Νe Appearance Research Articles

Experimental Prospect

This is the first conference of this series the three of the lepton mixing angles are known. The non-zero value of the third mixing angle (θ13) has been reported by νe appearance in accelerator νμ beam and by ν¯e disappearance in reactor experiments. The observation of the νe appearance in νμ beam is the first clear evidence of the flavor oscillations. The results also show that neutrino oscillations phenomena can be described by three-generation scheme to the first approximation, where mixing of neutrinos can be described by three angles and one complex phase. There are two main issues to be investigated by neutrino oscillation experiments. One is the study of CP violation in lepton secto. Namely, the measurement of CP violating complex phase δCP and the studies of the nature of CP violation phenomena in lepton sector. The other is search for neutrinos beyond three generations. There are indications of the existence of additional neutrinos, which should be tested by definitive experiments. The number of neutrino species has important implications not only in particle physics but also in physics of early Universe. Also many fundamental natures of neutrinos remain to be studied, such as absolute values of masses, nature of the particle (Majorana or Dirac particle). This article concentrates on the future experimental prospects on the study of neutrino physics by means of neutrino oscillation.

Status of sterile neutrino oscillations

There are several independent hints for neutrino oscillations with a mass-squared difference at the eV2 scale. If confirmed, this would imply the existence of sterile neutrinos. I discuss the present status of the hints for νe disappearance from reactor experiments and Gallium source experiments, as well as from the LSND and MiniBooNE νμ→νe appearance searches. A consistent interpretation of the global data in terms of neutrino oscillations is challenged by the non-observation of a positive signal in νμ disappearance experiments. There is a strong tension in the global data, irrespective of the number of eV-scale neutrino states.

Test of Lorentz and CPT violation with short baseline neutrino oscillation excesses

The sidereal time dependence of MiniBooNE νe and ν¯e appearance data is analyzed to search for evidence of Lorentz and CPT violation. An unbinned Kolmogorov–Smirnov (K–S) test shows both the νe and ν¯e appearance data are compatible with the null sidereal variation hypothesis to more than 5%. Using an unbinned likelihood fit with a Lorentz-violating oscillation model derived from the Standard Model Extension (SME) to describe any excess events over background, we find that the νe appearance data prefer a sidereal time-independent solution, and the ν¯e appearance data slightly prefer a sidereal time-dependent solution. Limits of order 10−20 GeV are placed on combinations of SME coefficients. These limits give the best limits on certain SME coefficients for νμ→νe and ν¯μ→ν¯e oscillations. The fit values and limits of combinations of SME coefficients are provided.

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.

The NOvA Experiment

NOvA is an off-axis long-baseline neutrino experiment, looking for νe appearance in an upgraded NuMI beam of νμ to search for θ13 acting in subdominant νμ→νe transitions. As an appearance experiment, NOvA might also be sensitive to CP-violating δ and the neutrino mass hierarchy. To maximize sensitivity to the resulting ∼GeV electromagnetic showers, the 14 kton Far Detector is “totally active”, comprised of liquid scintillator contained in 15.7 m long extruded PVC cells, with the scintillation light piped out in wavelength shifting fibers then digitized by avalanche photodiodes. Civil construction at the far detector site is underway, and the smaller near detector is being assembled at Fermilab.

T2K: Electron Neutrino Analysis At Near Detector ND280

Starting with a νμ beam T2K will search for νe appearance in the Far Detector (Super-Kamiokande) and aims to produce the first measurement of the neutrino mixing angle θ13. Beam contamination of νe will be one of the main background components. The Near Detector, ND280, is optimized for measuring the νe contamination through the reconstruction of νe interactions. The reconstruction of electron neutrinos at Near Detector and the method to estimate the νe beam contamination at Super-Kamiokande will be reviewed.

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.

The T2K ND280 off-axis pi–zero detector

The pi–zero detector (PØD) is one of the subdetectors that makes up the off-axis near detector for the Tokai-to-Kamioka (T2K) long baseline neutrino experiment. The primary goal for the PØD is to measure the relevant cross-sections for neutrino interactions that generate π0's, especially the cross-section for neutral current π0 interactions, which are one of the dominant sources of background to the νμ→νe appearance signal in T2K. The PØD is composed of layers of plastic scintillator alternating with water bags and brass sheets or lead sheets and is one of the first detectors to use Multi-Pixel Photon Counters (MPPCs) on a large scale.

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.

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.

Initial Performance from the NOνA Surface Prototype Detector

Abstract NOνA, the NuMI Off-Axis νe Appearance experiment, will study νμ → νe oscillations characterized by the mixing angle θ13. Provided θ13 is large enough, NOνA may ultimately determine the ordering of the neutrino masses and measure CP violation in neutrino oscillations. A complementary pair of detectors will be constructed ∼14 mrad off beam axis to optimize the energy profile of the neutrinos. This system consists of a surface based 14 kTon liquid scintillatior tracking volume located 810 km from the main injector source (NuMI) in Ash River, Minnesota and a smaller underground 222 Ton near detector at the Fermilab. The first neutrino signals at the Ash River Site are expected prior to the 2012 accelerator shutdown. In the meantime, a near detector surface prototype has been completed and neutrinos from two Fermilab sources have been observed using the same highly segmented PVC and liquid scintillator detector system that will be deployed in the full scale experiment. Design and initial performance characteristics of this prototype system are being fed back into the design for the full NOνA program.

NOvA Data Acquisition System

Abstract The NOνA (NuMI Off-Axis νe Appearance) experiment is a long-baseline neutrino experiment using the NuMI main injector neutrino beam at Fermilab and is designed to search for νμ (oνμ) to νe (oνe) oscillations. The experiment will consist of two detectors; both positioned 14 mrad off the beam axis: a 220 ton Near Detector to be located in an underground cavern at Fermilab and a 14 kton Far Detector to be located in Ash River, MN, 810 km from the beam source. In addition, a prototype Near Detector is currently in operation in a surface building at Fermilab. The detectors have similar design, and consist of planes of PVC extrusion cells containing liquid scintillator and wavelength shifting fibers. The fiber ends are readout by Avalanche Photodiodes (APDs). The primary task for the Data Acquisition (DAQ) system is to concentrate the data from the large number of APD channels (360000 channels at the Far Detector, 16000 channels at the Near Detector), buffer this data long enough to apply an online trigger, and record the selected data. The concentration of data is accomplished through the use of a custom hardware component Data Concentrator Module (DCM). The intermediate buffering of the data is accomplished through a computing buffer farm, in which each node runs software to apply an online trigger to a time slice of data received from the DCMs. Data correlated with the beam spill time as well as random data samples for calibration purposes and events with interesting topology may be selected by the online trigger. In addition to those components involved in managing the data flow, the DAQ system consists of components for control, configuration, monitoring and timing. The design of the DAQ system, with emphasis on the DAQ software, will be discussed as will experience with its deployment on the prototype Near Detector.

Improved Search for Muon-Neutrino to Electron-Neutrino Oscillations in MINOS

We report the results of a search for ν(e) appearance in a ν(μ) beam in the MINOS long-baseline neutrino experiment. With an improved analysis and an increased exposure of 8.2 × 10(20) protons on the NuMI target at Fermilab, we find that 2 sin(2) (θ(23))sin(2)(2θ(13))<0.12(0.20) at 90% confidence level for δ = 0 and the normal (inverted) neutrino mass hierarchy, with a best-fit of 2sin(2) (θ(23))sin(2)(2θ(13)) = 0.041(-0.031)(+0.047) (0.079(-0.053) (+0.071)). The θ(13) = 0 hypothesis is disfavored by the MINOS data at the 89% confidence level.

Indication of Electron Neutrino Appearance from an Accelerator-Produced Off-Axis Muon Neutrino Beam

The T2K experiment observes indications of ν(μ) → ν(e) appearance in data accumulated with 1.43×10(20) protons on target. Six events pass all selection criteria at the far detector. In a three-flavor neutrino oscillation scenario with |Δm(23)(2)| = 2.4×10(-3) eV(2), sin(2)2θ(23) = 1 and sin(2)2θ(13) = 0, the expected number of such events is 1.5±0.3(syst). Under this hypothesis, the probability to observe six or more candidate events is 7×10(-3), equivalent to 2.5σ significance. At 90% C.L., the data are consistent with 0.03(0.04) < sin(2)2θ(13) < 0.28(0.34) for δ(CP) = 0 and a normal (inverted) hierarchy.

SEARCH FOR νμ→νe OSCILLATIONS IN THE MINOS EXPERIMENT

The MINOS experiment uses the NuMI νμ beam to make precise measurements of neutrino flavor oscillations in the "atmospheric" neutrino sector. MINOS can also probe the yet-unknown neutrino mixing angle θ13 by searching for a νe appearance signal in the νμ beam. This paper reviews the techniques developed for the first νe appearance analysis in MINOS.

A BRIEF REVIEW OF MINOS NEUTRINO OSCILLATION RESULTS

The MINOS long-baseline experiment is using the NuMI neutrino beam to make precise measurements of neutrino flavor oscillations in the "atmospheric" neutrino sector. MINOS observes the νμ disappearance oscillations seen in atmospheric neutrinos, tests possible disappearance to sterile ν by measuring the neutral current flux, and extends our reach towards the so far unseen θ13 by looking for νe appearance in this νμ beam. The magnetized MINOS detectors also allow tests of CPT conservation by discriminating between neutrinos and anti-neutrinos on an event-by-event basis. The intense, well-understood NuMI neutrino beam created at Fermilab is observed 735 km away at the Soudan Mine in Northeast Minnesota. High-statistics studies of the neutrino interactions themselves and the cosmic rays seen by the MINOS detectors have also been made. MINOS started taking beam data in May 2005 and is now nearing the end of its five-year run. This paper reviews results published based on the first several years of data.

Current MINOS neutrino oscillation results

The MINOS experiment is now making precise measurements of the νμ disappearance oscillations seen in atmospheric neutrinos, tests possible disappearance to sterile ν by measuring the neutral current flux, and has extended our reach towards the so far unseen θ13 by looking for νe appearance in the νμ beam. It does so by using the intense, well-understood NuMI neutrino beam created at Fermilab and observing it 735km away at the Soudan Mine in Northeast Minnesota. High-statistics studies of the neutrino interactions themselves and the cosmic rays seen by the MINOS detectors have also been made. Results from MINOS' first three years of operations will be presented.

LIQUID ARGON DETECTORS FOR NEUTRINO PHYSICS

In this paper we give a short review of liquid argon detectors for neutrino physics. We will first introduce noble liquid detectors with particular emphasis on liquid argon and detectors of the time projection chamber variety, and we will explain why liquid argon detectors are good for neutrino physics, in particular the measurement of the mixing angle θ13, CP-violating phase δ CP and determination of the mass hierarchy through νe appearance on a νμ beam. We will stress what we consider the main achievements and the main challenges facing liquid argon detectors for neutrino physics.

New results from the MINOS Experiment

In this paper we present the latest results from the MINOS Experiment. This includes a new measurement of the oscillation parameters (|Δm232|, sin2(2θ23)) based on 3.36 × 1020 protons-on-target of data and a first analysis of neutral current events in the Far Detector. The prospects for νe appearance measurements in MINOS are also discussed.

MiniBooNE oscillation results and implications

The MiniBooNE Collaboration has reported first results of a search for νe appearance in a νμ beam. With two largely independent analyses, no significant excess was observed of events above background for reconstructed neutrino energies above 475 MeV and the data are consistent with no oscillations within a two neutrino appearance-only oscillation model. An excess of events (186 ± 27 ± 33 events) is observed below the 475 MeV oscillation search cut. This low-energy excess cannot be explained by a two-neutrino oscillation model. This report presents an overview of the MiniBooNE first result and decribes some initial cross checks and investigations associated with the low energy excess.