
\documentclass[border=5pt,multi=true]{standalone}
\usepackage{standalone}
\usepackage{ifthen}
\usepackage{rotating}
\usepackage{graphpap}
\usepackage{float}
\usepackage{placeins}
\usepackage{afterpage}
\usepackage{microtype}
\usepackage{lineno}
\usepackage{xspace}
\usepackage{graphicx}
\usepackage{color}
\usepackage{colortbl}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsfonts}
\usepackage{upgreek}
\usepackage{hyperref}
\usepackage{hypcap}
\usepackage{cite}
\usepackage{mciteplus}
\usepackage{longtable}


\graphicspath{{./figs/}}

\begin{document}
\DeclareGraphicsExtensions{.pdf}
\setlength{\unitlength}{1mm}
  \centering
   \begin{picture}(150,60)
    \put(0,0){
      \includegraphics*[width=75mm,height=60mm,%
      ]{Fig_1a.pdf}
    }
    \put(75,0){
      \includegraphics*[width=75mm,height=60mm,%
      ]{Fig_1b.pdf}
    }
    \put(-2, 13 ) { \small
      \begin{sideways}%
        Candidates/(10\ensuremath{{\mathrm{\,Me\kern -0.1em V\!/}c^2}}\xspace)
      \end{sideways}%
    }
    \put(72.5,13 ) { \small
      \begin{sideways}%
        Candidates/(10\ensuremath{{\mathrm{\,Me\kern -0.1em V\!/}c^2}}\xspace)
      \end{sideways}%
    }
    \put(28,-1)   { $m_{\ensuremath{{\ensuremath{J}\xspace\mskip -3mu/\mskip -2mu\ensuremath{\psi}\xspace\mskip 2mu}}\xspace\ensuremath{\ensuremath{\ensuremath{K}\xspace}\xspace^+}\xspace\ensuremath{\ensuremath{\ensuremath{K}\xspace}\xspace^-}\xspace\ensuremath{\ensuremath{\ensuremath{\pi}\xspace}\xspace^+}\xspace}$ }
    \put(52,-1)   { $\left[ \mathrm{GeV}/c^2\right]$}
    \put(107,-1)  { $m_{\ensuremath{{\ensuremath{J}\xspace\mskip -3mu/\mskip -2mu\ensuremath{\psi}\xspace\mskip 2mu}}\xspace\ensuremath{\ensuremath{\ensuremath{\pi}\xspace}\xspace^+}\xspace}$}
    \put(128,-1)  { $\left[ \mathrm{GeV}/c^2\right]$}
    \put(  50,45  ){ LHCb}
    \put( 125,45  ){ LHCb}
    \put(  15,45  ){ (a)}
    \put(  90,45  ){ (b)}
  \end{picture}
\end{document}
