Reduction of Statistical Power Per Event Due to Upper Lifetime Cuts in Lifetime Measurements

TL;DR

Applying upper lifetime cuts in lifetime measurements can significantly reduce statistical significance and increase uncertainty, even if the number of events remains nearly unchanged.

Contribution

This paper quantifies how upper lifetime cuts impact the statistical power of lifetime measurements, highlighting effects not previously well understood.

Findings

Moderate upper lifetime cuts can dramatically increase statistical uncertainty.

Event number reduction is not the main factor; cuts affect significance.

Implications for trigger design and data analysis in lifetime experiments.

Abstract

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.