Measurement of the moments of the hadronic invariant mass distribution in semileptonic B decays

Using 180 pb-1 of data collected with the CDF II detector in Run II of the Tevatron, we measure the first two moments of the invariant mass-squared distribution of the charm-hadron system in semileptonic B decays. We measure directly the first two moments of the D** component for a minimum lepton momentum in the B rest frame of 0.7 GeV/c to be 〈mD∗∗2〉=(5.83±0.16stat±0.08syst)GeV2, 〈(mD∗∗2−〈mD∗∗2〉)2〉=(1.30±0.69stat±0.20syst)GeV4. After combining them with the known contributions from D and D∗ we find for the moments of the charm-hadron system 〈MXc2〉−mD¯2=(0.459±0.037stat±0.065syst)GeV2, 〈(MXc2−〈MXc2〉)2〉=(1.04±0.25stat±0.12syst)GeV4, where mD¯ is the spin-averaged D mass and the systematic error is dominated by the uncertainty in the branching ratios used in the combination of the D, D∗ and D∗∗ pieces. From the moments we determine the non-perturbative HQET parameters Λ and λ1 in the pole and IS mass schemes.