Search for the Lepton-Number-Violating Decay Ξ-→pμ-μ-

A sensitive search for the lepton-number-violating decay Ξ → pμμ has been performed using a sample of ∼ 10 Ξ hyperons produced in 800GeV/c p-Cu collisions. We obtain B(Ξ → pμμ) < 4.0 × 10 at 90% confidence, improving on the best previous limit by four orders of magnitude. PACS numbers: 13.30.Ce, 11.30.Hv, 14.20.Jn, 14.60.St