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Hai-Yang Cheng

Publications and source records attributed to Hai-Yang Cheng.

At least 145 records · Page 8Linked to original sources
arXiv2003

Hadronic Charmed Meson Decays Involving Axial Vector Mesons

Cabibbo-allowed charmed meson decays into a pseudoscalar meson and an axial-vector meson are studied. The charm to axial-vector meson transition form factors are evaluated in the Isgur-Scora-Grinstein-Wise quark model. The dipole momentum dependence of the $D\to K$ transition form factor and the presence of a sizable long-distance $W$-exchange are the two key ingredients for understanding the data of $D\to \bar Ka_1$. The $K_{1A}-K_{1B}$ mixing angle of the strange axial-vector mesons is found to be $\approx \pm37^\circ$ or $\pm58^\circ$ from $τ\to K_1ν_τ$ decays. The study of $D\to K_1(1270)π, K_1(1400)π$ decays excludes the positive mixing-angle solutions. It is pointed out that an observation of the decay $D^0\to K_1^-(1400)π^+$ at the level of $5\times 10^{-4}$ will rule out $θ\approx -37^\circ$ and favor the solution $θ\approx -58^\circ$. Though the decays $D^0\to \bar K_1^0π^0$ are color suppressed, they are comparable to and even larger than the color-allowed counterparts: $\bar K_1^0(1270)π^0\sim K_1^-(1270)π^+$ and $\bar K_1^0(1400)π^0> K_1^-(1400)π^+$. The finite width effect of the axial-vector resonance is examined. It becomes important for $a_1(1260)$ in particular when its width is near 600 MeV.

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arXiv2003

Hadronic D Decays Involving Scalar Mesons

The nonleptonic weak decays of charmed mesons into a scalar meson and a pseudoscalar meson are studied. The scalar mesons under consideration are $σ$ [or $f_0(600)$], $κ$, $f_0(980)$, $a_0(980)$ and $K^*_0(1430)$. A consistent picture provided by the data implies that the light scalars below or near 1 GeV form an SU(3) flavor nonet and are predominately the $q^2\bar q^2$ states, while the scalar mesons above 1 GeV can be described as a $q\bar q$ nonet. Hence, we designate $q^2\bar q^2$ to $σ, κ, a_0(980), f_0(980)$ and $q\bar q$ to $K^*_0$. Sizable weak annihilation contributions induced from final-state interactions are essential for understanding the data. Except for the Cabibbo doubly suppressed channel $D^+\to f_0K^+$, the data of $D\toσπ, f_0π, f_0K, K^*_0π$ can be accommodated in the generalized factorization approach. However, the predicted rates for $D\to a_0π, a_0K$ are too small by one to two orders of magnitude when compared with the preliminary measurements. Whether or not one can differentiate between the two-quark and four-quark pictures for the $f_0(980)$ produced in the hadronic charm decays depends on the isoscalar $f_0-σ$ mixing angle in the $q\bar q$ model.

hep-ph↗
arXiv2002

Comments on the Quark Content of the Scalar Meson $f_0(1370)$

Based on the measurements of $(D_s^+,D^+)\to f_0(1370)π^+$ we determine, in a model independent way, the allowed $s\bar s$ content in the scalar meson $f_0(1370)$. We find that, on the one hand, if this isoscalar resonance is a pure $n\bar n$ state [ $n\bar n\equiv(u\bar u+d\bar d)/\sqrt{2} ]$, a very large $W$-annihilation term will be needed to accommodate $D_s^+\to f_0(1370)π^+$. On the other hand, the $s\bar s$ component of $f_0(1370)$ should be small enough to avoid excessive $D_s^+\to f_0(1370)π^+$ induced from the external $W$-emission. Measurement of $f_0(1370)$ production in the decay $D_s^+\to K^+K^-π^+$ will be useful to test the above picture. For the decay $D^0\to f_0(1370)\bar K^0$ which is kinematically barely or even not allowed, depending on the mass of $f_0(1370)$, we find that the finite width effect of $f_0(1370)$ plays a crucial role on the resonant three-body decay $D^0\to f_0(1370)\bar K^0\toπ^+π^-\bar K^0$.

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arXiv2002

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 $Λ_b\bar B N$ is larger than that for $Σ_b \bar BN$, the two-body charmful decay $B^-\toΣ_c^0\bar p$ has a rate larger than $\bar B^0\toΛ_c^+\bar p$ as the former proceeds via the $Λ_b$ pole while the latter via the $Σ_b$ pole. By the same token, the three-body decay $\bar B^0\toΣ_c^{++}\bar pπ^-$ receives less baryon-pole contribution than $B^-\toΛ_c^+\bar pπ^-$. However, because the important charmed-meson pole diagrams contribute constructively to the former and destructively to the latter, $Σ_c^{++}\bar pπ^-$ has a rate slightly larger than $Λ_c^+\bar pπ^-$. It is found that one quarter of the $B^-\to Λ_c^+\bar pπ^-$ rate comes from the resonant contributions. We discuss the decays $\bar B^0\toΣ_c^0\bar pπ^+$ and $B^-\toΣ_c^0\bar pπ^0$ and stress that they are not color suppressed even though they can only proceed via an internal W emission.

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arXiv2002

Three-Body Charmful Baryonic B Decays $\bar B\to D(D^*)N\bar N$

We study the charmful three-body baryonic B decays $\bar B\to D^{(*)}N\bar N$: the color-allowed modes $\bar B^0\to D^{(*)+}n\bar p$ and the color-suppressed ones $\bar B^0\to D^{(*)0}p\bar p$. While the $D^{*+}/D^+$ production ratio is predicted to be of order 3, it is found that $D^0p\bar p$ has a similar rate as $D^{*0}p\bar p$. It is pointed out that $\bar B^0\to D(D^*)N\bar N$ are dominated by the nucleon vector current or by vector meson intermediate states, whereas $\bar B^0\to D^0p\bar p$ proceeds mainly via the exchange of the axial-vector intermediate state $a_1(1260)$. The study of the $N\bar N$ invariant mass distribution in general indicates a threshold baryon pair production; that is, a recoil charmed meson accompanied by a low mass baryon pair except that the spectrum of $D^0p\bar p$ has a hump at large $p\bar p$ invariant mass $m_{p\bar p}\sim 3.0$ GeV.

hep-ph↗
arXiv2002

Nonresonant Three-body Decays of D and B Mesons

Nonresonant three-body decays of D and B mesons are studied. It is pointed out that if heavy meson chiral perturbation theory (HMChPT) is applied to the heavy-light strong and weak vertices and assumed to be valid over the whole kinematic region, then the predicted decay rates for nonresonant charmless 3-body B decays will be too large and especially B^- --> pi^- K^+ K^- greatly exceeds the current experimental limit. This can be understood as chiral symmetry has been applied there twice beyond its region of validity. If HMChPT is applied only to the strong vertex and the weak transition is accounted for by the form factors, the dominant B^* pole contribution to the tree-dominated direct three-body B decays will become small and the branching ratio will be of order 10^{-6}. The decay modes B^- --> (K^- h^+ h^-)_{NR} and bar{B}^0 --> (bar{K}^0 h^+h^-)_{NR} for h = pi, K are penguin dominated. We apply HMChPT in two different cases to study the direct 3-body D decays and compare the results with experiment. Theoretical uncertainties are discussed.

hep-ph↗
arXiv2002

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 $\B(B^-\to p \barΔ^{--})\sim 1\times 10^{-6}$. In general, $\bar B\to N\barΔ>\bar B\to N\bar N$ due to the large coupling constant for $Σ_b\to BΔ$. For three-body modes we focus on octet baryon final states. The leading three-dominated modes are $\bar B^0\to p\bar nπ^-(ρ^-), n\bar pπ^+(ρ^+)$ with a branching ratio of order $3\times 10^{-6}$ for $\bar B^0\to p\bar nπ^-$ and $8\times 10^{-6}$ for $\bar B^0\to p\bar nρ^-$. 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., $\bar B^0\to Σ^0\bar pπ^+, Σ^-\bar nπ^+$, have branching ratios of order $(1\sim 4)\times 10^{-6}$. In contrast, the decay rate of $\bar B^0\toΛ\bar pπ^+$ 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.

hep-ph↗
arXiv2002

Weak Annihilation and the Effective Parameters a_1 and a_2 in Nonleptonic D Decays

Based on SU(3) flavor symmetry, many of the quark-graph amplitudes in two-body nonleptonic decays of charmed mesons can be extracted from experiment, which enable us to see the relevance and importance of weak annihilation topologies and to determine the complex parameters $a_1$ and $a_2$ to test the factorization approach. It is found that $a_2$ in $D\to \bar K^*π$ and $D\to \bar Kρ$ can be different by a factor of 2, indicating that nonfactorizable corrections to the latter are far more important than the former. The relative phase between $a_1$ and $a_2$ is about $150^\circ$. Weak annihilation topologies induced by nearby resonances via final-state rescattering can be described in a model-independent manner. Although the W-exchange contribution in $D\to PP$ decays is dominated by resonant final-state interactions (FSIs), its amplitude in VP decays (V: vector meson, P: pseudoscalar meson) receives little contributions from FSIs in the quark-antiquark resonance formation. As a consequence, the sign flip of the W-exchange amplitude in $D\to\bar K^*π$ and $\bar Kρ$ decays, which is needed to explain the relatively real decay amplitudes of $D\to \bar Kρ$, remains unexplained. SU(3) symmetry is badly broken in some Cabibbo-suppressed modes and it can be accounted for by the accumulation of some modest SU(3) violation in individual quark-graph amplitudes.

hep-ph↗
arXiv2002

Implications of Recent $\bar{B}^0\to D^{(*)0}X^0$ Measurements

The recent measurements of the color-suppressed modes $\bar B^0\to D^{(*)0}π^0$ imply non-vanishing relative final-state interaction (FSI) phases among various $\bar B\to Dπ$ decay amplitudes. Depending on whether or not FSIs are implemented in the topological quark-diagram amplitudes, two solutions for the parameters $a_1$ and $a_2$ are extracted from data using various form-factor models. It is found that $a_2$ is not universal: $|a_2(Dπ)|= 0.40-0.55$ and $|a_2(D^*π)|= 0.25-0.35$ with a relative phase of order $(50-55)^\circ$ between $a_1$ and $a_2$. If FSIs are not included in quark-diagram amplitudes from the outset, $a_2^{eff}/a_1^{eff}$ and $a_2^{eff}$ will become smaller. The large value of $|a_2(Dπ)|$ compared to $|a_2^{eff}(Dπ)|$ or naive expectation implies the importance of long-distance FSI contributions to color-suppressed internal $W$-emission via final-state rescatterings of the color-allowed tree amplitude.

hep-ph↗
arXiv2002

B -> J/psi K^* Decays in QCD Factorization

The hadronic decay B -> J K^* is analyzed within the framework of QCD factorization. The spin amplitudes A_0, A_\parallel and A_\perp in the transversity basis and their relative phases are studied using various different form-factor models for B-K^* transition. The effective parameters a_2^h for helicity h=0,+,- states receive different nonfactorizable contributions and hence they are helicity dependent, contrary to naive factorization where a_2^h are universal and polarization independent. QCD factorization breaks down even at the twist-2 level for transverse hard spectator interactions. Although a nontrivial strong phase for the A_\parallel amplitude can be achieved by adjusting the phase of an infrared divergent contribution, the present QCD factorization calculation cannot say anything definite about the phase phi_\parallel. Unlike B -> J/psi K decays, the longitudinal parameter a_2^0 for B -> J/psi K^* does not receive twist-3 corrections and is not large enough to account for the observed branching ratio and the fraction of longitudinal polarization. Possible enhancement mechanisms for a_2^0 are discussed.

hep-ph↗
arXiv2002

Penguin-Induced Radiative Baryonic B Decays

Weak radiative baryonic B decays $B\to\B_1\ov \B_2γ$ mediated by the electromagnetic penguin process $b\to sγ$ have appreciable rates larger than their two-body counterparts $B\to\B_1\ov \B_2$. The branching ratios for $B^-\toΛ\bar pγ$ and $B^-\toΞ^0\barΣ^-γ$ are sizable, falling into the range of $(1\sim 6)\times 10^{-6}$ with the value preferred to be on the large side, and not far from the bottom baryon radiative decays $Λ_b\toΛγ$ and $Ξ_b\toΞγ$ due to the large short-distance enhancement for $b\to sγ$ penguin transition and the large strong coupling of the anti-triplet bottom baryons with the B meson and the light baryon. These penguin-induced radiative baryonic B decay modes should be accessible by B factories.

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arXiv2002

Charmful Baryonic B Decays $\bar B^0\toΛ_c\bar p$ and $\bar B\toΛ_c\bar pπ(ρ)$

We study the two-body and three-body charmful baryonic B decays: $\bar B^0\to Λ_c\bar p$ and $\bar B\to Λ_c \bar pπ(ρ)$. The factorizable W-exchange contribution to $\bar B^0\toΛ_c\bar p$ is negligible. Applying the bag model to evaluate the baryon-to-baryon weak transition matrix element, we find $B(\bar B^0\toΛ_c\bar p)\leq 1.1\times 10^{-5}|g_{B^0pΣ_b^+}/6|^2$ with $g_{B^0pΣ_b^+}$ being a strong coupling for the decay $Σ_b^+\to \bar B^0 p$ and hence the predicted branching ratio is well below the current experimental limit. The factorizable contributions to $B^-\toΛ_c\bar pπ^-$ can account for the observed branching ratio of order $6\times 10^{-4}$. The branching ratio of order $2\times 10^{-3}$ for $B^-\toΛ_c\bar pρ^-$ is larger than that of $B^-\toΛ_c\bar pπ^-$ by a factor of about 2.6. We explain why the three-body charmful baryonic B decay has a larger rate than the two-body one, contrary to the case of mesonic B decays.

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arXiv2001

Phenomenological Applications of QCD Factorization to Semi-inclusive B Decays

We have systematically investigated the semi-inclusive B decays $B\to MX$, which are manifestations of the quark decay $b \to Mq$, within a framework inspired by QCD-improved factorization. These decays are theoretically clean and have distinctive experimental signatures. We focus on a class of these that do not require any form factor information and therefore may be especially suitable for extracting information on the angles $α$ and $γ$ of the unitarity triangle. The strong phase coming from final-state rescattering due to hard gluon exchange between the final states can induce large rate asymmetries for tree-dominated color-suppressed modes $(π^0,ρ^0,ω)X_{\bar s}$. The nonfactorizable hard spectator interactions in the 3-body decay $B\to Mq_1\bar q_2$, though phase-space suppressed, are extremely important for the tree-dominated modes $(π^0,ρ^0,ω)X_{\bar s},~ϕX$, $J X_s,J X$ and the penguin-dominated mode $ωX_{s\bar s}$. Our result for ${\cal B}(B\to J X_s)$ is in agreement with experiment. $B^0_s\to (π^0,ρ^0,ω)X_{\bar s}$, $ρ^0X_{s\bar s}$, $B^0\to(K^-X,K^{*-}X)$ and $B^-\to (K^0X_s,K^{*0}X_s)$ are the most promising ones in searching for direct CP violation: they have branching ratios of order $10^{-6}-10^{-4}$ and CP rate asymmetries of order $(10-40)%$.

hep-ph↗
arXiv2001

Semi-inclusive B Decays and Direct CP Violation in QCD Factorization

We have systematically investigated the semi-inclusive B decays B->MX, which are manifestations of the quark decay b->Mq, within the framework of QCD-improved factorization. These decays are theoretically clean and have distinctive experimental signatures. We focus on a class of these that do not require any form factor information and therefore may be especially suitable for extracting information on the angles $α$ and $γ$ of the unitarity triangle. The nonfactorizable effects, such as vertex-type and penguin-type corrections to the two-body b decay and hard spectator corrections to the 3-body decay are calculable in the heavy quark limit. QCD factorization is applicable when the emitted meson is a light meson or a charmonium. We discuss the issue of the CPT constraint on partial rate asymmetries. The strong phase coming from final-state rescattering due to hard gluon exchange between the final states can induce large rate asymmetries for tree-dominated color-suppressed modes $(π^0,ρ^0,ω)X_{\bar s}$. The nonfactorizable hard spectator interactions in the 3-body decay, though phase-space suppressed, are extremely important for the tree-dominated modes $(π^0,ρ^0,ω)X_{\bar s}, ϕX$, $J X_s,J X$ and the penguin-dominated mode $ωX_{s\bar s}$. In fact, they are dominated by the hard spectator corrections. Our result for ${\cal B} (B\to J/ψX_s)$ is in agreement with experiment. The semi-inclusive decay modes: $B^0_s\to (π^0,ρ^0,ω)X_{\bar s}$, $ρ^0X_{s\bar s}$, $B^0\to(K^-X,K^{*-}X)$ and $B^-\to (K^0X_s,K^{*0}X_s)$ are the most promising ones in searching for direct CP violation. In fact, they have branching ratios of order $10^{-6}-10^{-4}$ and CP rate asymmetries of order $(10-40)%$.

hep-ph↗
arXiv2001

Charmless B -> VV Decays in QCD Factorization: Implications of Recent $B\to ϕK^*$ Measurement

In the heavy quark limit, both vector mesons in the charmless B -> VV decay should have zero helicity and the corresponding amplitude is proportional to the form factor difference $(A_1-A_2)$. The first observed charmless $B\to VV$ mode, $B\toϕK^*$, indicates that the form factors $A_1(q^2)$ and $A_2(q^2)$ cannot be very similar at low $q^2$ as shown in some form-factor models. The approach of QCD-improved factorization implies that the nonfactorizable correction to each partial-wave or helicity amplitude is not the same; the effective parameters $a_i$ vary for different helicity amplitudes. The leading-twist nonfactorizable corrections to the transversely polarized amplitudes vanish in the chiral limit and hence it is necessary to take into account twist-3 distribution amplitudes of the vector meson in order to have renormalization scale and scheme independent predictions. Branching ratios of $B\to VV$ decays are calculated in two different models for form factors, and the predicted decay rates are different by a factor of $1.5\sim 2$. Owing to the absence of (S-P)(S+P) penguin contributions to the W-emission amplitudes, tree-dominated decays tend to have larger branching ratios than the penguin-dominated ones.

hep-ph↗
arXiv2001

Analysis of B-> ϕK Decays in QCD Factorization

We analyze the decay $B\to ϕK$ within the framework of QCD-improved factorization. We found that although the twist-3 kaon distribution amplitude dominates the spectator interactions, it will suppress the decay rates slightly. The weak annihilation diagrams induced by $(S-P)(S+P)$ penguin operators, which are formally power-suppressed by order $(Λ/m_b)^2$, are chirally and logarithmically enhanced. Therefore, these annihilation contributions are not subject to helicity suppression and can be sizable. The predicted branching ratio of $B^-\toϕK^-$ is $(3.8\pm0.6)\times 10^{-6}$ in the absence of annihilation contributions and it becomes $(4.3^{+3.0}_{-1.4})\times 10^{-6}$ when annihilation effects are taken into account. The prediction is consistent with CLEO and BaBar data but smaller than the BELLE result.

hep-ph↗
arXiv2000

The Delta I=1/2 rule and epsilon'/epsilon

The $ΔI=1/2$ rule and direct CP violation $ε'/ε$ in kaon decays are studied within the framework of the effective Hamiltonian approach in conjunction with generalized factorization for hadronic matrix elements.

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