Make a standalone plot using TikZ

\documentclass{minimal}

\usepackage{tikz}

\usepackage[active,tightpage]{preview}
\PreviewEnvironment{tikzpicture}
\setlength\PreviewBorder{5pt}%


\begin{document}

\begin{tikzpicture}[scale=1.6]
    \draw[->] (0,0) -- (4,0) coordinate (x axis);
    \draw[->] (0,0) -- (0,3.5) coordinate (y axis);
  \shadedraw [shading=axis,shading angle=90, left color=blue!70,right color=blue!30, draw=blue!50!black] (0.2,0) rectangle (3.8,3.3);
    \shadedraw [shading=axis,shading angle=90] (0.6,0) rectangle (2.0,2.3);
 
 \node at(0.2,-0.2){{$20$}};
 \node at(0.6,-0.2){{$60$}};
 \node at(2.0, -0.2){{$600$}};
 \node at(3.8, -0.2){{$1400$}};
 \node at(4.5, 0){{$p_{T}$[GeV]}};

 \node at(-0.2, 2.3){{$2.8$}};
 \node at(-0.2, 3.3){{$4.4$}};
 \node at(-0.2, 3.7){{$|y|$}};

 %
 \node at(1.3, 1.3){{$17\,\,nb^{-1}$}};
 \node at(2.9, 2.6){{$40\,\,pb^{-1}$}};
    \end{tikzpicture}

\end{document}