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KM3Net-ORCA

March 17, 2017

20170317_102143KM3NeT is a multi-site, deep-sea infrastructure. One is ORcA, the other is called ARCA. Juergen Brunner (left) gave an overview of the project. They had a letter of intent in 2016, which covers schedules, technical and physics issues. The experiment has been selected by the ESFRI roadmap for Research infrastructures.

ORCA is a volume of 5.7 Mton instrumented with 115 strings of PMT detectors. 18 modules per string, and 31 PMT tubes instrument each module. With this they can aim for directional information, uniform coverage, and good background rejection.

At energies of 3-4 GeV there is a resonance in the mantle from neutrinos going through the Earth. This can be studied by ORCA. The speaker showed the topology expected for electron and muon neutrinos in the sensitive volume. They expect, after triggering and atmospheric muon rejection, 17300 electron neutrinos and 24800 muon neutrinos, plus 3100 tau neutrinos and in addition 5300 neutral current events.

The angular resolution for shower and track events is similar. The energy resolution is better than 30% in the relevant energy range of several GeV. It is also shown to be almost Gaussian. Measuring the energy versus zenith angle allows to see the different patterns expected from the hierarchy difference. Brunner showed how this is blurred by the resolutions but still quite observable for both electron and muon neutrinos.

The speaker showed also the discrimination of track-like and shower-like events using a random forest classifier. With that, one can perform pseudoexperiments when fits are made to oscillation parameters, to determine the experimental sensitivity. After 3 years, three-sigma sensitivities on the mass hierarchy is achievable. But at the same time one may measure the two atmospheric parameters for 2-3 mixing. This is shown to favourably compare to NOvA and T2K sensitivities.

There is an additional physics program, which encompasses tests of unitarity of the PMNS matrix, exotic physics searches like steriles and non-standard interactions, earth tomography studies, observation of transient cosmic phenomena, supernovae monitoring, and Earth and Sea science. There is also a neutrino beam from Protvino that can be studied.

For tau-neutrino appearance, which aims to test the PMNS unitarity and BSM theories, one can get about 3000 charged-current events per year with full ORCA, constraining the rate within 10% in one year. This could be an early physics measurement from the detector.

The sensitivity to galactic supernovaes is very good – 80% of them could be measured by ORCA. The detector could also be used to try independent detection of dark matter, looking at tau-tau events at low wimp masses.

In the far future they are also thinking about a neutrino beam from Protvino, with a baseline of 2600km to the ORCA site.

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