The Problem

The original MVD specifications in the CDR (see tables 5.3 and 5.4 of the CDR) specified alignment requirements. One requirement is the radial distance between the two Si layers, which we said must be known to 0.4mm. This requirement comes from the vertex finding algorithm, which must know the relative distance of the two Si layers from the beam. If the location of the beam itself is unknown in the radial direction, then this ratio of distances is also not known. The actual limit on the positioning of the MVD was later specified by Hubert van Hecke [1] to require a maximum displacement of the whole MVD of 1.3mm.

Long after writting this specification for the MVD, the possibility that the vertex position might me unknown and might vary from fill to fill by several mm came up. In either of these cases, the 1.3mm specification may be exceeded. Some of the 10K simulation runs have been done with . We have looked at these to try to estimate the MVD's ability to find the vertex when the beam position is off-center.

1) MVD alignment note.