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\begin{document}
  
  
  
      {\small
        \begin{tabular}{l cc cc}
          \multirow{2}{*}{Source of uncertainty}  & \multicolumn{2}{c}{ $ B\xspace\xspace^0\xspace\!\rightarrow\xspace  D\xspace\xspace^-\xspace\mu\xspace^+\xspace\nu\xspace\xspace_\mu\xspace X$ \xspace [ $ {\rm \,ns^{-1}}$ \xspace]}  & \multicolumn{2}{c}{ $ B\xspace\xspace^0\xspace\!\rightarrow\xspace  D\xspace\xspace^{*-}\xspace\mu\xspace^+\xspace\nu\xspace\xspace_\mu\xspace X$ \xspace [ $ {\rm \,ns^{-1}}$ \xspace]}  \\
                                             & Uncorrelated & Correlated  & Uncorrelated &  Correlated  \\
          \hline
              $ B\xspace\xspace^+$ \xspace\ background                 & 0.4  & 0.1  &  0.4  & --  \\
             Other backgrounds               & --   & 0.5  & --    & --  \\
             $k$-factor distribution         & 0.4  & 0.5  &  0.3  & 0.6  \\
             Other fit-related               & 0.5  & 0.4  &  0.3  & 0.5  \\ 
              \hline
              Total                          & 0.8  & 0.8 &  0.6 & 0.8 \\
        \end{tabular}
      }
  
\end{document}
