Measurement of muon antineutrino oscillations with an accelerator-produced off-axis beam.
Abstract:
T2K reports its first measurements of the parameters governing the disappearance of ν¯μ in an off-axis beam due to flavor change induced by neutrino oscillations. The quasimonochromatic ν¯μ beam, produced with a peak energy of 0.6 GeV at J-PARC, is observed at the far detector Super-Kamiokande, 295 km away, where the ν¯μ survival probability is expected to be minimal. Using a data set corresponding to 4.01×1020 protons on target, 34 fully contained μ-like events were observed. The best-fit oscillation parameters are sin2(θ¯23)=0.45 and |Δm¯232|=2.51×10−3 eV2 with 68% confidence intervals of 0.38–0.64 and 2.26–2.80×10−3 eV2, respectively. These results are in agreement with existing antineutrino parameter measurements and also with the νμ disappearance parameters measured by T2K.Measurement of the muon neutrino inclusive charged-current cross section in the energy range of 1–3 GeV with the T2K INGRID detector
Abstract:
We report a measurement of the νμ-nucleus inclusive charged-current cross section (=σcc) on iron using data from the INGRID detector 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 (10-38 cm2/nucleon), σcc(2.0 GeV)=2.07±0.27 (10-38 cm2/nucleon), and σcc(3.3 GeV)=2.29±0.45 (10-38 cm2/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 multiple-muon charge ratio in the MINOS Far Detector
Abstract:
The charge ratio, Rμ=Nμ+/Nμ−, for cosmogenic multiple-muon events observed at an underground depth of 2070 mwe has been measured using the magnetized MINOS Far Detector. The multiple-muon events, recorded nearly continuously from August 2003 until April 2012, comprise two independent data sets imaged with opposite magnetic field polarities, the comparison of which allows the systematic uncertainties of the measurement to be minimized. The multiple-muon charge ratio is determined to be Rμ=1.104±0.006(stat)+0.009−0.010(syst). This measurement complements previous determinations of single-muon and multiple-muon charge ratios at underground sites and serves to constrain models of cosmic-ray interactions at TeV energies.Upper bound on neutrino mass based on T2K neutrino timing measurements
Abstract:
The Tokai to Kamioka (T2K) long-baseline neutrino experiment consists of a muon neutrino beam, produced at the J-PARC accelerator, a near detector complex and a large 295-km-distant 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 sub-GeV neutrino beam in conjunction with timing precision of order tens of ns provide sensitivity to neutrino mass in the few MeV/c2 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 m2ν<5.6 MeV2/c4.Measurement of the νμ charged-current quasielastic cross section on carbon with the ND280 detector at T2K
Abstract:
This paper reports a measurement by the T2K experiment of the ν μ charged current quasielastic (CCQE) cross section on a carbon target with the off-axis detector based on the observed distribution of muon momentum ( p μ ) and angle with respect to the incident neutrino beam ( θ μ ). The flux-integrated CCQE cross section was measured to be ⟨ σ ⟩ = ( 0.83 ± 0.12 ) × 10 − 38 cm 2 . The energy dependence of the CCQE cross section is also reported. The axial mass, M QE A , 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) p μ − cos θ μ distribution, the effective M QE A parameter was measured to be 1.2 6 + 0.21 − 0.18 GeV / c 2 ( 1.4 3 + 0.28 − 0.22 GeV / c 2 ).