Detection of the Reactor Neutrino

The 1995 Nobel Prize in Physics is shared equally by the American physicists Frederick J. Reines and Martin L. Perl for their pioneering experimental contributions to lepton physics. Following is a brief account of their discoveries. This is the year of the leptons. Of the six leptons of today's particle physics, Nobel Prizes were awarded earlier for discovering two of them: the electron and the muon-neutrino. This year it is the turn of two more leptons, the electron-neutrino and the tau lepton, to acquire 'Nobelity'. aged 77, reported the first direct evidence for the existence of the 'neutrino' in 1956. He performed the experiments jointly with Clyde L. Cowan, Jr., who died in 1974. The neutrino is a tiny neutral particle hypothesized by Wolfgang Pauli, Jr. way back in 1930, and was thought to be unobservable. Twenty five years later and with the invention of the nuclear reactor it was possible to verify the neutrino hypothesis. assisted by a 35-member team, discovered the 'tau lepton' in 1975. This particle carries a unit of electric charge and weighs approximately twice as much as the proton. It is characterised by a shortlife of only a fraction of a pico-second and has the distinction of being the heaviest and the shortest-lived lepton. It is interesting that while Reines's neutrino results were long hoped for, Perl's tau discovery came as a complete surprise-that too at a time when people were busy establishing the charm flavour around the same mass. The tau lepton heralded the existence of the " third generation " of fundamental constituents of matter. 1 Brief History of the Neutrino " The neutrino is the smallest bit of material reality ever conceived of by man; the largest is the universe. To attempt to understand something of one in terms of the other is to attempt to span the dimension in which lie all manifestations of natural law. Yet even now, despite our shadowy knowledge of these limits, problems arise to try the imagination in such an attempt. " Neutrino 'was born' in a letter written by Pauli. This historic letter dated 4 December 1930 from Zürich, started with the unusual greeting " Dear Radioactive Ladies and Gentlemen " , and was read out at the Tübingen meeting. Pauli mentioned that he had hit upon the neutrino as a 'desperate remedy' to save, among other things, the principle of energy conservation in beta …