Long Baseline Neutrino Oscillation Research Articles

The NOvA experiment: status and outlook

The NOvA long-baseline neutrino oscillation experiment is currently under construction and will use an upgraded NuMI neutrino source at Fermilab and a 14-kton detector at Ash River, Minnesota to explore the neutrino sector. NOvA uses a highly active, finely segmented detector design that offers superb event identification capability, allowing precision measurements of νe/ν¯e appearance and νμ/ν¯μ disappearance, through which NOvA will provide constraints on θ13, θ23, |Δmatm2|, the neutrino mass hierarchy, and the CP-violating phase δ. In this article, we review NOvAʼs uniquely broad physics scope, including sensitivity updates in light of the latest knowledge of θ13, and we discuss the experimentʼs construction and operation timeline.

Long-Baseline Neutrino Oscillation Experiments

A review of accelerator long-baseline neutrino oscillation experiments is provided, including all experiments performed to date and the projected sensitivity of those currently in progress. Accelerator experiments have played a crucial role in the confirmation of the neutrino oscillation phenomenon and in precision measurements of the parameters. With a fixed baseline and detectors providing good energy resolution, precise measurements of the ratio of distance/energy (L/E) on the scale of individual events have been made and the expected oscillatory pattern resolved. Evidence for electron neutrino appearance has recently been obtained, opening a door for determining the CP violating phase as well as resolving the mass hierarchy and the octant ofθ23; some of the last unknown parameters of the standard model extended to include neutrino mass.

Pion emission from the T2K replica target: Method, results and application

The T2K long-baseline neutrino oscillation experiment in Japan needs precise predictions of the initial neutrino flux. The highest precision can be reached based on detailed measurements of hadron emission from the same target as used by T2K exposed to a proton beam of the same kinetic energy of 30GeV. The corresponding data were recorded in 2007–2010 by the NA61/SHINE experiment at the CERN SPS using a replica of the T2K graphite target. In this paper details of the experiment, data taking, data analysis method and results from the 2007 pilot run are presented. Furthermore, the application of the NA61/SHINE measurements to the predictions of the T2K initial neutrino flux is described and discussed.

The T2K fine-grained detectors

T2K is a long-baseline neutrino oscillation experiment searching for νe appearance in a νμ beam. The beam is produced at the J-PARC accelerator complex in Tokai, Japan, and the neutrinos are detected by the Super-Kamiokande detector located 295km away in Kamioka. A suite of near detectors (ND280) located 280 m downstream of the production target is used to characterize the components of the beam before they have had a chance to oscillate and to better understand various neutrino interactions on several nuclei. This paper describes the design and construction of two massive fine-grained detectors (FGDs) that serve as active targets in the ND280 tracker. One FGD is composed solely of scintillator bars while the other is partly scintillator and partly water. Each element of the FGDs is described, including the wavelength shifting fiber and Multi-Pixel Photon Counter used to collect the light signals, the readout electronics, and the calibration system. Initial tests and in situ results of the FGDs' performance are also presented.

Muon neutrino to electron neutrino oscillations in the MINOS experiment

MINOS is a long-baseline neutrino oscillation experiment situated along Fermilabʼs high-intensity NuMI neutrino beam. MINOS has completed an updated search for muon neutrino to electron neutrino transitions, observation of which would indicate a non-zero value for the neutrino mixing angle θ13. The present 7×1020 protons-on-target data set represents more than double the exposure used in the previous analysis. The new results are presented.

The MicroBooNE Experiment

MicroBooNE is a new experiment, currently under development, that will use a large, liquid-argon, time-projection chamber in the Fermilab Booster Neutrino Beam with the goal of studying the origin of the MiniBooNE anomalous signal of excess electron-like events in a muon-neutrino beam, which are not consistent with neutrino oscillations; it will also measure low-energy neutrino cross sections and has the potential to detect supernova neutrinos. At the same time, the project provides important R&D and proof-of-principle for potential, larger, detectors for studies of long-baseline neutrino oscillations and other physics.

Status of NOνA

NOνA is a long-baseline neutrino oscillation experiment looking for the appearance of electron neutrinos and anti-neutrinos in the NuMI neutrino beam. It is comprised of a near detector located on-site at Fermilab, approximately 1 km from the neutrino source and a far detector located 810 km from the source in northern Minnesota. Both detectors are positioned 14 mrad off the beam axis to observe a narrow range of neutrino energies peaked at 2.2 GeV. Construction of the NOνA experiment has begun and the details are outlined below.

An incremental approach to unravel the neutrino mass hierarchy and CP violation with a long-baseline superbeam for large θ 13

Recent data from long-baseline neutrino oscillation experiments have provided new information on \theta_{13}, hinting that 0.01\lesssim sin^2 2\theta_{13} \lesssim 0.1 at 2 sigma C.L. Confirmation of this result with high significance will have a crucial impact on the optimization of the future long-baseline oscillation experiments designed to probe the neutrino mass ordering and leptonic CP violation. In this context, we expound in detail the physics reach of an experimental setup where neutrinos produced in a conventional wide-band beam facility at CERN are observed in a proposed Giant Liquid Argon detector at the Pyh\"asalmi mine, at a distance of 2290 km. This particular setup would have unprecedented sensitivity to the mass ordering and CP violation in the light of large \theta_{13}. With a 10 to 20 kt `pilot' detector and just a few years of neutrino beam running, the mass hierarchy could be determined, irrespective of the true values of \delta_{CP} and the mass hierarchy, at 3 sigma (5 sigma) C.L. if sin^2 2\theta_{13}(true) = 0.05 (0.1). With the same exposure, we start to have 3 sigma sensitivity to CP violation if sin^2 2\theta_{13}(true) > 0.05, in particular testing maximally CP-violating scenarios at a high C.L. After optimizing the neutrino and anti-neutrino running fractions, we study the performance of the setup as a function of the exposure, identifying three milestones to have roughly 30%, 50% and 70% coverage in \delta_{CP}(true) for 3 sigma CP violation discovery. For comparison, we also study the CERN to Slanic baseline of 1540 km. This work demonstrates that an incremental program, staged in terms of the exposure, can achieve the desired physics goals within a realistically feasible timescale, and produce significant new results at each stage.

First muon-neutrino disappearance study with an off-axis beam

We report a measurement of muon-neutrino disappearance in the T2K experiment. The 295-km muon-neutrino beam from Tokai to Kamioka is the first implementation of the off-axis technique in a long-baseline neutrino oscillation experiment. With data corresponding to 1.43 10**20 protons on target, we observe 31 fully-contained single muon-like ring events in Super-Kamiokande, compared with an expectation of 104 +- 14 (syst) events without neutrino oscillations. The best-fit point for two-flavor nu_mu -> nu_tau oscillations is sin**2(2 theta_23) = 0.98 and |\Delta m**2_32| = 2.65 10**-3 eV**2. The boundary of the 90 % confidence region includes the points (sin**2(2 theta_23),|\Delta m**2_32|) = (1.0, 3.1 10**-3 eV**2), (0.84, 2.65 10**-3 eV**2) and (1.0, 2.2 10**-3 eV**2).

Current status of the T2K experiment

The T2K long-baseline neutrino-oscillation experiment was started in January 2010 for the purpose of physics data-taking. Until the massive earthquake on March 11, 2011 in Japan, 1.43 × 1020 pot data were accumulated. In this data, 6 possible νe appearance candidates are found for expected background of 1.5±0.3(syst.) if sin2 2θ13 = 0 is assumed. The probability that 6 or more events can be observed for 1.5±0.3 expected events is 7×10−3, equivalent to 2.5σ significance. This is the first indication of a νe appearance or, in other words, the first indication of a non-zero sin2 2θ13.

Precision Neutrino Oscillation Physics with MINOS

MINOS is a long-baseline neutrino oscillation experiment utilising Fermilabʼs NuMI beam and two functionally identical steel/scintillator calorimeter detectors. Here we describe the short and long term physics goals of MINOS and we give a brief overview of the beam and detector technology used to achieve them.

Oscillation Analysis with and without Solar Term Using Super-K-I and Super-K-II Atmospheric Neutrino data

As part of the European LAGUNA design study on a next-generation neutrino detector, we propose the liquid-scintillator detector LENA (Low Energy Neutrino Astronomy) as a multipurpose neutrino observatory. The outstanding successes of the Borexino and KamLAND experiments demonstrate the large potential of liquid-scintillator detectors in low-energy neutrino physics. Low energy threshold, good energy resolution and efficient background discrimination are inherent to the liquid-scintillator technique. A target mass of 50 kt will offer a substantial increase in detection sensitivity.At low energies, the variety of detection channels available in liquid scintillator will allow for an energy – and flavor-resolved analysis of the neutrino burst emitted by a galactic Supernova. Due to target mass and background conditions, LENA will also be sensitive to the faint signal of the Diffuse Supernova Neutrino Background. Solar metallicity, time-variation in the solar neutrino flux and deviations from MSW–LMA survival probabilities can be investigated based on unprecedented statistics. Low background conditions allow to search for dark matter by observing rare annihilation neutrinos. The large number of events expected for geoneutrinos will give valuable information on the abundances of Uranium and Thorium and their relative ratio in the Earth’s crust and mantle. Reactor neutrinos enable a high-precision measurement of solar mixing parameters. A strong radioactive or pion decay-at-rest neutrino source can be placed close to the detector to investigate neutrino oscillations for short distances and sub-MeV to MeV energies.At high energies, LENA will provide a new lifetime limit for the SUSY-favored proton decay mode into kaon and antineutrino, surpassing current experimental limits by about one order of magnitude. Recent studies have demonstrated that a reconstruction of momentum and energy of GeV particles is well feasible in liquid scintillator. Monte Carlo studies on the reconstruction of the complex event topologies found for neutrino interactions at multi-GeV energies have shown promising results. If this is confirmed, LENA might serve as far detector in a long-baseline neutrino oscillation experiment currently investigated in LAGUNA-LBNO.

Minimal models with light sterile neutrinos

We study the constraints imposed by neutrino oscillation experiments on the minimal extensions of the Standard Model (SM) with n R gauge singlet fermions (“righthanded neutrinos”), that can account for neutrino masses. We consider the most general coupling of the new fields to the SM fields, in particular those that break lepton number and we do not assume any a priori hierarchy in the mass parameters. We proceed to analyze these models starting from the lowest level of complexity, defined by the number of extra fermionic degrees of freedom. The simplest choice that has enough free parameters in principle (i.e. two mass differences and two angles) to explain the confirmed solar and atmospheric oscillations corresponds to n R = 1. This minimal choice is shown to be excluded by data. The next-to-minimal choice corresponds to n R = 2. We perform a systematic study of the full parameter space in the limit of degenerate Majorana masses by requiring that at least two neutrino mass differences correspond to those established by solar and atmospheric oscillations. We identify several types of spectra that can fit long-baseline reactor and accelerator neutrino oscillation data, but fail in explaining solar and/or atmospheric data. The only two solutions that survive are the expected seesaw and quasi-Dirac regions, for which we set lower and upper bounds respectively on the Majorana mass scale. Solar data from neutral current measurements provide essential information to constrain the quasi-Dirac region. The possibility to accommodate the LSND/MiniBoone and reactor anomalies, and the implications for neutrinoless double-beta decay and tritium beta decay are briefly discussed.

The T2K experiment

The T2K experiment is a long-baseline neutrino oscillation experiment. Its main goal is to measure the last unknown lepton sector mixing angle {\theta}_{13} by observing {\nu}_e appearance in a {\nu}_{\mu} beam. It also aims to make a precision measurement of the known oscillation parameters, {\Delta}m^{2}_{23} and sin^{2} 2{\theta}_{23}, via {\nu}_{\mu} disappearance studies. Other goals of the experiment include various neutrino cross section measurements and sterile neutrino searches. The experiment uses an intense proton beam generated by the J-PARC accelerator in Tokai, Japan, and is composed of a neutrino beamline, a near detector complex (ND280), and a far detector (Super-Kamiokande) located 295 km away from J-PARC. This paper provides a comprehensive review of the instrumentation aspect of the T2K experiment and a summary of the vital information for each subsystem.

A new approach to anti-neutrino running in long-baseline neutrino oscillation experiments

We study the possibility to replace the anti-neutrino run of a long baseline neutrino oscillation experiment, with anti-neutrinos from muon decay at rest. The low energy of these neutrinos allows the use of inverse beta decay for detection in a Gadolinium-doped water Cerenkov detector. We show that this approach yields a factor of five times larger anti-neutrino event sample. The resulting discovery reaches in theta_13, the mass hierarchy and leptonic CP violation are compared with those from a conventional superbeam experiment with combined neutrino and anti-neutrino running. We find that this approach yields a greatly improved reach for CP violation and theta_13 while leaving the ability to measure the mass hierarchy intact.

Towards seeking θ13: Status and initial data from T2K

T2K is a long-baseline neutrino oscillation experiment with the primary aim of measuring the smallest and most elusive neutrino mixing angle, θ13. 2010 saw the beginning of the T2K data-taking phase. This paper gives an overview of the T2K experiment, its goals and current status, and will discuss some of the initial data. All parts of the experiment: beamline, near detectors and far detector, are functioning well. In the far detector, 23 events have been selected from the first T2K dataset. Particle identification in the far detector also is discussed in this paper. Detailed analysis has not yet been completed.

Advantages of locating LAGUNA in Pyhäsalmi mine

LAGUNA is the next-generation underground Megaton-scale detector for the search for proton decay, for neutrino astrophysics and for the investigation of neutrino properties. A brief description of the three considered detector technologies is given and the main physics goals presented. While many of the research topics for LAGUNA are not affected by the geographical location of the detector, there are two areas where it is very important: low-energy neutrino measurements and long-baseline neutrino oscillations. Evaluation of the physics arguments in both cases indicates Pyhäsalmi mine as the best European site for LAGUNA.

Fermilab's Intensity Frontier

Particle physics experiments at the intensity frontier aim to probe nature through precision studies of the properties and interactions of its basic constituents, using intense particle beams and innovative detectors. We review the physics potential of several of these experiments, especially those that can be very effectively pursued at Fermilab in the near and intermediate future, assuming that a new intense proton source—Project X—will be available. We concentrate on flavor-violating phenomena that have been identified as the main particle physics drivers for Project X: the study of neutrino masses and mixing through long-baseline neutrino oscillations; searches for rare, flavor-violating muon processes; and precision measurements of kaon decays into neutrinos, [Formula: see text]. We also comment on other opportunities, such as measurements of the anomalous magnetic moment of muon and neutrino-matter scattering.

New MINOS Oscillation Results

The MINOS experiment (Main Injector Neutrino Oscillation Search) is a two detector long-baseline neutrino oscillation experiment. Oscillation parameters are determined by comparing the spectrum and composition of the neutrino beam measured at the far detector with that measured at the near detector. This paper summarises the four main beam neutrino oscillation results: muon neutrino and muon anti-neutrino disappearance, electron neutrino appearance and oscillations to sterile neutrinos, derived from the data collected during MINOS' first four years of operation.

A generic diagonalization of the [formula omitted] neutrino mass matrix and its implications on the [formula omitted] flavor symmetry and maximal CP violation

In the flavor basis where the mass eigenstates of three charged leptons are identified with their flavor eigenstates, one may diagonalize a 3×3 Majorana neutrino mass matrix Mν by means of the standard parametrization of the 3×3 neutrino mixing matrix V. In this treatment the unphysical phases of Mν have to be carefully factored out, unless a special phase convention for neutrino fields is chosen so as to simplify Mν to Mν′ without any unphysical phases. We choose this special flavor basis and establish some exact analytical relations between the matrix elements of Mν′Mν′† and seven physical parameters — three neutrino masses (m1, m2, m3), three flavor mixing angles (θ12, θ13, θ23) and the Dirac CP-violating phase (δ). Such results allow us to derive the conditions for the μ–τ flavor symmetry with θ23=π/4 and maximal CP violation with δ=±π/2, which should be useful for discussing specific neutrino mass models. In particular, we show that θ23=π/4 and δ=±π/2 keep unchanged when constant matter effects are taken into account for a long-baseline neutrino oscillation experiment.