T2K ND280 Research Articles

The Upgrade of the T2K ND280 Detector

The Tokai to Kamiokande (T2K) experiment is a long-baseline neutrino experiment taking data since 2010. The neutrino beam is detected on two sites, the near detector complex close to the neutrino production point, and Super-Kamiokande in a distance of 300 km. The ND280 detector is one of the near detectors and has the purpose to characterize the beam before oscillation as also the measurement of interaction cross sections. Both is crucial to reduce the systematic uncertainties. To improve the latter further, the T2K collaboration decided in 2016 an upgrade of ND280 which includes the installation of a novel scintillator tracker, two time projection chambers and a time of flight system. This upgrade, in combination of an increase of the neutrino beam power from currently 500 kW to 1.3 MW, will roughly increase the statistics by a factor 4 and reduce the systematic uncertainties from 6% to 4%. The new subdetectors are currently being assembled and will be installed in 2022. The upgraded ND280 will also serve as near detector of the next generation long-baseline neutrino oscillation experiment Hyper-Kamiokande.

Model-independent bounds on the nonoscillatory explanations of the MiniBooNE excess

We consider the non-oscillatory explanations of the low energy excess of events detected by MiniBooNE. We present a systematic search for phenomenological scenarios based on new physics which can produce the excess. We define scenarios as series of transitions and processes which connect interactions of accelerated protons in target with single shower events in the MiniBooNE detector. The key elements of the scenarios are production and decay of new light $\mathcal{O}(\text{keV}-100\,\text{MeV})$ particles (fermions or/and bosons). We find about $20$ scenarios with minimal possible number of new particles and interaction points. In practice, they are all reduced to few generic scenarios and in this way we develop the effective theory of the MiniBooNE excess. We consider tests of the scenarios with near or close detectors in neutrino experiments T2K ND280, NO$\nu$A, MINER$\nu$A as well as in NOMAD and PS191. The scenarios immediately connect the MiniBooNE excess and expected numbers of new physics events in these detectors. We compute the expected numbers of events as functions of lifetimes and masses of new particles and confront them with the corresponding experimental bounds. We indicate scenarios that are excluded or strongly disfavored by one or several experiments. Given our general approach, this work can also be regarded as the effective theory of new physics at accelerator based neutrino experiments, being relevant for future projects such as DUNE.

Search for neutral-current induced single photon production at the ND280 near detector in T2K

Neutrino neutral-current (NC) induced single photon production is a sub-leading order process for accelerator-based neutrino beam experiments including T2K. It is, however, an important process to understand because it is a background for electron (anti)neutrino appearance oscillation experiments. Here, we performed the first search of this process below 1 GeV using the fine-grained detector at the T2K ND280 off-axis near detector. By reconstructing single photon kinematics from electron–positron pairs, we achieved 95% pure gamma ray sample from protons-on-targets neutrino mode data. We do not find positive evidence of NC induced single photon production in this sample. We set the model-dependent upper limit on the cross-section for this process, at cm2 (90% C.L.) per nucleon, using the J-PARC off-axis neutrino beam with an average energy of GeV. This is the first limit on this process below 1 GeV which is important for current and future oscillation experiments looking for electron neutrino appearance oscillation signals.

Beam test results of 3D fine-grained scintillator detector prototype for a T2K ND280 neutrino active target

An upgrade of the long baseline neutrino experiment T2K ND280 near detector is under development with the goal to reduce systematic uncertainties in the prediction of number of events at the Super-Kamiokande far detector. The upgrade program includes the design and construction of a new neutrino target, a novel highly granular fully active scintillator detector with 3D WLS fiber readout. The ∼2 tonnes 192 × 192 × 56 cm3 detector will be assembled from 2 × 106 plastic scintillator cubes of 1 × 1 × 1 cm3 size. Each cube is read out by three orthogonal Kuraray Y11 WLS fibers threaded through the detector. A detector prototype made of 125 cubes was assembled and tested in a charged particle beam at CERN in October 2017. This paper presents results from studies of light yield, time resolution and optical cross-talk between the cubes.

Characterization of nuclear effects in muon-neutrino scattering on hydrocarbon with a measurement of final-state kinematics and correlations in charged-current pionless interactions at T2K

This paper reports measurements of final-state proton multiplicity, muon and proton kinematics, and their correlations in charged-current pionless neutrino interactions, measured by the T2K ND280 near detector in its plastic scintillator (C$_8$H$_8$) target. The data were taken between years 2010 and 2013, corresponding to approximately 6$\times10^{20}$ protons on target. Thanks to their exploration of the proton kinematics and of kinematic imbalances between the proton and muon kinematics, the results offer a novel probe of the nuclear-medium effects most pertinent to the (sub-)GeV neutrino-nucleus interactions that are used in accelerator-based long-baseline neutrino oscillation measurements. These results are compared to many neutrino-nucleus interaction models which all fail to describe at least part of the observed phase space. In case of events without a proton above a detection threshold in the final state, a fully consistent implementation of the local Fermi gas model with multinucleon interactions gives the best description of the data. In the case of at least one proton in the final state the spectral function model agrees well with the data, most notably when measuring the kinematic imbalance between the muon and the proton in the plane transverse to the incoming neutrino. A clear indication of existence of multinucleon interactions is observed. The effect of final-state interactions is also discussed.

Pion production in the T2K experiment

Background: Pion production gives information on the axial form factors of nucleon resonances. It also introduces a noticeable background to quasi-elastic measurements on nuclear targets and thus has a significant impact on precision studies of neutrino oscillation parameters. Purpose: To clarify neutrino-induced pion production on nucleons and nuclei. Method: The Giessen Boltzmann--Uehling--Uhlenbeck (GiBUU) model is used for the description of neutrino-nucleus reactions. Results: Theoretical results for differential cross sections for the T2K neutrino flux at the ND280 detector and integrated cross sections as a function of neutrino energy are given. Two sets of pion production data on elementary targets are used as inputs to obtain limits for pion production in neutrino-nucleus reactions. Conclusions: Pion production in the T2K ND280 detector can help to narrow down the uncertainties in the elementary pion production cross sections. It can also give valuable information on the nucleon-Delta axial form factor.

The T2K fine-grained detectors

The T2K Fine-Grained Detectors (FGDs) are segmented scintillator detectors that form part of the Tracker for T2K's ND280 near detector. The FGDs are composed of square scintillator bars glued together to form tracking planes. Each scintillator bar has a co-extruded titanium dioxide coating and a central hole that contains a wavelength-shifting fiber. These fibers carry scintillator light to Hamamatsu Multi-Pixel Photon Counters at one end of each fiber, with the far end of the fiber mirrored to increase the light yield. Photosensor readout is by waveform digitization. The FGDs serve as the primary target mass for neutrino interactions in the ND280's Tracker. The first FGD was fully assembled and partially instrumented in the fall of 2008. It was tested in the M11 secondary beamline at TRIUMF. Preliminary analysis of the beam test results indicate that the performance is as expected, and there is good agreement between measurements and GEANT4 based simulations.

The Fine Grained Detector for the T2K experiment

The T2K ND280 near detector will characterize the JPARC neutrino beam close to the production site, before any oscillation occurs. The Tracker section of this near detector is optimized for measurements of charged-current neutrino interactions and in conjunction with the surrounding electromagnetic calorimeter can also measure electromagnetic showers from neutral pion or single gamma production. The Fine Grained Detector, or FGD, provides an active target mass for these interactions. The FGD is composed of finely segmented plastic scintillators, which will allow for accurate tracking of short-ranged particles. Readout is accomplished using wavelength-shifting fibres coupled to multi-pixel photon counters and custom-built digitizing ASICs. The FGD also contains a water target, which will allow for the extraction of neutrino cross-sections on oxygen. This poster will focus on the expected capabilities of the FGD, as well as its ongoing construction and testing.

Characterization of a high resolution triple Gas Electron Multiplier (GEM) detector

The development of a Gas Electron Multiplier (GEM) readout as an option for the TPC of the near detector of the T2K neutrino experiment is presented. The low track density and the wide range in polar angle of particles produced by neutrino interactions drive the initial choice of relatively large squared pads (8 mm) for the performance study. The physics requirements [T2K ND280 Conceptual Design Report, http://dpnc.unige.ch:8080/nu/Members/nabgrall/t2kge/t2kge_doc/cdr.pdf ] are a momentum resolution better than 10 % at 1 GeV/c and a 3 σ dE/dx separation between muons and electrons. Micro-pattern Gas Detectors (MPGDs) such as GEMs or Micromegas show several beneficial features compared to the traditional Multi-Wire Proportional Chambers. They have been tested in the HARP TPC environment at CERN. Preliminary results form the GEM tests are reported here.

Test-bench for the Characterization of MicroMegas Modules for the T2K ND280 TPC

This proceeding reports on the design and construction of a test-bench to characterize the readout of the T2K ND280 TPC on a pad-per-pad basis. This procedure is an essential part of the ND280 calibration program as it will ensure that the criteria for the momentum and dE/dx resolutions are met.