Event Selection

In order to provide a fast event selection and rejection of nearly empty events the algorithm starts with the following criteria:

1. an event should contain at least two tracks which are not marked as clones by the clone removal algorithm [#!Ple!#],
2. at least one primary vertex consisting of more than three tracks or VDS segments should be reconstructed in the event.

The RTRA table contains all possible combinations of track segments, this leads to the fact that track segments can be used more than once. However, for the analysis purposes it is important to have a sample of tracks with a low number of clones (see Chapter 4). Therefore a standard procedure for clone removal was developed, based on the number of hits used in the track and the $\chi^2$ of the track. The performance of the algorithm was adjusted with the help of a $K^0_S$ reference data set (details about tests and the algorithm can be found in [#!Ple!#]).