# First observation of the decay $\bar{B}^0_s \to D^0 K^{*0}$ and a measurement of the ratio of branching fractions $\frac{{\cal B}(\bar{B}^0_s \to D^0 K^{*0})}{{\cal B}(\bar{B}^0 \to D^0 \rho^0)}$

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## Abstract

The first observation of the decay $\bar{B}^0_s \to D^0 K^{*0}$ using $pp$ data collected by the LHCb detector at a centre-of-mass energy of 7 TeV, corresponding to an integrated luminosity of 36 pb$^{-1}$, is reported. A signal of $34.4 \pm 6.8$ events is obtained and the absence of signal is rejected with a statistical significance of more than nine standard deviations. The $\bar{B}^0_s \to D^0 K^{*0}$ branching fraction is measured relative to that of $\bar{B}^0 \to D^0 \rho^0$: $\frac{{\cal B}(\bar{B}^0_s \to D^0 K^{*0})}{{\cal B}(\bar{B}^0 \to D^0 \rho^0)} = 1.48 \pm 0.34 \pm 0.15 \pm 0.12$, where the first uncertainty is statistical, the second systematic and the third is due to the uncertainty on the ratio of the $B^0$ and $B^0_s$ hadronisation fractions.

## Figures and captions

 The invariant mass distribution for the $\overline{ B }{} ^0 \rightarrow D ^0 \rho ^0$ decay mode for the $\texttt{TOSOnly}$ (left) and $\texttt{TIS}$ (right) trigger categories with the result of the fit superimposed. The black points correspond to the data and the fit result is represented as a solid line. The signal is fitted with a double Gaussian (dashed line), the partially reconstructed background with an exponential function (light grey area) and the combinatorial background with a flat distribution (dark grey area) as explained in the text. The contributions from cross-feed are too small to be visible. fig1a.eps [21 KiB] HiDef png [184 KiB] Thumbnail [196 KiB] *.C file fig1b.eps [21 KiB] HiDef png [191 KiB] Thumbnail [208 KiB] *.C file The invariant mass distribution for the $\overline{ B }{} ^0_s \rightarrow D ^0 K ^{*0}$ decay mode with the result of the fit superimposed. The black points correspond to the data and the fit result is represented as a solid line. The signal is fitted with a double Gaussian (dashed line), the partially reconstructed background with an exponential function (light grey area), the combinatorial background with a flat distribution (dark grey area) and the cross-feed from $\overline{ B }{} ^0 \rightarrow D ^0 \rho ^0$ (intermediate grey area) as explained in the text. fig2.eps [18 KiB] HiDef png [178 KiB] Thumbnail [182 KiB] *.C file The $\rho ^0$ (on the left) and $K ^{*0}$ (on the right) invariant mass distributions obtained from data using an sPlot technique. The level of non $K ^{*0}$ combinations in the $\overline{ B }{} ^0_s \rightarrow D ^0 K ^{*0}$ peak is negligible. Despite being mainly due to $D ^0 \rho ^0$ combinations, the $\overline{ B }{} ^0 \rightarrow D ^0 \rho ^0$ contains a significant contribution of "non- $\rho ^0$ " events. The black points correspond to the data and the fit result is represented as a solid line. The resonant component is fitted with a Breit-Wigner convoluted with a Gaussian (dashed line) and the non-resonant part, if present, with a second-order polynomial (grey area). fig3a.eps [16 KiB] HiDef png [182 KiB] Thumbnail [200 KiB] *.C file fig3b.eps [14 KiB] HiDef png [131 KiB] Thumbnail [140 KiB] *.C file Animated gif made out of all figures. PAPER-2011-008.gif Thumbnail

## Tables and captions

 Summary of the fitted yields for the different categories. The background yields are quoted for the full mass regions. Table_1.pdf [62 KiB] HiDef png [44 KiB] Thumbnail [22 KiB] tex code Summary of the contributions to the systematic uncertainties. The uncertainty on the $r$ ratio gives the range used for the systematic uncertainty extraction on the ratios of the branching fractions. Table_2.pdf [54 KiB] HiDef png [78 KiB] Thumbnail [36 KiB] tex code

Created on 18 October 2019.