\begin{table}%t1
\caption{\label{tab1}Expected $\Omega_{\rm min}$ for the main detector pairs, corresponding to a flat
  background spectrum and an integration time~$T = 1$~year, 
a detection rate $\alpha=90\%$  and a false alarm rate $\gamma=10\%$.
LHO and LLO stand for LIGO Hanford Observatory and  LIGO Livingston Observatory. } 
%\centering
\par
\begin{tabular}{lcccc}
\hline
\hline
& LHO-LHO & LHO-LLO & LLO-VIRGO & VIRGO-GEO  \\
\hline
Initial& $4 \times 10^{-7}$ & $4 \times 10^{-6}$ &  $8 \times 10^{-6}$
&  $8 \times 10^{-6}$  \\
Advanced & $6 \times 10^{-9}$  & $1 \times 10^{-9}$  & &  \\
\hline
\end{tabular}
\end{table}