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We propose a method for a QCD based calculation of one-particle inclusive decays of the form B to bar D X or B to bar D^* X. It is based on the heavy mass limit and a short distance expansion of the amplitudes, which yield a power series in the parameter 1/M^2_X for the spectra and in Lambda_QCD m_b/(m_b - m_c)^2 for the rates. We study the leading term of this expansion for the case of the semi--leptonic decays B to bar D X l^+ u.
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We develop a method to compute inclusive semi-leptonic decay rate of hadrons fully non-perturbatively using lattice QCD simulations. The sum over all possible final states is achieved by a calculation of the forward-scattering matrix elements on the lattice, and the phase-space integral is evaluated using their dependence on the time separation between two inserted currents. We perform a pilot lattice computation for the B_s -> X_c l nu decay with an unphysical bottom quark mass and compare the results with the corresponding OPE calculation. The method to treat the inclusive processes on the lattice can be applied to other processes, such as the lepton-nucleon inelastic scattering.
The most recent measurements of the observables $R_{D^{(*)}}$ are in tension with the Standard Model offering hints of New Physics in $brightarrow c ell bar{ u}_{ell}$ transitions. Motivated by these results, in this work we present an analysis on their $brightarrow u ell bar{ u}_{ell}$ counterparts (for $ell=e, ~mu, ~tau$). Our study has three main objectives. Firstly, using ratios of branching fractions, we assess the effects of beyond the Standard Model scalar and pseudoscalar particles in leptonic and semileptonic $B$ decays ($B^-rightarrow ell^- bar{ u}_{ell}$, $bar{B}rightarrow pi ell bar{ u}_{ell}$ and $bar{B}rightarrow rho ell bar{ u}_{ell}$). Here a key role is played by the leptonic $B$ processes, which are highly sensitive to new pseudoscalar interactions. In particular, we take advantage of the most recent measurement of the branching fraction of the channel $B^-rightarrow mu^-bar{ u}_{mu}$ by the Belle collaboration. Secondly, we extract the CKM matrix element $|V_{ub}|$ while accounting simultaneously for New Physics contributions. Finally, we provide predictions for the branching fractions of yet unmeasured leptonic and semileptonic $B$ decays.
We report on form factors for the B->K l^+ l^- semi-leptonic decay process. We use several lattice spacings from a=0.12 fm down to 0.06 fm and a variety of dynamical quark masses with 2+1 flavors of asqtad quarks provided by the MILC Collaboration. These ensembles allow good control of the chiral and continuum extrapolations. The b-quark is treated as a clover quark with the Fermilab interpretation. We update our results for f_parallel and f_perp, or, equivalently, f_+ and f_0. In addition, we present new results for the tensor form factor f_T. Model independent results are obtained based upon the z-expansion.
Semi-leptonic $B$ decays provide promising channels to test the Standard Model, search for signs of new physics, or determine fundamental parameters like CKM matrix elements. We present an update on our calculation of short distance contributions to GIM suppressed rare $B$ decays focusing in particular on $B_sto phi ell^+ ell^-$ decays. Furthermore we show first results for our calculation of $B_{(s)}to D_{(s)}^{(*)}ell u$ semi-leptonic decays involving $bto c$ transitions. Our calculations are based on RBC-UKQCDs 2+1 flavor domain-wall fermion and Iwasaki gauge field configurations featuring three lattice spacings in the range $1.73$ GeV $le a^{-1} le 2.77$ GeV and pion masses down to the physical value. We calculate the form factors by simulating $b$-quarks using the relativistic heavy quark action, create light $u/d$ and $s$ quarks with standard domain-wall kernel, and use optimised Mobius domain-wall fermions for charm quarks.
We propose a method to non-perturbatively calculate the forward-scattering matrix elements relevant to inclusive semi-leptonic B meson decays. Corresponding hadronic structure functions at unphysical kinematics are accessible through lattice QCD calculation of four-point correlation functions. The unphysical kinematical point may be reached by analytic continuation from the physical differential decay rate. A numerical test is performed for the B_s -> X_c l nu mode in the zero-recoil limit. We use lattice ensembles generated with 2+1 dynamical quark flavors. The valence charm quark mass is tuned to its physical value, while the bottom quark mass is varied in the range (1.56-2.44)m_c. From the numerical results we can identify the contributions of the ground state D_s^(*) meson as well as those of excited states or continuum states.
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