Measurement of the lepton energy in the decay B-bar -> X l nu-bar and determination of the Heavy Quark Expansion Parameters

TL;DR

This paper measures moments of the lepton energy spectrum in B meson decays to extract Heavy Quark Expansion parameters, which are then used to determine the CKM matrix element |V_cb| and the b-quark mass with improved precision.

Contribution

It provides new experimental measurements of lepton energy moments and derives HQE parameters, enabling a more precise determination of |V_cb| and the b-quark mass.

Findings

Measured lepton energy moments for p_l > 1.5 GeV/c.

Extracted HQE parameters Lambda-bar and lambda_1.

Determined |V_cb| with reduced uncertainties.

Abstract

We measured two moments of the lepton momentum spectrum in B -> X l nu, where l= e or mu, for p_l > 1.5 GeV/c. From these we derive the Heavy Quark Expansion (HQE) parameters Lambda-bar(MS-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, through order 1/M_B^3 in the non-perturbative expansion and beta_0 alpha_s^2 in the perturbative expansion. The theoretical expression needed to extract |V_cb| from the measured semileptonic width is evaluated using these HQE parameters. Combined with the world average of the semileptonic width, we find |V_cb|=(40.8 +- 0.5(Gamma_sl) +- 0.4(lambda_1,Lambda-bar) +- 0.9(th)) 10^{-3}. Finally, the short range b-quark mass m_b(1S) is evaluated and found to be 4.82 +- 0.07(exp) +- 0.11(th) GeV/c^2.