Constraints on | Ue3 | 2 from a three-neutrino oscillation analysis of the CHOOZ data

Abstract

Results of a new analysis of the CHOOZ data, performed in the framework of three-neutrino mixing, are presented. Both the cases of normal and inverted neutrino mass hierarchy are considered. The parameters characterizing the solar neutrino oscillations, Δm 2 ⊙ and tan 2 θ ⊙, are assumed to lie in the region of the large mixing angle (LMA) MSW solution of the solar neutrino problem, which is favored by the current solar neutrino data. At Δm 2 ⊙≲10 −4 eV 2 the new CHOOZ exclusion curve in the Δm 2 31–| U e3 | 2 plane practically coincides with the exclusion curve obtained in the two-neutrino mixing analysis. For Δm 2 ⊙≳2×10 −4 eV 2, the constraints of the CHOOZ data on | U e3 | 2 are more stringent. For, e.g., sin 2 θ ⊙=0.50 and Δm 2 ⊙=6×10 −4 eV 2, and at Δm 2 31=2.5×10 −3 eV 2 (the Super-Kamiokande best fit-point) we find that (at 90% C.L.) | U e3 | 2<1.7×10 −2, which is by more than a factor of 2 smaller than the upper bound obtained in the original two-neutrino mixing analysis of the CHOOZ data (| U e3 | 2<3.7×10 −2).