\begin{table}%t1
\caption{\label{tab_comp}\label{tab1}Combinations of $Z$ and $Y$ of the computed tracks.}
\small%\centering
\par
\begin{tabular}{cccccc}
\hline\hline
$Z$ & $Y$1 & $Y$2 & $Y$3 & $Y$4 & $Y$5 \\
\hline 
0.0001 & 0.23 & 0.26 & 0.30 &      & 0.40      \\
0.0004 & 0.23 & 0.26 & 0.30 &      & 0.40      \\
0.001  & 0.23 & 0.26 & 0.30 &      & 0.40      \\
0.002  & 0.23 & 0.26 & 0.30 &      & 0.40      \\
0.004  & 0.23 & 0.26 & 0.30 &      & 0.40      \\
0.008  & 0.23 & 0.26 & 0.30 & 0.34 & 0.40      \\
0.017  & 0.23 & 0.26 & 0.30 & 0.34 & 0.40      \\
0.040  &      & 0.26 & 0.30 & 0.34 & 0.40      \\
0.070  &      &      & 0.30 & 0.34 & 0.40      \\ 
\hline
\end{tabular} 
 \vspace*{4mm}
\end{table}