A Measurement of the Product Branching Ratio f(b->Lambda_b).BR(Lambda_b->Lambda X) in Z0 Decays

TL;DR

This paper reports a measurement of the combined probability that a b-quark decays into a Lambda_b baryon which subsequently decays into a Lambda particle, using data from the OPAL detector at LEP.

Contribution

It provides a new measurement of the product branching ratio for b->Lambda_b and Lambda_b->Lambda X decays, combining previous results for improved accuracy.

Findings

Measured product branching ratio: (2.67+-0.38(stat)+0.67-0.60(sys))%.

Combined with previous data, the ratio is (3.50+-0.32(stat)+-0.35(sys))%.

Demonstrates a method to distinguish signal from background using Lambda momentum spectra.

Abstract

The product branching ratio, f(b->Lambda_b).BR(Lambda_b->Lambda X), where Lambda_b denotes any weakly-decaying b-baryon, has been measured using the OPAL detector at LEP. Lambda_b are selected by the presence of energetic Lambda particles in bottom events tagged by the presence of displaced secondary vertices. A fit to the momenta of the Lambda particles separates signal from B meson and fragmentation backgrounds. The measured product branching ratio is f(b->Lambda_b).BR(Lambda_b->Lambda X) = (2.67+-0.38(stat)+0.67-0.60(sys))% Combined with a previous OPAL measurement, one obtains f(b->Lambda_b).BR(Lambda_b->Lambda X) = (3.50+-0.32(stat)+-0.35(sys))%.