
T2K Collaboration(Abe, K. et al), CerveraVillanueva, A., Escudero, L., GomezCadenas, J. J., Izmaylov, A., Monfregola, L., et al. (2013). Measurement of Neutrino Oscillation Parameters from Muon Neutrino Disappearance with an OffAxis Beam. Phys. Rev. Lett., 111(21), 211803–7pp.
Abstract: The T2K Collaboration reports a precision measurement of muon neutrino disappearance with an offaxis 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 SuperKamiokande 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 bestfit 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.



T2K Collaboration(Abe, K. et al), CerveraVillanueva, A., Escudero, L., Izmaylov, A., Monfregola, L., Sorel, M., et al. (2014). Precise Measurement of the Neutrino Mixing Parameter theta(23) from Muon Neutrino Disappearance in an OffAxis Beam. Phys. Rev. Lett., 112(18), 181801–8pp.
Abstract: New data from the T2K neutrino oscillation experiment produce the most precise measurement of the neutrino mixing parameter theta(23). Using an offaxis neutrino beam with a peak energy of 0.6 GeV and a data set corresponding to 6.57 x 10(20) protons on target, T2K has fit the energydependent nu(mu) oscillation probability to determine oscillation parameters. The 68% confidence limit on sin(2)(theta(23)) is 0.514(0.056)(+0.055) (0.511 +/ 0.055), assuming normal (inverted) mass hierarchy. The bestfit masssquared splitting for normal hierarchy is Delta m(32)(2) = (2.51 +/ 0.10) x 10(3) eV(2)/c(4) (inverted hierarchy: Delta m(13)(2) = (2.48 +/ 0.10) x 10(3) eV(2)/c(4)). Adding a model of multinucleon interactions that affect neutrino energy reconstruction is found to produce only small biases in neutrino oscillation parameter extraction at current levels of statistical uncertainty.



T2K Collaboration(Abe, K. et al), CerveraVillanueva, A., Escudero, L., Izmaylov, A., Sorel, M., & Stamoulis, P. (2016). Upper bound on neutrino mass based on T2K neutrino timing measurements. Phys. Rev. D, 93(1), 012006–15pp.
Abstract: The Tokai to Kamioka (T2K) longbaseline neutrino experiment consists of a muon neutrino beam, produced at the JPARC accelerator, a near detector complex and a large 295kmdistant far detector. The present work utilizes the T2K event timing measurements at the near and far detectors to study neutrino time of flight as a function of derived neutrino energy. Under the assumption of a relativistic relation between energy and time of flight, constraints on the neutrino rest mass can be derived. The subGeV neutrino beam in conjunction with timing precision of order tens of ns provide sensitivity to neutrino mass in the few MeV/c(2) range. We study the distribution of relative arrival times of muon and electron neutrino candidate events at the T2K far detector as a function of neutrino energy. The 90% C.L. upper limit on the mixture of neutrino mass eigenstates represented in the data sample is found to be m(v)(2) < 5.6 MeV2/c(4).



T2K Collaboration(Abe, K. et al), CerveraVillanueva, A., Escudero, L., Izmaylov, A., Sorel, M., & Stamoulis, P. (2015). Search for short baseline nu(e) disappearance with the T2K near detector. Phys. Rev. D, 91(5), 051102–8pp.
Abstract: The T2K experiment has performed a search for nu(e) disappearance due to sterile neutrinos using 5.9 x 10(20) protons on target for a baseline of 280 m in a neutrino beam peaked at about 500 MeV. A sample of nu(e) CC interactions in the offaxis near detector has been selected with a purity of 63% and an efficiency of 26%. The pvalue for the null hypothesis is 0.085 and the excluded region at 95% C.L. is approximately sin(2)2 theta(ee) > 0.3 for Delta m(eff)(2) > 7 eV(2)/c(4).



T2K Collaboration(Abe, K. et al), CerveraVillanueva, A., Escudero, L., Izmaylov, A., Sorel, M., & Stamoulis, P. (2015). Measurements of neutrino oscillation in appearance and disappearance channels by the T2K experiment with 6.6 x 10(20) protons on target. Phys. Rev. D, 91(7), 072010–50pp.
Abstract: We report on measurements of neutrino oscillation using data from the T2K longbaseline 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: sin(2)theta(23) = 0.514(0.055)(+0.056) and Delta m(32)(2) = (2.51 +/ 0.10) x 10(3) eV(2)/c(4) and inverted hierarchy: sin(2)theta(23) = 0.511 +/ 0.055 and Delta m(13)(2) = (2.48 +/ 0.10) x 10(3) eV(2)/c(4). The analysis accounts for multinucleon 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, vertical bar Delta m(2)vertical bar, sin(2)theta(23), sin(2)theta(13,) delta(CP), 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 delta(CP) = [0.15; 0.83]pi for normal hierarchy and delta(CP) = [0.08; 1.09]pi 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% onedimensional credible intervals for the other oscillation parameters, when reactor data are included, are sin(2)theta(23) = 0.528(0.055)(+0.038) and vertical bar Delta m(32)(2)vertical bar = (2.51 +/ 0.11) x 10(3) eV(2)/c(4).



T2K Collaboration(Abe, K. et al), CerveraVillanueva, A., Escudero, L., Izmaylov, A., Sorel, M., & Stamoulis, P. (2015). Measurement of the nu(mu) charged current quasielastic cross section on carbon with the T2K onaxis neutrino beam. Phys. Rev. D, 91(11), 112002–17pp.
Abstract: We report a measurement of the nu(mu) charged current quasielastic crosssections on carbon in the T2K onaxis neutrino beam. The measured charged current quasielastic crosssections on carbon at mean neutrino energies of 1.94 GeV and 0.93 GeV are (11.95 +/ 0.19(stat)(1.47)(+1.82)(syst)) x 10(39) cm(2)/neutron, and (10.64 +/ 0.37(stat)(1.65)(+2.03)(syst)) x 10(39) cm(2)/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 multinucleon interaction.



T2K Collaboration(Abe, K. et al), CerveraVillanueva, A., Escudero, L., Izmaylov, A., Sorel, M., & Stamoulis, P. (2015). Measurement of the electron neutrino chargedcurrent interaction rate on water with the T2K ND280 pi(0) detector. Phys. Rev. D, 91(11), 112010–11pp.
Abstract: This paper presents a measurement of the charged current interaction rate of the electron neutrino beam component of the beam above 1.5 GeV using the large fiducial mass of the T2K pi(0) detector. The predominant portion of the v(e) flux (similar to 85%) at these energies comes from kaon decays. 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 on water only from an event subtraction method is 0.87 +/ 0.33(stat) +/ 0.21(sys). This is the first measurement of the interaction rate of electron neutrinos on water, which is particularly of interest to experiments with water Cherenkov detectors.



T2K Collaboration(Abe, K. et al), CerveraVillanueva, A., Escudero, L., Izmaylov, A., Sorel, M., & Stamoulis, P. (2015). Measurement of the nu(mu) chargedcurrent quasielastic cross section on carbon with the ND280 detector at T2K. Phys. Rev. D, 92(11), 112003–14pp.
Abstract: This paper reports a measurement by the T2K experiment of the nu(mu) charged current quasielastic (CCQE) cross section on a carbon target with the offaxis detector based on the observed distribution of muon momentum (rho(mu)) and angle with respect to the incident neutrino beam (theta(mu)). The fluxintegrated CCQE cross section was measured to be <sigma > = (0.83 +/ 0.12) x 10(38) cm(2). The energy dependence of the CCQE cross section is also reported. The axial mass, MA(QE), of the dipole axial form factor was extracted assuming the SmithMoniz CCQE model with a relativistic Fermi gas nuclear model. Using the absolute (shapeonly) rho(mu)cos theta(mu) distribution, the effective MA(QE) parameter was measured to be 1.26(0.18)(+0.21) GeV/c(2) (1.43(0.22)(+0.28) GeV/c(2)).



T2K Collaboration(Abe, K. et al), CerveraVillanueva, A., Escudero, L., Izmaylov, A., Sorel, M., & Stamoulis, P. (2015). Neutrino oscillation physics potential of the T2K experiment. Prog. Theor. Exp. Phys., (4), 043C01–36pp.
Abstract: The observation of the recent electron neutrino appearance in a muon neutrino beam and the highprecision measurement of the mixing angle theta(13) have led to a reevaluation of the physics potential of the T2K longbaseline neutrino oscillation experiment. Sensitivities are explored for CP violation in neutrinos, nonmaximal sin(2) 2 theta(23), the octant of theta(23), and the mass hierarchy, in addition to the measurements of delta CP, sin(2) theta(23), and Delta m(32)(2), for various combinations of numode and (nu) over bar mode datataking. With an exposure of 7.8 x 10(21) protonsontarget, T2K can achieve 1 sigma resolution of 0.050 (0.054) on sin(2) theta(23) and 0.040 (0.045) x 10(3) eV(2) on Delta m(32)(2) for 100% (50%) neutrino beam mode running assuming sin(2) theta(23) = 0.5 and Delta m(32)(2) = 2.4 x 10(3) eV(2). T2K will have sensitivity to the CPviolating phase delta(CP) at 90% C.L. or better over a significant range. For example, if sin(2) 2 theta(23) is maximal (i.e.theta(23) = 45 degrees) the range is 115 degrees < delta(CP) < 60 degrees for normal hierarchy and +50 degrees < delta(CP) < + 130 degrees for inverted hierarchy. When T2K data is combined with data from the NO nu A experiment, the region of oscillation parameter space where there is sensitivity to observe a nonzero delta CP is substantially increased compared to if each experiment is analyzed alone.



T2K Collaboration(Abe, K. et al), CerveraVillanueva, A., Escudero, L., Izmaylov, A., Sorel, M., & Stamoulis, P. (2014). Measurement of the inclusive nu(mu) charged current cross section on iron and hydrocarbon in the T2K onaxis neutrino beam. Phys. Rev. D, 90(5), 052010–15pp.
Abstract: We report a measurement of the nu(mu) inclusive charged current cross sections on iron and hydrocarbon in the TokaitoKamioka (T2K) onaxis neutrino beam. The measured inclusive charged current cross sections on iron and hydrocarbon averaged over the T2K onaxis flux with a mean neutrino energy of 1.51 GeVare (1.444 +/ 0.002(stat)(0.157)(+0.189) (syst)) x 10(38) cm(2)/ nucleon and (1.379 +/ 0.009(stat)(0.147)(+0.178) (syst)) x 10(38) 38 cm(2)/ nucleon, respectively, and their crosssection ratio is 1.047 +/ 0.007(stat) +/ 0.035(syst). These results agree well with the predictions of the neutrino interaction model, and thus we checked the correct treatment of the nuclear effect for iron and hydrocarbon targets in the model within the measurement precisions.

