Search for neutral-current induced single photon production at the ND280 near detector in T2K
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
Search for light sterile neutrinos with the T2K far detector Super-Kamiokande at a baseline of 295 km
We perform a search for light sterile neutrinos using the data from the T2K far detector at a baseline of 295 km, with an exposure of 14.7(7.6)×1020 protons on target in neutrino (antineutrino) mode. A selection of neutral-current interaction samples is also used to enhance the sensitivity to sterile mixing. No evidence of sterile neutrino mixing in the 3+1 model was found from a simultaneous fit to the charged-current muon, electron and neutral-current neutrino samples. We set the most stringent limit on the sterile oscillation amplitude sin^2\theta_{24} for the sterile neutrino mass splitting \Delta m^2_{41}<3\times 10^{-3} eV^2/c^4.
link to publication : https://journals.aps.org/prd/abstract/10.1103/PhysRevD.99.071103
There is a data release for this paper here
Search for heavy neutrinos with ND280
This paper (Phys. Rev. D 100, 052006 (2019)) reports on the search for heavy neutrinos with masses in the range 140 < MN <493 MeV/c2 using the off-axis near detector ND280 of the T2K experiment. These particles can be produced from kaon decays in the standard neutrino beam and then subsequently decay in ND280. The decay modes under consideration are N→l_α π and N→l_α l_β ν (α,β=e,μ). A search for such events has been made using the Time Projection Chambers of ND280, where the background has been reduced to less that 2 events in the current dataset in all channels. No excess has been observed in the signal region. A combined Bayesian statistical approach has been applied to extract upper limits on the mixing elements of heavy neutrinos to electron-, muon- and tau- flavoured currents (Ue2, Uμ2, Uτ2) as a function of the heavy neutrino mass, e.g. Ue2 < 10^(−9) at 90% C.L. for a mass of 390MeV/c2. These constraints are competitive with previous experiments.
There is a data release for this paper here.
