The Belle II detector is situated at the asymmetric $e^{-}e^{+}$ collider SuperKEKB at KEK in Tsukuba in Japan, which operates with an energy slightly above the mass of the Y(4S) resonance. As a result, pairs of B mesons are predominantly produced. Due to the clean experimental environment, various measurements to test the Standard Model and precisely determine its parameters can be performed. This is e.g. the element $V_{ mathrm{cb}}$ of the CKM matrix among others, where one of the leading systematic uncertainties arises due to decays of the nature $B to D^{**} ell nu_{ ell}$ . This th...

We present a study of B semileptonic decays into charm final states based on 211.7 fb{sup -1} of data collected at the {Upsilon}(4S) resonance with the BABAR detector at the PEP-II e{sup +}e{sup -} storage ring. Using a novel technique based on the simultaneous fit of a set of variables reconstructed on the recoil of a B tagged in an hadronic decay mode, we measure the relative branching fractions {Lambda}(B{sup -} {yields} D{sup 0}{ell}{sup -}{bar {nu}}{sub {ell}}) = 0.611 {+-} 0.022 (stat.) {+-} 0.027 (syst.) and {Lambda}(B{sup -} {yields} D**{sup 0})(D{sup (*)}{pi}){ell}{sup -}{bar {nu}}{sub {ell}}/{Lambda}(B{sup -} {yields} DX{ell}{sup -}{bar {nu}}{sub {ell}}) = 0.173 {+-} 0.017 (stat.) {+-} 0.021 (syst.).

We determine the inclusive B [yields] X[sub c][ell][nu] branching fraction, [Beta][sub c[ell][nu]], the CKM matrix element V[sub cb], and other heavy-quark parameters from a simultaneous fit to moments of the hadronic-mass and lepton-energy distributions in semileptonic B-meson decays, measured as a function of the lower limit on the lepton energy, using data recorded with the BABAR detector. Using Heavy Quark Expansions (HQEs) to order 1/m[sub b][sup 3], we extract [Beta][sub ce[nu]] = (10.61 [+-] 0.16[sub exp] [+-] 0.06[sub HQE])% and V[sub cb] = (41.4 [+-] 0.4[sub exp] [+-] 0.4[sub HQE] [+-] 0.6[sub th]) x 10[sup -3]. The stated errors refer to the experimental, HQE, and additional theoretical uncertainties.

The absolute branching fractions for the decays D{sub s}− → l−{bar?}{sub l} (l = e,?, or?) are measured using a data sample corresponding to an integrated luminosity of 521 fb−1 collected at center of mass energies near 10.58 GeV with the BABAR detector at the PEP-II ee− collider at SLAC. The number of D{sub s}− mesons is determined by reconstructing the recoiling system DKX? in events of the type e+e−DKXD*{sub s}−, where D*{sub s}− → D{sub s}−? and X represents additional pions from fragmentation. The D{sub s}− → l°{nu}{sub {ell}} events are detected by full or partial reconstruction of the recoiling system DKX?{ell}. The branching fraction measurements are combined to determine the D{sub s}− decay constant f{sub D{sub s}} = (258.6 ± 6.4 ± 7.5) MeV, where the first uncertainty is statistical and the second is systematic.