Precision measurement of the Ξ^-<inf>b</inf>baryon lifetime

A sample of pp collision data, corresponding to an integrated luminosity of 5.5 fb-1 and collected by the LHCb experiment during LHC Run 2, is used to measure the ratio of the lifetime of the Ξ-b baryon to that of the Λ0b baryon, rτ ≡ τΞ-b=τΛ0b. The value rτ = 1.076 ± 0.013 ± 0.006 is obtained, where the first uncertainty is statistical and the second systematic. This value is averaged with the corresponding value from Run 1 to obtain rRun1,2τ = 1.078 ± 0.012 ± 0.007. Multiplying by the world-average value of the Λ0b lifetime yields τRun1,2Ξ-b = 1.578 ± 0.018 ± 0.010 ± 0.011 ps, where the uncertainties are statistical, systematic, and due to the limited knowledge of the Λ0b lifetime. This measurement improves the precision of the current world average of the Ξ-b lifetime by about a factor of 2, and is in good agreement with the most recent theoretical predictions.