Updated constraints on sterile neutrino mixing in the OPERA experiment using a new ν Identification Method

Abstract This paper describes a new ν$_{e}$ identification method specifically designed to improve the low-energy () ν$_{e}$ 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 ν$_{e}$ 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 ν$_{e}$ candidate is found. The analysis combined with the ν$_{τ}$ appearance results improves the upper limit on sin $^{2}$2θ$_{μe}$ to 0.016 at 90% C.L. in the MiniBooNE allowed region .