Neutrino
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eutrino1 S. M. Bilenky Joint Institute for Nuclear Research, Dubna, R141980, Russia Abstract—Neutrinos are the only fundamental fermions which have no electric charges. Because of that neu trinos have no direct electromagnetic interaction and at relatively small energies they can take part only in weak processes with virtual W ± and Z 0 bosons. Neutrino masses are many orders of magnitude smaller than masses of charged leptons and quarks. These two circumstances make neutrinos unique, special particles. The history of the neutrino is very interesting, exciting and instructive. We try here to follow the main stages of the neutrino history starting from the famous Pauli letter and finishing with the discovery and study of neutrino oscillations. Outstanding contribution to the neutrino physics of Bruno Pontecorvo is discussed in some details. DOI: 10.1134/S1063779613010024 1
1. INTRODUCTION
trinos were detected in the Reines and Cowan reactor neutrino experiments in the fifties. In 1946 Bruno Pontecorvo was the first who paid attention that reac tors are very intensive sources of (anti)neutrinos, the most appropriate (at that time) for reactor neutrino experiments [4]. In 2002 the Nobel Prize was awarded to R. Davis and M. Koshiba “for pioneering contribution to astro physics, in particular for detection of cosmic neutri nos”. In the Davis experiment the radiochemical method of the neutrino detection proposed by Bruno Pontecorvo in 1946 [4] was used.
Neutrinos are unique particles. They plaid an extremely important role in the establishment of V–A current × current theory of the weak interaction and the Standard Model (SM). Small neutrino masses and neutrino mixing discovered via observation of neu trino oscillations is the first particle physics signature of a beyond the SM physics. The first period of the history of neutrino was in essence the history of the weak interaction. This period started in 1930 with the famous Pauli letter in which idea of neutrino was proposed and finished with the creation of the SM. The second period of neutrino history is the history of the development of ideas of neutrino masses and mixing and history of challenging solar, atmospheric, reactor and accelerator neutrino experiments in which neutrino oscillations driven by small neutrino masses and neutrino masses were discovered and studied. This period started with ideas of neutrino oscillations put forward by Bruno Pontecorvo in 1957–58 [1, 2] soon after the twocomponent neutrino theory was proposed. Importance of neutrino for physics and astrophys ics is emphasized by the fact that three Nobel Prizes were given for discoveries in neutrino physics. In 1988 L. Lederman, M. Schwartz and J. Stein berger were awarded by the Nobel Prize for “for the neutrino beam method and the demonstration of the doublet structure of lepton through the discovery of the muon neutrino”. The experiment with accelerator neutrinos which allowed to prove that νμ and νe are dif ferent particles was proposed by Bruno Pontecorvo in 1959 [3]. In 1995 F.
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