Identification of the Planck cluster candidates with X-ray clusters from the MCXC catalogue. Black points are candidates firmly identified with MCXC clusters, while green points are candidates with no association. Left panel: distance of the Planck position to the position of the closest MCXC cluster as a function of the distance normalized to the cluster size . Middle panel: S/N normalized to the expected value as a function of normalized distance. Right panel: SZ flux, Y_500,PSX, re-extracted fixing the position and size to the X-ray value, as a function of expected values. The red line is the equality line. In all panels, , and are estimated from the cluster X-ray luminosity used as mass proxy (see text).