Measurement of Neutrino Interactions and Three Flavor Neutrino Oscillations in the T2K Experiment

Abstract

T2K is a long-baseline neutrino oscillation experiment. Muon neutrinos are generated by a proton beam, and are detected by near and far neutrino detectors. For a precise measurement of the neutrino oscillation, an accurate understanding of the neutrino beam and the neutrino interaction is essential. Therefore, the measurement of the neutrino beam properties and the neutrino interaction cross sections plays an important role in T2K.Neutrino event rate, neutrino beam direction and neutrino beam width were measured with the near neutrino detector called INGRID. They were confirmed to be stable within the physics requirements and agree well with the T2K neutrino flux predictions. In addition, this measurement reduced the neutrino flux uncertainty from the neutrino beam direction which was originally 7.0% at 1 GeV to 2.5%.The neutrino interaction cross sections in a few GeV region were also measured with INGRID. The charged current inclusive cross sections on iron and hydrocarbon and their cross section ratio were measured to be σ Fe CC = (1.444 ± 0.002(stat.) +0.189 −0.157 (syst.)) × 10 −38 cm 2 /nucleon, σ CH CC = (1.379 ± 0.009(stat.) +0.178 −0.147 (syst.)) × 10 −38 cm 2 /nucleon, and σ Fe CC /σ CH CC = 1.047 ± 0.007(stat.) ± 0.035(syst.), at a mean neutrino energy of 1.51 GeV. They agree well with the predicted values by the neutrino interaction models used in T2K. Since the neutrino cross section in a few GeV region is sensitive to the nuclear effect of the target material, this result demonstrates that the nuclear effect is well understood and correctly treated in the models on the 3% level. The measured charged current quasi-elastic cross sections are also consistent with the neutrino interaction models. However, the measured charged current coherent pion production cross section is significantly smaller than the prediction by the original Rein-Sehgal model that is widely used in neutrino experiments. Therefore, we reveal that the original Rein-Sehgal model breaks down in a few GeV region. Since this inconsistency is within the originally assigned uncertainty, all the cross section results from INGRID demonstrate the validity of the neutrino interaction models and their uncertainties in T2K.Finally, a neutrino oscillation analysis was performed using the neutrino flux prediction, the neutrino interaction models and the beam data in the near and far detectors. We performed a joint three-flavor neutrino oscillation analysis of the electron neutrino appearance and the muon neutrino disappearance for the first time. As the result, sin 2 2θ 13 for normal (inverted) neutrino mass hierarchy was determined to be sin 2 2θ 13 = 0.165 +0.044 −0.073 (0.191 +0.056 −0.084 ). The electron neutrino appearance in a muon neutrino beam was observed because the appearance signal corresponds to a significance of 7.3σ. We also obtained sin 2 θ 23 = 0.524 ± 0.058 (0.524 +0.058 −0.057 ) and ∆m 2 32 = (2.50 ± 0.11) × 10 −3 eV 2 (∆m 2 13 = (2.48 ± 0.11) × 10 −3 eV 2 ) for the normal (inverted) hierarchy. The measurement of sin 2 θ 23 ...

Neutrino–nucleus cross sections for oscillation experiments

“…Furthermore, the T2K results have been compared not only to the standard Rein-Sehgal model but also to the model of Alvarez-Ruso et al [349,350], representing the first example of microscopic models for the coherent pion production implemented in the Monte Carlo. Initial results of the T2K on-axis detector are also consistent with nonzero coherent pion production [138]. To summarize, from no positive results on this CC coherent channel, the field evolved so quickly to the situation of the high precision measurement!…”

“…The on-axis INGRID (Interactive Neutrino GRID) detector [135] is the iron-scintillator sandwich tracker designed to measure the neutrino-beam profile. INGRID itself can provide interesting data [136,137], but the fully active 'proton module' (full scintillator tracker) installed later can measure multi-track events and provide further high-precision data [138,139]. The offaxis ND280 detector consists of five sub-detectors: pi-zero detector (P0D) [140], fine-grained detector (FGD) [141], gas argon TPC [142], electromagnetic calorimeter (ECal) [143], and side muon range detector (SMRD) [144].…”

The Accelerator Neutrino-Neutron Interaction Experiment

“…MRD clusters were then given to an MRD track reconstruction algorithm, which estimates particle track parameters including MRD entry point, length, and energy loss. The MRD track reconstruction algorithm is based on a cellular automation algorithm used in the SciBooNE SciBar detector [200,201,202,203].…”

On the design of experiments based on plastic scintillators using GEANT4 simulations

“…3. Emission spectrum of the doped plastic scintillator (taken from [29]). shift) as possible to avoid self absorption of emitted photons.…”