On the impact of systematical uncertainties for the CP violation measurement in superbeam experiments

Abstract

Superbeam experiments can, in principle, achieve impressive sensitivities for CP violation in neutrino oscillations for large θ 13 . We study how those sensitivities depend on assumptions about systematical uncertainties. We focus on the second phase of T2K, the so-called T2HK experiment, and we explicitly include a near detector in the analysis. Our main result is that even an idealised near detector cannot remove the dependence on systematical uncertainties completely. Thus additional information is required. We identify certain combinations of uncertainties, which are the key to improve the sensitivity to CP violation, for example the ratio of electron to muon neutrino cross sections and efficiencies. For uncertainties on this ratio larger than 2%, T2HK is systematics dominated. We briefly discuss how our results apply to a possible two far detector configuration, called T2KK. We do not find a significant advantage with respect to the reduction of systematical errors for the measurement of CP violation for this setup.

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

“…In this study we are mainly interested in the ν μ → ν e and ν μ → ν μ oscillation modes and their charge conjugated ones. It is useful to write them down in the approximated analytic forms as [17] In these expressions we retain up to the sub-leading terms of 21 , sin 2 θ 13 and aL/4E. The corresponding probabilities for anti-neutrino oscillations can be obtained from the above expressions by reversing the sign of the matter effect term (a → −a) and the CP phase (δ CP → −δ CP ).…”

“…The blue (dashed-blue), green (dashed-green), orange (dashedorange) and red curves show the absolute value of the χ 2 MH , Eq. (3.8), for rejecting the wrong mass hierarchy when the ratio of the ν μ andν μ focusing beams is 5:0 (0:5), 4:1 (1:4), 3:2 (2:3) and 2.5:2.5 (×10 21 POT with the proton energy of 40 GeV), respectively. It is shown that includingν μ focusing beam can improve the sensitivity, especially in high sensitivity regions.…”

“…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].…”

Physics Performance of a Low-Luminosity Low Energy Neutrino Factory

“…An upgraded beam in the multi-MW range (superbeam) would obviously yield a much better physics potential [7]. However, these beams are eventually limited by intrinsic backgrounds and systematic effects: large flux uncertainties, combined with the inability to measure the final flavor cross sections at the near detector, introduce large systematical errors which are very difficult to control [8,9].For the determination of the CP phase a similar precision to that achieved in the quark sector is only offered by a neutrino factory (NF) [9,10]. In a NF a highly collimated beam of muon neutrinos and electron antineutrinos is produced from muon decays in a storage ring with long straight sections [11].…”

“…An upgraded beam in the multi-MW range (superbeam) would obviously yield a much better physics potential [7]. However, these beams are eventually limited by intrinsic backgrounds and systematic effects: large flux uncertainties, combined with the inability to measure the final flavor cross sections at the near detector, introduce large systematical errors which are very difficult to control [8,9].…”