A measurement of the Λ0 lifetime

The lifetime of the Λ b 0 baryon has been measured using 3.6 million hadronic Z 0 decays recorded by the OPAL detector at LEP from 1990 to 1994. A sample of Λ b 0 decays is obtained using partially reconstructed semileptonic decays involving Λ c + l − combinations, where the Λ c + is reconstructed from its decay to a pK − π + final state. From the 69 ± 13 Λ c + l − combinations attributed to Λ b 0 decays in this data sample, we measure τ ( Λ b 0 ) = 1.14 −0.19 +0.22 ± 0.07 ps, where the errors are statistical and systematic, respectively.