Abstract
The next generation of water Cherenkov neutrino telescopes in the Mediterranean Sea are under construction offshore France (KM3NeT/ORCA) and Sicily (KM3NeT/ARCA). The KM3NeT/ORCA detector features an energy detection threshold which allows to collect atmospheric neutrinos to study flavour oscillation. This paper reports the KM3NeT/ORCA sensitivity to this phenomenon. The event reconstruction, selection and classification are described. The sensitivity to determine the neutrino mass ordering was evaluated and found to be 4.4sigma if the true ordering is normal and 2.3sigma if inverted, after 3 years of data taking. The precision to measure varDelta m^2_{32} and theta _{23} were also estimated and found to be 85 . 10^{-6}~{mathrm{eV}^{2}} and (^{+1.9}_{-3.1})^{circ } for normal neutrino mass ordering and, 75 . 10^{-6}~{mathrm{eV}^{2}} and (^{+2.0}_{-7.0})^{circ } for inverted ordering. Finally, a unitarity test of the leptonic mixing matrix by measuring the rate of tau neutrinos is described. Three years of data taking were found to be sufficient to exclude event rate variations larger than 20% at 3sigma level.
Highlights
The standard framework of three neutrino flavour eigenstates, which are superpositions of the three mass eigenstates (ν1, ν2, ν3) with masses (m1, m2, m3), has been established with more than two decades of neutrino oscillation physics research
This paper reports the KM3NeT/ORCA sensitivity to this phenomenon
In case of detectors that cannot distinguish between neutrinos and anti-neutrinos on an event-by-event basis, the determination of the neutrino mass ordering (NMO) can be based on the observation of a net difference in the event rates of atmospheric neutrinos, resulting from a higher interaction cross section
Summary
The standard framework of three neutrino flavour eigenstates (νe, νμ, ντ ), which are superpositions of the three mass eigenstates (ν1, ν2, ν3) with masses (m1, m2, m3), has been established with more than two decades of neutrino oscillation physics research. The question of the neutrino mass ordering (NMO) is one of the main drivers of neutrino oscillation physics. Some questions remain: the determination of the value of δCP, the octant of θ23 (i.e. whether θ23 is greater or smaller than π/4) and the neutrino mass ordering (i.e. the sign of Δm223). The NMO can be determined by measuring the energy and zenith angle dependent oscillation pattern of few-GeV atmospheric neutrinos that have traversed the Earth [21]. In case of detectors that cannot distinguish between neutrinos and anti-neutrinos on an event-by-event basis, the determination of the NMO can be based on the observation of a net difference in the event rates of atmospheric neutrinos, resulting from a higher interaction cross section (factor ∼ 2)
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