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Chun-Khiang Chua

Publications and source records attributed to Chun-Khiang Chua.

At least 55 records · Page 3Linked to original sources
arXiv2009

Study of \bar B\to Λ_c\bar Λ_c and \bar B\to Λ_c\bar Λ_c \bar K

We study the doubly charmful two-body and three-body baryonic B decays $\bar B\to Λ_c^+\bar Λ_c^-$ and $\bar B\to Λ_c^+\bar Λ_c^- \bar K$. As pointed out before, a naive estimate of the branching ratio ${\cal O}(10^{-8})$ for the latter decay is too small by three to four orders of magnitude compared to experiment. Previously, it has been shown that a large enhancement for the $Λ_c^+\barΛ_c^-\bar K$ production can occur due to a charmonium-like resonance (e.g. X(4630) discovered by Belle) with a mass near the $Λ_c\barΛ_c$ threshold. Motivated by the BaBar's observation of a resonance in the $Λ_c \bar K$ system with a mass of order 2930 MeV, we study in this work the contribution to $\bar B\toΛ_c^+\barΛ_c^-\bar K$ from the intermediate state $Ξ_c(2980)$ which is postulated to be a first positive-parity excited $D$-wave charmed baryon state. Assuming that a soft $q\bar q$ quark pair is produced through the $σ$ and $π$ meson exchanges in the configuration for $\bar B\to Ξ_c(2980)\barΛ_c$ and $Λ_c\barΛ_c$, it is found that branching ratios of $\bar B\to Λ_c^+\bar Λ_c^- \bar K$ and $\bar B\to Λ_c^+\bar Λ_c^-$ are of order $3.5\times 10^{-4}$ and $5\times 10^{-5}$, respectively, in agreement with experiment except that the prediction for the $Λ_c\barΛ_c K^-$ is slightly smaller. In conjunction with our previous analysis, we conclude that the enormously large rate of $\bar B\to Λ_c^+\bar Λ_c^-\bar K$ arises from the resonances $Ξ_c(2980)$ and X(4630).

hep-ph↗
arXiv2008

Rescattering effects in charmless anti-B_{u,d,s} to PP decays

Final-state interaction effects in charmless B_{u,d,s} to PP decays are studied. We investigate the B(bar)^0 to pi^+ pi^-, pi^0 pi^0 rates and the K pi direct CP violations, which lead to the so-called K pi puzzle in CP violation (Delta A). We found that sizable and complex color-suppressed tree amplitudes, which are crucial for the large pi^0 pi^0 rate and Delta A, are generated through exchange rescattering. The correlation of the ratio B(pi^0 pi^0)/B(pi^+ pi^-) and Delta A is studied. Predictions on B_s rates, direct and time-dependent CP asymmetries are made.

hep-ph↗
arXiv2008

Lepton Flavor Violating $l \to l' γ$ and $Z \to l \bar l'$ Decays Induced by Scalar Leptoquarks

Motivated by the recent muon $g-2$ data, we study the lepton flavor violating $l \to l' γ$ and $Z \to l \bar l'$ ($l, l' = e, μ, τ$) decays with $l \neq l'$ in a scalar leptoquark model. Leptoquarks can produce sizable LFV $l\to l'γ$ decay rates that can be easily reached by present or near future experiments. % Leptoquark masses and couplings are constrained by the muon $g-2$ data and the current $l \to l' γ$ bounds. We predict $Br(Z \to τ^\mp e^\pm)$ reaching the present limit ($10^{-5}$) and $Br(Z \to μ^\mp τ^\pm)$ reaching $2\times 10^{-8}$, which will be accessible by future linear colliders, whereas, the current bounds on LFV impose very strong constraints on the $Br(Z \to μ^\mp e^\pm)$ and the ratio is too low to be observed in the near future.

hep-ph↗
arXiv2008

Rescattering effects in charmless B_{u,d,s} to P P decays

We study the final-state interaction (FSI) effects in charmless B_{u,d,s} to PP decays. We consider a FSI approach with both short- and long-distance contributions, where the former are from in-elastic channels and are contained in factorization amplitudes, while the latter are from the residual rescattering among PP states. Flavor SU(3) symmetry is used to constrain the residual rescattering S-matrix. We fit to all available data on the CP-averaged decay rates and CP asymmetries, and make predictions on unmeasured ones. Our main results are as follows: (i) Results are in agreement with data in the presence of FSI. (ii) For B decays, the pi^+pi^- and pi^0pi^0 rates are suppressed and enhanced respectively by FSI. (iii) The FSI has a large impact on direct CP asymmetries of many modes. (iv) The deviation (Delta A) between A(B{bar}^0 to K^-pi^+) and A(B^-to K^-π^0) can be understood in the FSI approach. (v) Sizable and complex color-suppressed tree amplitudes, which are crucial for the large π^0π^0 rate and Delta A, are generated through exchange rescattering. The correlation of the ratio B(pi^0pi^0)/B(pi^+pi^-) and Delta A is studied. (vi) The B^- to pi^-pi^0 direct CP violation is very small and is not affected by FSI. (vii) Several B_s decay rates are enhanced. In particular, the eta'eta' branching ratio is enhanced to the level of 1.0X10^{-4}, which can be checked experimentally. (viii) Time-dependent CP asymmetries S in B_{d,s} decays are studied. CP asymmetries in these modes will be useful to test the SM.

hep-ph↗
arXiv2007

Rescattering effects in B_{u,d,s}(bar) to D P, D(bar) P decays

We study quasi-elastic rescattering effects in B_{u,d,s}(bar) to DP, D(bar)P decays, where P is a light pseudoscalar. The updated measurements of B_{u,d}(bar) to DP decays are used to extract the effective Wilson coefficients a^{eff}_1 ~ 0.90, a^{eff}_2 ~ 0.23, three strong phases delta ~ 53 degree, theta ~ 18 degree, sigma ~ -88 degree, and the mixing angle tau ~ 9 degree. This information is used to predict rates of nineteen B_{s}(bar) to DP and B_{u,d,s}(bar) to D(bar)P decay modes, including modes of interests in the gamma/phi_3 program. Many decay rates are found to be enhanced. In particular, the B_s(bar) to D0 K0 rate is predicted to be 8\times 10^{-4}, which could be measured soon. The rescattering effects on the corresponding B_{u,d,s}(bar) to D(bar)P, DP amplitude ratios r_B, r_{B_s}, and the relative strong phases delta_B, delta_{B_s} are studied. Although the decay rates are enhanced in most cases, r_{B,B_s} values are similar to factorization expectation.

hep-ph↗
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.

hep-ph↗
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.

hep-ph↗
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 $Ξ_c(3077)$.

hep-ph↗
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 $f_0(1710)$.

hep-ph↗
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.

hep-ph↗
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.

hep-ph↗
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.

hep-ph↗
arXiv2005

Extracting the unitarity angle gamma in Bs to D0 h0, D0bar h0 Decays

The recently observed color-suppressed B0bar to D0 pi0, D0 eta, D0 eta', Ds+ K-, D0 K0bar, D0 rho0 and D0 omega decay modes all have rates larger than expected. The color-suppressed Bs to D0 phi, D0bar phi modes, which were suggested for the extraction of the unitarity angle gamma in the Gronau-London method, could be larger than the previous estimation by one order of magnitude. Several new theoretical clean modes in Bs decays are suggested for the extraction of gamma. The proposed Bs to D0 h0, D0bar h0 decay modes with h0 = pi0, eta, eta', rho0, omega in addition to h0 = phi are free from penguin contributions. Their decay rates can be estimated from the observed color-suppressed B0bar to D0 h0 rates through SU(3) symmetry. A combined study of these D0 h0, D0bar h0 modes in addition to the D0 phi, D0bar phi modes is useful in the extraction of gamma in the Bs system without involving the Bs-Bsbar mixing. Since the b to u and b to c transitions belong to the same topological diagram, the relative strong phase is likely to be small. In this case, the CP asymmetries are suppressed and the untagged rates are very useful in the gamma extraction.

hep-ph↗
arXiv2005

CP-violating asymmetries in B^0 decays to K^+K^-K_{S(L)}^0 and K_S^0K_S^0K_{S(L)}^0

Decay rates and time-dependent and direct CP asymmetries in the decays $B^0\to K^+K^-K_{S(L)}$ and $K_S K_S K_{S(L)}$ are studied. Resonant and nonresonant contributions to the three-body decays are carefully investigated. Nonresonant effects on 2-body and 3-body matrix elements are constrained by QCD counting rules. The predicted branching ratios are consistent with the data within the theoretical and experimental errors, though the theoretical central values are somewhat smaller than the experimental ones. Owing to the presence of color-allowed tree amplitudes in $B^0\to K^+K^-K_{S(L)}$, this penguin-dominated mode is subject to a significant tree pollution and the deviation of the mixing-induced \CP asymmetry from that measured in $B\to J/ψK_S$, namely, $Δ\sin 2β_{K^+K^-K_{S(L)}}\equiv \sin 2β_{K^+K^-K_{S(L)}}-\sin 2 β_{J/ψK_S}$, can be as large as O(0.10). In contrast, the $K_SK_SK_{S(L)}$ modes appear theoretically very clean in our picture with negligible $Δ\sin 2β_{K_SK_SK_{S(L)}}$. Direct CP asymmetries in $K^+K^-K_{S(L)}$ and $K_S K_S K_{S(L)}$ modes are found to be very small.

hep-ph↗
arXiv2005

Effects of Final-state Interactions on Mixing-induced CP Violation in Penguin-dominated B Decays

Motivated by the recent indications of the possibility of sizable deviations of the mixing-induced CP violation parameter, $S_f$, in the penguin-dominated $b\to sq\bar q$ transition decays such as $B^0\to (ϕ,ω,ρ^0,η',η,π^0,f_0)K_S$ from $\sin 2β$ determined from $B\to J/ψK_S$, we study final-state rescattering effects on their decay rates and CP violation. Recent observations of large direct CP asymmetry in modes such as $B^0\to K^+π^-,ρ^-π^+$ means that final state phases in 2-body B decays may not be small. It is therefore important to examine these long-distance effects on penguin-dominated decays. Such long-distance effects on $S_f$ are found to be generally small [i.e. ${\cal O}(1-2%)$] or negligible except for the $ωK_S$ and $ρ^0K_S$ modes where $S_f$ is lowered by around 15% for the former and increased by the same percentage for the latter. However, final-state rescattering can enhance the $ωK_S, ϕK_S, η'K_S, ρ^0K_S$ and $π^0K_S$ rates significantly and flip the signs of direct CP asymmetries of the last two modes. Direct CP asymmetries in $ωK_S$ and $ρ^0K_S$ channels are predicted to be $\A_{ωK_S}\approx -0.13$ and $\A_{ρ^0K_S}\approx 0.47$, respectively. However, direct CP asymmetry in all the other $b\to s$ penguin dominated modes that we study is found to be rather small (a few percents), rendering these modes a viable place to search for the CP-odd phases beyond the standard model.

hep-ph↗
arXiv2005

Implications of Bbar to D0 h0 Decays on Bbar to D Kbar, Dbar Kbar Decays

The recently observed color suppressed B0bar to D0 pi0, D0 eta, D0 eta', Ds+ K-and D0 K0bar decay modes all have rates larger than expected, hinting at the presence of final state interactions. We study rescattering effects in Bbar to D P, D Kbar and Dbar Kbar modes in the quasi-elastic approach, which is extended to accommodate D0 eta' without using U(3) symmetry. The D0bar Kbar modes are of interest in the determination of the unitarity angle phi3/gamma. The updated DP data are used to extract the effective Wilson coefficients a_1^{eff} ~ 0.92, a_2^{eff} ~ 0.22, three strong phases delta ~ 62 deg., theta ~ 24 deg., sigma ~ 127 deg., and the mixing angle tau~2 deg. The values of delta and theta are close to our previous results. The smallness of tau implies small mixing of D0 eta1 with other modes. Predictions for D0 K-, D+ K- and D0 K0bar agree with data. The framework applies to Bbar to Dbar Kbar decays, and rates for D0bar K-, D- K0, Ds- pi0, Ds- eta and Ds- eta' modes are predicted. From B- to D0bar K- and D0 K- rates, we find r_B=0.09\pm 0.02.

hep-ph↗