Updated constraints on sterile neutrino mixing in the OPERA experiment using a new ν e identification method

This paper describes a new νe identification method specifically designed to improve the low-energy (< 30 GeV) νe identification efficiency attained by enlarging the emulsion film scanning volume with the next-generation emulsion readout system. A relative increase of 25–70% in the νe low-energy region is expected, leading to improvements in the OPERA sensitivity to neutrino oscillations in the framework of the 3 + 1 model. The method is applied to a subset of data where the detection efficiency increase is expected to be more relevant, and one additional νe candidate is found. The analysis combined with the ντ appearance results improves the upper limit on sin 22θμe to 0.016 at 90% C.L. in the MiniBooNE allowed region Δm241 ∼ 0.3 eV2