Measurement of Moments of the Hadronic-Mass and -Energy Spectrum in Inclusive Semileptonic $\bar{B}\to X_c{\ell }^{-}\bar{\nu }$ Decays

Abstract

We present a measurement of moments of the inclusive hadronic-mass and -energy spectrum in semileptonic $\bar{B}\to X_c{\ell }^{-}\bar{\nu }$ decays. This study is based on a sample of 232 million ${\rm Y}(4S)\to B\bar{B}$ decays recorded by the BABAR detector at the PEP-II $e^{+}{e}^{-}$-storage rings. We reconstruct the semileptonic decay by identifying a lepton in events tagged by a fully reconstructed hadronic decay of the second $B$ meson. We report preliminary results for the moments $<m_X^k>$ with $k=1,...,6$ and $<n_X^k>$ with $k=2,4,6$ and $n_X^2=m_X^2{c}^4-2\tilde{\Lambda }{E}_X+{\tilde{\Lambda }}^2$, with $m_X$ the mass of the hadronic system, $E_X$ its energy, and $\tilde{\Lambda }$ a constant of $0.65\mathrm{GeV}$, for different minimal lepton momenta between 0.8 and $1.9\mathrm{GeV}/c$ measured in the $B$-meson rest frame. These are predicted in the framework of a Heavy Quark Expansion (HQE), which allows the extraction of the total semileptonic branching fraction, the CKM-matrix element $|V_{cb}|$, and the quark masses $m_b$ and $m_c$, together with the dominant non-perturbative HQE parameters. We find as preliminary results $|V_{cb}|=(41.88\pm 0.81)\cdot 10^{-3}$ and $m_b=(4.552\pm 0.055)\mathrm{GeV}/c^2$.

21 pages, 11 postscript figures, submitted to EPS-HEP2007