Accelerator Neutrino Beams Research Articles

Constraints on new physics with (anti)neutrino-nucleon scattering data

New physics contributions to the (anti)neutrino-nucleon elastic scattering process can be constrained by precision measurements, with controlled Standard Model uncertainties. In a large class of new physics models, interactions involving charged leptons of different flavor can be related, and the large muon flavor component of accelerator neutrino beams can mitigate the lepton mass suppression that occurs in other low-energy measurements. We employ the recent high-statistics measurement of the cross section for ν¯μp→μ+n scattering on the hydrogen atom by MINERvA to place new confidence intervals on tensor and scalar neutrino-nucleon interactions: ReCT=−1−13+14×10−4, |ImCT|≤1.3×10−3, and |ImCS|=45−19+13×10−3. These results represent a reduction in uncertainty by a factor of 2.1, 3.1, and 1.2, respectively, compared to existing constraints from precision beta decay.

Design and performance of a scintillation tracker for track matching in nuclear-emulsion-based neutrino interaction measurement

Precise measurement of neutrino–nucleus interactions with an accelerator neutrino beam is highly important for current and future neutrino oscillation experiments. To measure muon-neutrino charged-current interactions with nuclear-emulsion-based hybrid detector, muon track matching among the detectors are essential. We describe the design and performance of a newly developed scintillation tracker for the muon track matching in the neutrino–nucleus interaction measurement with nuclear emulsion detectors. The muon tracks are reconstructed using the scintillation tracker and another detector called Baby MIND, then, they are matched with the tracks in nuclear emulsion detectors.The scintillation tracker consists of four layers of horizontally and vertically aligned scintillator bars, covering an area of 1m×1m. In the layer, 24mm-wide plastic scintillator bars are specially arranged with deliberate gaps between each other. By recognizing the hit pattern of the four layers, a precise positional resolution of 2.5mm is achieved while keeping the number of readout channels as small as 256. The efficiency of the track matching is evaluated to be more than 97% for forward-going muons, and the positional and angular resolutions of the scintillation tracker are 2.5mm and 20–40mrad respectively. The results demonstrate the usefulness of the design of the scintillation tracker for the muon track matching in the nuclear-emulsion-based neutrino–nucleus interaction measurements.

Unraveling the flux-averaged neutrino–nucleus cross section

The interpretation of the nuclear cross sections measured using accelerator neutrino beams involve severe difficulties, arising primarily from the average over the incoming neutrino flux. The broad energy distribution of the beam particles hampers the determination of the energy transfer to the nuclear target, the knowledge of which is needed to pin down the dominant reaction mechanism. Overcoming this problem requires the development of a theoretical approach suitable to describe neutrino interactions at energies ranging from hundreds of MeV to few GeV. In this paper, it is argued that the approach based on the factorisation of the nuclear cross section provides a consistent framework for the calculation of neutrino-nucleus interactions in both the quasi elastic and inelastic channels. The near-degeneracy between theoretical models based on different assumptions, and the use of electron scattering data to advance the understanding of neutrino-nucleus cross sections are also discussed.

Design and Diagnostics of High-Precision Accelerator Neutrino Beams

Neutrino oscillation physics has entered a new precision era, which poses major challenges to the level of control and diagnostics of the neutrino beams. In this paper, we review the design of high-precision beams, their current limitations, and the latest techniques envisaged to overcome such limits. We put emphasis on “monitored neutrino beams” and advanced diagnostics to determine the flux and flavor of the neutrinos produced at the source at the per-cent level. We also discuss ab-initio measurements of the neutrino energy–i.e., measurements performed without relying on the event reconstruction at the ν detector–to remove any flux induced bias in the determination of the cross sections.

Three-Flavor Oscillations with Accelerator Neutrino Beams

The three-flavor neutrino oscillation paradigm is well established in particle physics thanks to the crucial contribution of accelerator neutrino beam experiments. In this paper, we review the most important contributions of these experiments to the physics of massive neutrinos after the discovery of θ 13 and future perspectives in such a lively field of research. Special emphasis is given to the technical challenges of high power beams and the oscillation results of T2K, OPERA, ICARUS, and NO ν A. We discuss in detail the role of accelerator neutrino experiments in the precision era of neutrino physics in view of DUNE and Hyper-Kamiokande, the program of systematic uncertainty reduction and the development of new beam facilities.

Neutrino Mass Ordering from Oscillations and Beyond: 2018 Status and Future Prospects

The ordering of the neutrino masses is a crucial input for a deep understanding of flavor physics, and its determination may provide the key to establish the relationship among the lepton masses and mixings and their analogous properties in the quark sector. The extraction of the neutrino mass ordering is a data-driven field expected to evolve very rapidly in the next decade. In this review, we both analyze the present status and describe the physics of subsequent prospects. Firstly, the different current available tools to measure the neutrino mass ordering are described. Namely, reactor, long-baseline (accelerator and atmospheric) neutrino beams, laboratory searches for beta and neutrinoless double beta decays and observations of the cosmic background radiation and the large scale structure of the universe are carefully reviewed. Secondly, the results from an up-to-date comprehensive global fit are reported: the Bayesian analysis to the 2018 publicly available oscillation and cosmological data sets provides \emph{strong} evidence for the normal neutrino mass ordering versus the inverted scenario, with a significance of 3.5 standard deviations. This preference for the normal neutrino mass ordering is mostly due to neutrino oscillation measurements. Finally, we shall also emphasize the future perspectives for unveiling the neutrino mass ordering. In this regard, apart from describing the expectations from the aforementioned probes, we also focus on those arising from alternative and novel methods, as 21~cm cosmology, core-collapse supernova neutrinos and the direct detection of relic neutrinos.

Measurement of neutrino mixing angle θ13 and mass difference [formula omitted] from reactor antineutrino disappearance in the RENO experiment

RENO (Reactor Experiment for Neutrino Oscillation) made a definitive measurement of the smallest neutrino mixing angle θ13 in 2012, based on the disappearance of reactor electron antineutrinos. The experiment has obtained a more precise value of the mixing angle and the first result on neutrino mass difference Δmee2 from an energy and baseline dependent reactor neutrino disappearance using ∼500 days of data. Based on the ratio of inverse-beta-decay (IBD) prompt spectra measured in two identical far and near detectors, we obtain sin2⁡(2θ13)=0.082±0.009(stat.)±0.006(syst.) and |Δmee2|=[2.62−0.23+0.21(stat.)−0.13+0.12(syst.)]×10−3 eV2. An excess of reactor antineutrinos near 5 MeV is observed in the measured prompt spectrum with respect to the most commonly used models. The excess is found to be consistent with coming from reactors. A successful measurement of θ13 is also made in an IBD event sample with a delayed signal of neutron capture on hydrogen. A precise value of θ13 would provide important information on determination of the leptonic CP phase if combined with a result of an accelerator neutrino beam experiment.

Physics potential of a long-baseline neutrino oscillation experiment using a J-PARC neutrino beam and Hyper-Kamiokande

Hyper-Kamiokande will be a next-generation underground water Cherenkov detector with a total (fiducial) mass of 0.99 (0.56) million metric tons, approximately 20 (25) times larger than that of Super-Kamiokande. One of the main goals of Hyper-Kamiokande is the study of |$CP$| asymmetry in the lepton sector using accelerator neutrino and anti-neutrino beams. In this paper, the physics potential of a long-baseline neutrino experiment using the Hyper-Kamiokande detector and a neutrino beam from the J-PARC proton synchrotron is presented. The analysis uses the framework and systematic uncertainties derived from the ongoing T2K experiment. With a total exposure of 7.5 MW |$\times 10^7$|s integrated proton beam power (corresponding to |$1.56 \times 10^{22}$| protons on target with a 30 GeV proton beam) to a |$2.5^\circ$| off-axis neutrino beam, it is expected that the leptonic |$CP$| phase |$\delta _{CP}$| can be determined to better than 19 degrees for all possible values of |$\delta _{CP}$|⁠, and |$CP$| violation can be established with a statistical significance of more than |$3\,\sigma$| (⁠|$5\,\sigma$|⁠) for |$76{\%}$| (⁠|$58{\%}$|⁠) of the |${\delta _{CP}}$| parameter space. Using both |$\nu _e$| appearance and |$\nu _\mu$| disappearance data, the expected 1|$\sigma$| uncertainty of |$\sin ^2\theta _{23}$| is 0.015(0.006) for |$\sin ^2\theta _{23}=0.5(0.45)$|⁠.

Daya Bay and Jiangmen Underground Neutrino Observatory (JUNO)neutrino experiments

Neutrino Physics is one of the most active branches in particle physics. Many puzzles remain in neutrinos, which may lead to new physics beyond the Standard Model of particle physics. We summarize the status and major scientific problems in neutrino physics, and introduce the neutrino program in China, with details on the on-going Daya Bay Neutrino Experiment and the being-built Jiangmen Underground Neutrino Observatory (JUNO). Daya Bay discovered a new type of neutrino oscillation in 2012 and measured the corresponding neutrino mixing angle <italic>q</italic>₁₃, by detecting reactor neutrinos. In this paper, we introduce the physics background and the project background of Daya Bay, summarize the experimental method and design principles, and describe the detector design and construction. Many new ideas and technical innovations have been implemented in the detector design and construction, thus a 0.2% relative uncertainty from detector is achieved. In the next decades, the Daya Bay results will be the most precise measurement on this fundamental parameter. JUNO was proposed in 2008 and formally approved in 2013. It will determine the neutrino mass hierarchy and precisely measure three neutrino mixing parameters by detecting reactor neutrinos at a distance of 53 km. With a 20 kton liquid scintillator detector of 3% energy resolution, JUNO will also be promising in studying supernovae neutrino, solar neutrino, geo-neutrino, atmospheric neutrino, as well as other exotic searches. It will be a multiple-purpose experimental platform for many world-leading researches. We introduce the progress on the experiment design and detector R&D. Besides Daya Bay and JUNO, we extend the neutrino studies by joining the neutrinoless double beta decay experiment EXO, and by starting R&D of MOMENT, a new idea to produce accelerator neutrino beam.

Requirements for a new detector at the South Pole receiving an accelerator neutrino beam

There are recent considerations to increase the photomultiplier density in the IceCube detector array beyond that of DeepCore, which will lead to a lower detection threshold and a huge fiducial mass for the neutrino detection. This initiative is known as "Phased IceCube Next Generation Upgrade" (PINGU). We discuss the possibility to send a neutrino beam from one of the major accelerator laboratories in the Northern hemisphere to such a detector. Such an experiment would be unique in the sense that it would be the only neutrino beam where the baseline crosses the Earth's core. We study the detector requirements for a beta beam, a neutrino factory beam, and a superbeam, where we consider both the cases of small theta_13 and large theta_13, as suggested by the recent T2K and Double Chooz results. We illustrate that a flavor-clean beta beam best suits the requirements of such a detector, in particular, that PINGU may replace a magic baseline detector for small values of theta_13 -- even in the absence of any energy resolution capability. For large theta_13, however, a single-baseline beta beam experiment cannot compete if it is constrained by the CERN-SPS. For a neutrino factory, because of the missing charge identification possibility in the detector, a very good energy resolution is required. If this can be achieved, especially a low energy neutrino factory, which does not suffer from the tau contamination, may be an interesting option for large theta_13. For the superbeam, where we use the LBNE beam as a reference, electron neutrino flavor identification and statistics are two of the main limitations. Finally, we demonstrate that, at least in principle, neutrino factory and superbeam can measure the density of the Earth's core to the sub-percent level for sin^2 2theta_13 larger than 0.01.

LAGUNA DESIGN STUDY, Underground infrastructures and engineering

The European Commission has awarded the LAGUNA project a grant of 1.7 million euro for a Design Study from the seventh framework program of research and technology development (FP7-INFRASTRUCTURES – 2007-1) in 2008. The purpose of this two year work is to study the feasibility of the considered experiments and prepare a conceptual design of the required underground infrastructure. It is due to deliver a report that allows the funding agencies to decide on the realization of the experiment and to select the site and the technology. The result of this work is the first step towards fulfilling the goals of LAGUNA. The work will continue with EU funding to study the possibilities more thoroughly. The LAGUNA project is included in the future plans prepared by European funding organizations. (Astroparticle physics in Europe). It is recommended that a new large European infrastructure is put forward, as a future international multi-purpose facility for improved studies on proton decay and low-energy neutrinos from astrophysical origin. The three detection techniques being studied for such large detectors in Europe, Water-Cherenkov (like MEMPHYS), liquid scintillator (like LENA) and liquid argon (like GLACIER), are evaluated in the context of a common design study which should also address the underground infrastructure and the possibility of an eventual detection of future accelerator neutrino beams. The design study is also to take into account worldwide efforts and converge, on a time scale of 2010, to a common proposal.

A study of the neutrino production of φ and D s + mesons

The charged current neutrino production of φ and D + s mesons is studied, using the data obtained with the SKAT bubble chamber exposed to the Serpukhov accelerator neutrino beam. It is found that the φ production occurs predominantly in the forward hemisphere of the hadronic c.m.s. (at x F > 0, x F being the Feynman variable), with the mean yield strongly exceeding the expected yield of directly produced φ mesons and varying from 〈n φ(x F s 0)〉 = (0.92 ± 0.34) × 10−2 at W > 2 GeV up to (1.23 ± 0.53) × 10−2 at W > 2.6 GeV and (1.44 ± 0.69) × 10−2 at W > 2.9 GeV, W being the invariant mass of the hadronic system. For the first time, the inclusive yield of leading D + s mesons carrying more than z = 0.85 of the current c-quark energy is estimated: 〈n D + s (z > 0.85, W > 2.9 GeV)〉 = (6.64 ± 1.91) × 10−2. It is shown that the shape of measured φ meson differential spectrum on xF is reproduced by that expected from the D + s → φX decays. An indication was obtained that this expected spectrum underestimates the measured φ yield.

Determination of the neutrino mass hierarchy at an intermediate baseline

It is generally believed that neutrino mass hierarchy can be determined at a long baseline experiment, often using accelerator neutrino beams. Reactor neutrino experiments at an intermediate baseline have the capability to distinguish normal or inverted hierarchy. Recently, it has been demonstrated that the mass hierarchy could possibly be identified using Fourier transform to the $L/E$ spectrum if the mixing angle ${sin}^{2}(2{\ensuremath{\theta}}_{13})&gt;0.02$. In this study, a more sensitive Fourier analysis is introduced. We found that an ideal detector at an intermediate baseline ($\ensuremath{\sim}60\text{ }\text{ }\mathrm{km}$) could identify the mass hierarchy for a mixing angle ${sin}^{2}(2{\ensuremath{\theta}}_{13})&gt;0.005$, without requirements on accurate information of reactor neutrino spectra and the value of $\ensuremath{\Delta}{m}_{32}^{2}$.

Long Baseline Neutrino Experiments: Present and Future Accelerator and Atmospheric Neutrino Experiments

Long Baseline Neutrino Experiments: Present and Future Accelerator and Atmospheric Neutrino Experiments Takaaki Kajita Research Center for Cosmic Neutrinos, Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan (Received 21 August 2007) The present status and future prospects of experimental studies of neutrino oscillations based on atmospheric neutrinos and long baseline neutrinos are discussed. Present neutrino oscillation data are explained very well with 2avor ! oscillations. The present knowledge of the relevant oscillation parameters is summarized. However, our understanding of the neutrino oscillation parameters is still incomplete. The future direction of the neutrino oscillation experiments based on accelerator neutrino beam is discussed. PACS numbers: 14.60.Pq, 96.40.Tv

Experimental study of the atmospheric neutrino backgrounds forp→e+π0searches in water Cherenkov detectors

The atmospheric neutrino background for proton decay via p→e + π 0 in ring imaging water Cherenkov detectors is studied with an artificial accelerator neutrino beam for the first time. In total, 3.14 × 10 5 neutrino events corresponding to about 10 megaton-years of atmospheric neutrino interactions were collected by a 1000 ton water Cherenkov detector (KT). The KT charged-current single π 0 production data are well reproduced by simulation programs of neutrino and secondary hadronic interactions used in the Super-Kamiokande (SK) proton decay search. The obtained p→ e + π 0 background rate by the KT data for SK from the atmospheric neutrinos whose energies are below 3 GeV is 1.63 +0.42 -0.33 (stat) +0.45 -0.51 (syst)(megaton-year) -1 . This result is also relevant to possible future, megaton-scale water Cherenkov detectors.

Hadron Production Measurements at CERN

Hadron production measurements for neutrino experiments is a well established field at CERN since the '70s. Precise prediction of atmospheric neutrino fluxes, characterization of accelerator neutrino beams, quantification of pion production and capture for neutrino factory designs, all of these would profit from hadron production measurements. In recent years, interest in such studies was revived and new generation of low-energy (from 3 to 400 GeV) hadron production experiments were built or proposed. Such experiments all share a basic design, consisting in the presence of open-geometry spectrometers, as close as possible to full angular coverage, and aiming at full particle identification. New results are now provided by Harp in the very low energy range (3 to 15 GeV/c) and by NA49 at 158 GeV/c. In the next years NA49- future will explore the medium energy range (30 to 400 GeV/c) and at LHC energies for the first time thanks to the TOTEM experiment, it will be possible to measure with unprecedented precision the total cross section beyond 1 TeV/c.

Hadron Production: Present Knowledge and Future Plans

Hadron production is a key ingredient in many aspects of neutrino physics. Precise prediction of atmospheric neutrino fluxes, characterization of accelerator neutrino beams, quantification of pion production and capture for neutrino factory designs, all of these would profit from hadron production measurements. For all these reasons this is a well established field since the '70s. In more recent times, low-energy hadron production experiments operating in the range from 1 GeV to 100 GeV are being operated, built or proposed. Such experiments all share a basic design, consisting in the presence of open-geometry spectrometers, as close as possible to full angular coverage, and the aim of full particle identification.

Theta-13 as a Probe of Mu-Tau symmetry for Leptons

Many experiments are being planned to measure the neutrino mixing parameter $\theta_{13}$ using reactor as well as accelerator neutrino beams. In this note, the theoretical significance of a high precision measurement of this parameter is discussed. It is emphasized that it will provide crucial information about different ways to understand the origin of large atmospheric neutrino mixing and move us closer towards determining the neutrino mass matrix. For instance if exact $\mu\leftrightarrow \tau$ symmetry in the neutrino mass matrix is assumed to be the reason for maximal $\nu_\mu-\nu_\tau$ mixing, one gets $\theta_{13}=0$. Whether $\theta_{13}\simeq \sqrt{\Delta m^2_{\odot}/\Delta m^2_A}$ or $\theta_{13}\simeq \Delta m^2_{\odot}/\Delta m^2_A$ can provide information about the way the $\mu\leftrightarrow \tau$ symmetry breaking manifests in the case of normal hierarchy. We also discuss the same question for inverted hierarchy as well as possible gauge theories with this symmetry.

FLUX OF ATMOSPHERIC NEUTRINOS

▪ Abstract Atmospheric neutrinos produced by cosmic-ray interactions in the atmosphere are of interest for several reasons. As a beam for studies of neutrino oscillations, they cover a range of parameter space hitherto unexplored by accelerator neutrino beams. The atmospheric neutrinos also constitute an important background and calibration beam for neutrino astronomy and for the search for proton decay and other rare processes. We review the literature on calculations of atmospheric neutrinos over the full range of energy, with particular attention to the aspects important for neutrino oscillations. Our goal is to assess how well the properties of atmospheric neutrinos are known at present.

Neutrino Oscillations

Experimental and theoretical works on neutrino oscillations have been recently boosted by new and sometimes unanticipated results from flavor transition searches with solar, atmospheric, and accelerator neutrino beams. In particular, the Super-Kamiokande experiment has found robust evidence for muon flavor disappearance in atmospheric neutrinos, with a preference for νμ → ντ transitions. The long-standing evidence for electron flavor disappearance in solar neutrinos νe → νX has been confirmed, although the specific oscillation mechanisms remain elusive. Weaker evidence for νμ → νe transitions has also been found in accelerator searches. These results globally suggest that all three active neutrinos νe,μ,τ (and possibly additional sterile neutrinos νs) have mass and are mixed, although an unambiguous theoretical pattern for the neutrino mass matrix has not yet emerged. An attempt is made to highlight the relevant issues in this growing and rapidly evolving field of research.