Precision measurement of the Ξ− b baryon lifetime

Abstract

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 Λ0 b baryon, rτ ≡ τΞ− b =τΛ0 b . The value rτ ¼ 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 rRun 1;2 τ ¼ 1.078 0.012 0.007. Multiplying by the world-average value of the Λ0 b lifetime yields τ Run 1;2 Ξ− b ¼ 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.