Phenomenological Analysis of D Meson Lifetimes

The QCD-based operator-product-expansion technique is systematically applied to the study of charmed meson lifetimes. We stress that it is crucial to take into account the momentum of the spectator light quark of charmed mesons, otherwise the destructive Pauli-interference effect in $D^+$ decays will lead to a negative decay width for the $D^+$. We have applied the QCD sum rule approach to estimate the hadronic matrix elements of color-singlet and color-octet 4-quark operators relevant to nonleptonic inclusive $D$ decays. The lifetime of $D_s^+$ is found to be longer than that of $D^0$ because the latter receives a constructive $W$-exchange contribution, whereas the hadronic annihilation and leptonic contributions to the former are compensated by the Pauli interference. We obtain the lifetime ratio $\tau(D_s^+)/\tau(D^0)$ $\approx 1.08\pm 0.04$, which is larger than some earlier theoretical estimates, but still smaller than the recent measurements by CLEO and E791.Comment: 14 pages, 3 figure

Updated study of the ηc\eta_c and ηc′\eta_c^\prime decays into light vector mesons

We re-investigate the exclusive decays of $\eta_c$ and $\eta_c^\prime$ to a pair of light vector mesons, i.e. $\eta_c (\eta_c')\to VV$. The long-distance intermediate meson loop (IML) effects are evaluated as a non-perturbative mechanism in addition to the short-distance $c\bar{c}$ annihilation contributions. We show that both processes can be reasonably well constrained with the help of the available experimental data. Since $\eta_c$ and $\eta_c'$ are the spin-0 partners of $J/\psi$ and $\psi'$, respectively, our study is useful for gaining insights into the pQCD helicity selection rule violations in charmonium decays and the long-standing "$\rho\pi$ puzzle".Comment: 11 pages, 4 eps figures; Improved formulation based on 1010.1343[hep-ph]; Revised version accepted by Phys. Lett.

Hadronic B Decays to Charmed Baryons

We study exclusive B decays to final states containing a charmed baryon within the pole model framework. Since the strong coupling for $\Lambda_b\bar B N$ is larger than that for $\Sigma_b \bar BN$, the two-body charmful decay $B^-\to\Sigma_c^0\bar p$ has a rate larger than $\bar B^0\to\Lambda_c^+\bar p$ as the former proceeds via the $\Lambda_b$ pole while the latter via the $\Sigma_b$ pole. By the same token, the three-body decay $\bar B^0\to\Sigma_c^{++}\bar p\pi^-$ receives less baryon-pole contribution than $B^-\to\Lambda_c^+\bar p\pi^-$. However, because the important charmed-meson pole diagrams contribute constructively to the former and destructively to the latter, $\Sigma_c^{++}\bar p\pi^-$ has a rate slightly larger than $\Lambda_c^+\bar p\pi^-$. It is found that one quarter of the $B^-\to \Lambda_c^+\bar p\pi^-$ rate comes from the resonant contributions. We discuss the decays $\bar B^0\to\Sigma_c^0\bar p\pi^+$ and $B^-\to\Sigma_c^0\bar p\pi^0$ and stress that they are not color suppressed even though they can only proceed via an internal W emission.Comment: 25 pages, 6 figure

Further study of the helicity selection rule evading mechanism in ηc\eta_c, χc0\chi_{c0} and hch_c decaying to baryon anti-baryon pairs

We investigate the long distance contribution via charmed hadron loops in the processes $\eta_c$, $\chi_{c0}$ and $h_c$ decaying to baryon anti-baryon pairs, which are supposed to be highly suppressed by the helicity selection rule as a consequence of the perturbative QCD framework. With an effective Lagrangian method, our estimation result indicates that such hadron loops play an important role in these hadronic decays. It is a further test of the evading mechanism for the helicity selection rule in charmonium baryon-antibaryon decays.Comment: 9 pages, 7 figures, to appear in J. Phys.

Charmless Exclusive Baryonic B Decays

We present a systematical study of two-body and three-body charmless baryonic B decays. Branching ratios for two-body modes are in general very small, typically less than $10^{-6}$, except that \B(B^-\to p \bar\Delta^{--})\sim 1\times 10^{-6}. In general, $\bar B\to N\bar\Delta>\bar B\to N\bar N$ due to the large coupling constant for $\Sigma_b\to B\Delta$. For three-body modes we focus on octet baryon final states. The leading three-dominated modes are $\bar B^0\to p\bar n\pi^-(\rho^-), n\bar p\pi^+(\rho^+)$ with a branching ratio of order $3\times 10^{-6}$ for $\bar B^0\to p\bar n\pi^-$ and $8\times 10^{-6}$ for $\bar B^0\to p\bar n\rho^-$. The penguin-dominated decays with strangeness in the meson, e.g., $B^-\to p\bar p K^{-(*)}$ and $\bar B^0\to p\bar n K^{-(*)}, n\bar n \bar K^{0(*)}$, have appreciable rates and the $N\bar N$ mass spectrum peaks at low mass. The penguin-dominated modes containing a strange baryon, e.g., $\bar B^0\to \Sigma^0\bar p\pi^+, \Sigma^-\bar n\pi^+$, have branching ratios of order $(1\sim 4)\times 10^{-6}$. In contrast, the decay rate of $\bar B^0\to\Lambda\bar p\pi^+$ is smaller. We explain why some of charmless three-body final states in which baryon-antibaryon pair production is accompanied by a meson have a larger rate than their two-body counterparts: either the pole diagrams for the former have an anti-triplet bottom baryon intermediate state, which has a large coupling to the $B$ meson and the nucleon, or they are dominated by the factorizable external $W$-emission process.Comment: 46 pages and 3 figures, to appear in Phys. Rev. D. Major changes are: (i) Calculations of two-body baryonic B decays involving a Delta resonance are modified, and (ii) Penguin-dominated modes B-> Sigma+N(bar)+p are discusse

Systematic Study on QCD Interactions of Heavy Mesons with ρ\rho Meson

The strong interactions of the negative-parity heavy mesons with $\rho$ meson may be described consistently in the context of an effective lagrangian, which is invariant under isospin SU(2) transformation. Four coupling constants $g_{HH\rho}$, $f_{H^*H\rho}$, $g_{H^*H^*\rho}$ and $f_{H^*H^*\rho}$ enter the effective lagrangian, where $H$ $(H^*)$ denotes a pseudoscalar bottom or charm meson (the corresponding vector meson). Using QCD light cone sum rule (LCSR) method and, as inputs, the hadronic parameters updated recently, we give an estimate of $g_{H^*H^*\rho}$ and $f_{H^*H^*\rho}$, about which little was known before, and present an improved result for $g_{HH\rho}$ and $f_{H^*H\rho}$. Also, we examine the heavy quark asymptotic behavior of these nonperturbative quantities and assess the two low energy parameters $\beta$ and $\lambda$ of the corresponding effective chiral lagrangian.Comment: 16 pages, 1 eps figure, version to appear in PL

Covariant Light-Front Approach for s-wave and p-wave Mesons: Its Application to Decay Constants and Form Factors

We study the decay constants and form factors of the ground-state s-wave and low-lying p-wave mesons within a covariant light-front approach. Numerical results of the form factors for transitions between a heavy pseudoscalar meson and an s-wave or p-wave meson and their momentum dependence are presented in detail. In particular, form factors for heavy-to-light and B to D** transitions, where D** denotes generically a p-wave charmed meson, are compared with other model calculations. The experimental measurements of the decays B^- to D** pi^- and B to D D**_s are employed to test the decay constants of D**_s and the B to D** transition form factors. The heavy quark limit behavior of the decay constants and form factors is examined and it is found that the requirement of heavy quark symmetry is satisfied. The universal Isgur-Wise (IW) functions, one for s-wave to s-wave and two for s-wave to p-wave transitions, are obtained. The values of IW functions at zero recoil and their slope parameters can be used to test the Bjorken and Uraltsev sum rules.Comment: 59 pages, 6 figures. Version to appear in Phys. Rev. D. Changes are: (i) D_s to phi transition form factors are discussed and compared with the recent FOCUS measurements and (ii) zero mode effects are clarifie

O(αs)O(\alpha_s) corrections to J/ψ+χcJJ/\psi+\chi_{cJ} production at BB factories

We investigate the ${\cal O}(\alpha_s)$ corrections to $e^+e^-\to J/\psi(\psi')+\chi_{cJ}$ ($J=0,1,2$) in the NRQCD factorization approach. These next-to-leading order (NLO) corrections are calculated at the level of helicity amplitude. We have made a detailed analysis for both polarized and unpolarized cross sections, and compared our predictions with the measurements at the $B$ factories. We also derive the asymptotic expressions for each of the NLO helicity amplitudes, and confirm the earlier speculation that at NLO in $\alpha_s$, the double logarithm of type $\ln^2 (s/m_c^2)$ appearing in the NRQCD short-distance coefficient is always associated with the helicity-suppressed channels.Comment: v3, 18+3 pages, 6 figures, 3 tables; some formulas corrected, erratum adde

Extraction of a1a_1 and a2a_2 from B→ψK(K∗), D(D∗)π(ρ)B\to \psi K(K^*),~ D(D^*)\pi(\rho) Decays

Based on the factorization approach, we show that the CLEO data for the ratio $\Gamma(B\to\psi K^*)/\Gamma(B\to \psi K)$ and the CDF measurement of the fraction of longitudinal polarization in $B\to\psi K^*$ can be accounted for by the heavy-flavor-symmetry approach for heavy-light form factors provided that the form factor $F_0$ behaves as a constant, while the $q^2$ dependence is of the monopole form for $F_1,~ A_0,~A_1$, and of the dipole behavior for $A_2$ and $V$. This $q^2$ extrapolation for form factors is further supported by $B\to K^*\gamma$ data and by a recent QCD-sum-rule analysis. We then apply this method to $B\to D(D^*)\pi(\rho)$ decays to extract the parameters $a_1$ and $a_2$. It is found that $a_1(B\to D^{(*)}\pi(\rho))=1.01\pm 0.06$ and $a_2(B\to D^{(*)}\pi(\rho))=0.23\pm 0.06\,$. Our result $a_2/a_1=0.22\pm 0.06$ thus significantly improves the previous analysis that leads to $a_2/a_1=0.23\pm 0.11$. We argue that, contrary to what anticipated from the leading $1/N_c$ expansion, the sign of a_2(B\to\psi\K) should be positive and a_2(B\to\psi\K)~{\large ^>_\sim}~ a_2(B\to D^{(*)}\pi(\rho)).Comment: 14 pages, revised versio

Nonspectator Effects and B Meson Lifetimes from a Field-theoretic Calculation

The B meson lifetime ratios are calculated to the order of $1/m_b^3$ in the heavy quark expansion. The predictions of those ratios are dependent on four unknown hadronic parameters $B_1$, $B_2$, $\epsilon_1$ and $\epsilon_2$, where $B_1$ and $B_2$ parametrize the matrix elements of color singlet-singlet four-quark operators and $\epsilon_1$ and $\epsilon_2$ the matrix elements of color octet-octet operators. We derive the renormalization-group improved QCD sum rules for these parameters within the framework of heavy quark effective theory. The results are $B_1(m_b)=0.96\pm 0.04$, $B_2(m_b)=0.95\pm 0.02$, $\epsilon_1(m_b)=-0.14\pm 0.01$, and $\epsilon_2(m_b)=-0.08\pm 0.01$ to zeroth order in $1/m_b$. The resultant $B$ meson lifetime ratios are $\tau(B^-)/\tau(B_d)=1.11\pm 0.02$ and $\tau(B_s)/\tau(B_d)\approx 1$ in SU(3) symmetry limit.Comment: 22 pages, 2 figures. (i) Sec.II is shortened, (ii) numerical results for epslion_i are revised, and (iii) Fig.2 is revise