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

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, Δm2⊙ and tan2θ⊙, 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 Δm2⊙≲10−4 eV2 the new CHOOZ exclusion curve in the Δm231–|Ue3|2 plane practically coincides with the exclusion curve obtained in the two-neutrino mixing analysis. For Δm2⊙≳2×10−4 eV2, the constraints of the CHOOZ data on |Ue3|2 are more stringent. For, e.g., sin2θ⊙=0.50 and Δm2⊙=6×10−4 eV2, and at Δm231=2.5×10−3 eV2 (the Super-Kamiokande best fit-point) we find that (at 90% C.L.) |Ue3|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 (|Ue3|2<3.7×10−2).