Precision measurement of the Ξ⁻_𝑏 baryon lifetime

A sample of 𝑝⁢𝑝 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 Λ⁰_𝑏 baryon, 𝑟_𝜏≡𝜏_Ξ−𝑏/𝜏_Λ0𝑏. The value 𝑟_𝜏=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 𝑟^Run 1,2_𝜏=1.078±0.012±0.007. Multiplying by the world-average value of the Λ⁰
_𝑏 lifetime yields 𝜏^Run 1,2_Ξ−𝑏=1.578±0.018±0.010±0.011  ps, where the uncertainties are statistical, systematic, and due to the limited knowledge of the Λ⁰_𝑏 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.