Neutrino experiments at J-PARC are reviewed. After an introduction to neutrino physics, with emphasis on neutrino oscillation, the T2K experiment at the Main Ring neutrino beam line and its peripheral experiments are introduced. Also future prospects of the Japanese long-baseline oscillation experiments are given. In addition, a new attempt to search for sterile neutrinos at the J-PARC MLF, JSNS$^2$ experiment, is introduced.
On April 2015, the J-PARC E56 (JSNS2: J-PARC Sterile Neutrino Search using neutrinos from J-PARC Spallation Neutron Source) experiment officially obtained stage-1 approval from J-PARC. We have since started to perform liquid scintillator R&D for improving energy resolution and fast neutron rejection. Also, we are studying Avalanche Photo-Diodes (SiPM) inside the liquid scintillator. In addition to the R&D work, a background measurement for the proton beam bunch timing using a small liquid scintillator volume was planned, and the safety discussions for the measurement have been done. This repor…
The J-PARC E56 experiment aims to search for sterile neutrinos at the J-PARC Materials and Life Science Experimental Facility (MLF). In order to examine the feasibility of the experiment, we measured the background rates of different detector candidate sites, which are located at the third floor of the MLF, using a detector consisting of plastic scintillators with a fiducial mass of 500 kg. The result of the measurements is described in this article. The gammas and neutrons induced by the beam as well as the backgrounds from the cosmic rays were measured.
At the 17th J-PARC PAC, which was held on September 2013, we proposed the sterile neutrino search at J-PARC MLF. After reviewing the proposal, PAC recommended to have a background measurement at the detector's candidate site location in their report to investigate whether the background rates can be manageable for the real experiment or not. Therefore, we have performed the background measurements (MLF; 2013BU1301 test experiment) during the summer of 2014, also following the 18th J-PARC PAC recommendations, and the measurements results are described here.
The JSNS2 (J-PARC E56) experiment aims to search for sterile neutrinos at the J-PARC Materials and Life Sciences Experimental Facility (MLF).After the submission of a proposal to the J-PARC PAC, stage-1 approval was granted to the JSNS2 experiment. The approval followed a series of background measurements which were performed in 2014. Subsequent for stage-1 approval, the JSNS2 collaboration has made continuous efforts to write a Technical Design Report (TDR).This TDR will include two major items as discussed in the previous status report for the 20th J-PARC PAC: (1) A realistic detector locati…
Precise neutrino--nucleus interaction measurements in the sub-multi GeV region are important to reduce the systematic uncertainty in future neutrino oscillation experiments. Furthermore, the excess of ${ν_e}$ interactions, as a possible interpretation of the existence of a sterile neutrino has been observed in such an energy region. The nuclear emulsion technique can measure all the final state particles with low energy threshold for a variety of targets (Fe, C, H${_2}$O, and so on). Its sub-$μ$m position resolution allows measurements of the ${ν_e}$ cross-section with good electron/gamma sepa…
The 3rd International Workshop on a Far Detector in Korea for the J-PARC Neutrino Beam was held at the Hongo Campus of Tokyo University, Tokyo, Japan on Sep. 30th and October 1, 2007. Forty seven physicists from Japan and Korea, as well as Europe and USA, participated in the workshop and discussed the physics opportunities offered by the J-PARC conventional neutrino beam detected by a new large underground neutrino detector in Korea. In this paper, we highlight some of the most relevant findings of the workshop.
The JSNS$^2$ (J-PARC E56) experiment aims to search for a sterile neutrino at the J-PARC Materials and Life Sciences Experimental Facility (MLF). After the submission of a proposal to the J-PARC PAC, Stage-1 approval was granted to the JSNS$^2$ experiment on April 2015.This approval followed a series of background measurements which were performed in 2014. Recently, funding (the grant-in-aid for scientific research (S)) in Japan for building one 25~ton fiducial volume detector module was approved for the experiment. Therefore, we aim to start the experiment with one detector in JFY2018-2019. W…
In order to explore CP asymmetry in the lepton sector, a power upgrade to the neutrino experimental facility at J-PARC is a key requirement for both the Tokai to Kamioka (T2K) long-baseline neutrino oscillation experiment and a future project with Hyper-Kamiokande. Based on five years of operational experience, the facility has achieved stable operation with 230 kW beam power without significant problems on the beam-line apparatus. After successful maintenance works in 2013-2014 to replace all electromagnetic horns and a production target, the facility is now ready to accomodate a 750-kW-rated…
In this document, the technical details of the JSNS$^2$ (J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron Source) experiment are described. The search for sterile neutrinos is currently one of the hottest topics in neutrino physics. The JSNS$^2$ experiment aims to search for the existence of neutrino oscillations with $Δm^2$ near 1 eV$^2$ at the J-PARC Materials and Life Science Experimental Facility (MLF). A 1 MW beam of 3 GeV protons incident on a spallation neutron target produces an intense neutrino beam from muon decay at rest. Neutrinos come predominantly from $μ^+$ decay: $μ^…
We propose a definite search for sterile neutrinos at the J-PARC Materials and Life Science Experimental Facility (MLF). With the 3 GeV Rapid Cycling Synchrotron (RCS) and spallation neutron target, an intense neutrino beam from muon decay at rest (DAR) is available. Neutrinos come from μ+ decay, and the oscillation to be searched for is (anti νμ-> anti νe) which is detected by the inverse βdecay interaction (anti νe + p -> e+ + n), followed by a gamma from neutron capture. The unique features of the proposed experiment, compared with the LSND and experiments using horn focused beams, are; (1)…
Recent neutrino oscillation results have shown that the existing long baseline experiments have some sensitivity to the effects of CP violation in the neutrino sector. This sensitivity is currently statistically limited, but the next generation of experiments, DUNE and Hyper-K, will provide an order of magnitude more events. To reach the full potential of these datasets we must achieve a commensurate improvement in our understanding of the systematic uncertainties that beset them. This talk describes two proposed intermediate detectors for the current and future long baseline oscillation exper…
As long-baseline neutrino experiments enter the precision era, the difficulties associated with understanding neutrino interaction cross sections on atomic nuclei are expected to limit experimental sensitivities to oscillation parameters. In particular, the ability to relate experimental observables to neutrino energy in previous experiments has relied solely on theoretical models of neutrino-nucleus interactions, which currently suffer from very large theoretical uncertainties. By observing charged current $ν_μ$ interactions over a continuous range of off-axis angles from 1 to 4 degrees, the …
The Tokai to Kamioka (T2K) experiment is a next generation long baseline neutrino oscillation experiment utilising the Japan Proton Accelerator Research complex (J-PARC) high intensity proton synchrotron. After a brief introduction of the current understanding of neutrino mixing, the T2K experiment, its current status and the expected physics results are presented. Then, possibilities for future neutrino oscillation experiments utilising J-PARC are discussed.
In Japan, as the first experiment utilizes J-PARC (Japan Proton Accelerator Research Complex) neutrino facility, T2K (Tokai to Kamioka Long Baseline Neutrino Experiment) starts operation. T2K is supposed to give critical information, which guides the future direction of the neutrino physics. Possible new generation discovery experiment based on T2K outcome is discussed. Especially, description of J-PARC neutrino beam upgrade plan and discussion on far detector options to maximize potential of the research are focused. European participation and CERN commitment on Japanese accelerator based neu…
Upgrades to the J-PARC accelerators and the neutrino experimental facility are of vital importance to the Tokai to Hyper-Kamiokande project (T2HK), which aims to explore CP asymmetry by the $ν_e$ appearance. In this talk I present overview of the T2HK project, current status of the beam operation at J-PARC, and prospect to realize the rated 750 kW operation in coming years.
The Tokai Intermediate Tank with Unoscillated Spectrum (TITUS) detector is a proposed addition to the Hyper-Kamiokande (HK) experiment located approximately 2 km from the J-PARC neutrino beam. The design consists of a 2 kton Gadolinium (Gd) doped water Cherenkov detector, surrounded by a magnetized iron detector designed to range-out muons. The target material and location are chosen so that the neutrino interactions and beam spectrum at TITUS will match those of HK. Including a 0.1% Gd concentration allows for neutrino/antineutrino discrimination via neutron tagging. The primary goal of TITUS…
In addition to the next generation of beam-based neutrino experiments and their associated detectors, a number of intense, low-energy neutrino production sources from decays at rest will be in operation. In this work, we explore the physics opportunities with decay-at-rest neutrinos for complementary measurements of oscillation parameters at long baselines. The J-PARC Spallation Neutron Source, for example, will generate neutrinos from a variety of decay-at-rest (DAR) processes, specifically those of pions, muons, and kaons. Other proposed sources will produce large numbers of stopped pions an…
We propose a new experiment sensitive to the detection of millicharged particles produced at the $30$ GeV proton fixed-target collisions at J-PARC. The potential site for the experiment is B2 of the Neutrino Monitor building, $280$ m away from the target. With $\textrm{N}_\textrm{POT}=10^{22}$, the experiment can provide sensitivity to particles with electric charge $3\times10^{-4}\,e$ for mass less than $0.2$ $\textrm{GeV}/\textrm{c}^2$ and $1.5\times10^{-3}\,e$ for mass less than $1.6$ $\textrm{GeV}/\textrm{c}^2$. This brings a substantial extension to the current constraints on the charge a…
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 document, 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 has been updated from the previous Letter of I…
Spin-physics projects at J-PARC are explained by including future possibilities. J-PARC is the most-intense hadron-beam facility in the high-energy region above multi-GeV, and spin physics will be investigated by using secondary beams of kaons, pions, neutrinos, muons, and antiproton as well as the primary-beam proton. In particle physics, spin topics are on muon $g-2$, muon and neutron electric dipole moments, and time-reversal violation experiment in a kaon decay. Here, we focus more on hadron-spin physics as for future projects. For example, generalized parton distributions (GPDs) could be …
An outline is explained for hadron-physics projects at J-PARC, which is considered to be one of the flagship facilities in hadron physics from 2008. The facility provides an intensity frontier with 50 GeV proton beam for nuclear and particle physics. It could cover a wide range of hadron physics from strongly interacting many-body systems with an extended hadronic degree of freedom, strangeness, to new forms of hadrons and hadronic matters. These studies lead not only to create innovative fields of hadron physics but also, possibly, to understand fundamental interactions because of recent prog…
The fundamental properties of neutrinos are reviewed in these lectures. The first part is focused on the basic characteristics of neutrinos in the Standard Model and how neutrinos are detected. Neutrino masses and oscillations are introduced and a summary of the most important experimental results on neutrino oscillations to date is provided. Then, present and future experimental proposals are discussed, including new precision reactor and accelerator experiments. Finally, different approaches for measuring the neutrino mass and the nature (Majorana or Dirac) of neutrinos are reviewed. The det…
The JSNS$^{2}$ (J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron Source) experiment will search for neutrino oscillations over a 24 m short baseline at J-PARC. The JSNS$^{2}$ inner detector will be filled with 17 tons of gadolinium-loaded liquid scintillator (LS) with an additional 31 tons of unloaded LS in the intermediate $γ$-catcher and outer veto volumes. JSNS$^{2}$ has chosen Linear Alkyl Benzene (LAB) as an organic solvent because of its chemical properties. The unloaded LS was produced at a refurbished facility, originally used for scintillator production by the RENO experime…
We present the numu to nue appearance and the numu disappearance results, using a total of 1.43 x 10^{20} protons on target collected with the T2K experiment. T2K is long baseline neutrino experiment in Japan with detectors located at J-PARC, Tokai, and at Kamioka in the Gifu Prefecture, situated 295 km away from J-PARC. The muon neutrino beam is produced and measured at the near detectors at J-PARC whilst the neutrino rates after oscillation are measured with the Super-Kamiokande detector, at Kamioka. A total of six events pass all the selection criteria for numu to nue oscillations at the fa…
In July 2013 ICFA established the Neutrino Panel with the mandate "To promote international cooperation in the development of the accelerator-based neutrino-oscillation program and to promote international collaboration in the development a neutrino factory as a future intense source of neutrinos for particle physics experiments". This, the Panel's Initial Report, presents the conclusions drawn by the Panel from three regional "Town Meetings" that took place between November 2013 and February 2014. After a brief introduction and a short summary of the status of the knowledge of the oscillation…
This study presents the recent progress made in developing a spiral fiber tracker (SFT) for use in the experiment TREK/E36 planned at the Japan Proton Accelerator Research Complex. This kaon decay experiment uses a stopped positive kaon beam to search for physics beyond the Standard Model through precision measurements of lepton universality and through searches for a heavy sterile neutrino and a dark photon. Detecting and tracking positrons and positive muons from kaon decays are of importance in achieving high-precision measurements; therefore, we designed and are developing the new tracking…
The discovery potentials of non-standard physics (NSP) which might be possessed by neutrinos are examined by taking a concrete setting of Tokai-to-Kamioka-Korea (T2KK) two detector complex which receives neutrino superbeam from J-PARC. We restrict ourselves into ν_μ and \barν_μ disappearance measurement. We describe here only the non-standard interactions (NSI) of neutrinos with matter and the quantum decoherence. It is shown in some favorable cases T2KK can significantly improve the current bounds on NSP. For NSI, for example, epsilon_{μτ} < 0.03, which is a factor 5 severer than the current …
The J-PARC is a hadron-accelerator facility to provide secondary beams of kaons, pions, neutrinos, muons, and the others together with the primary proton beam for investigating a wide range of science projects. High-energy hadron physics can be studied by using high-momentum beams of unseparated hadrons, which are essentially pions, and also primary protons. In this report, possible experiments are explained on color transparency and generalized parton distributions (GPDs). These projects are complementary to lepton-scattering experiments at JLab, COMPASS/AMBER, and future electron-ion collide…
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 d…
We investigate the ability of the upcoming Hyper-Kamiokande (Hyper-K) neutrino experiment to detect new physics phenomena beyond the standard, three-massive-neutrinos paradigm; namely the existence of a fourth, sterile neutrino or weaker-than-weak, non-standard neutrino interactions. With both beam-based neutrinos from the Japan Proton Accelerator Research Complex (J-PARC) and atmospheric neutrinos, Hyper-K is capable of exploring new ranges of parameter space in these new-physics scenarios. We find that Hyper-K has comparable capability to the upcoming Deep Underground Neutrino Experiment (DU…
The JSNS$^{2}$ (J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron Source) experiment aims to search for neutrino oscillations over a 24 m short baseline at J-PARC. The JSNS$^{2}$ inner detector is filled with 17 tons of gadolinium(Gd)-loaded liquid scintillator (LS) with an additional 31 tons of unloaded LS in the intermediate $γ$-catcher and an optically separated outer veto volumes. A total of 120 10-inch photomultiplier tubes observe the scintillating optical photons and each analog waveform is stored with the flash analog-to-digital converters. We present details of the data acqu…
T2K is a long-baseline neutrino oscillation experiment using a $ν_μ$ beam produced at the J-PARC facility. Neutrinos are detected at a Near Detector complex (ND280) and at the Far Detector (Super-Kamiokande). The most recent oscillation results presented by T2K are described in these proceedings. With these data T2K has produced the first constraints on $δ_{CP}$, excluding CP conserving values at 2$σ$ and the world best measurement of the $θ_{23}$ mixing angle.
The motivation for possible future long baseline neutrino experiments is discussed. The proposed experiments as well as their physics potential is reviewed.
We point out the possibility that reactor measurement of theta_{13}, when combined with high-statistics nu_e appearance accelerator experiments, can detect leptonic CP violation. Our proposal is based on a careful statistical analysis under reasonable assumptions on systematic errors, assuming 2 years running of the neutrino mode J-PARC -> Hyper-Kamiokande experiment and a few years running of a reactor experiment with 100 ton detectors at the Kashiwazaki-Kariwa nuclear power plant. We show that the method can be arranged to be insensitive to the intrinsic parameter degeneracy but is affected …
T2K is a long-baseline neutrino oscillation experiment, in which a muon-neutrino beam is directed over a 295 km baseline from the J-PARC facility to the Super-Kamiokande detector. This allows neutrino oscillation to be studied in two channels: disappearance of muon neutrinos and appearance of electron neutrinos. T2K has collected data using both a neutrino-enhanced and an antineutrino-enhanced beam, and these proceedings present the first T2K results using both neutrino and antineutrino oscillation data. Combining the two data sets gives the first ever sensitivity to neutrino-sector CP violati…
The Hyper-Kamiokande (HK) experiment centres around a proposed next-generation underground water Cherenkov detector that will be nearly 20 times larger than the highly successful Super-Kamiokande experiment and use significantly improved photodetectors with the same 40% photocoverage. HK will increase existing sensitivity to proton decay by an order of magnitude, and it will study neutrinos from various sources, including atmospheric neutrinos, solar neutrinos, and supernova neutrinos. In addition to operating as a standalone experiment, HK will serve as the far detector of a long-baseline neu…
Hyper-Kamiokande (Hyper-K) is a proposed next generation underground water Cherenkov (WCh) experiment. The far detector will measure the oscillated neutrino flux from the long-baseline neutrino experiment using 0.6 GeV neutrinos produced by a 1.3 MW proton beam at J-PARC. It has a broad program of physics and astrophysics mainly focusing on the precise measurement of the lepton neutrino mixing matrix and the CP asymmetry. The unoscillated neutrino flux will be measured by an intermediate WCh detector. One of the proposed designs is the Tokai Intermediate Tank for the Unoscillated Spectrum (TIT…
JSNS$^2$ (J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron Source) is an experiment that is searching for sterile neutrinos via the observation of $\barν_μ \to \barν_{e}$ appearance oscillations using muon decay-at-rest neutrinos. Before dedicated data taking in the first-half of 2021, we performed a commissioning run for 10 days in June 2020. Using the data obtained in this commissioning run, in this paper, we present an estimate of the correlated background which imitates the $\barν_{e}$ signal in a sterile neutrino search. In addition, in order to demonstrate future prospects of …
The main features of four-neutrino 3+1 and 2+2 mixing schemes are reviewed, after a discussion on the necessity of at least four massive neutrinos if the solar, atmospheric and LSND anomalies are due to neutrino oscillations. Complete list of references on four-neutrino mixing at http://www.to.infn.it/~giunti/neutrino
The Standard Model (SM) represents our best description of the subatomic world and it has been very successful in explaining how elementary particles interact under the influence of the fundamental forces. Despite its far reaching success in describing the building blocks of matter, the SM is still incomplete; falling short to explain dark matter, baryogenesis, neutrino masses and much more. The E36 experiment conducted at J-PARC in Japan, allows for sensitivity to search for light $U(1)$ gauge bosons, in the muonic $K^+$ decay channel. Such $U(1)$ bosons could be associated with dark matter o…
The current status of the phenomenology of short-baseline neutrino oscillations induced by light sterile neutrinos in the framework of 3+1 mixing is reviewed.
The theory and phenomenology of light sterile neutrinos at the eV mass scale is reviewed. The reactor, Gallium and LSND anomalies are briefly described and interpreted as indications of the existence of short-baseline oscillations which require the existence of light sterile neutrinos. The global fits of short-baseline oscillation data in 3+1 and 3+2 schemes are discussed, together with the implications for beta-decay and neutrinoless double-beta decay. The cosmological effects of light sterile neutrinos are briefly reviewed and the implications of existing cosmological data are discussed. The…
Neutrino oscillations were discovered by atmospheric and solar neutrino experiments, and have been confirmed by experiments using neutrinos from accelerators and nuclear reactors. It has been found that there are large mixing angles in the $ν_e \to ν_μ$ and $ν_μ\to ν_τ$ oscillations. The third mixing angle $θ_{13}$, which parameterizes the mixing between the first and the third generation, is constrainted to be small by the CHOOZ experiment result. The T2K experiment is a long baseline neutrino oscillation experiment that uses intense neutrino beam produced at J-PARC and Super-Kamiokande detec…
We propose a new experiment to search for a time-reversal (T) symmetry breaking process in muon decay and the Majoranality of the neutrinos. In the presence of V+A interactions, the Majoranality appears as a T-violating term in the muon decay width as shown by Doi et al, while in the Standard Model such a T-violating term is negligibly small. The presences of V+A interactions and the corresponding heavy right-handed Majorana neutrinos give us an important clue to solve two major issues in particle physics, the deficit of baryon asymmetry in the universe and the Majoranality of neutrinos. In th…
The JSNS^2 (J-PARC Sterile Neutrino Search at J-PARC Spallation Neutron Source) experiment aims to search for oscillations involving a sterile neutrino in the eV^2 mass-splitting range. The experiment will search for the appearance of electron antineutrinos oscillated from muon antineutrinos. The electron antineutrinos are detected via the inverse beta decay process using a liquid scintillator detector. A 1MW beam of 3 GeV protons incident on a spallation neutron target produces an intense and pulsed neutrino source from pion, muon, and kaon decay at rest. The JSNS^2 detector is located 24 m a…
A precise measurement of the hadron production from interactions of 30 GeV protons on carbon target is performed by NA61 (SHINE) experiment at the CERN SPS. The inclusive spectra of pions and kaons on the carbon target obtained from NA61 measurements constrain the neutrino flux in the T2K long baseline neutrino oscillation experiment at J-PARC, Japan. The article presents description of the NA61 apparatus together with the preliminary results from the pilot 2007 run.
Present results from neutrino experiments at accelerators and nuclear reactors are reviewed with emphasis on neutrino oscillation searches. Future prospects in this field are also discussed.
The indications in favor of the existence of light sterile neutrinos at the eV scale found in short-baseline neutrino oscillation experiments is reviewed. The future perspectives of short-baseline neutrino oscillation experiments and the connections with beta-decay measurements of the neutrino masses and with neutrinoless double-beta decay experiments are discussed.
The HARP and NA61/SHINE hadroproduction experiments as well as their implications for neutrino physics are discussed. HARP measurements have already been used for predictions of neutrino beams in K2K and Mini-BooNE/SciBooNE experiments and are also being used to improve the atmospheric neutrino flux predictions and to help in the optimization of neutrino factory and super-beam designs. First measurements released recently by the NA61/SHINE experiment are of significant importance for a precise prediction of the J-PARC neutrino beam used for the T2K experiment. Both HARP and NA61/SHINE experime…
After a short review of the current status of three-neutrino mixing, the implications for the values of neutrino masses are discussed. The bounds on the absolute scale of neutrino masses from Tritium beta-decay and cosmological data are reviewed. Finally, we discuss the implications of three-neutrino mixing for neutrinoless double-beta decay.
With the 1998 announcement of new evidence for muon neutrino disappearance observed by the Super-Kamiokande experiment, the more than a decade old atmospheric neutrino anomaly moved from a possible indication for neutrino oscillations to an almost inescapable implication. The evidence from all experiments is reviewed, and indications are presented that the oscillations are probably between muon and tau neutrinos with nearly maximal mixing. Implications and future directions in neutrino oscillations research are discussed.
T2K is a long-baseline neutrino oscillation experiment taking data since 2010. A neutrino beam is produced at the J-PARC accelerator in Japan and is sampled at a Near Detector complex 280 m from the neutrino production point and at the far detector, Super-Kamiokande, located 295 km from the source. Beams predominantly composed of muon neutrinos or muon anti-neutrinos have been produced by changing the currents in the magnetic focusing horns. This presentation will show the most recent T2K oscillation results obtained from a combined analysis of the entire available data set in the muon neutrin…
Current evidence for neutrino oscillation is reviewed, some areas for closer investigation are suggested, and a plausible future experimental program is summarized.
