De-synchronization problems of the BPM/Raster ADC for E93050

A sampling of eight runs (data taken at Q2 = 1 GeV2, summarized in Table 1) show that a lot of our data have a problem of de-synchronization, as far as the beam position measurements are concerned. More than 50% of the events are concerned, thus forbidding us to throw them away. In order to have a good knowledge of the angle and momentum of the real outgoing photon, we must know the vertical beam position with a good accuracy (better than 1 mm). Moreover a good horizontal beam position is necessary in order to make a good selection of the events on the vertex reconstruction (distance d = two armx-beamx). This means we have to apply a correction for the raster, which can be as big as +/- 5 mm in some extreme cases. The procedure available in Espace version 2.6 and 2.7 are based on the assumption of a perfect synchronization of the event with the recorded data of the raster and bpm adc. In this paper a study of this de-synchronization and a way to overcome the problem is presented. (author)