The Large Angle Veto (LAV) detector is one part of the overarching photon veto system in the NA62 experiment. It consists of 12 stations distributed along the decay volume and spaced by 6m in the upstream region and by up to 20m for the most downstream station (figure). In this configuration the Large Angle Veto (LAV) covers the angular region between 8.5 mr and 50 mrad.
The basic building blocks of this detector are lead glass crystals with attached photomultipliers (PMT) from the former OPAL electromagnetic calorimeter. Each LAV stations is made up of 4 or 5 rings of crystals, which are slightly staggered in azimuth providing a complete hermeticity for tracks in this angular region.
Photon vetoes are required to suppress the dominant background originating from the decay K+-> pi+ pi0 The average inefficiency for the rejection of the p0 should be smaller than 10-8. The photon vetoes need to have hermetic geometrical coverage up to 50 mrad (For photons originating from the kaon decays occurring in the decay region between 105 to 170m after the target).
The Large Angle Vetoes (LAV) covers the angular region between 8.5 mr and 50 mr. The 12 Stations are distributed along the decay volume and spaced by 6m in the upstream region and by 12m downstream, according to the layout below.