Measurement of Lepton Momentum Moments in the Decay bar{B} o X \ell \bar{ u} and Determination of Heavy Quark Expansion Parameters and |V_cb|

摘要

We measure the primary lepton momentum spectrum in B-bar to X l nu decays,for p_l > 1.5 GeV/c in the B rest frame. From this, we calculate variousmoments of the spectrum. In particular, we find R_0 = [int(E_l>1.7)(dGam/dE_sl)*dE_l] / [int(E_l>1.5) (dGam/dE_sl)*dE_l] = 0.6187 +/- 0.0014_stat+/- 0.0016_sys and R_1 = [int(E_l>1.5) E_l(dGam/dE_sl)*dE_l] / [int(E_l>1.5)(dGam/dE_sl)*dE_l] = (1.7810 +/- 0.0007_stat +/- 0.0009_sys) GeV. We use thesemoments to determine non-perturbative parameters governing the semileptonicwidth. In particular, we extract the Heavy Quark Expansion parametersLambda-bar = (0.39 +/- 0.03_stat +/- 0.06_sys +/- 0.12_th) GeV and lambda_1 =(-0.25 +/- 0.02_stat +/- 0.05_sys +/- 0.14_th) GeV^2. The theoreticalconstraints used are evaluated through order 1/M_B^3 in the non-perturbativeexpansion and beta_0*alpha__s^2 in the perturbative expansion. We use theseparameters to extract |V_cb| from the world average of the semileptonic widthand find |V_cb| = (40.8 +/- 0.5_Gam-sl +/- 0.4_(lambda_1,Lambda-bar)-exp +/-0.9_th) x 10^-3. In addition, we extract the short range b-quark mass m_b^1S =(4.82 +/- 0.07_exp +/- 0.11_th) GeV/c^2. Finally, we discuss the implicationsof our measurements for the theoretical understanding of inclusive semileptonicprocesses.