arXiv subjects

Hai-Yang Cheng

Publications and source records attributed to Hai-Yang Cheng.

At least 109 records · Page 6Linked to original sources

arXiv2008

Branching Ratios and Polarization in B-> VV,VA,AA Decays

We present a detailed study of charmless two-body B decays into final states involving two vector mesons (VV) or two axial-vector mesons (AA) or one vector and one axial-vector meson (VA), within the framework of QCD factorization, where $A$ is either a $^3P_1$ or $^1P_1$ axial-vector meson. The main results are as follows. (i) In the presence of NLO nonfactorizable corrections, effective Wilson coefficients $a_i^h$ are helicity dependent. For some penguin-dominated modes, the constructive (destructive) interference in the negative-helicity (longitudinal-helicity) amplitude of the $B\to VV$ decay will render the former comparable to the latter and push up the transverse polarization. (ii) In QCD factorization, the transverse polarization fraction can be large for penguin-dominated charmless $VV$ modes by allowing for sizable penguin annihilation contributions. (iii) Using the measured $\bar K^{*0}ρ^-$ channel as an input, we predict the branching ratios and polarization fractions for other $\ov B\to \bar K^*ρ$ decays. (iv) The smallness of the axial-vector decay constant of the $^1P_1$ axial vector meson can be tested by measuring various $b_1ρ$ modes to see if $Γ(\bar B^0\to b_1^-ρ^+)\ll Γ(\bar B^0\to b_1^+ρ^-)$ and $Γ(B^-\to b_1^-ρ^0)\ll Γ(B^-\to b_1^0ρ^-)$. (v) For the penguin-dominated modes $a_1K^*$ and $b_1K^*$, it is found that the former are dominated by transverse polarization amplitudes, whereas the latter are governed by longitudinal polarization states.

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arXiv2008

Charmful Three-body Baryonic B decays

We study the charmful three-body baryonic B decays with $D^{(*)}$ or $J/Ψ$ in the final state. We explain the measured rates of $\bar B^0\to n\bar p D^{*+}$, $\bar B^0\to p\bar p D^{(*)0}$, and $B^-\to Λ\bar p J/Ψ$ and predict the branching fractions of $\bar B^0\to Λ\bar p D^{*+}$, $\bar B^0\to Σ^0\bar p D^{*+}$, $B^-\toΛ\bar p D^{0}$, and $B^-\toΛ\bar p D^{*0}$ to be of order $(1.2, 1.1, 1.1, 3.9)\times 10^{-5}$, respectively. They are readily accessible to the $B$ factories.

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arXiv2008

Theoretical Overview of Hadronic Three-body B Decays

Charmless 3-body decays of B mesons are studied in a simple model based on the factorization approach. We have identified two distinct sources of nonresonant contributions: a small contribution from the tree transition and a large source of the nonresonant signal in the matrix elements of scalar densities, e.g., $ $, induced from the penguin transition. This explains the dominance of the nonresonant background in $B\to KKK$ decays, the sizable nonresonant fraction in $K^-π^+π^-$ and $\bar K^0π^+π^-$ modes and the smallness of nonresonant rates in $B\to πππ$ decays. The seemingly huge discrepancy between BaBar and Belle for the nonresonant contribution in the decay $B^-\to K^-π^+π^-$ is now relieved. We have computed the resonant and nonresonant contributions to charmless 3-body decays and determined the rates for the quasi-two-body decays $B\to VP$ and $B\to SP$. Time-dependent CP asymmetries $\sin2β_{\rm eff}$ and $A_{CP}$ in $K^+K^-K_S,K_SK_SK_S,K_Sπ^+π^-$ and $K_Sπ^0π^0$ modes are estimated.

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arXiv2008

Baryonic D Decay $D_s^+\to p\bar n$ and Its Implication

The channel $D_s^+\to p\bar n$ is the only kinematically allowed baryonic D decay. It proceeds solely through the W-annihilation topology. Hence, a recent observation of this mode by CLEO will shed light on the dynamics of W-annihilation. At the short-distance level, its branching ratio is very small, of order $10^{-6}$, owing to chiral suppression. It receives long-distance contributions through final-state scattering of the leading tree and color-suppressed amplitudes. Assuming that the long-distance enhancement of W-annihilation in the baryonic D decay is similar to that in the mesonic $D_s^+$ decay, where the latter can be obtained from the analysis of the diagrammatic approach, we find that $D_s^+\to p\bar n$ becomes visible. The observation of this baryonic D decay implies the dynamical enhancement of the W-annihilation topology in the $D_s^+$ decay.

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arXiv2007

Charmless 3-body B Decays: Resonant and Nonresonant Contributions

Charmless 3-body decays of $B$ mesons are studied using a simple model based on the framework of the factorization approach. We have identified a large source of the nonresonant signal in the matrix elements of scalar densities, e.g. $ $. This explains the dominance of the nonresonant background in $B\to KKK$ decays, the sizable nonresonant fraction of order $(35\sim 40)%$ in $K^-π^+π^-$ and $\bar K^0π^+π^-$ modes and the smallness of nonresonant rates in $B\to πππ$ decays. We have computed the resonant and nonresonant contributions to charmless 3-body decays and determined the rates for the quasi-two-body decays $B\to VP$ and $B\to SP$. Time-dependent CP asymmetries $\sin2β_{\rm eff}$ and $A_{CP}$ in $K^+K^-K_S,K_SK_SK_S,K_Sπ^+π^-$ and $K_Sπ^0π^0$ modes are estimated.

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arXiv2007

Hadronic charmless B decays B-> AP

The two-body hadronic decays of B mesons into pseudoscalar and axial vector mesons are studied within the framework of QCD factorization. The light-cone distribution amplitudes (LCDAs) for $^3P_1$ and $^1P_1$ axial-vector mesons have been evaluated using the QCD sum rule method. Owing to the G-parity, the chiral-even two-parton light-cone distribution amplitudes of the $^3P_1$ ($^1P_1$) mesons are symmetric (antisymmetric) under the exchange of quark and anti-quark momentum fractions in the SU(3) limit. For chiral-odd LCDAs, it is other way around. The main results are the following: (i) The predicted rates for $a_1^\pm(1260)π^\mp$, $b_1^\pm(1235)π^\mp$, $b_1^0(1235)π^-$, $a_1^+K^-$ and $b_1^+K^-$ modes are in good agreement with the data. However, the naively expected ratios $Br(B^-\to a_1^0π^-)/Br(\ov B^0\to a_1^+π^-)\leq 1$, $Br(B^-\to a_1^-π^0)/Br(\ov B^0\to a_1^-π^+)\sim {1\over 2}$ and $Br(B^-\to b_1^0K^-)/Br(\ov B^0\to b_1^+K^-)\sim {1\over 2}$ are not borne out by experiment. This should be clarified by the improved measurements of these decays. (ii) Since the $\bar B\to b_1K$ decays receive sizable annihilation contributions, their rates are sensitive to the interference between penguin and annihilation terms. The measurement of $Br(\bar B^0\to b_1^+K^-)$ implies a destructive interference which in turn indicates that the form factors for $B\to b_1$ and $B\to a_1$ transitions are of opposite signs. (iii) Sizable power corrections such as weak annihilation are needed to account for the observed rates of the penguin-dominated modes $K_1^-(1270)π^+$ and $K_1^-(1400)π^+$.

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arXiv2007

Charmless Three-body Decays of B Mesons

Charmless 3-body decays of B mesons are studied in the framework of the factorization approach. The nonresonant contributions arising from $B\to P_1P_2$ transitions are evaluated using heavy meson chiral perturbation theory (HMChPT). The momentum dependence of nonresonant amplitudes is assumed to be in the exponential form $e^{-α_{NR}} p_B\cdot(p_i+p_j)}$ so that the HMChPT results are recovered in the soft meson limit $p_i, p_j\to 0$. In addition, we have identified another large source of the nonresonant signal in the matrix elements of scalar densities, e.g. $ $, which can be constrained from the decay $\bar B^0\to K_SK_SK_S$ or $B^-\to K^-K_SK_S$. The intermediate vector meson contributions to 3-body decays are identified through the vector current, while the scalar meson resonances are mainly associated with the scalar density. Their effects are described in terms of the Breit-Wigner formalism. Our main results are: (i) All KKK modes are dominated by the nonresonant background. The predicted branching ratios of $K^+K^-K_{S(L)}$, $K^+K^-K^-$ and $K^-K_SK_S$ modes are consistent with the data within errors. (ii) Although the penguin-dominated $B^0\to K^+K^-K_{S}$ decay is subject to a potentially significant tree pollution, its effective $\sin 2β$ is very similar to that of the $K_SK_SK_S$ mode. However, direct CP asymmetry of the former, being of order -4%, is more prominent than the latter. (iii) For $B\to Kππ$ decays, we found sizable nonresonant contributions in $K^-π^+π^-$ and $\bar K^0π^+π^-$ modes, in agreement with the Belle measurements but larger than the BaBar result.

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arXiv2007

Spectroscopy and Strong Decays of Charmed Baryons

Spectroscopy and strong decays of the charmed baryons are reviewed. Possible spin-parity quantum numbers of several newly observed charmed baryon resonances are discussed. Strong decays of charmed baryons are analyzed in the framework of heavy hadron chiral perturbation theory in which heavy quark symmetry and chiral symmetry are synthesized.

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arXiv2007

Charmless B decays to a scalar meson and a vector meson

The hadronic charmless B decays into a scalar meson and a vector meson are studied within the framework of QCD factorization. The main results are: (i) The decay rates for the $f_0(980)K^{*-}$ and $f_0(980)\ov K^{*0}$ modes depend on the $f_0-σ$ mixing angle $θ$. The experimental measurements can be accommodated for $θ\approx 20^\circ$. (ii) If the $a_0(980)$ is a $q\bar q$ bound state, the predicted branching ratios for the channels $a_0^+ρ^-$ and $a_0^0ρ^-$ will be very large, of order $30\times 10^{-6}$ and $23\times 10^{-6}$, respectively. If the observation of or the experimental limit on theses two modes is much smaller than the expectation of $\sim 25\times 10^{-6}$, this could hint at a four-quark nature for the $a_0(980)$. (iii) For the $a_0(1450)$ channels, $a_0^+(1450)ρ^-$ and $a_0^0(1450)ρ^-$ are found to have branching ratios of order $16\times 10^{-6}$ and $22\times 10^{-6}$, respectively. A measurement of them at the predicted level will favor the $q\bar q$ structure for the $a_0(1450)$. (iv) Contrary to the naive expectation that $Γ(B^-\to a_0^0ρ^-)\sim {1\over 2}Γ(\bar B^0\to a_0^+ρ^-)$, we found that they have comparable rates due to additional contributions to the $a_0ρ^-$ mode from the $a_0^0$ emission. (v) The predicted central value of $Br(\bar B^0\to\ov K^{*0}_0(1430)ϕ)$ is larger than experiment, though it can be accommodated within theoretical errors. The decays $B\to K^{*}_0(1430)ρ$ are expected to have rates substantially larger than that of $B\to K^{*}_0(1430)π$ owing to the constructive (destructive) interference between the $a_4$ and $a_6$ penguin terms in the former (latter). Experimentally, it is thus important to check if the $B\to K^{*}_0ρ$ modes are enhanced relative to the corresponding $K_0^*π$ channels.

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arXiv2007

Theoretical issues with $ΔS$ in three-body B decays

Theoretical uncertainties with the time-dependent CP asymmetries $ΔS$ and $A_{\rm CP}$ in $B^0\to K^+K^-K_S$, $K_SK_SK_S$ and $K_Sπ^0π^0$ decays are discussed. In order to have a reliable estimate of CP asymmetries, it is very crucial to understand the underlying mechanism for the nonresonant background which dominates the KKK modes.

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arXiv2006

Strong Decays of Charmed Baryons in Heavy Hadron Chiral Perturbation Theory

Strong decays of charmed baryons are analyzed in the framework of heavy hadron chiral perturbation theory (HHChPT) in which heavy quark symmetry and chiral symmetry are synthesized. HHChPT works excellently for describing the strong decays of s-wave charmed baryons. For L=1 orbitally excited states, two of the unknown couplings, namely, $h_2$ and $h_{10}$, are determined from the resonant $Λ_c^+ππ$ mode produced in the $Λ_c(2593)$ decay and the width of $Σ_c(2800)$, respectively. Predictions for the strong decays of the p-wave charmed baryon states $Λ_c(2625)$, $Ξ_c(2790)$ and $Ξ_c(2815)$ are presented. Since the decay $Λ_c(2593)^+\toΛ_c^+ππ$ receives non-resonant contributions, our value for $h_2$ is smaller than the previous estimates. We also discuss the first positive-parity excited charmed baryons. We conjecture that the charmed baryon $Λ_c(2880)$ with $J^P=\frac52^+$ is an admixture of $Λ_{c2}(\frac52^+)$ with and $\tildeΛ''_{c3}(\frac52^+)$; both are L=2 orbitally excited states. The potential model suggests $J^P=\frac52^-$ or $\frac32^+$ for $Λ_c(2940)^+$. Measurements of the ratio of $Σ_c^*π/Σ_cπ$ will enable us to discriminate the $J^P$ assignments for $Λ_c(2940)$. We advocate that the $J^P$ quantum numbers of $Ξ_c(2980)$ and $Ξ_c(3077)$ are $\frac12^+$ and $\frac52^+$, respectively. Under this $J^P$ assignment, it is ready to understand why $Ξ_c(2980)$ is broader than $Ξ_c(3077)$.

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arXiv2006

Scalar Glueball, Scalar Quarkonia, and their Mixing

The isosinglet scalar mesons $f_0(1710)$, $f_0(1500)$, $f_0(1370)$ and their mixing are studied. We employ two recent lattice results as the starting point; one is the isovector scalar meson $a_0(1450)$ which displays an unusual property of being nearly independent of quark mass for quark masses smaller than that of the strange, and the other is the scalar glueball mass at 1710 MeV in the quenched approximation. In the SU(3) symmetry limit, $f_0(1500)$ turns out to be a pure SU(3) octet and is degenerate with $a_0(1450)$, while $f_0(1370)$ is mainly an SU(3) singlet with a slight mixing with the scalar glueball which is the primary component of $f_0(1710)$. These features remain essentially unchanged even when SU(3) breaking is taken into account. We discuss the sources of SU(3) breaking and their consequences on flavor-dependent decays of these mesons. The observed enhancement of $ωf_0(1710)$ production over $ϕf_0(1710)$ in hadronic $J/ψ$ decays and the copious $f_0(1710)$ production in radiative $J/ψ$ decays lend further support to the prominent glueball nature of $f_0(1710)$.

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arXiv2006

Mixing of Scalar Glueball and Scalar Quarkonia

The isosinglet scalar mesons $f_0(1710)$, $f_0(1500)$, $f_0(1370)$ and their mixing are studied. Two recent lattice results are employed as the starting point; one is the approximate SU(3) symmetry in the scalar sector above 1 GeV for the connected insertion part without $q\bar q$ annihilation, and the other is the scalar glueball mass at 1710 MeV in the quenched approximation. In the SU(3) symmetry limit, $f_0(1500)$ becomes a pure SU(3) octet and is degenerate with $a_0(1450)$, while $f_0(1370)$ is mainly an SU(3) singlet with a slight mixing with the scalar glueball which is the primary component of $f_0(1710)$. These features remain essentially unchanged even when SU(3) breaking is taken into account. The observed enhancement of $ωf_0(1710)$ production over $ϕf_0(1710)$ in hadronic $J/ψ$ decays and the copious $f_0(1710)$ production in radiative $J/ψ$ decays lend further support to the prominent glueball nature of $f_0(1710)$.

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arXiv2006

Status of baryonic B decays

An overview of exclusive two-body and three-body baryonic B decays is given. The threshold enhancement effect in the dibaryon invariant mass and the angular distributions in the dibaryon rest frame are stressed and explained. Weak radiative baryonic B decays mediated by the electromagnetic penguin process $b\to sγ$ are discussed. Apart from the first observation of the radiative penguin decay $B^-\toΛ\bar pγ$ with the baryonic final state, the decay $B^-\to Ξ^0\barΣ^-γ$ at the level of $6\times 10^{-7}$ may be accessible to B factories in the near future.

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arXiv2006

Production of P-wave Charmed Mesons in Hadronic B Decays

Production of even-parity charmed mesons in hadronic B decays is studied. Specifically, we focus on the Cabibbo-allowed decays $\bar B\to D^{**}π$ and $\bar D^{**}_sD^{(*)}$, where $D^{**}$ denotes generically a p-wave charmed meson. While the measured color-allowed decays $\bar B^0\to D^{**+}π^-$ are consistent with the theoretical expectation, the experimental observation of $B^-\to D^{**0}π^-$ for the broad $D^{**}$ states is astonishing as it requires that the color-suppressed contribution dominates over the color-allowed one, even though the former is $1/m_b$ suppressed in the heavy quark limit. In order to accommodate the data of $\bar B\to D^{**}π^-$, it is found that $a_2/a_1\approx -0.5$ with a sign opposite to that in $\bar B\to Dπ$ decays, where $a_1$ and $a_2$ are the effective Wilson coefficients for color-allowed and color-suppressed decay amplitudes, respectively. The decay constants and form factors for $D^{**}$ and the Isgur-Wise functions $τ_{1/2}(ω)$ and $τ_{3/2}(ω)$ are extracted from the data of $B\to D^{**}π$ decays. The Isgur-Wise functions calculated in the covariant light-front quark model are in good agreement with experiment. The neutral modes $\bar B^0\to D^{**0}π^0$ for $D^{**}=D^*_0(2400),D'_1(2430)$ and $\bar B^0\to D'^0_1(2430)ω$ are predicted to have branching ratios of order $10^{-4}$ which are also supported by isospin argument. The decay constants of $D_{s0}^*(2317)$ and $D'_{s1}(2460)$ are inferred from the measurements of $\bar B\to D_s^{**-}D$ to be $58\sim 86$ MeV and $130\sim 200$ MeV, respectively. Contrary to the decay constants $f_{D_0^*}$ and $f_{D'_1}$ which are similar in size, the large disparity between $f_{D_{s0}^*}$ and $f_{D'_{s1}}$ is surprising and unexpected.

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arXiv2006

Doubly Charmful Baryonic B Decays

There are two apparent puzzles connected with the two-body and three-body doubly charmed baryonic B decays. First, earlier calculations based on QCD sum rules or the diquark model predict $Br(\bar B^0\toΞ_c^+\barΛ_c^-)\approx Br(\bar B^0\to\B_c\bar N)$, while experimentally the former has a rate two orders of magnitude larger than the latter. Second, a naive estimate of the branching ratio $10^{-9}$ for the color-suppressed three-body decay $\bar B\toΛ_c^+\barΛ_c^-K$, which is highly suppressed by phase space, is too small by five to six orders of magnitude compared to experiment. We show that the great suppression for the $Λ_c^+\barΛ_c^-K$ production can be alleviated provided that there exists a narrow hidden charm bound state with a mass near the $Λ_c\barΛ_c$ threshold. This new state that couples strongly to the charmed baryon pair can be searched for in B decays and in $p\bar p$ collisions by studying the mass spectrum of $D^{(*)}\bar D^{(*)}$ or $Λ_c\barΛ_c$. The doubly charmful decay $\bar B\toΞ_c\barΛ_c$ has a configuration more favorable than the singly charmful one such as $\bar B^0\toΛ_c\bar p$ since no hard gluon is needed to produce the energetic $Ξ_c\barΛ_c$ pair in the former decay, while two hard gluons are needed for the latter process. Assuming that a soft $q\bar q$ quark pair is produced through the $σ$ and $π$ meson exchanges in the configuration for $\bar B\to Ξ_c\barΛ_c$, it is found that its branching ratio is of order $10^{-3}$, in agreement with experiment.

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arXiv2006

Exclusive Baryonic B Decays Circa 2005

The status of exclusive two-body and three-body baryonic B decays is reviewed. The threshold enhancement effect in the dibaryon invariant mass and the angular distributions in the dibaryon rest frame are stressed and explained. Weak radiative baryonic B decays mediated by the electromagnetic penguin process $b\to sγ$ are discussed. Puzzles with the correlation observed in $B^-\to p\bar pK^-$ decay and the unexpectedly large rate observed for $B\toΛ_c\barΛ_cK$ are examined. The former may indicate that the $p\bar p$ system is produced through some intermediate states, while the latter implies the failure of naive factorization for $Λ\barΛK$ modes and may hint at the importance of final-state rescattering effects.

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arXiv2005

Charmless hadronic B decays involving scalar mesons: Implications to the nature of light scalar mesons

The hadronic charmless B decays into a scalar meson and a pseudoscalar meson are studied within the framework of QCD factorization. Although the light scalar mesons $f_0(980)$ and $a_0(980)$ are widely perceived as primarily the four-quark bound states, in practice it is difficult to make quantitative predictions based on the four-quark picture for light scalars. Hence, predictions are made in the 2-quark model for the scalar mesons. Based on the QCD sum rule method, we have derived the leading-twist light-cone distribution amplitudes of scalar mesons and their decay constants. The short-distance approach suffices to explain the observed large rates of $f_0(980)K^-$ and $f_0(980)\bar K^0$ that receive major penguin contributions from the $b\to ss\bar s$ process. When $f_0(980)$ is assigned as a four-quark bound state, there exist extra diagrams contributing to $B\to f_0(980)K$. Therefore, a priori the $f_0(980)K$ rate is not necessarily suppressed for a four-quark state $f_0(980)$. The calculated $\bar B^0\to a_0^+(980)π^-$ and $a_0^+(980)K^-$ rates exceed slightly the current experimental limits. If the branching ratio of $\bar B^0\to a_0^+(1450)π^-$ is measured at the level of $(4\sim 6)\times 10^{-6}$ while $a_0^+(980)π^-$ is found to be smaller, say, of order $(1\sim 2)\times 10^{-6}$ or even smaller than this, it will be likely to imply a 2-quark nature for $a_0(1450)$ and a four-quark assignment for $a_0(980)$. The penguin-dominated modes $a_0(980)K$ and $a_0(1450)K$ receive dominant weak annihilation contributions.

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