Two of the main objectives of the KM3NeT collaboration are i) the determination of the ordering of the neutrino mass eigenstates with the KM3NeT/ORCA detector and ii) the discovery and subsequent observation of high-energy neutrino sources in the Universe with the KM3NeT/ARCA detector [1].
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@@ -9,6 +10,31 @@ The KM3NeT neutrino detectors will continuously register neutrinos from the whol
(Taken from Grant Agreement)
**Astro Physics**
The main science objective of KM3NeT/ARCA is the detection of high-energy neutrinos of cosmic origin. Neutrinos represent an alternative to photons and cosmic rays to explore the high-energy Universe. Neutrinos can emerge from dense objects and travel large distances, without being deflected by magnetic fields or interacting with radiation and matter. Thus, even modest numbers of detected neutrinos can be of utmost scientific relevance, by indicating the astrophysical objects in which cosmic rays are accelerated, or pointing to places where dark matter particles annihilate or decay.
The detector design of the KM3NeT/ARCA has been optimised to target astrophysical neutrinos at TeV energies and above in order to maximise the sensitivity to detect neutrinos from the cosmic ray accelerators in our Galaxy. In a neutrino telescope like ARCA, two main event topologies can be identified are: The 'track' topology that indicates the presence of muons produced in \nu_\mu CC interactions and \nu_\tau interactions with muonic tau decays; and the 'shower' topology that includes the NC interaction of all three neutrino flavours, the CC interaction of \nu_e, and \nu_\tau interactions with non-muonic tau decays.
The preferred search strategy is to identify upward-moving muon tracks, which unambiguously indicates neutrino reactions since only neutrinos can traverse the Earth without being absorbed. A neutrino telescope in the Mediterranean Sea on the Northern hemisphere of the Earth is ideal for this purpose, since most of the potential Galactic sources are in the Southern sky.
The ARCA detector allows to reconstruct the arrival direction of TeV-PeV neutrinos to sub-degree resolution for track-like events and a ~2 degree for shower-like events. The energy resolution is about ~0.27 in log10(E_\mu) for muons above 10TeV, while for showers a ~5% resolution on the visible energy is achieved. In order to achieve these resolutions, typically a set of quality selection criteria are applied based on the output of the event reconstructions.
Further details on the detector performance can be found in [1].
**Neutrino Physics**
Neutrinos have the peculiar feature that they can change from one flavour to another when propagating over macroscopic distances. This phenomenon of neutrino flavour change is known as `neutrino oscillation'. The Nobel Prize in Physics of the year 2015 was awarded to T. Kajita and A. B. McDonald for the discovery of neutrino oscillations, which shows that neutrinos have mass [1]. One open question is the so-called 'neutrino mass ordering'. It refers to the sign of one of the two independent neutrino mass differences, the absolute value of which has already been known for more than two decades.
The main science objective of KM3NeT/ORCA is the determination of the ordering of the three neutrino mass eigenstates by measuring the oscillation pattern of atmospheric neutrinos. Atmospheric neutrinos are produced in cosmic-ray air-showers in the Earth atmosphere. When produced on the other side of the Earth and traversing the Earth towards the detector, atmospheric neutrinos do oscillate, ie. change their flavour between production and detection. The oscillation pattern in the few-GeV energy range is sensitive to the neutrino mass ordering other oscillation parameters.
Besides determining the neutrino mass ordering, additional science topics of ORCA include: testing the unitary of the neutrino mixing matrix by studying tau-neutrino appearance; indirect searches for sterile neutrinos, non-standard interactions and other exotic physics; indirect searches for dark matter; testing the chemical composition of the Earth's core (Earth tomography); and low-energy neutrino astrophysics. Preliminary performance expectations are briefly summarised in [2].
The detector design of the KM3NeT/ORCA has been optimised to for atmospheric neutrinos in the 1-100GeV energy range in order to maximise the sensitivity to determine the neutrino mass ordering. For neutrino oscillation measurements with KM3NeT/ORCA, the capability to differentiate the two event topologies, ie track-shower separation power, is very important.
The detector performance of the ORCA detector is summarised in detail in [1].
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[1] [Adrian-Martnez S et al (KM3NeT Collaboration) 2016 J. Phys. G 43 084001](https://iopscience.iop.org/article/10.1088/0954-3899/43/8/084001)
