Exclusive semileptonic b->u l nu decays are an active area of experimental and theoretical study. These rare processes can be used to extract the magnitude of Vub, one of the smallest and least well known elements of the Cabibbo-Kobayashi-Maskawa (CKM) quark-mixing matrix Because |Vub/Vcb| is about 0.08, the branching fractions for exclusive b->u l nu processes are small, of order 10^-4, and they have only recently become experimentally accessible. The present analysis confirms the initial CLEO observation of B->rho l nu, improves the precision on the branching fraction and |Vub|, and provides the first information on the q2 dependence for this decay.

Using a sample of 3.3 million Y(4S)->BBbar events collected with the CLEO II detector at the Cornell Electron Storage Ring (CESR), we measure the branching fraction for B->rho l nu, |Vub|, and the partial rate (Delta Gamma) in three bins of q2 = (pB-prho)^2. We find B(B^0->rho^- l^+ nu) = (2.69 +- 0.41 +0.35-0.40 +- 0.50) x 10^-4, |Vub| = (3.23 +- 0.24 +0.23-0.26 +- 0.58) x 10^-3, Delta Gamma (0 lt q2 lt 7 GeV^2/c^4) = (7.6 +- 3.0 +0.9-1.2 +- 3.0) x 10^-2 ns^-1, Delta Gamma (7 lt q2 lt 14 GeV^2/c^4) = (4.8 +- 2.9 +0.7-0.8 +- 0.7) x 10^-2 ns^-1, and Delta Gamma (14 lt q2 lt 21 GeV^2/c^4) = (7.1 +- 2.1 +0.9-1.1 +- 0.6) x 10^-2 ns^-1. Here, l=e or mu, but not both, and the quoted errors are statistical, systematic, and theoretical. The method is sensitive primarily to B->rho l nu decays with leptons in the energy range above 2.3 GeV. Averaging with the previously published CLEO results for B->rho l nu, we obtain B(B^0->rho^- l^+ nu) = (2.57 +- 0.29 +0.33-0.46 +- 0.41) x 10^-4 and |Vub| = (3.25 +- 0.14 +0.21-0.29 +- 0.55) x 10^-3.

Public documentation:

• Preprint version of submission to PRD.
• Here are links to gif and ps versions of each of the figures:
• Figure #1 gif, postscript.
• Figure #2 gif, postscript.
• Figure #3 gif, postscript.
• Figure #4 gif, postscript.
• Figure #5 gif, postscript.
• Figure #6 gif, postscript.
• Figure #7 gif, postscript.
• Figure #8 gif, postscript.
• Figure #9 gif, postscript.
• Figure #10 gif, postscript.
• Figure #11 gif, postscript.
• Figure #12 gif, postscript.
• Figure #13 gif, postscript.
• Figure #14 gif, postscript.
• Figure #15 gif, postscript.
• Figure #16 gif, postscript.

• Transparencies presented by David Lange at the XIth Rencontres de Blois in June of 1999. Here are links to postscript files for some of the figures in the talk:
• Page #4, CLEO II and II.V integrated luminosity.
• Page #5, Lepton energy distribution for b->c and b->u contributions.
• Page #6, Predicted dG/dq2 distributions for all lepton energies and for those greater than 2.3 GeV.
• Page #9, M(pipi) and DeltaE distributions for Elep>2.3 GeV.
• Page #9, M(pipi) and DeltaE distributions for 2.0<Elep<2.3 GeV.
• Page #10, Elep and q2 distributions.
• Page #11, Results of average with previous CLEO analysis.
• Page #12, Simulated Dalitz plot for B->rholnu decay.
• Page #13, Measured dG/q2 distribution.
• Page #14, Comparison with other measurements of |Vub|.

• This is the thesis work of David Lange. His thesis (7.4 Mb) can be found here.

For more information on this measurement, contact

• David Lange.
• Jeff Richman.

For more information on this and other CLEO analysis, contact the CLEO analysis coordinator.