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Small Angle Detectors

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 $\theta$. 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.