the asymmetric radiation discovered by Cerenkov. This radiation is produced when electrons traverse a material medium with a velocity greater than the velocity of light in that medium. It was found for several solids and liquids that the direction of the emission of the radiation is accurately expressed by the relation, cos 6-l/(3n, and that the intensity maximum is quite sharp. The nature of the radiation from all solids and liquids investigated was found to be continuous and identical in appearance. The radiation apparently extends with increasing intensity from the infra-red to the ultraviolet absorption limit of the medium in which it is produced. Rough quantitative measurements of its intensity indicate that one 1.9 million volt electron in being brought to rest in water produces 40 quanta in a wave-length range 4000A to 6700A. These results are in good agreement with the classical explanation of the phenomenon given by Frank and Tamm.

associated with phase diffusion brought about by a random noise perturbation due to thermal fluctuations. In the quantum theory, the process of contraction of the density matrix after the decay of each injected atom would convert even a pure case into a mixture, so that Eqs. (2) really describe an ensemble of lasers for which phase information is gradually lost. The density matrix does not describe the laser but rather our state of knowledge of the ensemble of lasers under consideration. If we knew initially that a single laser had a nonvanishing electric field, a density matrix with nonzero off-diagonal elements would be required for the initial description, and the average electric field would only decay with the very long mean life of 1/D.

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