Measurement of the muon neutrino charged-current single $\pi^+$ production on hydrocarbon using the T2K off-axis near detector ND280
We report the measurements of the single and double differential cross section of muon neutrino charged-current interactions on carbon with a single positively charged pion in the final state at the T2K off-axis near detector using 5.56 × 10^20 protons on target. The analysis uses data control samples for the background subtraction and the cross section signal, defined as a single negatively charged muon and a single positively charged pion exiting from the target nucleus, is extracted using an unfolding method. The model-dependent cross section, integrated over the T2K off-axis neutrino beam spectrum peaking at 0.6 GeV, is measured to be σ = (11.76 +- 0.44 (stat) +- 2.39 (syst) × 10^-40 cm^2/nucleon. Various differential cross sections are measured, including the first measurement of the Adler angles for single charged pion production in neutrino interactions with heavy nuclei target.
Measurement of neutrino- and antineutrino-oxygen neutral-current quasielastic-like interaction cross sections by detecting nuclear de-excitation gamma-rays at the far detector with Run1-9 FHC and RHC data
Neutrino- and antineutrino-oxygen neutral-current quasielasticlike interactions are measured at Super- Kamiokande using nuclear deexcitation γ rays to identify signal-like interactions in data from a 14.94(16.35) × 10^20 protons-on-target exposure of the T2K neutrino (antineutrino) beam. The measured flux-averaged cross sections on oxygen nuclei are 1.70 +- 0.17(stat)+-0.51(syst) × 10^-38 cm2/oxygen with a flux flux-averaged energy of 0.68 GeV, for neutrinos and antineutrinos, respectively. These results are the most precise to date, and the antineutrino result is the first cross section measurement of this channel. They are compared with various theoretical predictions. The impact on evaluation of backgrounds to searches for supernova relic neutrinos at present and future water Cherenkov detectors is also discussed.
Published in Phys.Rev. D100 (2019) no.11, 112009
DOI: 10.1103/PhysRevD.100.112009
e-Print: arXiv:1910.09439 [hep-ex]
Measurement of the muon neutrino charged-current cross sections on water, hydrocarbon and iron, and their ratios, with the T2K on-axis detectors
We report a measurement of the flux-integrated νμ charged-current cross sections on water, hydrocarbon, and iron in the T2K on-axis neutrino beam with a mean neutrino energy of 1.5 GeV. The measured cross sections on water, hydrocarbon, and iron are
σ^{H2O}_{CC}=(0.840±0.010(stat.)+0.10−0.08(syst.))×10−38cm2/nucleon, σ^{CH}_{CC}=(0.817±0.007(stat.)+0.11−0.08(syst.))×10−38cm2/nucleon, and σ^{Fe}_CC=(0.859±0.003(stat.)+0.12−0.10(syst.))×10−38cm2/nucleon,
respectively, for a restricted phase space of induced muons: θμ<45∘ and pμ>0.4 GeV/c in the laboratory frame. The measured cross section ratios are σ^{H2O}_{CC}/σ^{CH}_CC=1.028±0.016(stat.)±0.053(syst.), σ^{Fe}_{CC}/σ^{H2O}_{CC}=1.023±0.012(stat.)±0.058(syst.), and σ^{Fe}_{CC}/σ^{CH}_{CC}=1.049±0.010(stat.)±0.043(syst.). These results, with an unprecedented precision for the measurements of neutrino cross sections on water in the studied energy region, show good agreement with the current neutrino interaction models used in the T2K oscillation analyses.
Search for neutral-current induced single photon production at the ND280 near detector in T2K
Neutrino neutral-current 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 5.738×10^{20} protons-on-targets neutrino mode data. We do not find positive evidence of neutral current induced single photon production in this sample. We set the model-dependent upper limit on the cross-section for this process, at 0.114×10^{−38} cm^2 (90\% C.L.) per nucleon, using the J-PARC off-axis neutrino beam with an average energy of ⟨Eν⟩∼0.6 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.
DOI: https://dx.doi.org/10.1088/1361-6471/ab227d
ArXiv: https://arxiv.org/abs/1902.03848
Physics World: https://physicsworld.com/a/t2k-searches-for-single-gamma-rays-from-neutrino-interactions
Search for light sterile neutrinos with the T2K far detector Super-Kamiokande at a baseline of 295 km
We perform a search for light sterile neutrinos using the data from the T2K far detector at a baseline of 295 km, with an exposure of 14.7(7.6)×1020 protons on target in neutrino (antineutrino) mode. A selection of neutral-current interaction samples is also used to enhance the sensitivity to sterile mixing. No evidence of sterile neutrino mixing in the 3+1 model was found from a simultaneous fit to the charged-current muon, electron and neutral-current neutrino samples. We set the most stringent limit on the sterile oscillation amplitude sin^2\theta_{24} for the sterile neutrino mass splitting \Delta m^2_{41}<3\times 10^{-3} eV^2/c^4.
link to publication : https://journals.aps.org/prd/abstract/10.1103/PhysRevD.99.071103
There is a data release for this paper here
Search for heavy neutrinos with ND280
This paper (Phys. Rev. D 100, 052006 (2019)) reports on the search for heavy neutrinos with masses in the range 140 < MN <493 MeV/c2 using the off-axis near detector ND280 of the T2K experiment. These particles can be produced from kaon decays in the standard neutrino beam and then subsequently decay in ND280. The decay modes under consideration are N→l_α π and N→l_α l_β ν (α,β=e,μ). A search for such events has been made using the Time Projection Chambers of ND280, where the background has been reduced to less that 2 events in the current dataset in all channels. No excess has been observed in the signal region. A combined Bayesian statistical approach has been applied to extract upper limits on the mixing elements of heavy neutrinos to electron-, muon- and tau- flavoured currents (Ue2, Uμ2, Uτ2) as a function of the heavy neutrino mass, e.g. Ue2 < 10^(−9) at 90% C.L. for a mass of 390MeV/c2. These constraints are competitive with previous experiments.
There is a data release for this paper here.
Search for CP violation in Neutrino and Antineutrino Oscillations by the T2K experiment with 2.2E21 protons on target
The T2K experiment measures muon neutrino disappearance and electron neutrino appearance in accelerator-produced neutrino and antineutrino beams. With an exposure of 14.7(7.6)×1020 protons on target in (anti)neutrino mode, 89 electron neutrino candidates and 7 electron antineutrino candidates were observed while 67.5 and9.0 are expected for δCP=0 and normal mass ordering. The obtained 2σ confidence interval for the CP violating phase, δCP , does not include the CP-conserving cases (δCP=0, π). The best-fit values of other parameters are sin^2_θ23 = 0.526+0.032 −0.036 and ∆m^2_32 = 2.463 ± 0.065E−3 eV2/c4 .
Published in Phys.Rev.Lett. 121 (2018) no.17, 171802
DOI: 10.1103/PhysRevLett.121.171802
Measurement of muon- antineutrino and neutrino charged-current inclusive cross sections and their ratio with the T2K off-axis near detector
We report a measurement of cross section σ(νμ+nucleus→μ-+X) and the first measurements of the cross section σ(ν¯μ+nucleus→μ++X) and their ratio R(σ(ν¯)σ(ν)) at (anti) neutrino energies below 1.5 GeV. We determine the single momentum bin cross section measurements, averaged over the T2K ν¯/ν-flux, for the detector target material (mainly carbon, oxygen, hydrogen and copper) with phase space restricted laboratory frame kinematics of θμ<32° and pμ>500 MeV/c. The results are σ(ν¯)=(0.900±0.029(stat)±0.088(syst))×10-39 and σ(ν)=(2.41±0.022(stat)±0.231(syst))×10-39 in units of cm2/nucleon and R(σ(ν¯)σ(ν))=0.373±0.012(stat)±0.015(syst).
Measurement of inclusive double-differential νμ charged-current cross section with improved acceptance
We report a measurement of the flux-integrated cross section for inclusive muon neutrino charged-current interactions on carbon. The double differential measurements are given as function of the muon momentum and angle. Relative to our previous publication on this topic, these results have an increased angular acceptance and higher statistics. The data sample presented here is 5.7 × 10^20 protons-on-target. The total flux-integrated cross section is measured to be (6.950 ± 0.662) × 10^−39 cm^2/nucleon and is consistent with our simulation.
Characterisation of nuclear effects in neutrino scattering with a measurement of final-state kinematics (2018)
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 (C8H8) target. The data were taken between years 2010 and 2013, corresponding to approximately 6×10^20 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.
