Experiment	Measurement	Reference
Belle	< \(2.5 \times 10^{-5}\)	PRD 71, 091107(R)(2005)
BaBar	< \(0.52 \times 10^{-4}\)	PRD 71 071103 (2005)
Average	< \(\mathbf{2.5 \times 10^{-5}}\)