Measurement of Lepton Momentum Moments in the Decay barB X and Determination of Heavy Quark Expansion Parameters and |Vcb|
Abstract
We measure the primary lepton momentum spectrum in B-bar to X l nu decays, for pl > 1.5 GeV/c in the B rest frame. From this, we calculate various moments of the spectrum. In particular, we find R0 = [int(El>1.7) (dGam/dEsl)*dEl] / [int(El>1.5) (dGam/dEsl)*dEl] = 0.6187 +/- 0.0014stat +/- 0.0016sys and R1 = [int(El>1.5) El(dGam/dEsl)*dEl] / [int(El>1.5) (dGam/dEsl)*dEl] = (1.7810 +/- 0.0007stat +/- 0.0009sys) GeV. We use these moments to determine non-perturbative parameters governing the semileptonic width. In particular, we extract the Heavy Quark Expansion parameters Lambda-bar = (0.39 +/- 0.03stat +/- 0.06sys +/- 0.12th) GeV and lambda1 = (-0.25 +/- 0.02stat +/- 0.05sys +/- 0.14th) GeV2. The theoretical constraints used are evaluated through order 1/MB3 in the non-perturbative expansion and beta0*alpha_s2 in the perturbative expansion. We use these parameters to extract |Vcb| from the world average of the semileptonic width and find |Vcb| = (40.8 +/- 0.5Gam-sl +/- 0.4(lambda1,Lambda-bar)-exp +/- 0.9th) x 10-3. In addition, we extract the short range b-quark mass mb1S = (4.82 +/- 0.07exp +/- 0.11th) GeV/c2. Finally, we discuss the implications of our measurements for the theoretical understanding of inclusive semileptonic processes.
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