Re-evaluation of the T2KK physics potential with simulations including backgrounds

TL;DR

This study re-evaluates the T2KK neutrino experiment's ability to determine neutrino mass hierarchy and CP violation, accounting for realistic backgrounds and energy smearing, and finds it feasible under certain conditions.

Contribution

It provides a detailed simulation including backgrounds and energy resolution effects, enhancing the understanding of T2KK's sensitivity to mass hierarchy and CP violation.

Findings

Mass hierarchy can be determined at 3sigma with current exposure if sin^22θ13 > 0.08.

π^0 backgrounds weaken hierarchy determination and CP phase measurement.

Higher exposure is needed to accurately measure δ_mns within ±30 degrees.

Abstract

The Tokai-to-Kamioka-and-Korea (T2KK) neutrino oscillation experiment under examination can have a high sensitivity to determine the neutrino mass hierarchy for a combination of relatively large (\sim 3.0^circ) off-axis angle beam at Super-Kamiokande (SK) and small (\sim 0.5^circ) off-axis angle at L \sim 1,000km in Korea. We elaborate previous studies by taking into account smearing of reconstructed neutrino energy due to finite resolution of electron or muon energies, nuclear Fermi motion and resonance production, as well as the neutral current \pi^0 production background to the nu_mu to nu_e oscillation signal. It is found that the mass hierarchy pattern can still be determined at 3sigma level if sin^22thata_rct \quiv 4|U_{e3}|^2(1-|U_{e3}|^2) \gsim 0.08(0.09) when the hierarchy is normal (inverted) with 5 \times10^{21} POT exposure, or 5 years of the T2K experiment, if a 100kton water cherenkov detector is placed in Korea. The \pi^0 backgrounds deteriorate the capability of the mass hierarchy determination, whereas the events from nuclear resonance productions contribute positively to the hierarchy discrimination power. We also find that the \pi^0 backgrounds seriously affect the CP phase measurement. Although \delta_mns can still be constrained with an accuracy of \sim \pm 45^circ (\pm 60^circ) at 1sigma level for the normal (inverted) hierarchy with the above exposure if sin^22theta_rct \gsim 0.04, CP violation can no longer be established at 3sigma level even for delta_mns=\pm 90^circ and sin^22theta_rct=0.1. About four times higher exposure will be needed to measure delta_mns with \pm 30^circ accuracy.