The Kamioka Liquid-scintillator Anti-Neutrino Detector
Exploring the ultimate structure of matter, the fundamental principles of nature and the birth, evolution and death of the universe is an inevitable practice, which is imposed on the human beings. In order to study these sub jects, experimental approaches in particle physics tend to pioneer the two different research fields with the opposite side energy. One is the ultra-high energy side, which is realized by high-energy particle accelerators. The other is the ultra-low energy side, where large volume and high sensitive particle detectors are equipped in a deep underground. In particular large volume underground detectors give opportunities for exploring the most important unsolved sub jects on particle physics, astrophysics and cosmology.
The KamLAND pro ject of Tohoku University was launched in 1997 with main ob jectives of(1) measurement of the neutrino masses and mixings through a search for neutrino oscillations of antineutrinos from faraway nuclear power reactors,(2) observation of 7 Be and 8 B solar neutrinos in order to understand an evolution of main sequence stars, and(3) the first observation of geo-neutrinos for studies of the earth formation and evolution.
The construction was finished in 2001 and the data taking started from January 2002. The striking first results, ”evidence of reactor anti-neutrino disappearance,” has been announced in the end of 2002. It solves the long-standing (more than 30 years) solar neutrino problem. In 2004 after accumulating more data, the second results, ”evidence of spectral distortion,” has established the cause of the disappearance as neutrino oscil- lations, observing oscillatory behavior of neutrino survival probability. KamLAND has pin-pointed neutrino oscillation parameters and consequently neutrino became a good probe for exploring the interior of the earth. In 2005, KamLAND just realized the geo- neutrino observation and pioneered a new field, ”Neutrino Geophysics”. And ”Neutrino Astrophysics” with an observation of low energy solar neutrinos will be also accomplished by on-going big efforts shortly.