Precise determination of the Bs0 – B¯s0 oscillation frequency

Mesons comprising a beauty quark and strange quark can oscillate between particle (Bs0) and antiparticle (B¯s0) flavour eigenstates, with a frequency given by the mass difference between heavy and light mass eigenstates, Δm_s. Here we present a measurement of Δm_s using Bs0→Ds−π⁺ decays produced in proton–proton collisions collected with the LHCb detector at the Large Hadron Collider. The oscillation frequency is found to be Δm_s = 17.7683 ± 0.0051 ± 0.0032 ps⁻¹, where the first uncertainty is statistical and the second is systematic. This measurement improves on the current Δm_s precision by a factor of two. We combine this result with previous LHCb measurements to determine Δm_s = 17.7656 ± 0.0057 ps⁻¹, which is the legacy measurement of the original LHCb detector.