Determination of heavy quark non-perturbative parameters from spectral moments in semileptonic B decays

TL;DR

The paper reports a comprehensive analysis of semi-leptonic B decays using DELPHI data to extract spectral moments of hadronic mass and lepton energy. By fitting these moments within the kinetic scheme of the OPE, it determines heavy-quark parameters m_b(1 GeV), m_c(1 GeV), μ_π^2(1 GeV), and tilde ρ_D^3, and uses them to obtain a precise value of |V_cb|. The study also characterizes D** production, including masses, widths, and non-resonant contributions, and validates the methodology by cross-consistency across hadronic and leptonic observables. Overall, the work provides a robust calibration of non-perturbative QCD parameters and a competitive determination of |V_cb| that combines inclusive-width measurements with spectral moments.

Abstract

Moments of the hadronic invariant mass and of the lepton energy spectra in semileptonic B decays have been determined with the data recorded by the DELPHI detector at LEP. From measurements of the inclusive b-hadron semileptonic decays, and imposing constraints from other measurements on b- and c-quark masses, the first three moments of the lepton energy distribution and of the hadronic mass distribution, have been used to determine parameters which enter into the extraction of |V_cb| from the measurement of the inclusive b-hadron semileptonic decay width. The values obtained in the kinetic scheme are: m_b(1 GeV) = 4.591 +/- 0.062 +/- 0.039 +/- 0.005 GeV/c^2 m_c(1 GeV) = 1.170 +/- 0.093 +/- 0.055 +/- 0.005 GeV/c^2 mu_{pi}^2(1 GeV) = 0.399 +/- 0.048 +/- 0.034 +/- 0.087 GeV^2 \tildeρ_D^3 = 0.053 +/- 0.017 +/- 0.011 +/- 0.026 GeV^3, and include corrections at order 1/m_b^3. Using these results, and present measurements of the inclusive semileptonic decay partial width of b-hadrons at LEP, an accurate determination of |V_cb| is obtained: |V_cb| = 0.0421 x (1 +/- 0.014 (meas.) +/- 0.014 (fit) +/- 0.015 (th.)).

Figures (14)

• Figure 1: ${\rm D}^0$, ${\rm D}^+$ and ${\rm D}^{\ast +}$ signals used in the present analysis, in which the ${\rm D}^0$ meson decays into charged particles only and which correspond to events registered in 1992-95. Intervals used to define the signal and sideband regions are indicated.
• Figure 2: Left: Distributions of the decimal logarithm of the $\chi^2$ probability for secondary ${\rm D}^0 \pi \ell^-$ vertices in events selected in the sidebands of the signal obtained using real (points with error bars) and simulated (histogram) events. Right: Distributions of the values of the discriminant variable corresponding to events selected in the sidebands of the signal for real data (points with error bars) and simulated events (shadowed histogram). The other histogram (hatched) corresponds to simulated events from combinatorial background situated in the signal mass region. The histograms have been normalized to the same number of entries.
• Figure 3: Discriminant variable distributions for a) ${\rm D}^{\ast +} \pi^-$ and b) ${\rm D}^{\ast +} \pi^+$ candidates. Points with error bars correspond to real events whereas the histograms show the fitted components. The fake lepton background in these plot includes $\tau$ events.
• Figure 5: Comparison between $\Delta_m$ distributions obtained for combinatorial background events selected in the sidebands for real data (stars) and simulation (diamonds) corresponding to the channel ${\rm D}^0 \pi^+$ in the 1994-1995 data sample. The two distributions have been normalized to the same number of entries. The curve fitted to simulated events has been superimposed.
• Figure 6: $\Delta_m$ distributions for right-sign events corresponding to the three ${\rm D}^{(*)}\pi$ combinations.The fitted signal contributions are superimposed.