Precision measurement of the Bs-⁰ Bs⁰ oscillation frequency with the decay Bs- ⁰→ Dsπ^-+

A key ingredient to searches for physics beyond the Standard Model in B _s- ⁰ mixing phenomena is the measurement of the B _s- ⁰ oscillation frequency, which is equivalent to the mass difference Δm _s of the B _s- ⁰ mass eigenstates. Using the world's largest B _s- ⁰ meson sample accumulated in a dataset, corresponding to an integrated luminosity of 1.0 fb ^-1, collected by the LHCb experiment at the CERN LHC in 2011, a measurement of Δm _s is presented. A total of about 34 000 B _s- ⁰ → D _sπ ^-+ signal decays are reconstructed, with an average decay time resolution of 44 fs. The oscillation frequency is measured to be Δm _s = 17.768 ± 0.023 (stat) ± 0.006 (syst) ps ^-1, which is the most precise measurement to date.