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\graphicspath{{./figs/}}

\begin{document}
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  \centering
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    \put( 0, 0){
      \includegraphics*[width=75mm,height=60mm,%
      ]{Fig1a.pdf}
    }
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      \includegraphics*[width=75mm,height=60mm,%
      ]{Fig1b.pdf}
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    \put( 20, 50){ a)}
    \put( 95, 50){ b)}
    \put( 38, 49){ $\begin{array}{l}\mathrm{LHCb} \\  \ensuremath{\ensuremath{\ensuremath{B}\xspace}\xspace_\ensuremath{\ensuremath{c}\xspace}\xspace^+}\xspace\ensuremath{\rightarrow}\xspace\ensuremath{{\ensuremath{J}\xspace\mskip -3mu/\mskip -2mu\ensuremath{\psi}\xspace\mskip 2mu}}\xspace\ensuremath{\ensuremath{\ensuremath{\pi}\xspace}\xspace^+}\xspace \end{array}$ }
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    \put( -1, 20) { \small \begin{sideways}Candidates/(5\ensuremath{{\mathrm{\,Me\kern -0.1em V\!/}c^2}}\xspace)\end{sideways} }
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    \put( 38,  0) { $m_{\ensuremath{{\ensuremath{J}\xspace\mskip -3mu/\mskip -2mu\ensuremath{\psi}\xspace\mskip 2mu}}\xspace\ensuremath{\ensuremath{\ensuremath{\pi}\xspace}\xspace^+}\xspace}$ }
    \put(112,  0) { $m_{\ensuremath{{\ensuremath{J}\xspace\mskip -3mu/\mskip -2mu\ensuremath{\psi}\xspace\mskip 2mu}}\xspace\ensuremath{\ensuremath{\ensuremath{K}\xspace}\xspace^+}\xspace}$  }
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