arXiv subjects

B. Tseng

Publications and source records attributed to B. Tseng.

18 recordsLinked to original sources

arXiv2000

Exclusive Hadronic D Decays to $η'$ or $η$: Addendum on Resonant Final-State Interactions

For hadronic two-body decays of charmed mesons involving $η$ or $η'$, resonance-induced final-state interactions (FSI) that mimic the W-exchange or the W-annihilation topology can play an essential role. In particular, the decays $D^0\to\bar K^0η'$ and $D^+\toπ^+η$, which are largely suppressed in the absence of FSI, are enhanced dramatically by resonant FSI. It is stressed that the effect of resonant FSI is negligible for $ρ^+(η,η')$ final states because of the mismatch of the G parity of $ρ^+(η,η')$ and the J=0, I=1 meson resonance. We argue that a possible gluon-mediated process in which two gluons couple directly to the gluonic component of the $η'$, e.g. the gluonium, rather than to the flavor-singlet $η_0$, can enhance both modes $D_s^+\toρ^+η'$ and $D_s^+\toρ^+η$, especially the former; that is, this new mechanism can account for the unexpectedly large branching ratio of $ρ^+η'$ without suppressing $ρ^+η$.

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arXiv1999

Charmless Hadronic Two-body Decays of B_u and B_d Mesons

Two-body charmless nonleptonic decays of B_u and B_d mesons are studied within the framework of generalized factorization in which the effective Wilson coefficients $c^{eff}_i$ are renormalization-scale and -scheme independent while factorization is applied to the tree-level hadronic matrix elements. Contrary to previous studies, our $c_i^{eff}$ do not suffer from gauge and infrared problems. Nonfactorizable effects are parametrized in terms of N_c(LL) and N_c(LR), the effective numbers of colors arising from (V-A)(V-A) and (V-A)(V+A) four-quark operators, respectively. Tree and penguin transitions are classified into six different classes. The data of $B^-\toρ^0π^-$ and $B^-\toϕK^-$ clearly indicate that $N_c(LR)\neq N_c(LL)$: The first measurement of the b -> u mode $B^-\toρ^0π^-$ and the experimental information on the tree-dominated mode $B^-\toωπ^-$ all imply that Nc(LL) is less than 3, whereas the CLEO measurement of $B^-\toϕK^-$ shows Nc(LR)>3. For given input parameters, the prediction of ${\cal B}(B\toη' K)$ is largely improved by setting Nc(LL)~2 and Nc(LR)>Nc(LL); in particular, the charm content of the eta' contributes in the right direction. The decay rate of $B\toϕK^*$ is very sensitive to the form-factor ratio A_2/A_1; the absence of $B\toϕK$ events does not necessarily invalidate the factorization approach. If the branching ratio of $B^-\toωK^-$ is experimentally found to be significantly larger than that of $B^-\toρ^0 K^-$, we argue that inelastic final-state rescattering may account for the disparity between $ωK^-$ and $ρ^0 K^-$.

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arXiv1999

Charmless Hardronic Decays $B_u \to V V $: Angular Distributions, Direct CP Violation and Determination of the Unitary Triangle

Two-body charmless nonleptonic decays of $B_u \to V V$ are studied within the generalized factorization approach using a recent calculation of the effective Wilson coefficients $c^{eff}_i$, which are not only renormalization-scale and -scheme independent but also gauge invariant and infrared finite. After making a universal ansatz for the nonfactorizable contributions, we parametrize these effects in terms of $N_c^{eff}(LL)$ and $N_c^{eff}(LR)$, the effective numbers of colors arising from $(V-A)(V-A)$ and $(V-A)(V+A)$ four-quark operators, respectively. Three different schemes for these contributions are considered: (i) the naive factorization, (ii) the large-N_c improved factorization, and (iii) our preferred choice: $(N_c^{eff}(LL), N_c^{eff}(RR))=(2,5)$. We present the full angular distribution of all charmless $B_u \to V V$ decays in both transversity and helicity frames.Direct CP violation in these normalized angular correlation coefficients is not negligible in $B^-_u \to K^{*-} ρ^0, K^{*-} ω$, and direct CP violation in the partial rate difference for $B^-_u \to K^{*-} ω, K^{*-} ρ$ and $ρ^- ω$ can be as large as 45%, 25%, -10%, respectively. Due to the sizable QCD penguin contributions in $ρ^- ω$, the determination of the unitary triangle $α$ via this decay mode is more promising than via $ρ^- ρ^0$. It is also encouraging to determine the unitary triangle $γ$ through $B^-_u \to K^{*-} ρ$ because of $N_c$-insensitivity and the not-so-small tree contribution. The impacts of a negative $ρ$ on the branching ratios and CP violation are studied. We also comment on the theoretical uncertainties and their possible impacts.

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arXiv1998

Exclusive charmless $B_s$ hadronic decays into $η'$ and $η$

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arXiv1998

Charmless Hadronic Two-body Decays of the B_s Mesons

Two-body charmless nonleptonic decays of the B_s meson are studied within the framework of generalized factorization in which factorization is applied to the tree level matrix elements while the effective Wilson coefficients are $μ$ and renormalization scheme independent, and nonfactorizable effects are parametrized in terms of N_c(LL) and N_c(LR), the effective numbers of colors arising from (V-A)(V-A) and (V-A)(V+A) four-quark operators, respectively. Branching ratios of $B_s\to PP,PV,VV$ decays are calculated as a function of N_c(LR) with two different considerations for N_c(LL). We find that (i) the electroweak penguin contributions account for about 85% (for N_c(LL)=2) of the decay rates of $B_s\to ηπ,η'π,ηρ,η'ρ,ϕπ,ϕρ$, which receive contributions only from tree and electroweak penguin diagrams; a measurement of them will provide a clean determination of the electroweak penguin coefficient a_9, (ii) electroweak penguin corrections to $B_s\toω\etapp,ϕη,ωϕ,K^{(*)}ϕ,ϕϕ$ are in general as significant as QCD penguin effects and even play a dominant role; their decay rates depend strongly on N_c(LR), (iii) the branching ratio of $B_s\to ηη'$ is of order 2x10^{-5}, (iv) the contribution from the $η'$ charm content is important for $B_s\toη'η'$, but less significant for $B_s\toηη'$, and (v) the decay rates for the final states $K^{+(*)}K^{-(*)}$ follow the pattern: $Γ(B_s\to K^+K^-)>Γ(B_s\to K^+K^{*-})\geqΓ(B_s\to K^{*+}K^{*-}) >Γ(B_s\to K^{+*}K^-)$, as a consequence of various interference effects between the penguin amplitudes governed by the coefficients a_4 and a_6.

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arXiv1998

Exclusive Hadronic D Decays to eta' and eta

Hadronic decay modes $D^0\to(\bar K^0, \bar K^{*0})η,η'$ and $(D^+,D_s^+)\to(π^+,ρ^+)η,η'$ are studied in the generalized factorization approach. Form factors for $(D,D_s^+)\to(η,η')$ transitions are carefully evaluated by taking into account the wave function normalization of the eta and eta'. The predicted branching ratios are generally in agreement with experiment except for $D^0\to\bar K^0η', D^+\toπ^+η$ and $D_s^+\toρ^+η'$; the calculated decay rates for the first two decay modes are too small by an order of magnitude. We show that the weak decays $D^0\to K^-π^+$ and $D^+\to K^+\bar K^0$ followed by resonance-induced final-state interactions (FSI), which are amenable technically, are able to enhance the branching ratios of $D^0\to\bar K^0η'$ and $D^+\toπ^+η$ dramatically without affecting the agreement between theory and experiment for $D^0\to\bar K^0η$ and $D^+\toπ^+η'$. We argue that it is difficult to understand the observed large decay rates of $D_s^+\to ρ^+η'$ and $ρ^+η$ simultaneously; FSI, W-annihilation and the production of excess eta' from gluons are not helpful in this regard. The large discrepancy between the factorization hypothesis and experiment for the ratio of $D_s^+\toρ^+ η'$ and $D_s^+\toη' e^+ν$ remains as an enigma.

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arXiv1998

Exclusive charmless $B_s$ hadronic decays into $η'$ and $η$

Using the next-to-leading order QCD-corrected effective Hamiltonian, charmless exclusive nonleptonic decays of the $B_s$ meson into $η$ or $η'$ are calculated within the generalized factorization approach. Nonfactorizable contributions, which can be parametrized in terms of the effective number of colors $N_c^{\rm eff}$ for $P P$ and $V P$ decay modes, are studied in two different schemes: (i) the one with the "homogeneous" structure in which $(N_c^{\rm eff})_1 \approx (N_c^{\rm eff})_2 \approx ... \approx (N_c^{\rm eff})_{10}$ is assumed, and (ii) the "heterogeneous" one in which the possibility of $N_c^{\rm eff}(V+A) \neq N_c^{\rm eff}(V-A)$ is considered, where $N_c^{\rm eff}(V+A)$ denotes the effective value of colors for the $(V-A)(V+A)$ penguin operators and $N_c^{\rm eff}(V-A)$ for the $(V-A)(V-A)$ ones. For processes depending on the $N_c^{\rm eff}$-stable $a_i$ such as $\bar{B_s} \to (π,ρ) (η^{'},η)$, the predicted branching ratios are not sensitive to the factorization approach we choose. While for the processes depending on the $N_c^{\rm eff}$-sensitive $a_i$ such as $\bar{B_s} \to ωη^{(')}$, there is a wide range for the branching ratios depending on the choice of the $N_c^{\rm eff}$ involved. We have included the QCD anomaly effect in our calculations and found that it is important for $\bar{B_s} \to η^{(')} η^{(')}$. The effect of the $(c\bar c) \to η'$ mechanism is found to be tiny due to a possible CKM-suppression and the suppression in the decay constants except for the $\bar{B_s} \to ϕη$ decay within the "naive" factorization approach, where the internal $W$ diagram is CKM-suppressed and the penguin contributions are compensated.

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arXiv1998

Nonfactorizable Effects in Spectator and Penguin Amplitudes of Hadronic Charmless B Decays

Nonfactorizable effects in hadronic charmless B -> PP, VP decays can be parametrized in terms of the effective number of colors N_c in the effective parameters $a_i^{eff}$ that are linear combinations of Wilson coefficients. It is shown that N_c(V+A) in the penguin amplitudes induced by the (V-A)(V+A) four-quark operators is different from N_c(V-A) in the decay amplitudes arising from the (V-A)(V-A) operators. Central values of the branching ratios of $B^\pm\toωπ^\pm$ and $B\toππ$ decays favor $N_c(V-A)\approx 2$, in accordance with the nonfactorizable effect observed in $B\to D^{(*)}π(ρ)$. Measurements of the interference effects in $B^-\toπ^-(ρ^-)π^0 (ρ^0)$ decays will provide a more decisive test on the parameter N_c(V-A). However, $N_c(V+A)\sim 2$ is ruled out by $B^\pm\toϕK^\pm$ and $B\toϕK^*$. We find that N_c(V+A) lies in the range $10\geq N_c(V+A)\geq 4.3$, subject to the corrections from W-annihilation and space-like penguin effects. With $N_c(V-A)\approx 2$ we show that the branching ratio of $B\toη' K$ is enhanced considerably at small values of 1/N_c(V+A) so that it is compatible with experiment. In particular, the measurement of $B^0\toη' K^0$ is now well explained without resorting to any new mechanism or new physics beyond the Standard Model. Finally, we point out that it is difficult to understand the observed large branching ratio of $B^\pm\toωK^\pm$ within the present framework. Inelastic final-state interactions may alleviate the difficulty with this decay mode.

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arXiv1997

Solution of $a_2/a_1$ sign problem in heavy meson decays: nonfactorizable soft gluons in nonleptonic heavy meson decays

For the first time, a solution to the $a_2/a_1$ sign problem in heavy meson decay based on PQCD factorization theorems. The point is to include QCD evolution effort characteristic scales involved in decay processes.

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arXiv1997

Enhanced $b\to sg$ Decay, Inclusive $η^\prime$ Production, and the Gluon Anomaly

The experimental hint of large $B\to η^\prime + X_s$ is linked to the $b\to s$ penguins via the gluon anomaly. Using running $α_s$ in the $η^\prime$-$g$-$g$ coupling, the standard $b\to sg^*$ penguin alone seems insufficient, calling for the need of dipole $b\to sg$ at 10% level from new physics, which could also resolve the ${\cal B}_{s.l.}$ and charm counting problems. The intereference of standard and new physics contributions may result in direct CP asymmetries at 10% level, which could be observed soon at B Factories.

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arXiv1997

Charmless B decays to eta' and eta

Exclusive charmless B decays to $η'$ and $η$ are studied in the standard effective Hamiltonian approach. The effective coefficients that take into account nonfactorizable effects in external and internal W-emission amplitudes are fixed by experiment. Factorization is applied to the matrix elements of QCD, electroweak penguin operators and next-to-leading corrections to penguin Wilson coefficients, which are renormalization-scheme dependent, are included, but the resultant amplitude is renormalization-scheme and -scale independent. We show that the unexpectedly large branching ratio of $B^\pm\to η' K^\pm$ measured by CLEO can be explained by the Cabibbo-allowed internal W-emission process $b\to c\bar cs$ followed by a conversion of the $c\bar c$ pair into the $η'$ via gluon exchanges characterized by a decay constant of order -50 MeV. Implications are discussed. The mechanism of the transition $c\bar c\toη'$, if correct, will enhance the decay rates of $B\to η' K^{*}$ by more than an order of magnitude. However, it plays only a minor role to the rare decays $B\to η'(η)π(ρ)$. The predicted branching ratio of $B^\pm\to ηπ^\pm$ for positive $ρ$ is marginally ruled out by experiment, indicating that the favored Wolfenstein parameter $ρ$ is negative.

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arXiv1997

Nonfactorizable Effects in Exclusive Charmless B Decays

Nonfactorizable effects in charmless $B\to PP, VP$ decays can be lumped into the effective parameters a_i that are linear combinations of Wilson coefficients, or equivalently absorbed into the effective number of colors N_c. Naive factorization with N_c=3 fails to explain the CLEO data of $B^\pm \to ωK^\pm$, showing the first evidence for the importance of nonfactorizable contributions to the penguin amplitude. The decays $B^\pm \to ωπ^\pm$ dominated by tree amplitudes are sensitive to the interference between external and internal W-emission diagrams. Destructive interference implied by $N_c=\infty$ leads to a prediction of ${\cal B}(B^\pm \to ωπ^\pm)$ which is about $2σ$ too small compared to experiment. Therefore, the CLEO data of $B^\pm \to ωK^\pm, ωπ^\pm$ suffice to rule out N_c=3 and strongly disfavor $N_c=\infty$ for rare charmless B decays. Factorization based on $N_c\approx 2$ can accommodate the data of $B^\pm \to ωK^\pm$, but it predicts a slightly smaller branching ratio of $B^\pm \to ωπ^\pm$ with ${\cal B}(B^\pm \to ωπ^\pm)/{\cal B} (B^\pm \to ωK^\pm)=0.6$. We briefly explain why the 1/N_c expansion is still applicable to the B meson decay once the correct large-N_c counting rule for the Wilson coefficient c_2(m_b) is applied.

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arXiv1997

Nonfactorizable soft gluons in nonleptonic heavy meson decays

We include nonfactorizable soft gluon corrections into the perturbative QCD formalism for exclusive nonleptonic heavy meson decays, which combines factorization theorems and effective field theory. These corrections are classified according to their color structures, and exponentiated separately to complete the Sudakov resummation up to next-to-leading logarithms. The nonfactorizable contributions in nonleptonic decays are clearly identified in our formalism, and found to be positive for bottom decays and negative for charm decays. Our analysis confirms that the large-$N_c$ approximaton is applicable to charm decays, but not to bottom decays, consistent with the phenomenological implications of experimental data. The comparision of our predictions with those from QCD sum rules is also made.

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arXiv1996

Analysis of Two-Body Decays of Charmed Baryons Using the Quark-Diagram Scheme

We give a general formulation of the quark-diagram scheme for the nonleptonic weak decays of baryons. We apply it to all the decays of the antitriplet and sextet charmed baryons and express their decay amplitudes in terms of the quark-diagram amplitudes. We have also given parametrizations for the effects of final-state interactions. For SU(3) violation effects, we only parametrize those in the horizontal $W$-loop quark diagrams whose contributions are solely due to SU(3)-violation effects. In the absence of all these effects, there are many relations among various decay modes. Some of the relations are valid even in the presence of final-state interactions when each decay amplitude in the relation contains only a single phase shift. All these relations provide useful frameworks to compare with future experiments and to find out the effects of final-state interactions and SU(3) symmetry violations.

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arXiv1995

1/M Corrections to Baryonic Form Factors in the Quark Model

Weak current-induced baryonic form factors at zero recoil are evaluated in the rest frame of the heavy parent baryon using the nonrelativistic quark model. Contrary to previous similar work in the literature, our quark model results do satisfy the constraints imposed by heavy quark symmetry for heavy-heavy baryon transitions at the symmetric point $v\cdot v'=1$ and are in agreement with the predictions of the heavy quark effective theory for antitriplet-antitriplet heavy baryon form factors at zero recoil evaluated to order $1/m_Q$. Furthermore, the quark model approach has the merit that it is applicable to any heavy-heavy and heavy-light baryonic transitions at maximum $q^2$. Assuming a dipole $q^2$ behavior, we have applied the quark model form factors to nonleptonic, semileptonic and weak radiative decays of the heavy baryons. It is emphasized that the flavor suppression factor occurring in many heavy-light baryonic transitions, which is unfortunately overlooked in most literature, is very crucial towards an agreement between theory and experiment for the semileptonic decay $Λ_c\toΛe^+ν_e$. Predictions for the decay modes $\b,~Λ_c \to pϕ,~Λ_b\toΛγ$, $Ξ_b\toΞγ$, and for the semileptonic decays of $Λ_b,~Ξ_{b,c}$ and $Ω_b$ are presented. }

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arXiv1994

Extraction of $a_1$ and $a_2$ from $B\to ψK(K^),~ D(D^)π(ρ)$ Decays

Based on the factorization approach, we show that the CLEO data for the ratio $Γ(B\toψK^*)/Γ(B\to ψK)$ and the CDF measurement of the fraction of longitudinal polarization in $B\toψK^*$ 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 $B\to K^*γ$ data and by a recent QCD-sum-rule analysis. We then apply this method to $B\to D(D^*)π(ρ)$ decays to extract the parameters $a_1$ and $a_2$. It is found that $a_1(B\to D^{(*)}π(ρ))=1.01\pm 0.06$ and $a_2(B\to D^{(*)}π(ρ))=0.23\pm 0.06\,$. 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 $a_2(B\toψ\K)$ should be positive and $a_2(B\toψ\K)~{\large ^>_\sim}~ a_2(B\to D^{(*)}π(ρ))$.

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arXiv1994

The $Λ_b\to J/ψ+Λ$ Decay Revisited

The $\b$ decay does not receive any nonspectator contributions and hence its theoretical calculation is relatively clean. Two different methods are employed for the study of $\b$. In the first method, both $b$ and $s$ quarks are treated as heavy and leading $1/m_s$ as well as $1/m_b$ corrections are included. The branching ratio and the asymmetry parameter $α$ are found to be $(0.7-1.5)\times 10^{-3}$ and $0.18$, respectively. In the second method, only the $b$ quark is treated as heavy. The prediction of the decay rate is very sensitive to the choice of the $q^2$ dependence for form factors. We obtain $α=0.31$ and ${\cal B}(\b) \simeq 1.6\times 10^{-4}$ for dipole $q^2$ behavior as well as $8.2\times 10^{-4}$ for monopole $q^2$ dependence. We conclude that ${\cal B}(\b)~{\large ^<_{\sim}}~10^{-3}$ and $α$ is of order $0.20\sim 0.30$ with a positive sign.

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arXiv1993

Cabibbo-allowed nonleptonic weak decays of charmed baryons

Cabibbo-allowed nonleptonic weak decays of charmed baryons $\lamc,~\xin,~\xip$ and $Ω_c^0$ into an octet baryon and a pseudoscalar meson are analyzed. The nonfactorizable contributions are evaluated under pole approximation, and it turns out that the $s$-wave amplitudes are dominated by the low-lying $\halfm$ resonances, while $p$-wave ones governed by the ground-state $\halfp$ poles. The MIT bag model is employed to calculate the coupling constants, form factors and baryon matrix elements. Our conclusions are: (i) $s$ waves are no longer dominated by commutator terms; the current-algebra method is certainly not applicable to parity-violating amplitudes, (ii) nonfactorizable $W$ exchange effects are generally important; they can be comparable to and somtimes even dominate over factorizable contributions, depending on the decay modes under consideration, (iii) large-$N_c$ approximation for factorizable amplitudes also works in the heavy baryon sector and it accounts for the color nonsuppression of $\lamc\ri p\bar{K}^0$ relative to $\lamc\riΛπ^+$, (iv) a measurement of the decay rate and the sign of the $α$ asymmetry parameter of certain proposed decay modes will help discern various models; especially the sign of $α$ in $\lamc\riΣπ$ decays can be used to unambiguously differentiate recent theoretical schemes from current algebra, and (v) $p$ waves are the dominant contributions to the decays $\lamc\riΞ^0 K^+$ and $\xin\riΣ^+ K^-$, but they are subject to a large cancellation; this renders present theoretical predictions on these two channels unreliable.

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