Our intention in this book is to work through the theoretical principles of elementary particle physics. Today we know of the existence of a whole series of elementary particles. Examples are the electron (e), the photon (γ), the proton (p), the neutron (n), the pi-mesons or pions (π), the K-mesons (K), and the hyperons (Λ, Σ, etc.). Of these, the electron and the proton have been known for the longest time. At the time when the electron was discovered (Thomson 1897), there was still a general belief in the validity of classical physics in which particles and waves were totally separate concepts. It is really no more than a historical accident that electrons were first observed in an experiment in which they behaved like classical particles, whilst experiments in which electron beams show a wave-like character were not carried out until much later (Davisson 1927; Thomson 1927). In the case of light quanta, the situation was exactly the reverse. The wave nature of light was a dogma of the nineteenth century. It was only with the discovery of the photoelectric effect that physicists were forced to think again. The revolutionary idea of Einstein—the hypothesis of light quanta, in which light is also assumed to possess a particle nature (Einstein 1905)—at first met with great scepticism. It took approximately 20 years before the γ-quantum was accepted as a “particle” (see the historical survey of Pais (1979)). In the meantime, with the rise of quantum mechanics, it had been realized that particles and waves cannot be regarded as strictly separate phenomena, but must instead be considered as two aspects of the same phenomenon.
KeywordsClassical Physic Particle Data Group Photoelectric Effect Light Quantum Elementary Particle Physic
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