Super-Kamiokande and Neutrino Oscillation Good evening . Thanks for giving chance of talk to me. First, let me introduce my subject. My subject is neutrino physics and super-kamiokande. So this evening I will show you why neutrino mass is so important and how super-kamiokade proved the existence of neutrino mass. Hui-Young Ryu Pusan National University hyryu@pusan.ac.kr

Contents Ⅰ. Motivation Ⅱ. Theoretical Background Ⅲ. Experiment Ⅳ. Data Review Ⅴ. Summary My talk sequence is like this..

Ⅰ. Motivation 1. Solar neutrino problem A lot of electron neutrinos are produced as a result of nuclear fusion in the Sun. The number of neutrinos at the Earth is . But measured neutrinos are only 40 % of them. catch only 40% of them… First of all, I want to introduce how people have been so interested in neutrino. Actually there are many interesting subjects, here I will introduce two famous problem. The first famous thing is solar neutrino problem (……) Why ?

2. Cosmic Ray neutrino ratio Theoretical Expectaion : In the atmosphere, Measurement : On the Earth Next cosmic ray neutrino ratio In the atmosphere, cosmic ray collides with the nucleus in the atmosphere. This event causes the plenty creation of neutrinos and our calcul- ation expect that the ratio of and is 1 to 2. Why ?

Ⅱ. Theoretical Background 1. Brief summary of neutrino history 1.1 The neutrino hypothesis There exists a neutral, spin ½ particle which is simultaneously emitted with the electron in beta-decay. This hypothesis resolves the following difficulties (1) The apparent non-conservation of energy in beta-decay (2) The apparent non-conservation of angular momentum in certain beta-decay Before we attack this problems, I will review brief summary of neutrino. At first, in 1932 Pauli suggested the neutrino hypothesis to solve the Non-conservation of mass and non-conservaiton of angular momentum In beta decay. The neutrino hypothesis is as following.

1.2 Two kinds of beta-decay (Example) (Example) There are two kinds of beta-decay Beta plus decay is proton number minus process. And as a result, positron and electron neutrino are produced. On the other hand, beta minus decay is proton number plus process. In this process, electron and anti-neutrino are produced.

1.3 Fermi’s Beta-decay theory When Fermi in 1933 considered beta-decay, he thought that the electron and neutrino can be created Within -range due to uncertainty principle, His theory was very successful in leading-order, but divergent in next-to-leading-order. (Fermi assumed that mass of neutrino is zero)

1.4 Experimental evidence of existence of In present, we think there are three neutrinos: muon neutrino, electron neutrino and tau neutrino. The electron neutrino was found in 1956. The muon neutrino was found in 1962. The tau neutrino have not directly found yet. But there are many indirect evidence of existence of tau neutrino.

2. Neutrino Oscillation Neutrino oscillation is the key to determine whether the neutrino mass is zero or not. If a neutrino mass is not zero, neutrino can be changed to other neutrino (by neutrino oscillation), and this phenomena can solve the solar neutrino problem and cosmic ray neutrino problem. Neutrino oscillation is somewhat old idea which explains the transition of particles.

In electro-magnetic theory, neutrinos propagate through space as a superposition of mass eigenstates From the above, we can express

From the oscillation idea, we can derive where Because is very small, is almost near to 1for small L. But if L is large enough, can be non-zero. From the oscillation idea, we can derive…. P(mu->mu) means the probability of muon neutrino translate to own And P(mu->e) means the probability of muon neutrino change to electron neutrino. Both of them are dependent of the distance of traveled

We can describe this idea by using plot. From the previous equations, we can get Now we assume neutrino behavior as a plan wave, i.e. Then ,with initial conditions, we can get

It is easy to get the following results by the previous equations To make the equation simple , for (….) we can choose the parameter to best fit

When the phase difference is From the above result, we can plot When the phase difference is zero, There is only muon neutrino On the other hand, if the phase difference is pi, There is no muon neutrino We can describe this situation by two mass eigenstates phase

So if we compare the ratio to the theoretical value, we would know that the neutrino mass is zero or not. That is what the Super-Kamiokande did

Ⅲ. Experiment 1. Super Kamiokande - Overview Size : Cylinder of 41.4m(Height), 39.3m(Diameter) Weight : 50,000 tons of pure water Light Sensitivity : 11,200 PMT (50cm each in diameter - the biggest size in the world) (They are very sensitive light detectors and they can detect single photons. They are looking into the the inner volume of water) 4) Location : Kamioka-cho, Yoshiki-gun (1,000m underground at the Mozumi mine) Next let’s consider how to experiment. It is brief summary of super-kamiokande

2. Outside and Inside

3. Sequence of process Cosmic ray In the S-K 2 muon neutrinos and 1 electron neutrino In the S-K A neutrino interact with water An electron produces Cerenkov light PMTs count the numbers of neutrino

Ⅳ. Data Review From the data collected for 500 days in the Super-Kamiokande, a significant anisotropy was observed in the angular distribution of atmospheric neutrinos. Oscillations of muon neutrinos fit best the observations <Distributions of lepton zenith angles > ※Blue lines are for distributions expected without oscillations, red - with the best fit oscillation parameters.

The Nobel Prize in Physics 2002 " for pioneering contributions to astrophysics, in particular for the detection of cosmic neutrinos" "for pioneering contributions to astrophysics, which have led to the discovery of cosmic X-ray sources" Raymond Davis Jr. Masatoshi Koshiba Riccardo Giacconi ¼ of the prize USA ¼ of the prize Japan ½ of the prize University of Pennsylvania Philadelphia, PA, b. 1914 University of Tokyo Tokyo, Japan b. 1926 Associated Universities Inc. Washington, DC, USA b. 1931 (in Genoa, Italy)

Ⅴ. Summary ■ Number of neutrino was different form what our theory expected. (Solar neutrino problem and cosmic ray neutrino problem, etc.) ■ Neutrino oscillation solved these problems by assumption of non-zero neutrino mass. ■ From the supernova in 1998 Super-Kamiokande observed vital evidences of non-zero neutrino mass. ■ Super-Kamiokande has been used for detecting proton-decay and its exploration is still going on.