Measurement of the muon neutrino inclusive charged-current cross section in the energy range of 1-3 GeV with the T2K INGRID detector
We report a measurement of the νμ-nucleus inclusive charged current cross section (=σcc) on iron using data from exposed to the J-PARC neutrino beam. The detector consists of 14 modules in total, which are spread over a range of off-axis angles from 0° to 1.1°. The variation in the neutrino energy spectrum as a function of the off-axis angle, combined with event topology information, is used to calculate this cross section as a function of neutrino energy. The cross section is measured to be σcc(1.1 GeV)=1.10±0.15 (10−38cm2/nucleon), σcc(2.0 GeV)=2.07±0.27 (10−38cm2/nucleon), and σcc(3.3 GeV)=2.29±0.45 (10−38cm2/nucleon), at energies of 1.1, 2.0, and 3.3 GeV, respectively. These results are consistent with the cross section calculated by the neutrino interaction generators currently used by T2K. More importantly, the method described here opens up a new way to determine the energy dependence of neutrino-nucleus cross sections.
Measurement of the Electron Neutrino Charged-current Interaction Rate on Water with the T2K ND280 pi-zero Detector
The first direct observation of the appearance of electron neutrinos in a muon neutrino beam through neutrino oscillation was recently reported by the T2K experiment. The main background in this observation was the presence of the electron neutrino component of the beam, which accounts for 1.2% of the beam below the 1.2 GeV threshold. This paper presents a measurement of the charged current interaction rate of the electron neutrino beam component using the large fiducial mass of the T2K π0 detector. The measured ratio of the observed beam interaction rate to the predicted rate in the detector with water targets filled is 0.89 ±0.08 (stat.) ±0.11 (sys.), and with the water targets emptied is 0.90 ±0.09 (stat.) ±0.13 (sys.). The ratio obtained for the interactions only on-water only an event subtraction method is 0.87 ±0.33 (stat.) ±0.21 (sys.). These are pioneering measurements of the νe interaction rate, particularly on water, which will become crucial in future CP-violation searches in the lepton sector.
Measurement of the νμ charged current quasi-elastic cross-section on carbon with the T2K on-axis neutrino beam
We report a measurement of the νμ charged current quasi-elastic cross-sections on carbon in the T2K on-axis neutrino beam. The measured charged current quasi-elastic cross-sections on carbon at mean neutrino energies of 1.94 GeV and 0.93 GeV are (11.95±0.19(stat.)+1.82−1.47(syst.))×10−39cm2/neutron and (10.64±0.37(stat.)+2.03−1.65(syst.))×10−39cm2/neutron, respectively. These results agree well with the predictions of neutrino interaction models. In addition, we investigated the effects of the nuclear model and the multi-nucleon interaction.
Measurements of neutrino oscillation in appearance and disappearance channels by the T2K experiment with 6.6E20 protons on target
We report on measurements of neutrino oscillation using data from the T2K long-baseline neutrino experiment collected between 2010 and 2013. In an analysis of muon neutrino disappearance alone, we find the following estimates and 68% confidence intervals for the two possible mass hierarchies:
Normal Hierarchy: sin2θ23=0.514+0.055−0.056 and Δm232=(2.51±0.10)×10−3 eV2/c4
Inverted Hierarchy: sin2θ23=0.511±0.055 and Δm232=(2.48±0.10)×10−3 eV2/c4
The analysis accounts for multi-nucleon mechanisms in neutrino interactions which were found to introduce negligible bias.
We describe our first analyses that combine measurements of muon neutrino disappearance and electron neutrino appearance to estimate four oscillation parameters and the mass hierarchy. Frequentist and Bayesian intervals are presented for combinations of these parameters, with and without including recent reactor measurements. At 90% confidence level and including reactor measurements, we exclude the region:
δCP=[0.15,0.83]π for normal hierarchy and δCP=[−0.08,1.09]π for inverted hierarchy.
The T2K and reactor data weakly favor the normal hierarchy with a Bayes Factor of 2.2. The most probable values and 68% 1D credible intervals for the other oscillation parameters, when reactor data are included, are:
sin2θ23=0.528+0.055−0.038 and |Δm232|=(2.51±0.11)×10−3 eV2/c4.
The Charged-Current Quasi-Elastic (CCQE) interaction, νl+n→l−+p, is the dominant CC process at Eν∼1 GeV and contributes to the signal in accelerator-based long-baseline neutrino oscillation experiments operating at intermediate neutrino energies. This paper reports a measurement by the T2K experiment of the νμ CCQE cross section on a carbon target with the off-axis detector based on the observed distribution of muon momentum (pμ) and angle with respect to the incident neutrino beam (θμ). The flux-integrated CCQE cross section was measured to be (0.83±0.12)×10−38 cm2 in good agreement with NEUT MC value of 0.88×10−38 cm2. The energy dependence of the CCQE cross section is also reported. The axial mass, MAQE, of the dipole axial form factor was extracted assuming the Smith-Moniz CCQE model with a relativistic Fermi gas nuclear model. Using the absolute (shape-only) pμcosθμ distribution, the effective MAQE parameter was measured to be 1.26+0.21−0.18 GeV/c2 (1.43+0.28−0.22 GeV/c2).
The T2K experiment has performed a search for νe disappearance due to sterile neutrinos using 5.9×1020 protons on target for a baseline of 280m in a neutrino beam peaked at about 500MeV. A sample of νe CC interactions in the off-axis near detector has been selected with a purity of 63% and an efficiency of 26%. The p-value for the null hypothesis is 0.085 and the excluded region at 95% CL is approximately sin22θee > 0.3 for Δm2eff > 7eV2/c4.
The observation of the recent electron neutrino appearance in a muon neutrino beam and the high-precision measurement of the mixing angle θ13 have led to a re-evaluation of the physics potential of the T2K long-baseline neutrino oscillation experiment. Sensitivities are explored for CP violation in neutrinos, non-maximal sin22θ23, the octant of θ23, and the mass hierarchy, in addition to the measurements of δCP, sin2θ23, and Δm232, for various combinations of neutrino-mode and anti-neutrino-mode data-taking.
With an exposure of 7.8×1021~protons-on-target, T2K can achieve 1-σ resolution of 0.050(0.054) on sin2θ23 and 0.040(0.045)×10−3 eV2 on Δm232 for 100%(50%) neutrino beam mode running assuming sin2θ23=0.5 and Δm232=2.4×10−3 eV2. T2K will have sensitivity to the CP-violating phase δCP at 90% C.L. or better over a significant range. For example, if sin22θ23 is maximal (i.e θ23=45°) the range is −115°<δCP<−60° for normal hierarchy and +50°<δCP<+130° for inverted hierarchy. When T2K data is combined with data from the NOνA experiment, the region of oscillation parameter space where there is sensitivity to observe a non-zero δCP is substantially increased compared to if each experiment is analyzed alone.
Measurement of the inclusive νμ charged current cross section on iron and hydrocarbon in the T2K on-axis neutrino beam
We report a measurement of the νμ inclusive charged current cross sections on iron and hydrocarbon in the T2K on-axis neutrino beam. The measured inclusive charged current cross sections on iron and hydrocarbon averaged over the T2K on-axis flux with a mean neutrino energy of 1.51 GeV are (1.444±0.002(stat.)+0.189−0.157(syst.))×10−38cm2/nucleon, and (1.379±0.009(stat.)+0.178−0.147(syst.))×10−38cm2/nucleon, respectively, and their cross section ratio is 1.047±0.007(stat.)±0.035(syst.). These results agree well with the predictions of neutrino interaction model and thus demonstrate the correct treatment of the nuclear effect for iron and hydrocarbon targets in the model.
Measurement of the Inclusive Electron Neutrino Charged Current Cross Section on Carbon with the T2K Near Detector
The T2K off-axis near detector, ND280, is used to make the first differential cross-section measurements of electron neutrino charged current interactions at energies ∼1 GeV as a function of electron momentum, electron scattering angle and four-momentum transfer of the interaction. The total flux-averaged νe charged current cross-section on carbon is measured to be <σ>ϕ = 1.11±0.09(stat) ±0.18(syst)×10-38 cm2/nucleon.
The differential and total cross-section measurements agree with the predictions of two leading neutrino interaction generators, NEUT and GENIE. The NEUT prediction is 1.23×10-38 cm2/nucleon and the GENIE prediction is 1.08×10-38 cm2/nucleon. The total νe charged current cross-section result is also in agreement with data from the Gargamelle experiment.
Measurement of the neutrino-oxygen neutral-current interaction cross section by observing nuclear deexcitation γ rays
We report the first measurement of the neutrino-oxygen neutral-current quasielastic (NCQE) cross section. It is obtained by observing nuclear deexcitation γ-rays which follow neutrino-oxygen interactions at the Super-Kamiokande water Cherenkov detector. We use T2K data corresponding to 3.01 × 1020 protons on target. By selecting only events during the T2K beam window and with well-reconstructed vertices in the fiducial volume, the large background rate from natural radioactivity is dramatically reduced. We observe 43 events in the 4-30 MeV reconstructed energy window, compared with an expectation of 51.0, which includes an estimated 16.2 background events. The background is primarily nonquasielastic neutral-current interactions and has only 1.2 events from natural radioactivity. The flux-averaged NCQE cross section we measure is 1.55 × 10-38 cm2 with a 68% confidence interval of (1.22, 2.20) × 10-38 cm2 at a median neutrino energy of 630 MeV, compared with the theoretical prediction of 2.01 × 10-38 cm2.