Study of the KL→π0νν¯ Decay at the J-PARC KOTO Experiment

The rare decay K_{L}→π^{0}νν[over ¯] was studied with the dataset taken at the J-PARC KOTO experiment in 2016, 2017, and 2018. With a single event sensitivity of (7.20±0.05_{stat}±0.66_{syst})×10^{-10}, three candidate events were observed in the signal region. After unveiling them, contaminations from K^{±} and scattered K_{L} decays were studied, and the total number of background events was estimated to be 1.22±0.26. We conclude that the number of observed events is statistically consistent with the background expectation. For this dataset, we set an upper limit of 4.9×10^{-9} on the branching fraction of K_{L}→π^{0}νν[over ¯] at the 90% confidence level

Tar Reforming in Model Gasifier Effluents: Transition Metal/Rare Earth Oxide Catalysts

The removal of tars from syngas generated in biomass or coal/biomass gasifiers plays an important role in syngas cleanup. Rare earth oxides (REOs, e.g., Ce/LaOx) mixed with transition metals (e.g., Mn, Fe) were synthesized by various methods and in some cases supported on a thermally stable alumina. These catalysts were applied to tar removal in the temperature range \u3c1100 K using synthetic syngas mixtures with C H as a tar model compound, both with and without H S. Some commercial Ni reforming catalyst formulations were examined comparatively. Fresh and used catalysts were characterized by XANES, XAFS, XRD, TPO, and BET. We found that the C H is reformed to at least methane, although further reforming to CO and H is not always achieved. While CO , H S, and coke formation all inhibited or deactivated the catalysts at certain temperatures and to different extents, it was determined that Fe- or Mn-doped supported REOs are promising tar cleanup catalysts. They exhibited higher sulfur tolerance, less coking, and less methanation than typical Ni-based high temperature reforming catalysts. This behavior is in part attributed to enhanced generation of oxygen vacancies in the doped REOs. © 2014 American Chemical Society. 10 8 2 10 8 2 2