Antineutrino Beam Research Articles

Study of Neutrino Oscillations in the NOvA Experiment

NOvA is a neutrino experiment deployed at Fermi National Accelerator Laboratory (FNAL, USA) and designed for studying oscillations—namely, the appearance of electron neutrinos and the survival of muon neutrinos. Two detectors, a near and a far one, are separated by a distance of 810 km and are positioned at an angle of 14 mrad with respect to the axis of a beam from the NuMI accelerator complex. This configuration provides an optimum relationship between the energy and distance for neutrino oscillations. The experiment is aimed at measuring the neutrino mass hierarchy, determining the phase of $$CP$$ violation in the lepton sector, and refining value of the parameters $$\theta_{23}$$ and $$\Delta m^{2}_{32}$$ , as well as at performing some other tasks. The results of the NOvA analysis performed jointly for a $$8.85\times 10^{20}$$ proton-on-target (POT) neutrino beam and a $$12.33\times 10^{20}$$ POT antineutrino beams are discussed. Also, further prospects of the experiment are outlined.

Measurement of the charged-current electron (anti-)neutrino inclusive cross-sections at the T2K off-axis near detector ND280

The electron (anti-)neutrino component of the T2K neutrino beam constitutes the largest background in the measurement of electron (anti-)neutrino appearance at the far detector. The electron neutrino scattering is measured directly with the T2K off-axis near detector, ND280. The selection of the electron (anti-)neutrino events in the plastic scintillator target from both neutrino and anti-neutrino mode beams is discussed in this paper. The flux integrated single differential charged-current inclusive electron (anti-)neutrino cross-sections, dσ/dp and dσ/d cos(θ), and the total cross-sections in a limited phase-space in momentum and scattering angle (p > 300 MeV/c and θ ≤ 45°) are measured using a binned maximum likelihood fit and compared to the neutrino Monte Carlo generator predictions, resulting in good agreement.

KEK and its plans

There are two campuses in KEK, Tsukuba and Tokai. In the Tsukuba campus, the operation of the SuperKEKB accelerator just started with the full Belle II detector from March 2019. SuperKEKB and Belle II had been upgraded from KEKB and Belle, respectively. The luminosity exceeded 1.6× 1034 cm−1s−1 in April 2020 with lower total beam current as compared with KEKB due to smaller vertical focussing length at the interaction point (βy*). It indicates that the upgrade accelerator can provide higher luminosity with higher beam current in the near future after sufficient vacuum scrubbing. The Belle II detector is basically working well. The time-depenednt B0−B̄0 mixing was clearly demonstrated as an example. In the Tokai campus, the high intensity proton accelerator (J-PARC) has been operated for more than 10 years. The facility provides us various particle beams (pion, kaon, neutron, muon and neutrino). Several nuclear experiments have been carried out using pion and kaon beams. The T2K experiment provides some results for the CP-violation in the neutrino sector using neutrino and antineutrino beams. New project, Hyper-Kamiokande (HK) was officially approved in January 2020. The detector and the beam line for the COMET experiment (the search for the charged lepton flavor violation) have been constructed steadly to aim the run start in 2023. The material and other sciences have been performed utilizing neutron and muon beams.

Search for Electron Antineutrino Appearance in a Long-Baseline Muon Antineutrino Beam.

Electron antineutrino appearance is measured by the T2K experiment in an accelerator-produced antineutrino beam, using additional neutrino beam operation to constrain parameters of the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) mixing matrix. T2K observes 15 candidate electron antineutrino events with a background expectation of 9.3 events. Including information from the kinematic distribution of observed events, the hypothesis of no electron antineutrino appearance is disfavored with a significance of 2.40σ and no discrepancy between data and PMNS predictions is found. A complementary analysis that introduces an additional free parameter which allows non-PMNS values of electron neutrino and antineutrino appearance also finds no discrepancy between data and PMNS predictions.

Study of Charged-Current neutrino interactions on water with nuclear emulsion in the NINJA experiment

Neutrino-nucleus interaction is one of the major sources of the uncertainty for neutrino oscillation experiments. The NINJA experiment aims to measure neutrino-water interactions containing low-momentum secondary particles using a nuclear emulsion detector. Since the nuclear emulsion has sub-micron position resolution, it allows us to observe the interaction vertices clearly. Short proton tracks down to 200 MeV/c momentum are expected to be observed, which are hardly reconstructed in plastic scintillator based detectors. A series of test experiments has been carried out with prototype detectors at J-PARC. In a test run in 2017-2018, a 3 kg water target detector was exposed to anti-neutrino beam corresponding to 0.7 × 1021 POT (protons on target). We have successfully detected low momentum protons above 200 MeV/c threshold from neutrino-water interactions.

Recent T2K Neutrino Oscillation Results

T2K is a long baseline neutrino experiment producing a beam of muon neutrinos at the Japan Particle Accelerator Research Centre on the East coast of Japan and measuring their oscillated state 295 km away at the Super Kamiokande detector. Since, 2017 T2K has doubled its data in both neutrino and anti-neutrino beam modes. Coupled with improvements in analysis techniques, this has enabled the experiment to make world-leading measurements of the PMNS oscillation parameters , sin2(θ 23) and the CP violating phase δCP . In particular, the CP conserving values of δCP now appear to be disfavoured at the 95% CL and there are regions of parameter space excluded at the 99.7% CL. This talk will describe these results and the analysis improvements that have enabled them.

Measurement of neutrino and antineutrino neutral-current quasielasticlike interactions on oxygen by detecting nuclear deexcitation γ rays

Neutrino- and antineutrino-oxygen neutral-current quasielastic-like interactions are measured at Super-Kamiokande using nuclear de-excitation $\gamma$-rays to identify signal-like interactions in data from a $14.94 \ (16.35)\times 10^{20}$ protons-on-target exposure of the T2K neutrino (antineutrino) beam. The measured flux-averaged cross sections on oxygen nuclei are $\langle \sigma_{\nu {\rm -NCQE}} \rangle = 1.70 \pm 0.17 ({\rm stat.}) ^{+ {\rm 0.51}}_{- {\rm 0.38}} ({\rm syst.}) \times 10^{-38} \ {\rm cm^2/oxygen}$ with a flux-averaged energy of 0.82 GeV and $\langle \sigma_{\bar{\nu} {\rm -NCQE}} \rangle = 0.98 \pm 0.16 ({\rm stat.}) ^{+ {\rm 0.26}}_{- {\rm 0.19}} ({\rm syst.}) \times 10^{-38} \ {\rm cm^2/oxygen}$ with a flux-averaged energy of 0.68 GeV, for neutrinos and antineutrinos, respectively. These results are the most precise to date, and the antineutrino result is the first cross section measurement of this channel. They are compared with various theoretical predictions. The impact on evaluation of backgrounds to searches for supernova relic neutrinos at present and future water Cherenkov detectors is also discussed.

Results on Neutrino and Antineutrino Oscillations from the NOvA Experiment

NOvA is a two-detector long-baseline neutrino oscillation experiment using Fermilab’s 700 kW NuMI muon neutrino beam. With a total exposure of 8.85×1020 +12.33×1020 protons on target delivered to NuMI in the neutrino + antineutrino beam mode (78% more antineutrino data than in 2018), the experiment has made a 4.4q-significant observation of the ve appearance in a vм beam, measured oscillation parameters |Δm232|, sin2O23, and excluded most values near бCP = п/2 for the inverted neutrino mass hierarchy by more than 3q.

Latest Results from the T2K Neutrino Experiment

The T2K long baseline neutrino oscillation experiment measures muon neutrino disappearance and electron neutrino appearance in accelerator-produced neutrino and anti-neutrino beams. This presentation reports on the analysis of our data from an exposure of 2 . 6 × 10 21 protons on target. Results for oscillation parameters, including the CP violation parameter and neutrino mass ordering, are shown.

Neutrino–oxygen CC0π scattering in the SuSAv2-MEC model

We present the predictions of the joint SuperScaling Approach version 2—Meson Exchange Currents model for the double differential charged-current muonic neutrino (antineutrino) cross section on water for the T2K neutrino (antineutrino) beam. We validate our model by comparing with the available inclusive electron scattering data on oxygen and compare our predictions with the recent T2K νμ-16O data (Abe et al (T2K Collaboration) 2018 Phys. Rev. D 97 012001), finding good agreement at all kinematics. We show that the results are very similar to those obtained for νμ-12C scattering, except at low energies, and we comment on the origin of this difference. A factorized spectral function model of 16O is also included for purposes of comparison.

Statistical significance of CP violation in long baseline neutrino experiments

The p-value or statistical significance of a CP conservation null hypothesis test is determined from counting electron neutrino and antineutrino appearance oscillation events. The statistical estimates include cases with background events and different data sample sizes, graphical plots to interpret results and methods to combine p-values from different experiments. These estimates are useful for optimizing the search for CP violation with different amounts of neutrino and antineutrino beam running, comparing results from different experiments and for simple cross checks of more elaborate statistical estimates that use likelihood fitting of neutrino parameters.

Quantum correlations and the neutrino mass degeneracy problem

Many facets of nonclassicality are probed in the context of three flavour neutrino oscillations including matter effects and CP violation. The analysis is carried out for parameters relevant to two ongoing experiments hbox {NO}nu hbox {A} and T2K, and also for the upcoming experiment DUNE. The various quantum correlations turn out to be sensitive to the mass-hierarchy problem in neutrinos. This sensitivity is found to be more prominent in DUNE experiment as compared to hbox {NO}nu hbox {A} and T2K experiments. This can be attributed to the large baseline and high energy of the DUNE experiment. Further, we find that to probe these correlations, the neutrino (antineutrino) beam should be preferred if the sign of mass square difference varDelta _{31} turns out to be positive (negative).

Search for CP Violation in Neutrino and Antineutrino Oscillations by the T2K Experiment with 2.2×10^{21} Protons on Target.

The T2K experiment measures muon neutrino disappearance and electron neutrino appearance in accelerator-produced neutrino and antineutrino beams. With an exposure of 14.7(7.6)×10^{20} protons on target in the neutrino (antineutrino) mode, 89 ν_{e} candidates and seven anti-ν_{e} candidates are observed, while 67.5 and 9.0 are expected for δ_{CP}=0 and normal mass ordering. The obtained 2σ confidence interval for the CP-violating phase, δ_{CP}, does not include the CP-conserving cases (δ_{CP}=0, π). The best-fit values of other parameters are sin^{2}θ_{23}=0.526_{-0.036}^{+0.032} and Δm_{32}^{2}=2.463_{-0.070}^{+0.071}×10^{-3} eV^{2}/c^{4}.

Nonstandard neutrino self-interactions in a supernova and fast flavor conversions

We study the effects of non-standard self-interactions (NSSI) of neutrinos streaming out of a core-collapse supernova. We show that with NSSI, the standard linear stability analysis gives rise to linearly as well as exponentially growing solutions. For a two-box spectrum, we demonstrate analytically that flavor-preserving NSSI lead to a suppression of bipolar collective oscillations. In the intersecting four-beam model, we show that flavor-violating NSSI can lead to fast oscillations even when the angle between the neutrino and antineutrino beams is obtuse, which is forbidden in the Standard Model. This leads to the new possibility of fast oscillations in a two-beam system with opposing neutrino-antineutrino fluxes, even in the absence of any spatial inhomogeneities. Finally, we solve the full non-linear equations of motion in the four-beam model numerically, and explore the interplay of fast and slow flavor conversions in the long-time behavior, in the presence of NSSI.

Laser-Assisted Generation and Detection of Non-Nuclear Low-Energy Neutrino-Antineutrino Beams

It is argued that conservation of energy, momentum, and spin, and QM transition probabilities, allow the generation and detection of low-energy (eV) neutrinos and antineutrinos in intra-atomic (non-nuclear) laser transitions. Two-quantum transitions between an upper and lower excited state in a lasing medium can support paired emissions of a neutrino and a recoiling counter-propagating anti-neutrino, each carrying half of the lasing transition energy. Their propagations are in opposite directions along the same axis as that of the intracavity laser beam in the lasing medium. Estimates show that the probability of this two-quantum event is on the order of 10−7 compared to a one-quantum stimulated emission of a laser photon. Absorptions or emissions of single antineutrinos or neutrinos by molecular/atomic matter are impossible because they carry spins s = ±h/2 which violates Δs = ±nh (n = integer) required for such processes. However, inside a laser, emissions of photons from excited states can be stimulated by neutrinos or anti-neutrinos passing through, provided their undulation frequency is resonant with the transition frequency. This is because in stimulated emissions, neutrinos or antineutrinos are not absorbed, and spin conservation violation is not an issue. Thus, detection of the passage of a laser-generated antineutrino or neutrino beam through a second “receiver” laser is possible provided that the transition energy in the second laser equals half the transition energy of the laser that emits the antineutrino-neutrino beam to be detected.

Prospects of light sterile neutrino oscillation and CP violation searches at the Fermilab Short Baseline Neutrino Facility

We investigate the ability of the Short Baseline Neutrino (SBN) experimental program at Fermilab to test the globally-allowed (3+$N$) sterile neutrino oscillation parameter space. We explicitly consider the globally-allowed parameter space for the (3+1), (3+2), and (3+3) sterile neutrino oscillation scenarios. We find that SBN can probe with $5\sigma$ sensitivity more than 85\%, 95\% and 55\% of the parameter space currently allowed at 99\% confidence level for the (3+1), (3+2) and (3+3) scenarios, respectively. In the case of the (3+2) and (3+3) scenarios, CP-violating phases appear in the oscillation probability terms, leading to observable differences in the appearance probabilities of neutrinos and antineutrinos. We explore SBN's sensitivity to those phases for the (3+2) scenario through the currently planned neutrino beam running, and investigate potential improvements through additional antineutrino beam running. We show that, if antineutrino exposure is considered, for maximal values of the (3+2) CP-violating phase $\phi_{54}$, SBN could be the first experiment to directly observe $\sim 2\sigma$ hints of CP violation associated with an extended lepton sector.

A search for sterile neutrinos at the NOvA Far Detector

NOvA is the current United States flagship long-baseline neutrino experiment designed to study the properties of neutrino oscillations. It consists of two functionally identical detectors each located 14.6 mrad off the central axis from the Fermilab NuMI neutrino beam. The Near Detector is located 1 km downstream from the beam source, and the Far Detector is located 810 km away in Ash River, Minnesota. This long baseline, combined with the ability of the NuMI facility to switch between nearly pure neutrino and anti-neutrino beams, allows NOvA to make precision measurements of neutrino mixing angles, potentially determine the neutrino mass hierarchy, and begin searching for CP violating effects in the lepton sector. However, NOvA can also probe more exotic scenarios, such as oscillations between the known active neutrinos and new sterile species. We will showcase the first search for sterile neutrinos in a 3 + 1 model at NOvA. The analysis presented searches for a deficit in the rate of neutral current events at the Far Detector using the Near Detector to constrain the predicted spectrum. This analysis was performed using data taken between February 2014 and May 2016 corresponding to 6.05 × 1020 protons on target.

Neutrinos from a pion beam line: nuPIL

We describe a novel configuration for a neutrino beam line that can simultaneously support both long and short baseline experiments. The neutrino beams originate from pions that are first focused by a magnetic horn, as in a conventional neutrino beam. However, in the case of nuPIL, the horn is followed by a magnetic lattice that is used to select the pion charge and then transports the pions in a production straight. This produces extremely pure neutrino and anti-neutrino beams, while minimizing the amount of beam power that is transported underground for the long-baseline physics program. This configuration greatly simplifies the civil construction leading to a large cost reduction. The principles of the design of nuPIL are presented, together with tracking results and the resulting neutrino flux. The potential of the facility for CP-violation searches, in the framework of the DUNE experiment, is discussed and compared to that of an optimized beam from LBNF.

Muon neutrino and anti-neutrino selection in the tracker of the T2K off-axis near detector

T2K (Tokai to Kamioka) is a long-baseline neutrino oscillation experiment located in Japan. Since its discovery of electron neutrino appearance in 2013 excluding θ13 = 0 with a significance of 7.3σ, T2K has switched its beam magnet polarities to run in anti-neutrino beam mode in order to enhance its sensitivity to measure anti-electron neutrino appearence. The beam is dominated by muon antineutrinos; however it also contains a sizable contamination from muon neutrinos. The analysis of both νµ and interactions in the off-axis near detector ND280, provides a significant reduction of the flux prediction and cross-section modelling systematic uncertainties in the oscillation analysis. ND280 data also gives us the opportunity to measure cross-sections for processes that have not yet been thoroughly studied for antineutrinos at the energy range of ∼1 GeV. The second largest reaction type at this energy range after the charged-current (CC) quasi-elastic reaction are processes involving pion production. The poster will present the selections of CC interactions of both antineutrinos and neutrinos in the ND280 tracker. It will also cover the separation into three sub-samples of the CC sample based on the pion content in each event.

Neutrino properties determined in the T2K oscillation experiment

The T2K long baseline neutrino oscillation experiment is composed of a near detector at 280 m and a far detector Super-Kamiokande, located 295 km from the source of neutrinos. The 30 GeV proton beam at JPARC is used to produce a beam of mainly muon neutrinos which are directed toward the large Cherenkov detector. The goal of the experiment is oscillation measurements, such as electron neutrino appearance and θ23 mixing angle measurements from muon neutrino disappearance. By reversing the beam polarity antineutrino oscillations may also be studied. Muon antineutrino disappearance and electron antineutrino appearance have been studied with 4×1020 protons on target in antineutrino beam mode. The most recent oscillation results from T2K for neutrinos and antineutrinos are presented here. Future long baseline oscillation projects in short and long time scale are briefly mentioned.