| Summary: | A search for rare charmless decays of Bd 0 and Bs 0 mesons has been performed in the exclusive channels Bd(s) 0 →ηη, Bd(s) 0 →ηπ0 and Bd(s) 0 →π0π0. The data sample consisted of three million hadronic Z decays collected by the L3 experiment at LEP from 1991 through 1994. No candidate event has been observed and the following upper limits at 90% confidence level on the branching ratios have been set: Br(B() d→ηη) <4.1 x 10-4, Br(B() s→ηη) < 1.5 x 10-3, Br(B() d→ηφ()) < 2.5 x 10-4, Br(B() s→ηphi;()) < 1.0 x 10-3, Br(B() d→phi;()phi;()) < 6.0 x 10-5, Br(B() s→phi;()phi;()) < 2.1 x 10-4. These are the first experimental limits on Bd 0→ηη and on the Bs 0 neutral charmless modes. © 1995.
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