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Register a new userStudy of intermediate states in the inclusive semileptonic $B rightarrow X_c l u$ decay structure function
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We analyze the inclusive semileptonic $B to X_c ell u$ structure functions in 2+1-flavor lattice QCD. The Mobius domain-wall fermion action is used for light, strange, charm and bottom quarks. The structure function receives contributions from various exclusive modes, including the dominant S-wave states $D^{(*)}_s$ as well as the P-wave states $D_s^{**}$. We can identify them in the lattice data, from which we put some constraints on the $B_s to D_s^{**}ell u$ form factors.
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We present our study on $B to pi l u$ semileptonic decay form factors with NRQCD action for heavy quark from a quenched lattice QCD simulation at $beta$=5.9 on a $16^3times 48$ lattice. We obtain form factors defined in the context of heavy quark effective theory by Burdman et al. and find that their $1/m_B$ correction is small. The limit of physical heavy and light quark masses can be performed without introducing any model function, and we obtain a prediction for the differential decay rate $dGamma/dq^2$. We also discuss the soft pion limit of the form factors.
We present a lattice QCD calculation of $Bto pi l u$ semileptonic decay form factors in the small pion recoil momentum region. The calculation is performed on a quenched $16^3 times 48$ lattice at $beta=5.9$ with the NRQCD action including the full 1/M terms. The form factors $f_1(vcdot k_{pi})$ and $f_2(vcdot k_{pi})$ defined in the heavy quark effective theory for which the heavy quark scaling is manifest are adpoted, and we find that the 1/M correction to the scaling is small for the $B$ meson. The dependence of form factors on the light quark mass and on the recoil energy is found to be mild, and we use a global fit of the form factors at various quark masses and recoil energies to obtain model independent results for the physical differential decay rate. We find that the $B^*$ pole contribution dominates the form factor $f^+(q^2)$ for small pion recoil energy, and obtain the differential decay rate integrated over the kinematic region $q^2 >$ 18 GeV$^2$ to be $|V_{ub}|^2 times (1.18 pm 0.37 pm 0.08 pm 0.31)$ psec$^{-1}$, where the first error is statistical, the second is that from perturbative calculation, and the third is the systematic error from finite lattice spacing and the chiral extrapolation. We also discuss the systematic errors in the soft pion limit for $f^0(q^2_{max})$ in the present simulation.
Inclusive semileptonic B_s^0 -> X^+ l^- u decays are studied for the first time using a 23.6 fb^{-1} data sample collected on the Y(5S) resonance with the Belle detector at the KEKB asymmetric energy e^+ e^- collider. These decays are identified by the means of a lepton accompanied by a same-sign D_s^+ meson originating from the other B_s^0 in the event. The semileptonic branching fractions are measured in the electron and muon channels to be Bf(B_s^0 -> X^+ e^- u) = (10.9 pm 1.0 pm 0.9)% and Bf(B_s^0 -> X^+ mu^- u) = (9.2 pm 1.0 pm 0.8)%, respectively. Assuming an equal electron and muon production rate in B_s^0 decays, a combined fit yields an average leptonic branching fraction Bf(B_s^0 -> X^+ l^- u) = (10.2 pm 0.8 pm 0.9)%.
We report recent progress in calculating semileptonic form factors for the $bar{B} to D^ast ell bar{ u}$ and $bar{B} to D ell bar{ u}$ decays using the Oktay-Kronfeld (OK) action for bottom and charm quarks. We use the second order in heavy quark effective power counting $mathcal{O}(lambda^2)$ improved currents in this work. The HISQ action is used for the light spectator quarks. We analyzed four $2+1+1$-flavor MILC HISQ ensembles with $aapprox 0.09,mathrm{fm}$, $0.12,mathrm{fm}$ and $M_pi approx 220,mathrm{MeV}$, $310,mathrm{MeV}$: $a09m220$, $a09m310$, $a12m220$, $a12m310$. Preliminary results for $Bto D^astell u$ decays form factor $h_{A_1}(w)$ at zero recoil ($w=1$) are reported. Preliminary results for $B to D,ell u$ decays form factors $h_pm(w)$ over a kinematic range $1<w<1.3$ are reported as well.
We present the measurement of the first to fourth order moments of the four-momentum transfer squared, $q^2$, of inclusive $B rightarrow X_c ell^+ u_{ell}$ decays using the full Belle data set of 711 $mathrm{fb}^{-1}$ of integrated luminosity at the $Upsilon(4S)$ resonance where $ell = e, mu$. The determination of these moments and their systematic uncertainties open new pathways to determine the absolute value of the CKM matrix element $V_{cb}$ using a reduced set of matrix elements of the heavy quark expansion. In order to identify and reconstruct the $X_c$ system, we reconstruct one of the two $B$-mesons using machine learning techniques in fully hadronic decay modes. The moments are measured with progressively increasing threshold selections on $q^2$ starting with a lower value of 3.0 $mathrm{GeV}^2$ in steps of 0.5 $mathrm{GeV}^2$ up to a value of 10.0 $mathrm{GeV}^2$. The measured moments are further unfolded, correcting for reconstruction and selection effects as well as QED final state radiation. We report the moments separately for electron and muon final states and observe no lepton flavor universality violating effects.
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