Constraints on exclusive branching fractions $BF_i(B^+\to X_c^il^+\nu)$ from moment measurements in inclusive $B\to X_cl\nu$ decays

Abstract

As an alternative to direct measurements, we extract exclusive branching fractions of semileptonic B-meson decays to charmed mesons, $BF_i(B\to X_c^il\nu)$ with $X_c^i = D, D^*, D_0, D'_1, D_1, D_2, D', D'^*$ and non-resonant final states $(D^{(*)}\pi)_{nr}$, from a fit to electron energy, hadronic mass and combined hadronic mass-energy moments measured in inclusive $B\to X_cl\nu$ decays. The fit is performed by constraining the sum of exclusive branching fractions to the measured value of $BF(B\to X_cl\nu)$, and with different sets of additional constraining terms for the directly measured branching fractions. There is no fit scenario in which a single branching fraction alone is enhanced to close the gap between $BF(B\to X_cl\nu)$ and the sum of known branching fractions $BF_i(B\to X_c^il\nu)$. The fitted $BF(B\to D^*l\nu)$ is 5% to 10% larger than the direct measurement depending on whether or not $BF(B\to D^*l\nu)$ is constrained to its direct measurement. $BF(B\to Dl\nu)$ values are in good agreement with the direct measurement unless $BF(B\to D^*l\nu)$ is constrained, which results in a higher $BF(B\to Dl\nu)$ value. Within large uncertainties, $BF(B\to D'_1l\nu)$ agrees with direct measurements. Depending on the fit scenario, $BF(B\to D_0l\nu)$ is consistent with or larger than its direct measurement. The fit is not able to easily disentangle $B\to D_1l\nu$ and $B\to D_2l\nu$, and tends to increase the sum of these two branching fractions. $BF(B\to (D^{(*)}\pi)_{nr}l\nu)$ with non-resonant $(D^{(*)}\pi)_{nr}$ final states is found to be 0.2-0.4%, consistent with $B\to D^{(*)}\pi l\nu$ and $B\to D^{**}(D^{(*)}\pi)l\nu$ measurements. No indication is found for significant contributions from so far unmeasured $B\to D'^{(*)}l\nu$ decays assuming that the $D'$ and $D'^*$ can be identified with the observed $D(2550)$, respectively, $D^*(2600)$ state.