In order to measure particles leaving the collision point at very
small angles, DELPHI has two small angle detectors. The main
purpose of these are to record Bhabha events and thereby
accurately determine the luminosity recorded by the experiment.
The main detector for luminosity measurements is called STIC (Small
angle TIle Calorimeter) [10] and covers an angular region
between 29 and 185 mrad in . The resolution varies from
0.25-1.2 mm in different parts of the detector and the energy
precision is in the order of 2.7% at 45 GeV. Primarily built as a
luminosity monitor the Very Small Angle Tagger (VSAT) [11]
was constructed to register electrons between 5 and 8 mrad. This
is the main detector used for this analysis and its performance
will be described in detail below.