The earth matter effects in neutrino oscillation experiments from Tokai to Kamioka and Korea

Abstract

We study the earth matter effects in the Tokai-to-Kamioka-and-Korea experiment (T2KK), which is a proposed extension of the T2K (Tokai-to-Kamioka) neutrino oscillation experiment between J-PARC at Tokai and Super-Kamiokande (SK) in Kamioka, where an additional detector is placed in Korea along the same neutrino beam line. By using recent geophysical measurements, we examine the earth matter effects on the oscillation probabilities at Kamioka and Korea. The average matter density along the Tokai-to-Kamioka baseline is found to be 2.6 g/cm 3 , and that for the Tokai-to-Korea baseline is 2.85, 2.98, and 3.05 g/cm 3 for the baseline length of L-= 1000, 1100, and 1200 km, respectively. The uncertainty of the average density is about 6%, which is determined by the uncertainty in the correlation between the accurately measured sound velocity and the matter density. The effect of the matter density distribution along the baseline is studied by using the step function approximation and the Fourier analysis. We find that the ν µ → ν e oscillation probability is dictated mainly by the average matter density, with small but non-negligible contribution from the real part of the first Fourier mode. We also find that the sensitivity of the T2KK experiment on the neutrino mass hierarchy does not improve significantly by reducing the matter density error from 6% to 3%, since the measurement is limited by statistics for the minimum scenario of T2KK with SK at Kamioka and a 100 kt detector in Korea considered in this report. The sensitivity of the T2KK experiment on the neutrino mass hierarchy improves significantly by splitting the total beam time into neutrino and anti-neutrino runs, because the matter effect term contributes to the oscillation amplitudes with the opposite sign. *

Determination of mass hierarchy with medium baseline reactor neutrino experiments

“…with a baseline length L. We have neglected the matter effect because it is small enough for the energy range and the baseline lengths we concern in this study [24]. In obtaining the second line of (2.4) we have also ignored the tiny energy difference between the three mass eigenstates,…”

Revisiting T2KK and T2KO physics potential and $$\nu _\mu $$ ν μ – $${\bar{\nu }}_\mu $$

“…Ideas of extending the Tokai-to-Kamioka (T2K) experiment with additional waterČerenkov detectors placed in Korea (Tokai-to-Kamioka-and-Korea, T2KK, experiment [15][16][17][18][19][20][21][22][23][24][25][26]) or in Oki island (Tokai-to-Kamioka-and-Oki, T2KO, experiment [25,27]) have been proposed to address those questions. 1 It has been shown that the T2KK experiment with a 100 kton fiducial-volume detector in Korea in addition to the SK detector is an appealing proposal if we can use the J-PARC neutrino beam with 0.64 MW beam power and the 2.5 • -3.0 • off-axis angle at the SK [17,18,20,22,24].…”

“…1 It has been shown that the T2KK experiment with a 100 kton fiducial-volume detector in Korea in addition to the SK detector is an appealing proposal if we can use the J-PARC neutrino beam with 0.64 MW beam power and the 2.5 • -3.0 • off-axis angle at the SK [17,18,20,22,24]. The authors of Ref.…”

“…The impacts of including theν μ focusing beam in the T2KK experiment was studied in Ref. [24]. The authors considered the running ratio of the ν μ andν μ focusing beams of 5:0 and 2.5:2.5 in the units of protons on target (POT) and argued that including theν μ focusing beam improves the sensitivity to the mass-hierarchy determination significantly.…”

“…The physics potential of the T2KO experiment was also investigated [25] with a similar analysis and conclusion as in Ref. [24]. However, those studies again did not consider the effects of the NC π 0 backgrounds, miss-identified muon, and events from other neutrino-nucleus interactions than the charged-current quasi-elastic (CCQE) one.…”