Tau Neutrino Appearance via Neutrino Oscillations in Atmospheric ...

1Chapter 1Introduction1.1 NeutrinosNeutrinos are everywhere and are one of the most common particles aroundus, yet we know the least about them. This elusive particle comes from manydifferent sources, such as human body via the β-decay of 40 K to 39 K, naturalradioactive materials on the Earth, nuclear reactors around the world, theupper atmosphere of the Earth, the Sun, and the Universe (e.g. Supernovaeand the Big Bang). Although neutrinos are abundant in nature, they wereonly first postulated theoretically by Wolfgang Pauli in 1930 [1]. In β-decay,the measured energy spectrum of the emitted electrons was continuous insteadof the expected monoenergetic distribution in two body decay. This observationseemed to violate the law of energy conservation. As a solution to theproblem, Pauli proposed that there could exist another neutral particle emittedin β-decay, which carried away the missing energy and made the electronenergy spectrum continuous. He wrote his famous letter, “Liebe RadioaktiveDamen und Herren (Dear Radioactive Ladies and Gentlemen”to the Tubingencongress on 4th December 1930.Dear Radioactive Ladies and Gentlemen,As the bearer of these lines, to whom I graciously ask you to listen,will explain to you in more detail, how because of the ”wrong”statistics of the N and 6 Li nuclei and the continuous beta spectrum,I have hit upon a desperate remedy to save the ”exchange theorem”of statistics and the law of conservation of energy. Namely,the possibility that there could exist in the nuclei electrically neutralparticles, that I wish to call neutrons 1 , which have spin 1/21 This is what he called the neutrino when he first came up with the idea. The