T2K Collaboration(Abe, K. et al), Cervera-Villanueva, A., Escudero, L., Gomez-Cadenas, J. J., Izmaylov, A., Monfregola, L., et al. (2013). Measurement of Neutrino Oscillation Parameters from Muon Neutrino Disappearance with an Off-Axis Beam. Phys. Rev. Lett., 111(21), 211803–7pp.
Abstract: The T2K Collaboration reports a precision measurement of muon neutrino disappearance with an off-axis neutrino beam with a peak energy of 0.6 GeV. Near detector measurements are used to constrain the neutrino flux and cross section parameters. The Super-Kamiokande far detector, which is 295 km downstream of the neutrino production target, collected data corresponding to 3.01 x 10(20) protons on target. In the absence of neutrino oscillations, 205 +/- 17 (syst) events are expected to be detected while only 58 muon neutrino event candidates are observed. A fit to the neutrino rate and energy spectrum, assuming three neutrino flavors and normal mass hierarchy yields a best-fit mixing angle sin(2) (theta(23)) = 0.514 +/- 0.082 and mass splitting vertical bar Delta m(32)(2)vertical bar = 2.44(-0.15)(+0.17) x 10(-3) eV(2)/c(4). Our result corresponds to the maximal oscillation disappearance probability.
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T2K Collaboration(Abe, K. et al), Cervera-Villanueva, A., Escudero, L., Gomez-Cadenas, J. J., Izmaylov, A., Monfregola, L., et al. (2014). Observation of Electron Neutrino Appearance in a Muon Neutrino Beam. Phys. Rev. Lett., 112(6), 061802–8pp.
Abstract: The T2K experiment has observed electron neutrino appearance in a muon neutrino beam produced 295 km from the Super-Kamiokande detector with a peak energy of 0.6 GeV. A total of 28 electron neutrino events were detected with an energy distribution consistent with an appearance signal, corresponding to a significance of 7.3 sigma when compared to 4.92 +/- 0.55 expected background events. In the Pontecorvo-Maki-Nakagawa-Sakata mixing model, the electron neutrino appearance signal depends on several parameters including three mixing angles theta(12), theta(23), theta(13), a mass difference vertical bar Delta m(32)(2)vertical bar and a CP violating phase delta(CP). In this neutrino oscillation scenario, assuming vertical bar Delta m(32)(2)vertical bar = 2.4 x 10(-3) eV(2), sin theta(2)(23) = 0.5, and vertical bar Delta m(32)(2)vertical bar > 0 (vertical bar Delta m(32)(2)vertical bar < 0), a best- fit value of sin2 theta(2)(13) = 0.140(- 0.032)(+0.038) (0.170(-0.037)(+0.045)) is obtained at delta(CP) = 0. When combining the result with the current best knowledge of oscillation parameters including the world average value of theta(13) from reactor experiments, some values of delta(CP) are disfavored at the 90% C. L.
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T2K Collaboration(Abe, K. et al), Cervera-Villanueva, A., Escudero, L., Gomez-Cadenas, J. J., Izmaylov, A., Monfregola, L., et al. (2014). Measurement of the intrinsic electron neutrino component in the T2K neutrino beam with the ND280 detector. Phys. Rev. D, 89(9), 092003–18pp.
Abstract: The T2K experiment has reported the first observation of the appearance of electron neutrinos in a muon neutrino beam. The main and irreducible background to the appearance signal comes from the presence in the neutrino beam of a small intrinsic component of electron neutrinos originating from muon and kaon decays. In T2K, this component is expected to represent 1.2% of the total neutrino flux. A measurement of this component using the near detector (ND280), located 280 m from the target, is presented. The charged current interactions of electron neutrinos are selected by combining the particle identification capabilities of both the time projection chambers and electromagnetic calorimeters of ND280. The measured ratio between the observed electron neutrino beam component and the prediction is 1.01 +/- 0.10 providing a direct confirmation of the neutrino fluxes and neutrino cross section modeling used for T2K neutrino oscillation analyses. Electron neutrinos coming from muons and kaons decay are also separately measured, resulting in a ratio with respect to the prediction of 0.68 +/- 0.30 and 1.10 +/- 0.14, respectively.
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T2K Collaboration(Abe, K. et al), Cervera-Villanueva, A., Escudero, L., Gomez-Cadenas, J. J., Izmaylov, A., Monfregola, L., et al. (2014). Measurement of the neutrino-oxygen neutral-current interaction cross section by observing nuclear deexcitation gamma rays. Phys. Rev. D, 90(7), 072012–11pp.
Abstract: We report the first measurement of the neutrino-oxygen neutral-current quasielastic (NCQE) cross section gamma It is obtained by observing nuclear deexcitation. rays which follow neutrino-oxygen interactions at the Super-Kamiokande water Cherenkov detector. We use T2K data corresponding to 3.01 x 10(20) 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 x 10(-38) cm(2) with a 68% confidence interval of (1.22, 2.20) x 10(-38) cm(2) at a median neutrino energy of 630 MeV, compared with the theoretical prediction of 2.01 x 10(-38) cm(2).
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T2K Collaboration(Abe, K. et al), Cervera-Villanueva, A., Escudero, L., Gomez-Cadenas, J. J., Hansen, C., Monfregola, L., et al. (2011). Indication of Electron Neutrino Appearance from an Accelerator-Produced Off-Axis Muon Neutrino Beam. Phys. Rev. Lett., 107(4), 041801–8pp.
Abstract: The T2K experiment observes indications of nu(mu) -> nu(mu) e appearance in data accumulated with 1.43 x 10(20) protons on target. Six events pass all selection criteria at the far detector. In a three-flavor neutrino oscillation scenario with |Delta m(23)(2)| = 2.4 x 10(-3) eV(2), sin(2)2 theta(23) = 1 and sin(2)2 theta(13) = 0, the expected number of such events is 1.5 +/- 0.3(syst). Under this hypothesis, the probability to observe six or more candidate events is 7 x 10(-3), equivalent to 2.5 sigma significance. At 90% C.L., the data are consistent with 0.03(0.04) < sin(2)2 theta(13) < 0.28(0.34) for delta(CP) = 0 and a normal (inverted) hierarchy.
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T2K Collaboration(Abe, K. et al), Cervera-Villanueva, A., Escudero, L., Gomez-Cadenas, J. J., Hansen, C., Monfregola, L., et al. (2011). The T2K experiment. Nucl. Instrum. Methods Phys. Res. A, 659(1), 106–135.
Abstract: The T2K experiment is a long baseline neutrino oscillation experiment. Its main goal is to measure the last unknown lepton sector mixing angle theta(13) by observing nu(e) appearance in a nu(mu) beam. It also aims to make a precision measurement of the known oscillation parameters, Delta m(23)(2) and sin(2)2 theta(23), via nu(mu) disappearance studies. Other goals of the experiment include various neutrino cross-section measurements and sterile neutrino searches. The experiment uses an intense proton beam generated by the J-PARC accelerator in Tokai, Japan, and is composed of a neutrino beamline, a near detector complex (ND280), and a far detector (Super-Kamiokande) located 295 km away from J-PARC. This paper provides a comprehensive review of the instrumentation aspect of the T2K experiment and a summary of the vital information for each subsystem.
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T2K Collaboration(Abe, K. et al), Cervera-Villanueva, A., Escudero, L., Gomez-Cadenas, J. J., Hansen, C., Monfregola, L., et al. (2012). First muon-neutrino disappearance study with an off-axis beam. Phys. Rev. D, 85(3), 031103–8pp.
Abstract: We report a measurement of muon-neutrino disappearance in the T2K experiment. The 295-km muon-neutrino beam from Tokai to Kamioka is the first implementation of the off-axis technique in a long-baseline neutrino oscillation experiment. With data corresponding to 1.43 x 10(20) protons on target, we observe 31 fully-contained single mu-like ring events in Super-Kamiokande, compared with an expectation of 104 +/- 14 (syst) events without neutrino oscillations. The best-fit point for two-flavor nu(mu) -> nu(tau) oscillations is sin(2)(2 theta(23)) = 0.98 and vertical bar Delta m(32)(2)vertical bar = 2.65 x 10(-3) eV(2). The boundary of the 90% confidence region includes the points sin(2)(2 theta(23)), vertical bar Delta m(32)(2)vertical bar = (1.0, 3.1 x 10(-3) eV(2)), (0.84, 2.65 x 10(-3) eV(2)) and (1.0, 2.2 x 10(-3) eV(2)).
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T2K Collaboration(Abe, K. et al), Cervera-Villanueva, A., Escudero, L., Gomez-Cadenas, J. J., Hansen, C., Monfregola, L., et al. (2012). Measurements of the T2K neutrino beam properties using the INGRID on-axis near detector. Nucl. Instrum. Methods Phys. Res. A, 694, 211–223.
Abstract: Precise measurement of neutrino beam direction and intensity was achieved based on a new concept with modularized neutrino detectors. INGRID (Interactive Neutrino GRID) is an on-axis near detector for the T2K long baseline neutrino oscillation experiment. INGRID consists of 16 identical modules arranged in horizontal and vertical arrays around the beam center. The module has a sandwich structure of iron target plates and scintillator trackers. INGRID directly monitors the muon neutrino beam profile center and intensity using the number of observed neutrino events in each module. The neutrino beam direction is measured with accuracy better than 0.4 mrad from the measured profile center. The normalized event rate is measured with 4% precision. (C) 2012 Elsevier B.V. All rights reserved.
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T2K Collaboration(Abe, K. et al), Antonova, M., Cervera-Villanueva, A., & Novella, P. (2020). Simultaneous measurement of the muon neutrino charged-current cross section on oxygen and carbon without pions in the final state at T2K. Phys. Rev. D, 101(11), 112004–32pp.
Abstract: This paper reports the first simultaneous measurement of the double differential muon neutrino chargedcurrent cross section on oxygen and carbon without pions in the final state as a function of the 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 oscillation analyses. 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-going muons. Overall, of the models tested, the result is best described using local Fermi gas descriptions of the nuclear ground state with RPA suppression.
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T2K Collaboration(Abe, K. et al), Antonova, M., Cervera-Villanueva, A., & Novella, P. (2021). Measurements of (nu)over-bar(mu) and (nu)over-bar(mu) + nu(mu) charged-current cross-sections without detected pions or protons on water and hydrocarbon at a mean anti-neutrino energy of 0.86 GeV. Prog. Theor. Exp. Phys., 2021(4), 043C01–28pp.
Abstract: We report measurements of the flux-integrated (nu) over bar (mu) and (nu) over bar (mu) + nu(mu) charged-current cross -sections on water and hydrocarbon targets using the T2K anti-neutrino beam with a mean beam energy of 0.86 GeV. The signal is defined as the (anti -)neutrino charged-current interaction with one induced mu(+/-) and no detected charged pion or proton. These measurements are performed using a new WAGASCI module recently added to the T2K setup in combination with the INGRID Proton Module. The phase space of muons is restricted to the high-detection efficiency region, p(mu) > 400 MeV/c and theta(mu) < 30 degrees, in the laboratory frame. An absence of pions and protons in the detectable phase spaces of p(pi) > 200 MeV/c, theta(pi) < 70 degrees and p(p) > 600 MeV/c, theta(p) < 70 degrees is required. In this paper, both the <(nu)over bar>(mu), cross-sections and (nu) over bar (mu) + nu(mu), cross-sections on water and hydrocarbon targets and their ratios are provided by using the D'Agostini unfolding method. The results of the integrated (nu) over bar (mu), cross-section measurements over this phase space are sigma(H2O) = (1.082 +/- 0.068(stat.)(+0.145)(-0.128)(syst.)) x 10(-39) cm(2)/nucleon, sigma(CH) = (1.096 +/- 0.054 (stat.)(+0.132)(-0.117)(syst.)) x 10(-39) cm(2) /nucleon, and sigma(H2O)/sigma(CH) = 0.987 +/- 0.078 (stat.)(+0.093)(-0.090)(syst.). The (nu) over bar (mu), + nu(mu), cross-section is sigma(H2O) = (1.155 +/- 0.064(stat.)(+0.148)(-0.129)(syst.)) x 10(-39) cm(2)/nucleon, sigma(CH) = (1.159 +/- 0.049(stat.)(+0.129)(-0.115)(syst.)) x 10(-39) cm(2)/nucleon, and sigma(H2O)/sigma(CH) = 0.996 +/- 0.069(stat.)(+0.083)(-0.078)(syst.).
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