Semileptonic B Decays into Excited Charmed Mesons (D1D_1, D2∗D^*_2) in HQEFT

Exclusive semileptonic B decays into excited charmed mesons ($D_1$, $D^*_2$) are studied up to the order of $1/m_Q$ in the framework of the heavy quark effective field theory (HQEFT), which contains the contributions of both particles and antiparticles. Two wave functions $\eta^b_0$ and $\eta^c_0$, which characterize the contributions from the kinematic operator at the order of $1/m_Q$, are calculated by using QCD sum rule approach in HQEFT. Zero recoil values of other two wave functions $\kappa'_1$ and $\kappa'_2$ are extracted from the excited charmed-meson masses. Possible effects from the spin-dependent transition wave functions which arise from the magnetic operators at the order of $1/m_Q$ are analyzed. It is shown that the experimental measurements for the branching ratios of $B \to D_1 l\nu$ and $B \to D^*_2 l\nu$ can be understood in the framework of HQEFT.Comment: 27 pages, RevTex, 4 figures, 3 tables, to be published in IJMP

Heavy Quark Symmetry Violation in Semileptonic Decays of D Mesons

The decays of $D$ mesons to $K l \nu$ and $K^* l \nu$ final states exhibit significant deviations from the predictions of heavy-quark symmetry, as one might expect since the strange quark's mass is of the same order as the QCD scale. Nonetheless, in order to understand where the most significant effects might lie for heavier systems (such as $B \to D l\nu$ and $B \to D^* l\nu$), the pattern of these deviations is analyzed from the standpoint of perturbative QCD and ${\cal O}(1/m_s)$ corrections. Two main effects are noted. First, the perturbative QCD corrections lead to an overall decrease of predicted rates, which can be understood in terms of production of excited kaonic states. Second, ${\cal O}(1/m_s)$ effects tend to cancel the perturbative QCD corrections in the case of $Kl\nu$ decay, while they have minimal effect in $K^*l\nu$ decay.Comment: 25 pages (LaTeX) + 7 pages of Postscript figures (included at end), EFI-92-3

Exclusive semileptonic B_s decays to excited D_s mesons: Search of D_{sJ}(2317) and D_{sJ}(2460)

We study the exclusive semileptonic decays B_s->D_{s0}^*\ell\bar\nu and B_s->D_{s1}^*\ell\bar\nu, where p-wave excited D_{s0}^* and D_{s1}^* states are identified with the newly observed D_{sJ}(2317) and D_{sJ}(2460) states. Within the framework of HQET the Isgur-Wise functions up to the subleading order of the heavy quark expansion are calculated by QCD sum rules. The decay rates and branching ratios are computed with the inclusion of the order of 1/m_Q corrections. We point out that the investigation of the B_s semileptonic decays to excited D_s mesons may provide some information about the nature of the new D_{sJ}^* mesons.Comment: 15 pages, 6 eps figures, RevTeX 4, accepted for publication in Phys. Rev.

Semileptonic B decays to excited charmed mesons

Exclusive semileptonic B decays into excited charmed mesons are investigated at order $\Lambda_{QCD}/m_Q$ in the heavy quark effective theory. Differential decay rates for each helicity state of the four lightest excited $D$ mesons ($D_1$, $D_2^*$, $D_0^*$, and $D_1^*$) are examined. At zero recoil, $\Lambda_{QCD}/m_Q$ corrections to the matrix elements of the weak currents can be written in terms of the leading Isgur-Wise functions for the corresponding transition and meson mass splittings. A model independent prediction is found for the slope parameter of the decay rate into helicity zero $D_1$ at zero recoil. The differential decay rates are predicted, including $\Lambda_{QCD}/m_Q$ corrections with some model dependence away from zero recoil and including order $\alpha_s$ corrections. Ratios of various exclusive branching ratios are computed. Matrix elements of the weak currents between $B$ mesons and other excited charmed mesons are discussed at zero recoil to order $\Lambda_{QCD}/m_Q$. These amplitudes vanish at leading order, and can be written at order $\Lambda_{QCD}/m_Q$ in terms of local matrix elements. Applications to $B$ decay sum rules and factorization are presented.Comment: 39 pages revtex including 10 figures, uses epsf. Substantial improvements throughout the pape

Scale Setting in QCD and the Momentum Flow in Feynman Diagrams

We present a formalism to evaluate QCD diagrams with a single virtual gluon using a running coupling constant at the vertices. This method, which corresponds to an all-order resummation of certain terms in a perturbative series, provides a description of the momentum flow through the gluon propagator. It can be viewed as a generalization of the scale-setting prescription of Brodsky, Lepage and Mackenzie to all orders in perturbation theory. In particular, the approach can be used to investigate why in some cases the ``typical'' momenta in a loop diagram are different from the ``natural'' scale of the process. It offers an intuitive understanding of the appearance of infrared renormalons in perturbation theory and their connection to the rate of convergence of a perturbative series. Moreover, it allows one to separate short- and long-distance contributions by introducing a hard factorization scale. Several applications to one- and two-scale problems are discussed in detail.Comment: eqs.(51) and (83) corrected, minor typographic changes mad

Semileptonic B decays into excited charmed mesons from QCD sum rules

Exclusive semileptonic $B$ decays into excited charmed mesons are studied with QCD sum rules in the leading order of heavy quark effective theory. Two universal Isgur-Wise functions \tau and \zeta for semileptonic B decays into four lowest lying excited $D$ mesons ($D_1$, $D_2^*$, $D'_0$, and $D'_1$) are determined. The decay rates and branching ratios for these processes are calculated.Comment: RevTeX, 17 pages including 2 figure

Hadronic Invariant Mass Spectrum in B -> X_u l nu Decay with Lepton Energy Cut

We discuss the implications of charged lepton energy cut to the hadronic invariant mass spectrum in charmless semileptonic B decays. Charged-lepton energy cut is inevitable in order to remove secondary leptonic events such as b -> c, tau -> l, and to identify the chaged leptons at detectors experimentally. We consider three possible lepton energy cuts, E_l^{cuts} = 0.6,1.5,2.3 GeV, and found that with the most probable cuts E_l^{cut} = 1.5 GeV and M_X^{max} = 1.5~(1.86) GeV, 45 ~ 60 % ~(58 ~ 67 %) of decay events survive. Therefore, B -> X_u l nu decay events can be efficiently distinguished from B -> X_c l nu decay events. We also discuss the possible model dependence on the results.Comment: 19 pages, 3 figure

Direct CP Violation in B -> X_s gamma Decays as a Signature of New Physics

We argue that the observation of a sizable direct CP asymmetry A_{CP} in the inclusive decays B -> X_s gamma would be a clean signal of New Physics. In the Standard Model, A_{CP} can be calculated reliably and is found to be below 1% in magnitude. In extensions of the Standard Model with new CP-violating couplings, large CP asymmetries are possible without conflicting with the experimental value of the branching ratio for the decays B -> X_s gamma. In particular, large asymmetries arise naturally in models with enhanced chromo-magnetic dipole operators. Some generic examples of such models are explored and their implications for the semileptonic branching ratio and charm yield in B decays discussed.Comment: several references added and some numerical results updated to include QED corrections (version to appear in Physical Review D