Study of the B^0 Semileptonic Decay Spectrum at the Upsilon(4S) Resonance

TL;DR

This paper presents the first measurement of the lepton momentum spectrum in B0 semileptonic decays at the Upsilon(4S), comparing it with the inclusive spectrum to determine B meson branching fractions and production ratios.

Contribution

It provides the first measurement of the B0 lepton spectrum and derives semileptonic branching fractions and production ratios from experimental data.

Findings

The lepton spectra are consistent above 1.5 GeV/c.

Measured B0 and B+ semileptonic branching fractions.

Determined the ratio of B+ to B0 production at the Upsilon(4S).

Abstract

We have made a first measurement of the lepton momentum spectrum in a sample of events enriched in neutral B's through a partial reconstruction of B0 --> D*- l+ nu. This spectrum, measured with 2.38 fb**-1 of data collected at the Upsilon(4S) resonance by the CLEO II detector, is compared directly to the inclusive lepton spectrum from all Upsilon(4S) events in the same data set. These two spectra are consistent with having the same shape above 1.5 GeV/c. From the two spectra and two other CLEO measurements, we obtain the B0 and B+ semileptonic branching fractions, b0 and b+, their ratio, and the production ratio f+-/f00 of B+ and B0 pairs at the Upsilon(4S). We report b+/b0=0.950 (+0.117-0.080) +- 0.091, b0 = (10.78 +- 0.60 +- 0.69)%, and b+ = (10.25 +- 0.57 +- 0.65)%. b+/b0 is equivalent to the ratio of charged to neutral B lifetimes, tau+/tau0.