1. Weighing the Neutrino - Prof. Chung Wook Kim

In spite of its long history of more than 8 decades, the Pauli's mystery particle, neutrino, still remains as the least known particle among the fundamental building blocks of the Universe. The mystery is attributed to its feeble interactions with others. In an open letter to a 1930 Tübingen conference, which starts with "Dear Radioactive Ladies and Gentlemen", Pauli introduced a neutral fermion (a spin half particle) calling it neutron. This was his desperate attempt to rescue the law of energy and momentum conservation which seemed to be violated in beta-decay processes. After Chadwick's discovery of the real neutron in 1932, this neutral fermion was renamed by Fermi as neutrino in 1933. In the same year at the Solvay conference, Pauli also speculated that neutrinos may be massless. It has taken almost 70 years to find that neutrinos do have mass. In 1998, a new phenomenon called neutrino oscillation, as observed in the cosmic rays neutrinos or atmospheric neutrinos with Super-Kamiokande in Japan, was definitively confirmed. Neutrino oscillations can take place if and only if neutrinos are massive (rigorously speaking, at least two out of three types of neutrinos are massive) and also mixed. However, the absolute values of neutrino masses still remains unknown due to the fact that in the neutrino oscillations, individual neutrino masses are not manifested, instead only in the form of mass-square differences. As of now, the neutrino oscillation approach has been the only one to have shown the massive neutrinos. In this talk, a brief history of the neutrino and various on-going efforts to find the mass will be presented, including direct measurements in beta-decay, neutrinoless double beta-decays, oscillations experiments with nuclear reactor and accelerator neutrinos as well as the solar neutrinos. The prospect of finding neutrino mass from the cosmic microwave background radiation is also discussed.

2. θ₁₃ and Neutrino Mass Hierarchy using Reactor Neutrinos - Prof. Soo-Bong Kim

Netrino physics has gone through remarkable progress during the last two decades. RENO, the first Korean neutrino experiment, was able to start data-taking from August, 2011 using identical near and far detectors, to search for the last, smallest mixing angle. It successfully loaded 0.1% Gadolinium into liquid scintillator to maximize the detection efficiency of reactor neutrinos, and has not seen any detector degradation at all. RENO observed a clear disappearance of reactor antineutrinos, and obtained a definitive measurement of θ_13. A surprisingly large value of θ₁₃ has opened a new window to find the leptonic CP phase angle and the neutrino mass hierarchy, and thus has promoted the next round of neutrino experiments. RENO has elevated the Korean neutrino physics to the world-leading class level. RENO will continue data-taking for the next 3 or 4 more years, reaching its sensitivity limit, in order to obtain a precise measurement of the mixing angle. Korean reactors can be freely used as an intense neutrino source to study unknown neutrino properties. We need a next, flagship neutrino experiment continuously to play a world-leading role in neutrino physics. RENO-50, a multi-purpose neutrino detector, is proposed to determine the neutrino mass hierarchy, measure θ₁₂ and mass difference of m₁ and m₂ in unprecedentedly high precision, and detect neutrinos from interesting astrophysical sources.