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First observation and measurement of the branching fraction for the decay $B^0_s \to D_s^{*\mp} K^{\pm}$

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Abstract

The first observation of the $B^0_s \to D_s^{*\mp} K^{\pm}$ decay is reported using 3.0$fb^{-1}$ of proton-proton collision data collected by the LHCb experiment. The $D_s^{*\mp}$ mesons are reconstructed through the decay chain $D_s^{*\mp} \to \gamma D_s^{\mp}(K^{\mp}K^{\pm}\pi^{\mp})$. The branching fraction relative to that for $B^0_s \to D_s^{*-} \pi^{+}$ is measured to be $0.068 \pm 0.005 ^{+0.003}_{-0.002}$, where the first uncertainty is statistical and the second is systematic. Using a recent measurement of $BR(B^0_s \to D_s^{*-} \pi^{+})$ the absolute branching fraction of $B^0_s \to D_s^{*\mp} K^{\pm}$ is measured as ( 16.3 $\pm$ 1.2 (stat) $^{+0.7}_{-0.5}$ (syst) $\pm$ 4.8 (norm) ) $\times$ 10$^{-5}$, where the third uncertainty is due to the uncertainty on the branching fraction of the normalisation channel.

Figures and captions

Feynman diagrams of the processes under study. The upper diagrams represent the two tree topologies ($b \rightarrow c$ and $b \rightarrow u$ transitions, respectively) by which a $ B ^0_ s $ meson decays into the $ D ^{*\mp}_ s $ $ K ^\pm$ final state; the lower diagrams show the tree diagram of $ B ^0_ s $ $\rightarrow $ $ D ^{*-}_ s $ $\pi ^+$ and the $ W $ -exchange topology of $ B ^0_ s $ $\rightarrow $ $ D ^{*-}_ s $ $ K ^+$ .

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(left) The $ K ^-$ $ K ^+$ $\pi ^-$ invariant mass and (right) mass difference $\Delta_{M}$ of the $ B ^0_ s $ $\rightarrow $ $ D ^{*-}_ s $ $\pi ^+$ candidates. The points represent data. On the right plot the solid line represents the signal expected from the simulations.

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Invariant mass distribution of (top) $ B ^0_ s $ $\rightarrow $ $ D ^{*-}_ s $ $\pi ^+$ and (bottom) $ B ^0_ s $ $\rightarrow $ $ D ^{*\mp}_ s $ $ K ^\pm$ candidates with fit results superimposed. The fitted signal corresponding to the first observation of $ B ^0_ s $ $\rightarrow $ $ D ^{*\mp}_ s $ $ K ^\pm$ is shown by the dotted line in the lower plot.

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Distributions of (left) $\eta$ and (right) $p_{\rm T}$ of the photons for the $ D ^{*-}_ s $ $\pi ^+$ (blue) and $ D ^{*\mp}_ s $ $ K ^\mp$ (magenta) decays. Data, background-subtracted using the sPlot method, are represented by points, and simulations by solid lines.

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Animated gif made out of all figures.

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Tables and captions

Estimated systematic uncertainties on ${\cal R}^*$.

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Created on 09 December 2018.Citation count from INSPIRE on 18 December 2018.