Tau Neutrino Appearance Research Articles

New signal of atmospheric tau neutrino appearance: Sub-GeV neutral-current interactions in JUNO

We propose the first practical method to detect atmospheric tau neutrino appearance at sub-GeV energies, which would be an important test of νμ→ντ oscillations and of new-physics scenarios. In the Jiangmen Underground Neutrino Observatory (JUNO; starts in 2024), active-flavor neutrinos eject neutrons from carbon via neutral-current quasielastic scattering. This produces a two-part signal: the prompt part is caused by the scattering of the neutron in the scintillator, and the delayed part by its radiative capture. Such events have been observed in KamLAND, but only in small numbers and were treated as a background. With νμ→ντ oscillations, JUNO should measure a clean sample of 55 events/yr; with simple νμ disappearance, this would instead be 41 events/yr, where the latter is determined from Super-Kamiokande charged-current measurements at similar neutrino energies. Implementing this method will require precise laboratory measurements of neutrino-nucleus cross sections or other developments. With those, JUNO will have 5σ sensitivity to tau-neutrino appearance in five years of exposure, and likely sooner. Published by the American Physical Society 2024

Tau neutrino identification in atmospheric neutrino oscillations without particle identification or unitarity

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 $U_{\tau1}$, $U_{\tau2}$, and $U_{\tau3}$ are not all zero even with limited particle identification.

Measuring tau neutrino appearance probability via unitarity

We propose a unitarity method for determining $\ensuremath{\tau}$ neutrino appearance probability $P({\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{\ensuremath{\tau}})$ in long-baseline (LBL) accelerator experiments and atmospheric neutrino observations. When simultaneous in situ measurements of $P({\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{\ensuremath{\mu}})$ and $P({\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{e})$ proceed, as is typical in the LBL experiments, one can use unitarity to ``measure'' $P({\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{\ensuremath{\tau}})$. A theorists' toy analysis for the model-independent determination of $P({\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{\ensuremath{\mu}})$ and $P({\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{e})$ is presented by using the NOvA data. It is shown in our analysis that $\ensuremath{\lesssim}5%$ (8%) measurement of $\ensuremath{\tau}$ neutrino appearance probability in neutrino (antineutrino) mode is possible in the peak region $1.5\ensuremath{\lesssim}{E}_{\ensuremath{\nu}}\ensuremath{\lesssim}2.5\text{ }\text{ }\mathrm{GeV}$. The $\ensuremath{\nu}\mathrm{SM}$-independent nature of determination of the probabilities is emphasized.

Physics Potential of the IceCube Upgrade

The IceCube Neutrino Observatory is a cubic-kilometer Cherenkov detector at the South Pole. The planned Upgrade project, which consists of seven new strings, will be deployed with densely spaced optical modules to improve the neutrino detection capability at a few GeV level. The goal of IceCube Upgrade is to provide world-leading sensitivity to neutrino oscillations and to take unique measurements of tau neutrino appearance with high precision. It also serves as a R&D platform for the future IceCube-Gen2 experiment. The newly designed DOMs will provide improved detection efficiency and directional resolution for Cherenkov photons. Furthermore, new calibration devices will be introduced which will provide a better understanding of the ice properties, thereby reduce the detector systematic uncertainties. The resulting calibration improvement from the Upgrade will be applied to the entire archival data of IceCube collected for more than 10 years, with an expected improvement of the angular and spatial resolution of the detected astrophysical neutrino events. The Upgrade can be regarded as the first stage in the development of IceCube-Gen2, the next-generation neutrino telescope at the South Pole.

More results from the OPERA experiment

The OPERA experiment reached its main goal by proving the appearance of tau-neutrinos in the CNGS muon-neutrino beam. A total sample of 5 candidates fulfilling the analysis defined in the proposal was detected with a S/B ratio of about ten allowing to reject the null hypothesis with a significance of 5.1 σ. The search was extended to ½T-like interactions failing the kinematical analysis defined in the experiment proposal, to obtain a statistically enhanced, lower purity, signal sample. One such interesting neutrino interaction showing a double vertex topology with a high probability of being a tau-neutrino interaction with charm production will be reported. Based on the enlarged data sample the estimation of (math) in appearance mode is presented. The search for ½e interactions has been extended over the full data set with a more than twofold increase in statistics with respect to published data. The analysis of the νμ → νe channel is updated and the implications of the electron-neutrino sample in the framework of the 3+1 sterile model is discussed. An analysis of the νμ → ντ oscillations in the framework of the sterile neutrino model has also been performed.

Measuring the neutrino mass hierarchy with KM3NeT/ORCA

ORCA is the low-energy branch of KM3NeT, the next-generation research infrastructure hosting underwater Cherenkov detectors in the Mediterranean Sea. ORCA’s primary goal is the determination of the neutrino mass hierarchy by measuring the matter- induced modifications on the oscillation probabilities of few-GeV atmospheric neutrinos. The technical design of the ORCA detector foresees a dense configuration of optical modules, optimised for the study of interactions of neutrinos in the energy range of 3–30 GeV. The first ORCA detection string was successfully deployed on 22nd September 2017 and is providing high-quality data since then.With an instrumented mass of 8 Mton for the full-size ORCA detector, it will be possible to probe with a high-statistics neutrino sample a wide range of energies and baselines through the Earth. This allows to detmerine the neutrino mass hierarchy with 3 σ after 3–4 years of operation, to probe the unitarity assumption of 3-neutrino mixing with a high-statistics measurement of tau-neutrino appearance in the atmospheric neutrino flux, and to improve the measurement precision on other oscillation parameters.

New results from the OPERA experiment in the CNGS neutrino beam

A new analysis of full OPERA data set was performed, based on looser selection criteria and multivariate approach. Oscillation parameters and tau neutrino cross-section have been determined with a reduced statistical uncertainty, and the discovery of tau neutrino appearance is confirmed at 6.1σ level. Moreover, the search for electron neutrino events has been extended to the full dataset, exploiting an improved method for the electron neutrino energy estimation. New limits have been set in the 3+1 neutrino model.

Final results on neutrino oscillation parameters from the OPERA experiment in the CNGS beam

The OPERA experiment has conclusively observed the appearance of tau neutrinos in the muon neutrino CNGS beam. Exploiting the OPERA detector capabilities, it was possible to isolate high purity samples of $\nu_{e}$, $\nu_{\mu}$ and $\nu_{\tau}$ charged current weak neutrino interactions, as well as neutral current weak interactions. In this Letter, the full dataset is used for the first time to test the three-flavor neutrino oscillation model and to derive constraints on the existence of a light sterile neutrino within the framework of the $3+1$ neutrino model. For the first time, tau and electron neutrino appearance channels are jointly used to test the sterile neutrino hypothesis. A significant fraction of the sterile neutrino parameter space allowed by LSND and MiniBooNE experiments is excluded at 90% C.L. In particular, the best-fit values obtained by MiniBooNE combining neutrino and antineutrino data are excluded at 3.3 $\sigma$ significance.

Physics with beam tau-neutrino appearance at DUNE

We explore the capabilities of the upcoming Deep Underground Neutrino Experiment (DUNE) to measure $\nu_\tau$ charged-current interactions and the associated oscillation probability $P(\nu_\mu \to \nu_\tau)$ at its far detector, concentrating on how such results can be used to probe neutrino properties and interactions. DUNE has the potential to identify significantly more $\nu_\tau$ events than all existing experiments and can use this data sample to nontrivially test the three-massive-neutrinos paradigm by providing complementary measurements to those from the $\nu_e$ appearance and $\nu_\mu$ disappearance channels. We further discuss the sensitivity of the $\nu_\tau$ appearance channel to several hypotheses for the physics that may lurk beyond the three-massive-neutrinos paradigm: a non-unitary lepton mixing matrix, the $3+1$ light neutrinos hypothesis, and the existence of non-standard neutral-current neutrino interactions. Throughout, we also consider the relative benefits of the proposed high-energy tune of the Long-Baseline Neutrino Facility (LBNF) beam-line.

Measurement of atmospheric tau neutrino appearance with IceCube DeepCore

We present a measurement of atmospheric tau neutrino appearance from oscillations with three years of data from the DeepCore sub-array of the IceCube Neutrino Observatory. This analysis uses atmospheric neutrinos from the full sky with reconstructed energies between 5.6 GeV and 56 GeV to search for a statistical excess of cascade-like neutrino events which are the signature of nutau interactions. For CC+NC (CC-only) interactions, we measure the tau neutrino normalization to be 0.73 +0.30 -0.24 (0.57 +0.36 -0.30) and exclude the absence of tau neutrino oscillations at a significance of 3.2 sigma (2.0 sigma) These results are consistent with, and of similar precision to, a confirmatory IceCube analysis also presented, as well as measurements performed by other experiments.

Particle Physics with ORCA

KM3NeT is a Megaton-scale neutrino telescope currently under construction at the bottom of the Mediterranean Sea. When completed, it will consist of two separate detectors: ARCA (Astroparticle Research with Cosmics in the Abyss), optimised for high-energy neutrino astronomy, and ORCA (Oscillation Research with Cosmics in the Abyss) for neutrino oscillation studies of atmospheric neutrinos. The main goal of ORCA is the determination of the neutrino mass ordering (NMO). Nevertheless it is possible to exploit ORCA’s configuration to make other important measurements, such as sterile neutrinos, non standard interactions, tau-neutrino appearance, neutrinos from Supernovae, Dark Matter and Earth Tomography studies. Part of these analyses are summarized here.

Measurement of the tau neutrino cross section in atmospheric neutrino oscillations with Super-Kamiokande

Using 5326 days of atmospheric neutrino data, a search for atmospheric tau neutrino appearance has been performed in the Super-Kamiokande experiment. Super-Kamiokande measures the tau normalization to be 1.47±0.32 under the assumption of normal neutrino hierarchy, relative to the expectation of unity with neutrino oscillation. The result excludes the hypothesis of no-tau appearance with a significance level of 4.6σ. The inclusive charged-current tau neutrino cross section averaged by the tau neutrino flux at Super-Kamiokande is measured to be (0.94±0.20)×10−38 cm2. The measurement is consistent with the Standard Model prediction, agreeing to within 1.5σ.9 MoreReceived 27 November 2017DOI:https://doi.org/10.1103/PhysRevD.98.052006Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasNeutrino oscillationsPhysical SystemsNeutrinosParticles & Fields

Final results of the search for \u03bd\u03bc \u2192 \u03bde oscillations with the OPERA detector in the CNGS beam

The OPERA experiment has discovered the tau neutrino appearance in the CNGS muon neutrino beam, in agreement with the 3 neutrino flavour oscillation hypothesis. The OPERA neutrino interaction target, made of Emulsion Cloud Chambers, was particularly efficient in the reconstruction of electromagnetic showers. Moreover, thanks to the very high granularity of the emulsion films, showers induced by electrons can be distinguished from those induced by π0s, thus allowing the detection of charged current interactions of electron neutrinos. In this paper the results of the search for electron neutrino events using the full dataset are reported. An improved method for the electron neutrino energy estimation is exploited. Data are compatible with the 3 neutrino flavour mixing model expectations and are used to set limits on the oscillation parameters of the 3+1 neutrino mixing model, in which an additional mass eigenstate m4 is introduced. At high Δm412 (≳0.1 eV2), an upper limit on sin2 2θμe is set to 0.021 at 90% C.L. and Δm412 ≳ 4 × 10− 3 eV2 is excluded for maximal mixing in appearance mode.

KM3NeT-ORCA: Oscillation Research with Cosmics in the Abyss

KM3NeT, currently under construction in the abysses of the Mediterranean Sea, is a distributed research infrastructure that will host a km3-scale neutrino telescope (ARCA) for high-energy neutrino astronomy, and a megaton scale detector (ORCA) for neutrino oscillation studies of atmospheric neutrinos. ORCA is optimised for a measurement of the mass hierarchy, providing a sensitivity of 3σ after 3-4 years. It will also measure the atmospheric mixing parameters Δm2atm and θ23 with a precision comparable to the NOvA and T2K experiments using both the muon neutrino disappearance and tau neutrino appearance channels. It will provide a measurement of the tau neutrino appearance rate with better than 10% precision, a crucial ingredient for tests of unitarity. It will probe the octant of the mixing angle θ23 via matter resonance effects on neutrinos and antineutrinos crossing the core and mantle, which are largely independent on the CP phase. The observation of neutrino oscillations over a wide range of baselines and energies will provide broad sensitivity to new physics such as non-standard neutrino interactions (NSI) and sterile neutrinos.

NOvA short-baseline tau-neutrino search

Three-flavor neutrino oscillations have successfully explained a wide range of neutrino oscillation experiment results. However, anomalous results, such as the electron-antineutrino appearance excess seen by LSND and MiniBooNE, do not fit the three-flavor paradigm and can be explained by the addition of a sterile neutrino at a larger mass scale than the existing three flavor mass states. This paper will present a novel method for selecting tau-neutrino interactions with high purity at the NOvA Near Detector using a convolutional neural network. Based on this method, the sensitivity to anomalous short-baseline tau-neutrino appearance due to sterile neutrino oscillations will be shown.

Atmospheric neutrinos and proton decay in Super-Kamiokande and Hyper-Kamiokande

Super-Kamiokande is a 50 kton water Cherenkov detector, which has been in operation since 1996. Super-Kamiokande atmospheric neutrino data have a preference for the normal neutrino mass hierarchy (Δχ2=χNH2−χIH2=−4.3) when the constraints from reactor neutrino experiments are included. The search for tau neutrino appearance from neutrino oscillations has resulted in a 4.6σ exclusion of the hypothesis of no tau appearance. Hyper-Kamiokande is a proposed next-generation water Cherenkov detector, which will be a natural extension of Super-Kamiokande. The proposed experiment will have two cylindrical tanks containing 520 kton of water in total. Hyper-K will search for CP violation using the neutrino beam from J-PARC, and will have a broad physics program including studies of atmospheric neutrinos, supernova burst neutrinos, geo-neutrinos and searches for proton decay.

Enhanced tau neutrino appearance through invisible decay

The decay of neutrino mass eigenstates leads to a change of the conversion and survival probability of neutrino flavor eigenstates. Remarkably, we find that the neutrino decay provides an enhancement of the expected tau appearance signal with respect to the standard oscillation scenario for the long-baseline OPERA experiment. The increase of the $\nu_\mu \rightarrow \nu_\tau$ conversion probability by the decay of one of the mass eigenstates is due to a reduction of the "destructive interference" among the different massive neutrino components. Motivated by the recently released results of the OPERA Collaboration showing a number of observed $\nu_\tau$ events larger than expected, we perform a statistical analysis including the invisible decay hypothesis. We obtain a very mild preference for invisible decays, with a best fit value $\tau_3/m_3 \simeq 2.6\times 10^{-13} $ s/eV, and a constraint at the 90$\%$ confidence level for the neutrino decay lifetime to be $\tau_3/m_3 \gtrsim 1.3\times 10^{-13}$ s/eV.

Search for sterile neutrino mixing in the muon neutrino to tau neutrino appearance channel with the OPERA detector

The OPERA experiment observed νμ → ντ oscillations in the atmospheric sector. To this purpose the hybrid OPERA detector was exposed to the CERN Neutrinos to Gran Sasso beam from 2008 to 2012, at a distance of 730 km from the neutrino source. Charged-current interactions of ντ were searched for through the identification of τ lepton decay topologies. The five observed ντ interactions are consistent with the expected number of events in the standard three neutrino framework. Based on this result, new limits on the mixing parameters of a massive sterile neutrino may be set. Preliminary results of the analysis performed in the 3+1 neutrino framework are here presented.

The Tau Neutrino Appearance Experiment with Nuclear Emulsion, OPERA

The Tau Neutrino Appearance Experiment with Nuclear Emulsion, OPERA

Observation of tau neutrino appearance in the CNGS beam with the OPERA experiment

The OPERA experiment is searching for nu_mu -> nu_tau oscillations in appearance mode i.e. via the direct detection of tau leptons in nu_tau charged current interactions. The evidence of nu_mu -> nu_tau appearance has been previously reported with three nu_tau candidate events using a sub-sample of data from the 2008-2012 runs. We report here a fourth nu_tau candidate event, with the tau decaying into a hadron, found after adding the 2012 run events without any muon in the final state to the data sample. Given the number of analysed events and the low background, nu_mu -> nu_tau oscillations are established with a significance of 4.2sigma.