The T2K Experiment

Simultaneous measurement of the muon neutrino charged-current cross section on oxygen and carbon without pions in the final state at T2K

May 11, 2021

This paper reports the first simultaneous measurement of the double differential muon neutrinocharged-current cross section on oxygen and carbon without pions in the final state as a function ofthe outgoing muon kinematics, made at the ND280 off-axis near detector of the T2K experiment. The ratio of the oxygen and carbon cross sections is also provided to help validate various models’ability to extrapolate between carbon and oxygen nuclear targets, as is required in T2K oscillationanalyses. The data are taken using a neutrino beam with an energy spectrum peaked at 0.6 GeV.The extracted measurement is compared with the prediction from different Monte Carlo neutrino-nucleus interaction event generators, showing particular model separation for very forward-goingmuons. Overall, of the models tested, the result is best described using Local Fermi Gas descriptionsof the nuclear ground state with RPA suppression.

arXiv preprint: https://arxiv.org/abs/2004.05434
DOI: https://doi.org/10.1103/PhysRevD.101.112004
Reference: Phys.Rev.D 101 (2020) 11, 112004

T2K measurements of muon neutrino and antineutrino disappearance using 3.13E21 protons on target

May 10, 2021

We report measurements by the T2K experiment of the parameters θ23 and Δm322, which govern the disappearance of muon neutrinos and antineutrinos in the three-flavor PMNS neutrino oscillation model at T2K’s neutrino energy and propagation distance. Utilizing the ability of the experiment to run with either a mainly neutrino or a mainly antineutrino beam, muon-like events from each beam mode are used to measure these parameters separately for neutrino and antineutrino oscillations. Data taken from 1.49×1021 protons on target (POT) in neutrino mode and 1.64×1021 POT in antineutrino mode are used. The best-fit values obtained by T2K were sin2(θ23)=0.51-0.07+0.06(0.43-0.05+0.21) and Δm322=2.47-0.09+0.08(2.50-0.13+0.18)×10-3 eV2/c4 for neutrinos (antineutrinos). No significant differences between the values of the parameters describing the disappearance of muon neutrinos and antineutrinos were observed. An analysis using an effective two-flavor neutrino oscillation model where the sine of the mixing angle is allowed to take nonphysical values larger than 1 is also performed to check the consistency of our data with the three-flavor model. Our data were found to be consistent with a physical value for the mixing angle.

arXiv preprint: https://arxiv.org/abs/2008.07921
DOI: https://doi.org/10.1103/PhysRevD.103.L011101
Reference: Phys.Rev.D 103 (2021) 1, L011101

First Measurement of the Charged Current antinumu Double Differential Cross Section on a Water Target without Pions in the final state

April 29, 2021

This paper reports the first differential measurement of the charged-current muon-antineutrino interaction cross section on water with no pions in the final state. The unfolded flux-averaged measurement using the T2K off-axis near detector is given in double-differential bins of $μ^{+}$ momentum and angle. The integrated cross section in a restricted phase space is $σ = (1.11 \pm 0.18) \times {10E}^{- 38} {cm}^{2}$ per water molecule. Comparisons with several nuclear models are also presented.

arXiv preprint: https://arxiv.org/abs/1908.10249
DOI: https://doi.org/10.1103/PhysRevD.102.012007
Reference: Phys.Rev.D 102 (2020) 1, 012007

Constraint on the matter–antimatter symmetry-violating phase in neutrino oscillations

April 16, 2020

Nature Nature 580, 339–344 (2020)

The charge-conjugation and parity-reversal (CP) symmetry of fundamental particles is a symmetry between matter and antimatter. Violation of this CP symmetry was first observed in 1964¹, and CP violation in the weak interactions of quarks was soon established². Sakharov proposed³ that CP violation is necessary to explain the observed imbalance of matter and antimatter abundance in the Universe. However, CP violation in quarks is too small to support this explanation. So far, CP violation has not been observed in non-quark elementary particle systems. It has been shown that CP violation in leptons could generate the matter–antimatter disparity through a process called leptogenesis⁴. Leptonic mixing, which appears in the standard model’s charged current interactions^5,6, provides a potential source of CP violation through a complex phase δ_CP, which is required by some theoretical models of leptogenesis^7,8,9. This CP violation can be measured in muon neutrino to electron neutrino oscillations and the corresponding antineutrino oscillations, which are experimentally accessible using accelerator-produced beams as established by the Tokai-to-Kamioka (T2K) and NOvA experiments^10,11. Until now, the value of δ_CPhas not been substantially constrained by neutrino oscillation experiments. Here we report a measurement using long-baseline neutrino and antineutrino oscillations observed by the T2K experiment that shows a large increase in the neutrino oscillation probability, excluding values of δ_CP that result in a large increase in the observed antineutrino oscillation probability at three standard deviations (3σ). The 3σ confidence interval for δ_CP, which is cyclic and repeats every 2π, is [−3.41, −0.03] for the so-called normal mass ordering and [−2.54, −0.32] for the inverted mass ordering. Our results indicate CP violation in leptons and our method enables sensitive searches for matter–antimatter asymmetry in neutrino oscillations using accelerator-produced neutrino beams. Future measurements with larger datasets will test whether leptonic CP violation is larger than the CP violation in quarks.

Data release: https://t2k-experiment.org/results/2020-constraint-cp-phase/
DOI: https://doi.org/10.1038/s41586-020-2177-0
arXiv preprint: https://arxiv.org/abs/1910.03887
Reference: Nature 580 (2020) 7803, 339-344

Measurement of the charged-current electron (anti-)neutrino inclusive cross-sections at the T2K off-axis near detector ND280

April 15, 2020

The electron (anti-)neutrino component of the T2K neutrino beam constitutes the largest background in the measurement of electron (anti-)neutrino appearance at the far detector. The electron neutrino scattering is measured directly with the T2K off-axis near detector, ND280. The selection of the electron (anti-)neutrino events in the plastic scintillator target from both neutrino and anti-neutrino mode beams is discussed in this paper. The flux integrated single differential charged-current inclusive electron (anti-)neutrino cross-sections, dσ/dp, and the total cross-sections in a limited phase-space in momentum and scattering angle (p > 300 MeV/c and θ ≤ 45◦ ) are measured using a binned maximum likelihood fit and compared to the neutrino Monte Carlo generator predictions, resulting in good agreement.

arXiv preprint: https://arxiv.org/abs/2002.11986
DOI: https://doi.org/10.1007/JHEP10(2020)114
Data release: https://t2k-experiment.org/results/2020_nuecc/
Reference: JHEP 10 (2020) 114

First combined measurement of the muon neutrino and antineutrino charged-current cross section without pions in the final state at T2K

February 21, 2020

This paper presents the first combined measurement of the double-differential muon neutrino and antineutrino charged-current cross sections with no pions in the final state on hydrocarbon at the off-axis near detector of the T2K experiment. The data analyzed in this work comprise 5.8×1020 and 6.3×1020 protons on target in neutrino and antineutrino mode respectively, at a beam energy peak of 0.6 GeV. Using the two measured cross sections, the sum, difference and asymmetry were calculated with the aim of better understanding the nuclear effects involved in such interactions. The extracted measurements have been compared with the prediction from different Monte Carlo generators and theoretical models showing that the difference between the two cross sections have interesting sensitivity to nuclear effects. Data release can found

arXiv preprint: https://arxiv.org/abs/2002.09323
Data release: https://t2k-experiment.org/results/first-combined-measurement-of-the-muon-neutrino-and-antineutrino-charged-current-cross-section-without-pions-in-the-final-state-at-t2k/
DOI: https://doi.org/10.1103/PhysRevD.101.112001
Reference: Phys.Rev.D 101 (2020) 11, 112001

Measurement of the muon neutrino charged-current single $\pi^+$ production on hydrocarbon using the T2K off-axis near detector ND280

February 11, 2020

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.

arXiv preprint: https://arxiv.org/abs/1909.03936
Data release: https://t2k-experiment.org/results/data-release-for-measurement-of-the-muon-neutrino-charged-current-single-pi-production-on-hydrocarbon-using-the-t2k-off-axis-near-detector-nd280/
DOI: https://doi.org/10.1103/PhysRevD.101.012007
Reference: Phys.Rev.D 101 (2020) 1, 012007

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

December 30, 2019

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]

arXiv preprint: https://arxiv.org/abs/1910.09439
DOI: https://doi.org/10.1103/PhysRevD.100.112009
Reference: Phys.Rev.D 100 (2019) 11, 112009

Measurement of the muon neutrino charged-current cross sections on water, hydrocarbon and iron, and their ratios, with the T2K on-axis detectors

September 26, 2019

We report a measurement of the flux-integrated

ν_{μ}

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

$σ_{C C}^{H_{2} O} = (0.840 \pm 0.010 (s t a t .)_{- 0.08}^{+ 0.10} (s y s t .)) \times 10^{- 38} {c m}^{2}$ /nucleon, $σ_{C C}^{C H} = (0.817 \pm 0.007 (s t a t .)_{- 0.08}^{+ 0.11} (s y s t .)) \times 10^{- 38} {c m}^{2}$ /nucleon, and $σ_{C C}^{F e} = (0.859 \pm 0.003 (s t a t .)_{- 0.10}^{+ 0.12} (s y s t .)) \times 10^{- 38} {c m}^{2}$ /nucleon,

respectively, for a restricted phase space of induced muons: $θ_{μ} < 45^{\circ}$ and $p_{μ} >$ 0.4 GeV/ $c$ in the laboratory frame. The measured cross section ratios are $σ_{C C}^{H_{2} O} / σ_{C C}^{C H} = 1.028 \pm 0.016 (s t a t .) \pm 0.053 (s y s t .)$ ⁠, $σ_{C C}^{F e} / σ_{C C}^{H_{2} O} = 1.023 \pm 0.012 (s t a t .) \pm 0.058 (s y s t .)$ ⁠, and $σ_{C C}^{F e} / σ_{C C}^{C H} = 1.049 \pm 0.010 (s t a t .) \pm 0.043 (s y s t .)$ ⁠. 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.

arXiv preprint: https://arxiv.org/abs/1904.09611
DOI: https://doi.org/10.1093/ptep/ptz070
Reference: PTEP 2019 (2019) 9, 093C02

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

June 20, 2019

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

arXiv preprint: https://arxiv.org/abs/1902.03848
DOI: https://doi.org/10.1088/1361-6471/ab227d
Reference: J.Phys.G 46 (2019) 8, 08LT01

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