Study of tau neutrinos and non-unitary neutrino mixing with the first six detection units of KM3NeT/ORCA

AbstraktAbstract

Oscillations of atmospheric muon and electron neutrinos produce tau neutrinos with energies in the GeV range, which can be observed by the ORCA detector of the KM3NeT neutrino telescope in the Mediterranean Sea. First measurements with ORCA6, an early subarray corresponding to about 5% of the final detector, are presented. A sample of 5828 neutrino candidates has been selected from the analysed exposure of 433 kton-years. The nu(tau) normalisation, defined as the ratio between the number of observed and expected tau neutrino events, is measured to be S-tau= 0.48+0.5(-0.33). This translates into a nu(tau) charged-current cross section measurement of sigma(meas)(tau)= (2.5(-1.8)(+2.6))x10(-38) cm(2) nucleon(-1) at the median nu(tau) energy of 20.3 GeV. The result is consistent with the measurements of other experiments. In addition, the current limit on the non-unitarity parameter affecting the tau-row of the neutrino mixing matrix was improved, with alpha(33) > 0.95 at the 95% confidence level.

Oscillations of atmospheric muon and electron neutrinos produce tau neutrinos with energies in the GeV range, which can be observed by the ORCA detector of the KM3NeT neutrino telescope in the Mediterranean Sea. First measurements with ORCA6, an early subarray corresponding to about 5% of the final detector, are presented. A sample of 5828 neutrino candidates has been selected from the analysed exposure of 433 kton-years. The nu(tau) normalisation, defined as the ratio between the number of observed and expected tau neutrino events, is measured to be S-tau= 0.48+0.5(-0.33). This translates into a nu(tau) charged-current cross section measurement of sigma(meas)(tau)= (2.5(-1.8)(+2.6))x10(-38) cm(2) nucleon(-1) at the median nu(tau) energy of 20.3 GeV. The result is consistent with the measurements of other experiments. In addition, the current limit on the non-unitarity parameter affecting the tau-row of the neutrino mixing matrix was improved, with alpha(33) > 0.95 at the 95% confidence level.