unique background adds to the statistical evidence of a signal appearing among the untagged events.

Detector Description
====================

![\[vetofigure1\]An image of the passive Gd-loaded polypropylene sections of the veto detector partially assembled around the ZEPLIN–III instrument. Thirty-two such sections form a closed barrel and a roof plug is lowered onto the barrel to enclose ZEPLIN–III completely. The active scintillator modules are then placed around the polypropylene, and make up in total 30 cm thickness hydrocarbon shielding.](vetofigure1.eps){width="8.6cm"}

![\[vetofigure2\]An aerial view of the completed veto detector before the Pb castle is built up around the entire assembly. The Gd-loaded polypropylene sections have been completely enclosed by the scintillator modules. Thirty-two sections make up the barrel with a further twenty modules on the roof above ZEPLIN–III. The enclosures for the PMTs attached to the scintillators on the roof can be seen whereas those on the standing barrel scintillators are in recesses built into the polypropylene sections. The outer diameter of the barrel is 160 cm.](vetofigure2.eps){width="8.6cm"}

![\[cad\]Cross-sectional view of the ZEPLIN-III experiment in its second science run configuration. In the centre is the ZEPLIN-III detector (labelled A) showing the outer copper vacuum vessel. Forming a barrel around ZEPLIN-III are the 32 Gd-loaded polypropylene pieces 