Measurement of B→ρlν decay and |Vub| -: art. no. 052001

Using a sample of 3.3 X 10(6) Y (4S) --> B (B) over bar events collected with the CLEO II detector at the Cornell Electron Storage Ring (CESR), we measure B(B --> rho l nu), \V-ub\, and the partial rate (Delta Gamma) in three bins of q(2) = (p(B) - p(rho))(2). We find B(B-0 --> rho (-)l(+) nu) = (2.69+/-0.4(-0.40)(+0.35)+/-0.50) X 10(-4), \V-ub\ = (3 23+/-0.24(-0.26)(+0.23)+/-0.58) X 10(-3), Delta Gamma(0 < q(2) < 7 GeV2/c(4)) = (7.6+/-3.0(-1.2)(+0.9)+/-3.0) X 10(-2) ns(-1), Delta Gamma(7 < q(2) < 14 GeV2/c(4)) = (4.8+/-2.9(-0.8)(+0.7)+/-0.7) X 10(-2) ns(-1), and Delta Gamma(14 < q(2) < 21 GeV2/c(4)) = (7.1+/-2.1(-1.1)(+0.9)+/-0.6) X 10(-2) ns(-1). Here, l = e or mu, but not both, and the 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(-0.46)(+0.33)+/-0.41) X 10(-4) and \V-ub\ = (3.25+/-0.14(-0.29)(+0.21)+/-0.55) X 10(-3).