Recent results of the T2K experiment
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cent Results of the T2K Experiment M. M. Khabibullin Institute for Nuclear Research, Russian Academy of Sciences, Moscow, 117312 Russia e-mail: [email protected] Abstract—The accelerator-based neutrino experiment Tokai-to-Kamioka (T2K) in Japan ran in the neutrino mode since 2010 and then switched to the antineutrino mode in 2014. The initial results of the data analysis obtained with antineutrinos are reported here. DOI: 10.1134/S1063779617060247
1. MAJOR GOALS OF THE T2K EXPERIMENT T2K (for Tokai-to-Kamioka) is a long-baseline neutrino oscillation experiment in which muon (anti)neutrinos from the J-PARK proton accelerator in the Tokai village are directed towards the SuperKamiokande (SK) detector over a baseline of 295 km [1]. The experiment was originally aimed at observing the ν μ → ν e transition driven by a nonzero mixing angle θ13, and at accurately estimating the parameters of the ν μ → ν μ oscillation. Upon the discovery of a nonzero value of θ13, the search for CP violation in the lepton sector emerges as the major experimental task. The T2K experiment ran in the neutrino mode since 2010 and then switched to antineutrinos in 2014. Here, we report the preliminary analysis results for the antineutrino data and the most salient results earlier obtained with the neutrino data. 2. LAYOUT OF THE T2K EXPERIMENT The muon (anti)neutrinos employed by T2K result from the decays of charged mesons formed in proton interactions with the nuclei of a graphite target. Charged mesons are focused by three electromagnets and directed to the decay zone. Switching between the neutrino and antineutrino modes is done by switching the pulse current direction in the electromagnets. T2K pioneered the technique of the off-axis neutrino detector: one of the near detectors (ND280) and the far detector (SK) are deployed at a nonzero angle of 2.5° with respect to the beam axis. This renders the neutrino energy spectrum almost monochromatic with a maximum flux at Eν = 600 MeV which corresponds to the oscillation maximum, whereby the background created by high-energy neutrinos is suppressed.
The near detectors INGRID and ND280, required for probing the neutrino beam prior to oscillations, are located at a distance of 280 m from the target. The direction and intensity of the neutrino beam are monitored on line using the on-axis INGRID (for Interactive Neutrino Grid) detector [2]. The off-axis near detector ND280 comprises a tracker and other detecting elements placed inside the UA1 magnet. It serves for determining the neutrino beam composition and for reducing the systematic errors arising from the uncertainties of the neutrino flux and interaction cross sections. The far detector of the T2K experiment is the well-known SK water-Cherenkov detector containing 50 kt of water in a cylindrical tank, in which the Cherenkov rings generated by muons and electrons are discriminated with an efficiency over 99% [3]. The signals from the near and far detectors are synchronized using the Global Positioning System (GPS). 3. DATA ANALYSIS AND RECENT T2K RES
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