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内容記述 |
The Tokai-to-Kamioka (T2K) neutrino oscillation experiment will start in 2009.<br>In T2K. the center of the neutrino beam from J-PARC at Tokai will go through<br>underground beneath Super-Kamiokande (SK), reach the sea level in the Japan<br>(east) sea near Korean shore. When the beam center is 2.5°(3.0°) downward SK,<br>the neutrino beam with an off-axis angle greater than 1.0°(0.5°) can be observed<br>in Korea. We study the physics potential of the Tokai-to-Kamioka-and-Korea<br>(T2KK) experiment when an additional 100 kt-level Water Čerenkov detector is<br>placed in Korea during the T2K experimental period. We find that the matter<br>effect, which arises from the coherent interaction of <i><small>V</small>e</i> (or <i>‾<small>V</small>e</i>) off the electrons in<br>the earth matter, is a powerful tool to determine the sign of (<i>m</i><sup>2</sup><sub>3</sub>−<i>m</i><sup>2</sup><sub>1</sub>), and the<br>CP phase, σ<small>MNS</small>, of the lepton flavor mixing matrix. The best combination of the<br>off-axis angles at each detector and the length for the Tokai-to-Korea baseline is<br>found to be 3.0°at SK ( <i>L</i> = 295 km) and 0.5° at <i>L</i> =1000km. If we choose this<br>combination, and if the densities along the baselines are 2.8 g/cm<sup>3</sup> for Tokai-to-<br>Kamioka baseline and 3 g / cm<sup>3</sup> for Tokai-to-Korea baseline with 3% uncertainties,<br>the mass hierarchy pattern can be determined at 3-σ level for sin<sup>2</sup> 2θ<small>RCT</small>＞<sub>～</sub> 0.09,<br>and the CP phase can be constrained with ± 30°error for sin<sup>2</sup> 2θ<small>RCT</small>0.06, after<br>5 years of running (5 × 10<sup>21</sup> POT). When we combine the result of the future<br>reactor neutrino ercperiments, such as Double-CHOOZ, RENO, DAYA-BAY, the<br>capability of determining the mass hierarchy pattern in T2KK is enhanced, and the<br>hierarchy pattern can be constrained at 3-σ level for sin<sup>2</sup>2θ<small>RCT</small>＞<sub>～</sub> 0.055. Because<br>of the importance of the matter effect, we study the matter profile along the<br>baselines of the T2KK experiment by using the recent geophysical measurements.<br>The average matter density along the Tokai-to-Korea baselines is found to be 2.96,<br>3.01, and 3.03 g/cm<sup>3</sup> for the baseline length of L = 1000, 1100, and 1200 km,<br>respectively, with about 6% uncertainty. Only the real part of the first Fourier<br>mode gives non-negligible but very small contribution to the up <i>v</i>μ→<i>ve</i> oscillation<br>probability. We find that, even if we enhance the error of the average matter<br>density from 3% to 6%, the capability of determining the neutrino mass hierarchy<br>pattern in T2KK does not deteriorate significantly because the measurement error<br>is dominated by statistics. |
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