Precise determination of the B0s-B0sbar oscillation frequency

The LHCb collaboration
Aaij, R. , Beteta, C. Abellán , Ackernley, T. , Adeva, B. , Adinolfi, M. , Afsharnia, H. , Aidala, C.A. , Aiola, S. , Ajaltouni, Z. , Akar, S.
Nature Phys. 18 (2022) 1-5, 2022.

Abstract (data abstract)
Mesons comprising a beauty quark and a strange quark can oscillate between particle ($B^{0}_{s}$) and antiparticle ($\bar{B}^{0}_{s}$) flavour eigenstates, with a frequency given by the mass difference between heavy and light mass eigenstates, $\Delta m_s$. Here we present a measurement of $\Delta m_s$ using $B^{0}_{s} \to D_{s}^{-} \pi^{+}$ decays produced in proton-proton collisions collected with the LHCb detector at the Large Hadron Collider. This measurement improves upon the current $\Delta m_s$ precision by a factor of two. The oscillation frequency is found to be $\Delta m_s = 17.7683 \pm 0.0051 \pm 0.0032$ ps$^{-1}$ where the first uncertainty is statistical and the second systematic. We combine this result with previous LHCb measurements to determine $\Delta m_s = 17.7656 \pm 0.0057$ ps$^{-1}$.

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