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Measurement of the $B^0_s-\overline{B}^0_s$ oscillation frequency $\Delta m_s$ in $B^0_s \to D^-_s (3)\pi$ decays

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Abstract

The B^0_s-\bar{B}^0_s oscillation frequency Delta m_s is measured with 36 pb^{-1} of data collected in pp collisions at \sqrt{s} = 7 TeV by the LHCb experiment at the Large Hadron Collider. A total of 1381 B^0_s -> D_s^- \pi^+ and \B^0_s -> D_s^- pi^+ pi^- pi^+ signal decays are reconstructed, with average decay time resolutions of 44 fs and 36 fs, respectively. An oscillation signal with a statistical significance of 4.6 sigma is observed. The measured oscillation frequency is Delta m_s = 17.63 \pm 0.11 (stat) \pm 0.02 (syst) ps^{-1}.

Figures and captions

Mass distributions for a) $ B ^0_s \!\rightarrow D ^-_s (\phi \pi ^- )\pi ^+ $ , b) $ B ^0_s \!\rightarrow D ^-_s ( K ^{*0} K ^- )\pi ^+ $ , c) $ B ^0_s \!\rightarrow D ^-_s ( K ^+ K ^- \pi ^- )\pi ^+ $ and d) $ B ^0_s \!\rightarrow D ^-_s \pi ^+ \pi ^- \pi ^+ $ candidates. The fits and the various background components are described in the text. "Partial" refers to background from partially reconstructed $B^0_s$ decays, "mis-id" refers to background from fully or partially reconstructed $B^0$ and $\Lambda_b$ decays with one mis-identified daughter particle, and "comb" refers to combinatorial background.

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Decay time distributions for a) $ B ^0_s \!\rightarrow D ^-_s (\phi \pi ^- )\pi ^+ $ , b) $ B ^0_s \!\rightarrow D ^-_s ( K ^{*0} K ^- )\pi ^+ $ , c) $ B ^0_s \!\rightarrow D ^-_s ( K ^+ K ^- \pi ^- )\pi ^+ $ and d) $ B ^0_s \!\rightarrow D ^-_s \pi ^+ \pi ^- \pi ^+ $ candidates. The data and the fit projection are from a mass range of $\pm$ 3$\sigma_m$ around the reconstructed $ B ^0_s$ mass. The abbreviations for the various fit components are introduced in Fig. 1.

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Likelihood scan for $\Delta m_{ s }$ in the range [0.0, 25.0] ps$^{-1}$. The line at $-2\Delta \ln L$ = 20.9 indicates the value in the limit $\Delta m_{ s }$ = $\infty$.

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Measured asymmetry for $ B ^0_s$ candidates in bins of the decay time $t$ modulo $2\pi / \Delta m_{ s } $. The projection of the likelihood fit is superimposed.

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Animated gif made out of all figures.

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Tables and captions

$B^0_s$ signal yields.

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Summary of the systematic uncertainties on $\Delta m_{ s }$ . The total systematic uncertainty is defined as the quadratic sum of the individual components.

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Created on 09 December 2018.Citation count from INSPIRE on 09 December 2018.