  It is now widely accepted that a new middle baseline disappearance reactor
neutrino experiment with multiple detectors could provide a clean measurement
of the $\theta_{13}$ mixing angle, free from any parameter degeneracies and
correlations induced by matter effect and the unknown leptonic Dirac CP phase.
The current best constraint on the third mixing angle comes from the Chooz
reactor neutrino experiment $\sin^{2}(2\theta_{13})<0.2$ (90$ %$ C.L., $\Delta
m_{\rm atm}^{2}=2.0 10^{-3}$ eV$^{2}$). Several projects of experiment, with
different timescales, have been proposed over the last two years all around the
world. Their sensitivities range from $\sin^{2}(2\theta_{13})<$ 0.01 to 0.03,
having thus an excellent discovery potential of the $\nu_e$ fraction of
$\nu_3$.
