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\graphicspath{{./figs/}}

\begin{document}
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  \centering
  \begin{picture}(156,124)
    \put(0,62){
      \includegraphics*[width=78mm,height=62mm%
      ]{figs/Fig4a.pdf}
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    \put(0,0){
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      ]{figs/Fig4c.pdf}
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    \put(78,62){
      \includegraphics*[width=78mm,height=62mm%
      ]{figs/Fig4b.pdf}
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    \put(14, 115) {(a)}
    \put(19 ,115) { \small $\ensuremath{\ensuremath{\ensuremath{B}\xspace}\xspace^0_\ensuremath{\ensuremath{s}\xspace}\xspace}\xspace\ensuremath{\rightarrow}\xspace\ensuremath{{\ensuremath{J}\xspace\mskip -3mu/\mskip -2mu\ensuremath{\psi}\xspace\mskip 2mu}}\xspace\ensuremath{\eta}\xspace$} 
    \put(19 ,110) { \small $(\ensuremath{\eta}\xspace\ensuremath{\rightarrow}\xspace\ensuremath{\ensuremath{\ensuremath{\gamma}\xspace}\xspace{}\ensuremath{\ensuremath{\gamma}\xspace}\xspace}\xspace$)} 
    \put(61, 115) {LHCb}
    \put(93, 115) {(b)}
    \put(99,115) {\small $\ensuremath{\ensuremath{\ensuremath{B}\xspace}\xspace^0_\ensuremath{\ensuremath{s}\xspace}\xspace}\xspace\ensuremath{\rightarrow}\xspace\ensuremath{{\ensuremath{J}\xspace\mskip -3mu/\mskip -2mu\ensuremath{\psi}\xspace\mskip 2mu}}\xspace\ensuremath{\eta}\xspace$} 
    \put(99,110) {\small $(\ensuremath{\eta}\xspace\ensuremath{\rightarrow}\xspace3\ensuremath{\pi}\xspace)$} 
    \put(139, 115) {LHCb}
    \put(15, 52) {(c)}
    \put(21 ,52) {\small $\ensuremath{\ensuremath{\ensuremath{B}\xspace}\xspace^0_\ensuremath{\ensuremath{s}\xspace}\xspace}\xspace\ensuremath{\rightarrow}\xspace\ensuremath{{\ensuremath{J}\xspace\mskip -3mu/\mskip -2mu\ensuremath{\psi}\xspace\mskip 2mu}}\xspace\ensuremath{\eta}\xspace^{\prime}$} 
    \put(21 ,47) {\small $(\ensuremath{\eta}\xspace^{\prime}\ensuremath{\rightarrow}\xspace\ensuremath{\rho}\xspace^0\ensuremath{\ensuremath{\gamma}\xspace}\xspace)$} 
    \put(61, 52) {LHCb}
    \put(93, 52) {(d)}
    \put(98,52) { \small $\ensuremath{\ensuremath{\ensuremath{B}\xspace}\xspace^0_\ensuremath{\ensuremath{s}\xspace}\xspace}\xspace\ensuremath{\rightarrow}\xspace\ensuremath{{\ensuremath{J}\xspace\mskip -3mu/\mskip -2mu\ensuremath{\psi}\xspace\mskip 2mu}}\xspace\ensuremath{\eta}\xspace^{\prime}$} 
    \put(98,47) { \small $(\ensuremath{\eta}\xspace^{\prime}\ensuremath{\rightarrow}\xspace\ensuremath{\pi}\xspace\ensuremath{\pi}\xspace\ensuremath{\eta}\xspace)$} 
    \put(139, 52) {LHCb}
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\end{document}
