Tau Neutrino Identification in Atmospheric Neutrino Oscillations Without Particle Identification or Unitarity

Abstract

The largest tau neutrino dataset to date is IceCube's atmospheric tau neutrino appearance dataset containing $>1,000$ tau neutrino and antineutrino events as determined by a fit to a standard three-flavor oscillation framework. On an event-by-event basis, however, it is impossible to know that any given event is a tau neutrino as they are identical to either an electron neutrino charged-current event or a neutral-current interaction of any active flavor. Nonetheless, we conclusively show that, using only the cascade sample even without knowledge of the oscillation parameters and without assuming that the lepton mixing matrix is unitary, tau neutrino identification is still possible and there is no viable scenario in which all of the tau neutrino candidates are actually electron neutrinos. This is primarily due to the matter effect and the tau lepton production threshold, as well as the fact that tau neutrinos are systematically reconstructed at a lower energy than electron neutrinos due to one or more outgoing neutrinos. This conclusively shows that it is possible for an atmospheric neutrino oscillation experiment to confirm that $U_{\tau 1}$, $U_{\tau 2}$, and $U_{\tau 3}$ are not all zero even with limited particle identification.

10 pages, 3 figures, 2 tables; comments welcome! v2: refs added, clarifying remarks, matches published version

References in corpus (9)

• The Reactor Antineutrino Anomaly
• Statistical Significance of the Gallium Anomaly
• Unitarity of the Leptonic Mixing Matrix
• CP-violation from non-unitary leptonic mixing
• Measurement of Atmospheric Tau Neutrino Appearance with IceCube DeepCore
• Improved constraints on neutrino mixing from the T2K experiment with $3.13\times 10^{21}$ protons on target
• Precision constraints for three-flavor neutrino oscillations from the full MINOS+ and MINOS data set
• Unitarity violation in sequential neutrino mixing in a model of extra dimensions
• Measuring tau neutrino appearance probability via unitarity

Cited by in corpus (8)

• Snowmass White Paper: Beyond the Standard Model effects on Neutrino Flavor
• Tau Neutrinos in the Next Decade: from GeV to EeV
• New oscillation and scattering constraints on the tau row matrix elements without assuming unitarity
• Model-Independent Constraints on Non-Unitary Neutrino Mixing from High-Precision Long-Baseline Experiments
• Measuring Oscillations with A Million Atmospheric Neutrinos
• A simulation study of tau neutrino events at the ICAL detector in INO
• New Signal of Atmospheric Tau Neutrino Appearance: Sub-GeV Neutral-Current Interactions in JUNO
• Excess of Tau events at SND@LHC, FASER$\nu$ and FASER$\nu$2