Measurement of the B-Meson Inclusive Semileptonic Branching Fraction and Electron-Energy Moments

TL;DR

This work presents a high-precision measurement of the inclusive semileptonic B decay spectrum $B\to X e\nu$ using CLEO II dilepton events at the $\Upsilon(4S)$ resonance, enabling a model-independent determination of ${\mathcal B}(B\to X e\nu)=(10.91\pm0.09\pm0.24)\%$ and the electron-energy moments across $E_{\min}=0.6$–$1.5$ GeV. The analysis disentangles primary $B$-decay electrons from secondary charm backgrounds by exploiting charge correlations, a diagonal cut, and $B^0\overline{B^0}$ mixing, with careful treatment of efficiencies and backgrounds. Subtractions for $B\to X_u\ell\nu$ are performed to extract moments associated with $B\to X_c\ell\nu$, which are then corrected for boosts and electroweak radiation; the largest systematic arises from the radiative corrections. The results provide stringent tests of HQET/OPE predictions and inform global fits for nonperturbative parameters, contributing to a more consistent picture of inclusive B decays and CKM phenomenology.

Abstract

We report a new measurement of the B-meson semileptonic decay momentum spectrum that has been made with a sample of 9.4/fb of electron-positron annihilation data collected with the CLEO II detector at the Y(4S) resonance. Electrons from primary semileptonic decays and secondary charm decays were separated by using charge and angular correlations in Y(4S) events with a high-momentum lepton and an additional electron. We determined the semileptonic branching fraction to be (10.91 +- 0.09 +- 0.24)% from the normalization of the electron-energy spectrum. We also measured the moments of the electron energy spectrum with minimum energies from 0.6 GeV to 1.5 GeV.

Figures (9)

• Figure 1: Monte Carlo simulation of electron momentum versus the cosine of the opening angle between the tag lepton and the signal electron ($\cos\ \theta_{le}$) for unlike-sign dilepton pairs from opposite $B$'s (top) and from the same $B$ (right). The line indicates $p_{e} + \cos\theta_{le} = 1$.
• Figure 2: Secondary correction factor $\Delta(p)$.
• Figure 3: Electron-momentum spectra for (left) unlike-sign pairs passing the diagonal cut, and (right) like-sign pairs without the cut. The points represent data collected on the $\Upsilon(4S)$ peak and the histograms are the estimated continuum contributions determined with scaled below-resonance data.
• Figure 4: Continuum-subtracted unlike-sign (left) and like-sign (right) spectra, showing the breakdown of backgrounds computed as described in the text.
• Figure 5: Unlike-sign (left) and like-sign (right) electron spectra after all backgrounds have been subtracted. These are the spectra that were passed to Eqs. (\ref{['eq:primary']}) and (\ref{['eq:secondary']}).