General considerations

QIPBTAG is an algorithm for tagging the presence of long-lived particles written by D. Brown and M. Frank.

It computes the impact parameter of tracks relative to the primary vertex reconstructed using the QFNDIP subroutine (4.17 on p. ). After calibration, the algorithm converts the track signed impact parameter significance into a probability that the track came from the primary vertex found by QFNDIP. Track probabilities are combined to give jet, hemisphere and event probabilities.

Several important modifications have been done to the original QIPBTAG, especially to take into account the new VDET for data from 1996 and after (VDET96 option, J.Carr and M. Thulasidas, June 1997), to have a consistent b-tag for LEP2 data, and to get from the database bank QIPC the calibration constants which are dependant on the period of data taking.

The last version released with ALPHA124.05 (thanks to I. Tomalin, April 1999) recognises automatically the type of data being read and gives the best possible b-tagging efficiency. See ALPHA124.NEWS for more details.

To use QIPBTAG properly, one must read the complete description of the method and of the package in the Aleph Note 92-135 (August 1992).