Super-Kamiokande Detector Research Articles

Study of neutrino interactions at the T2K near detector

The Tokai-To-Kamioka (T2K) experiment was designed to measure the oscillation of muon neutrinos produced at the J-PARC accelerator in Japan. The Super-Kamiokande detector acts as the far detector and a near detector is installed in the path of the neutrino beam to reduce uncertainties on the flux and cross sections. This near detector, called ND280, is located 280 m from the production target of the T2K neutrino beamline in order to measure the characteristics of the beam prior to any oscillation. The first ND280 analysis of the momentum-angle distribution of the muon produced by muon neutrino charged current interactions has been performed. These results have also been used to determine a flux-averaged cross section.

Evidence of electron neutrino appearance in a muon neutrino beam

The T2K Collaboration reports evidence for electron neutrino appearance at the atmospheric mass splitting, |Δm322|≈2.4×10−3 eV2. An excess of electron neutrino interactions over background is observed from a muon neutrino beam with a peak energy of 0.6 GeV at the Super-Kamiokande (SK) detector 295 km from the beam’s origin. Signal and background predictions are constrained by data from near detectors located 280 m from the neutrino production target. We observe 11 electron neutrino candidate events at the SK detector when a background of 3.3±0.4(syst) events is expected. The background-only hypothesis is rejected with a p value of 0.0009 (3.1σ), and a fit assuming νμ→νe oscillations with sin22θ23=1, δCP=0 and |Δm322|=2.4×10−3 eV2 yields sin22θ13=0.088−0.039+0.049(stat+syst).35 MoreReceived 4 April 2013DOI:https://doi.org/10.1103/PhysRevD.88.032002© 2013 American Physical Society

Status of the Super-Kamiokande gadolinium project

The diffuse flux of neutrinos released from all past supernova explosions in the universe is known as the supernova relic neutrinos (SRN). Super-Kamiokande (SK) has conducted searches for these SRN events via their inverse beta decay interactions in the detector, in the process establishing the world's best limits on this still unobserved flux. These limits are within about a factor of two of the theoretically predicted fluxes. But these searches are background limited, and without some major improvement further progress will be difficult. The addition of gadolinium (Gd) compound into the SK detector was proposed to reduce background. Gd has the largest thermal neutron capture cross-section among all stable nuclei and emits an 8MeV γ cascade following the capture. By coincidental tagging of positrons with the γ rays from Gd neutron capture, we can identify the dominant SRN signal in SK: inverse beta decay. This Gd-loading technique should allow SK to make the world's first observation of a SRN signal. We will demonstrate the principle of a Gd-doped water Cherenkov detector (transparency of the Gd-doped water, Gd-doped water circulation method, neutron capture efficiency, etc) with a dedicated test facility named EGADS. EGADS consists of a 200ton water Cherenkov detector, a Gd dissolving pre-treatment device, a Gd-capable water circulation system, and a custom-built water transparency measurement device. We have evaluated Gd-doped water circulation using the main EGADS water system since 2012. The evaluation of the overall performance of EGADS will start in 2013 after PMT installation.

T2K Results and Perspectives

The Tokai-to-Kamioka (T2K) experiment studies neutrino oscillations in a 600 MeV off-axis, high intensity muon-neutrino beam sent 295 km from the Japan Proton Accelerator Complex (J-PARC) to the Super Kamiokande (SK) detector in Kamioka. The primary goals of T2K are the search for the appearance of electron neutrinos at SK resulting from θ13>0 and a precise measurement of θ23 and Δm322 via the νμ disappearance channel. The T2K collaboration has already published indications of electron neutrino appearance [K. Abe et al., Phys. Rev. Lett. 107, 041801 (2011)] and a first measurement of sin2(θ23) from muon neutrino disappearance [K. Abe et al., Phys. Rev. D 85,(2011) 031103] using the data collected until March 11, 2011. An improved analysis and all the data taken through June 9, 2012 provide now 11 electron neutrino candidates in the far detector, corresponding to 3.2 standard deviations from the θ13=0 hypothesis. This excess is currently the strongest evidence of electron neutrino appearance and it yields, for normal hierarchy and δCP=0,0.053<sin22θ13<0.141 at 68% confidence level.

Optimization of Neutrino Oscillation Parameters Using Differential Evolution

We show how the traditional grid based method for finding neutrino oscillation parameters Δm2 and tan2 θ can be combined with an optimization technique, Differential Evolution (DE), to get a significant decrease in computer processing time required to obtain minimal chi-square (χ2) in four different regions of the parameter space. We demonstrate efficiency for the two-neutrinos case. For this, the χ2 function for neutrino oscillations is evaluated for grids with different density of points in standard allowed regions of the parameter space of Δm2 and tan2 θ using experimental and theoretical total event rates of chlorine (Homestake), Gallex+GNO, SAGE, Superkamiokande, and SNO detectors. We find that using DE in combination with the grid based method with small density of points can produce the results comparable with the one obtained using high density grid, in much lesser computation time.

R&D project for Gd-doped water Cherenkov detector

A dedicated test facility for a proposed Gadolinium doped water Cherenkov detector is being constructed in the Kamioka mine near the Super Kamiokande detector. Anti-electron neutrinos (v̄e) from inverse beta decay can be identified with high efficiency by taking advantage of Gd's large cross section on thermal neutron capture and by taking coincidence of a prompt positron and the delayed 8 MeV gamma cascades.

T2K results and future plans

We present the νμ → νe appearance and the νμ disappearance results, using a total of 1.43 × 1020 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 νμ → νe oscillations at the far detector Super-Kamiokande, leading to 0.03(0.04) < sin2 2θ13 < 0.28(0.34) for δCP = 0 and normal (inverted) hierarchy at 90% C.L. The νμ disappearance analysis excludes no oscillations at 4.3σ. At 90% C.L., the best fit values are sin2 2θ23 > 0.84 and 2.1 × 10−3 < Δm223(eV2) < 3.1 × 10−3. Finally, we present an overview of the T2K plans from 2011 onwards.

Recent neutrino oscillation results from T2K

The Tokai-to-Kamioka (T2K) experiment studies neutrino oscillations in a ~600 MeV muon neutrino beam sent at 295 km from the Japan Proton Accelerator Complex (J-PARC) to the Super Kamiokande (SK) detector in Kamioka. The primary goals of T2K are to search for the appearance of electron neutrinos at SK resulting from θ13 > 0 and to precisely measure θ23 and \(\Delta m^2_{32}\) via νμ disappearance. We report on T2K results obtained from neutrino data taken in 2010 and 2011.

The T2K Side Muon Range Detector (SMRD)

The T2K experiment is a long baseline neutrino oscillation experiment aiming to observe the appearance of νe in a νμ beam. The νμ beam is produced at the Japan Proton Accelerator Research Complex (J-PARC), observed with the 295km distant Super-Kamiokande Detector and monitored by a suite of near detectors at 280m from the proton target. The near detectors include a magnetized off-axis detector (ND280) which measures the unoscillated neutrino flux and neutrino cross-sections. The present paper describes the outermost component of ND280 which is a Side Muon Range Detector (SMRD) composed of scintillation counters with embedded wavelength shifting fibers and Multi-Pixel Photon Counter readout. The components, performance and response of the SMRD are presented.

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.

Search for Supernova Relic Neutrinos at Super-Kamiokande

The search for a supernova relic neutrino (SRN) signal at the Super-Kamiokande detector is limited by irreducible backgrounds. New work has improved our cuts to dramatically improve efficiency, lower energy threshold, and better control our backgrounds, and a new likelihood method has been developed for our limit extraction.

Indirect WIMP search for the Sun, Earth, and galactic center using upward going muon event in Super-Kamiokande

We present the result of indirect search for WIMPs using upward-going muon(upmu) events at the Super-Kamiokande detector. We searched upmu events for the direction of the Sun, Earth and galactic center(GC), and set the limits on upmu fluxes and WIMP-nucleon cross sections.

Detection of Supernova Neutrinos

Prospects for the future detection of supernova neutrinos are considered, with primary emphasis on water Cherenkov detectors. In particular, for the last seven years R&D on a potential upgrade to the Super–Kamiokande detector has been underway. Enriching Super–K with 100,000 kilograms of a water-soluble gadolinium compound – thereby enabling it to detect thermal neutrons and dramatically improving its performance, particularly as a detector for supernova neutrinos and reactor neutrinos – is discussed, as are some of the studies both ongoing and planned to help make this ambitious proposal a reality, including the construction of a large-scale, dedicated gadolinium testing facility in the Kamioka mine.

Supernova relic neutrinos at Super-Kamiokande

The diffuse supernova relic neutrino signal has never been observed. Currently the world's best upper flux limit comes from a search for inverse beta decay of anti-neutrinos in the Super-Kamiokande (SK) detector. A new SK study utilizes a novel method of spallation tagging, improved event selection, and an expanded data set to lower the analysis energy threshold and improve overall accuracy. Full results of this new study (including a combined upper flux limit of 2.8−3.1 ν̄e events cm−2 s−1 Eν > 17.3 MeV) are presented, as well as a short update on the research and development of using Gadolinium for neutron tagging.

T2K: New physics results

The T2K experiment is designed to probe the θ13 neutrino mixing parameter by looking for the appearance of νe in a pure νμ beam and to precisely measure atmospheric Δm2 and θ23 parameters. A neutrino beam produced at J-PARC, Japan, is aimed at 2.5° off-axis angle to the Super-Kamiokande far neutrino detector, 295km away. The narrow energy neutrino beam peaked at about 600 MeV is optimized to maximize the probability of oscillation at the atmospheric Δm2 scale. The neutrino beam is monitored by a complex of neutrino near detectors at 280m from the production target. T2K has successfully operated since January 2010. Data-taking has been presently paused due to the recent earthquake in Japan. Results on measurements of νe appearance and νμ disappearance are reported.

T2K: A LONG-BASELINE EXPERIMENT TO STUDY NEUTRINOS

T2K is the first of a new generation of long baseline neutrino oscillation experiments that will measure neutrino oscillations parameters. The experiment uses the J-PARC accelerator complex on the east cost of Japan to sent a neutrino beam to the Kamioka mine, located 295 km to the west. It consists of a dedicated beam-line, a near detector complex to characterize the beam and the well-known Super-Kamiokande detector to measure the oscillation signal. This paper describes the experimental setup, the results of the first measurement campaign as well as giving an outlook on the future potential of the experiment.

ND280 TPC contribution to recent T2K results

The T2K (Tokai to Kamioka) experiment is a long baseline neutrino oscillation experiment designed to measure the θ13 neutrino mixing parameter by looking for the appearance of νe in an almost pure νμ beam. The concurrent measurement of νμ disappearance allows refined measurements of the atmospheric Δm2 and of the θ23 mixing parameters.A neutrino beam is produced at the Japan Proton Accelerator Research Complex (J-PARC) in Tokai, Japan, and aimed at 2.5° off the direction of the Super-Kamiokande (SK) detector, 295 km away. The resulting narrow energy band neutrino beam at the SK location, peaked at about 600 MeV, is optimized to maximize the probability of oscillation at the atmospheric Δm2 scale, minimizing at the same time the backgrounds for νe searches. The neutrino beam is monitored before the oscillation by a Near Detector, ND280 located at J-PARC at 280 m from the target. A key element of the T2K Near Detector is composed of three large TPCs instrumented with MicroMEGAS detectors used to measure the neutrino spectrum and flavor composition before the oscillation. The charge and momentum of the charged particles crossing the TPCs are reconstructed, as well as the ionization energy loss in the TPCs allowing to distinguish electrons from muons.T2K has successfully operated since January 2010, and it has presently been paused due to the recent earthquake in Japan. Results on the search for νe appearance and of νμ disappearance have been presented in this talk, particularly stressing the inputs to these measurements from the TPCs.

T2K experiment: Status and first results

The long baseline neutrino oscillation experiment T2K, which uses a high intensity off-axis muon neutrino beam produced at JPARC, aims at a discovery of oscillation of muon neutrinos into electron neutrinos and measurement of the mixing angle θ13, a key parameter for further search for CP violation in the lepton sector. T2K is also designed to precisely measure the oscillation parameters Δm223 and θ23 in a disappearance oscillation mode. The major components of T2K include a neutrino beam line, muon monitors, a near detector complex ND280 located at 280 m from the proton interaction target, and the far detector Super-Kamiokande (295 km from the neutrino source), at a 2.5 degree off-axis angle from the beam. The measured neutrino spectrum at ND280 and measurements of the primary proton beam combined with the NA61 hadron production data will be used to predict the unoscillated spectrum at Super-Kamiokande. The oscillation analysis will be done by comparing the observed and predicted spectra at the far detector. The construction of the T2K neutrino beam line and the near neutrino detectors is completed. For the first data taking period with the neutrino beam, about 3 × 1019 30 GeV protons on target were accumulated. The design, performance, current status of the experiment and near future perspectives will be discussed. The results of the first physics run will be presented.

The T2K Near Detector Data Acquisition Systems

T2K is a second generation long-baseline experiment in Japan, designed to perform precision studies of neutrino oscillations. A neutrino beam originating at the J-PARC facility is sampled by two near detectors, approximately 280 m distant from the source and directed towards the Kamioka underground facility, 295 km distant, where the Super-Kamiokande water Cerenkov detector is situated. Both the on-axis (INGRID) and off-axis (ND280) near detectors employ the MIDAS framework for their data acquisition systems. Events are selected via a flexible hardware trigger, which allows mixed operating modes incorporating beam spill, cosmic and calibration triggers. Data are acquired from the front-end electronics over optical Gigabit Ethernet links by custom MIDAS front-end applications distributed over a cluster of Linux computers. Event fragments from all sub-detectors are merged and logged on a central backend processor and then copied to remote storage for long-term archival. The system is also designed to allow flexible partitioning of sub-detectors for standalone diagnostics and calibration. We present the design of the DAQ system and report on experience gathered during early operation of the near detectors.

Time projection chambers for the T2K near detectors

The T2K experiment is designed to study neutrino oscillation properties by directing a high intensity neutrino beam produced at J-PARC in Tokai, Japan, towards the large Super-Kamiokande detector located 295 km away, in Kamioka, Japan. The experiment includes a sophisticated near detector complex, 280 m downstream of the neutrino production target in order to measure the properties of the neutrino beam and to better understand neutrino interactions at the energy scale below a few GeV. A key element of the near detectors is the ND280 tracker, consisting of two active scintillator–bar target systems surrounded by three large time projection chambers (TPCs) for charged particle tracking. The data collected with the tracker are used to study charged current neutrino interaction rates and kinematics prior to oscillation, in order to reduce uncertainties in the oscillation measurements by the far detector. The tracker is surrounded by the former UA1/NOMAD dipole magnet and the TPCs measure the charges, momenta, and particle types of charged particles passing through them. Novel features of the TPC design include its rectangular box layout constructed from composite panels, the use of bulk micromegas detectors for gas amplification, electronics readout based on a new ASIC, and a photoelectron calibration system. This paper describes the design and construction of the TPCs, the micromegas modules, the readout electronics, the gas handling system, and shows the performance of the TPCs as deduced from measurements with particle beams, cosmic rays, and the calibration system.