A cut on the maximum lifetime in a lifetime fit not only reduces the number
of events, but also, in some circumstances dramatically, decreases the
statistical significance of each event. The upper impact parameter cut in the
hadronic B trigger at CDF, which is due to technical limitations, has the same
effect. In this note we describe and quantify the consequences of such a cut on
lifetime measurements. We find that even moderate upper lifetime cuts, leaving
event numbers nearly unchanged, can dramatically increase the statistical
uncertainty of the fit result.Comment: Changes to latest revision: added DOI link, took the opportunity to
correct some minor typos added one small clarificatio
