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Observation of $B^0_s \to K^{*\pm}K^\mp$ and evidence for $B^0_s \to K^{*-}\pi^+$ decays

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Abstract

Measurements of the branching fractions of $B^0_s \to K^{*\pm}K^\mp$ and $B^0_s \to K^{*\pm}\pi^\mp$ decays are performed using a data sample corresponding to $1.0 \ {\rm fb}^{-1}$ of proton-proton collision data collected with the LHCb detector at a centre-of-mass energy of $7\mathrm{ TeV}$, where the $K^{*\pm}$ mesons are reconstructed in the $K^0_{\rm S}\pi^\pm$ final state. The first observation of the $B^0_s \to K^{*\pm}K^\mp$ decay and the first evidence for the $B^0_s \to K^{*-}\pi^+$ decay are reported with branching fractions \begin{eqnarray} {\cal B}(B^0_s \to K^{*\pm}K^\mp) & = & (12.7\pm1.9\pm1.9) \times 10^{-6}, \\ {\cal B}(B^0_s \to K^{*-}\pi^+) & = & (3.3\pm1.1\pm0.5) \times 10^{-6}, \end{eqnarray} where the first uncertainties are statistical and the second are systematic. In addition, an upper limit of ${\cal B}(B^0 \to K^{*\pm}K^\mp) < 0.4 \ (0.5) \times 10^{-6}$ is set at $90 % \ (95 %)$ confidence level.

Figures and captions

(a) Tree and (b) loop diagrams for the decay $ B ^0_ s \rightarrow K ^{*+} K ^- $ .

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Results of the fit to $ K ^{*\pm} K ^\mp $ candidates projected onto (a,b) $ B $ candidate and (c,d) $ K ^*$ candidate mass distributions, for (a,c) long and (b,d) downstream candidates. The total fit result (solid black line) is shown together with the data points. Components for the $ B ^0$ (pink dash double-dotted line) and $ B ^0_ s $ (red dash dotted line) signals are shown together with the $ B ^0_ s $ nonresonant component (dark red falling-hatched area), charmless partially reconstructed and cross-feed background (blue long-dashed line), and combinatorial background (green long-dash dotted line) components. The $ B ^+ \rightarrow \overline{ D }{} {}^0 h ^+ $ background component has a negative yield (consistent with zero) and so is not directly visible but causes the total PDF to go below the level of the combinatorial background on the left of the $ B $ candidate mass spectrum.

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fitted_KstK_Model_DD_Kst_M.pdf

Results of the fit to $ K ^{*\pm} \pi ^\mp $ candidates projected onto (a,b) $ B $ candidate and (c,d) $ K ^*$ candidate mass distributions, for (a,c) long and (b,d) downstream candidates. The total fit result (black solid line) is shown together with the data points. Components for the $ B ^0$ (red dash dotted line) and $ B ^0_ s $ (pink dash double-dotted line) signals are shown together with $ B ^0$ (dark red falling-hatched area) and $ B ^0_ s $ (purple rising-hatched area) nonresonant components, partially reconstructed and cross-feed background (blue long-dashed line), and combinatorial background (green long-dash-dotted line) components.

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fitted_Kstpi_Model_LL_B_M.pdf
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fitted_Kstpi_Model_DD_B_M.pdf
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fitted_Kstpi_Model_LL_Kst_M.pdf
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fitted_Kstpi_Model_DD_Kst_M.pdf

Background-subtracted distribution of $\cos{\theta_{ K ^* }}$ for (a,b) $ B ^0 \rightarrow K ^{*+} \pi ^- $ and (c,d) $ B ^0_ s \rightarrow K ^{*\pm} K ^\mp $ signals from the samples with (a,c) long and (b,d) downstream candidates. Results of fits with second-order polynomial functions are shown as the solid lines.

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data_Bd2Kstpi_theta_LL.pdf
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data_Bd2Kstpi_theta_DD.pdf
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data_Bs2KstK_theta_LL.pdf
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data_Bs2KstK_theta_DD.pdf

Animated gif made out of all figures.

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Tables and captions

Yields and relative yields obtained from the fits to $ K ^{*\pm} K ^\mp $ and $ K ^{*\pm} \pi ^\mp $ candidates. The relative yields of nonresonant (NR) $B^0_{(s)}$ decays are constrained to be identical in long and downstream categories. Only statistical uncertainties are given.

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Systematic uncertainties on the relative branching fraction measurements. The total uncertainty is obtained by combining all sources in quadrature.

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Created on 27 April 2024.