arXiv subjects

Shang-Yuu Tsai

Publications and source records attributed to Shang-Yuu Tsai.

12 recordsLinked to original sources

arXiv2021

Semileptonic $B^{-}\toπ^{+}π^{-}\ell^{-}\barν_\ell$ decay with $ππ$ invariant mass spectrum

BELLE has recently reported the measurement of the branching fraction of the semileptonic $B^{-}\toπ^{+}π^{-}\ell^{-}\barν_\ell$ decay, where $\ell$ represents an electron or a muon. With the new information on the $ππ$ invariant mass spectrum, we extract $|V_{ub}|=(3.31\pm 0.61)\times 10^{-3}$ in agreement with those from the other exclusive $B$ decays. In particular, we determine the non-resonant $B\toππ$ transition form factors, and predict the non-resonant branching fraction ${\cal B}(B^{-}\toπ^{+}π^{-}\ell^{-}\barν_\ell)=(3.5\pm 1.4^{+4.3}_{-2.4})\times 10^{-5}$, which is accessible to the BELLEII and LHCb experiments.

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arXiv2020

Charmed $Ω_c$ weak decays into $Ω$ in the light-front quark model

More than ten $Ω_c^0$ weak decay modes have been measured with the branching fractions relative to that of $Ω^0_c\toΩ^-π^+$. In order to extract the absolute branching fractions, the study of $Ω^0_c\toΩ^-π^+$ is needed. In this work, we predict ${\cal B}_π\equiv {\cal B}(Ω_c^0\toΩ^-π^+)=(5.1\pm 0.7)\times 10^{-3}$ with the $Ω_c^0\toΩ^-$ transition form factors calculated in the light-front quark model. We also predict ${\cal B}_ρ\equiv {\cal B}(Ω_c^0\toΩ^-ρ^+)=(14.4\pm 0.4)\times 10^{-3}$ and ${\cal B}_e\equiv{\cal B}(Ω_c^0\toΩ^-e^+ν_e)=(5.4\pm 0.2)\times 10^{-3}$. The previous values for ${\cal B}_ρ/{\cal B}_π$ have been found to deviate from the most recent observation. Nonetheless, our ${\cal B}_ρ/{\cal B}_π=2.8\pm 0.4$ is able to alleviate the deviation. Moreover, we obtain ${\cal B}_e/{\cal B}_π=1.1\pm 0.2$, which is consistent with the current data.

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arXiv2020

Direct CP violation in internal W-emission dominated baryonic B decays

The observation of CP violation has been experimentally verified in numerous $B$ decays but is yet to be confirmed in final states with half-spin particles. We focus our attention on baryonic $B$-meson decays mediated dominantly through internal $W$-emission processes and show that they are promising processes to observe for the first time the CP violating effects in $B$ decays to final states with half-spin particles. Specifically, we study the $\bar B^0\to p\bar pπ^0(ρ^0)$ and $\bar B^0\to p\bar pπ^+π^-$ decays. We obtain ${\cal B}(\bar B^0\to p\bar pπ^0)=(5.0\pm 2.1)\times 10^{-7}$, in agreement with current data, and ${\cal B}(\bar B^0\to p\bar pρ^0)\simeq {\cal B}(\bar B^0\to p\bar pπ^0)/3$. Furthermore, we find ${\cal A}_{CP}(\bar B^0\to p\bar pπ^0,p\bar pρ^0,p\bar pπ^+π^-) =(-16.8\pm 5.4,-12.6\pm 3.0,-11.4\pm 1.9)\%$. With measured branching fractions ${\cal B}(\bar B^0\to p\bar pπ^0,p\bar pπ^+π^-)\sim {\cal O}(10^{-6})$, we point out that ${\cal A}_{CP}\sim -(10-20)\%$ can be new observables for CP violation, accessible to the Belle~II and/or LHCb experiments.

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arXiv2020

Testing the W-exchange mechanism with two-body baryonic B decays

The role of $W$-exchange diagrams in baryonic $B$ decays is poorly understood, and often taken as insignificant and neglected. We show that charmful two-body baryonic $B\to {\bf B}_c \bar {\bf B}'$ decays provide a good test-bed for the study of the $W$-exchange topology, whose contribution is found to be non-negligible; here ${\bf B}_c$ is an anti-triplet or a sextet charmed baryon, and ${\bf \bar B}'$ an octet charmless (anti-)baryon. In particular, we calculate that ${\cal B}(\bar B^0\toΣ_c^{+}\bar p)=(2.9^{+0.8}_{-0.9})\times 10^{-6}$ in good agreement with the experimental upper bound. Its cousin $\bar B_s^0$ mode, $\bar B_s^0\toΛ^+_c\bar p$, is a purely $W$-exchange decay, hence is naturally suited for the study of the role of the $W$-exchange topology. We predict ${\cal B}(\bar B_s^0\toΛ^+_c\bar p)=(0.8\pm 0.3)\times 10^{-6}$, a relatively large branching ratio to be tested with a future measurement by the LHCb collaboration. Other predictions, such as ${\cal B}(\bar B^0\toΞ_c^+\barΣ^-)=(1.1\pm 0.4)\times 10^{-5}$, can be tested with future Belle II measurements.

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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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arXiv2004

Extraction of Axial Form Factors from Bbar0 --> D+ K- K{*0} Decay

Based on Bbar to D{(*)}K-K{*0} decay data, which supports factorization, we propose to extract the kaon axial form factor in the factorization framework. Experiment indicates that the K-K{*0} pair is produced by an axial current where only one out of three axial form factors is dominant. The axial form factor can be extracted by fitting the K-K{*0} mass spectrum with an a_1(1260)-resonance plus QCD-motivated non-resonant contributions, which can be improved as data improves.

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arXiv2004

Evidence for Factorization in Three-body $\bar B\to D^{(*)} K^- K^0$ Decays

Motivated by experimental results on $\bar B\to D^{(*)}K^-K^{0}$, we use a factorization approach to study these decays. Two mechanisms concerning kaon pair production arise: current-produced (from vacuum) and transition (from the $B$ meson). The kaon pair in the $\bar B {}^0\to D^{(*)+}K^-K^0$ decays can be produced only by the vector current (current-produced), whose matrix element can be extracted from $e^+e^-\to K\bar K$ processes via isospin relations. The decay rates obtained this way are in good agreement with experiment. The $B^-\to D^{(*)0}K^-K^0$ decays involve both current-produced and transition processes. By using QCD counting rules and the measured $B^-\to D^{(*)0} K^- K^0$ decay rates, the measured decay spectra can be understood.

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arXiv2002

Evidence for Factorization in Three-body B --> D(*) K- K0 Decays

Motivated by recent experimental results, we use a factorization approach to study the three-body B --> D(*) K- K0 decay modes. Two mechanisms are proposed for kaon pair production: current-produced (from vacuum) and transition (from B meson). The Bbar0 --> D(*)+ K- K0 decay is governed solely by the current-produced mechanism. As the kaon pair can be produced only by the vector current, the matrix element can be extracted from e+ e- --> K Kbar processes via isospin relations. The decay rates obtained this way are in good agreement with experiment. Both current-produced and transition processes contribute to B- --> D(*)0 K- K0 decays. By using QCD counting rules and the measured B- --> D(*)0 K- K0 decay rates, the measured decay spectra can be understood.

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arXiv2002

Charmless Three-Body Baryonic B Decays

Motivated by recent data on B-> p pbar K decay, we study various charmless three-body baryonic B decay modes, including Lambda pbar pi, Sigma0 pbar pi, p pbar pi, p pbar Kbar0, in a factorization approach. These modes have rates of order 10^{-6}. There are two mechanisms for the baryon pair production, current-produced and transition. The behavior of decay spectra from these baryon production mechanisms can be understood by using QCD counting rules. Predictions on rates and decay spectra can be checked in the near future.

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arXiv2002

Possible Hints and Search for Glueball Production in Charmless Rare B Decays

Recent data on B->p pbar K, K0 pi pi and K Kbar K hint at a $\sim 2.3$ GeV object recoiling against a kaon. This could be the narrow state observed in J/ψ-> gamma xi. Nonobservation in p pbar annihilation implies ${\cal B}(ξ\to p\bar p) \sim$ few $\times 10^{-3}$, consistent with eta_c and J/ψdecays, but there are actual hints in p pbar -> phi phi and p p-> p pi^+ pi^- pi^+ pi^- p. Simple modeling shows ${\cal B}(B \to ξK){\cal B}(ξ\to p\bar p) \sim 1\times 10^{-6}$, appearing as a spike in the $p\bar p$ spectrum, with $\sim$ 30 events per 100 fb$^{-1}$; modes such as K K_s K_s, K phi phi, K4 pi (K f_2 pi pi) etc. should be explored. The underlying dynamics of g* -> g xi is analogous to g* -> g etaprime or gluon fragmentation. Discovery of sizable B -> xi K could be useful for CP violation studies.

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arXiv2001

Prediction of Three-body $B^0\to ρ^-p\bar{n}, π^-p\bar{n}$ Decay Rates

We predict the rates of the charmless three-body $B^0\to ρ^-p\bar{n}$ and $π^-p\bar{n}$ modes due to weak vector current contributions to be $\sim 4\times 10^{-6}$ and $2\times 10^{-6}$, respectively. The basis is a factorization approach of current produced nucleon pairs, together with an isospin transformation that relates nucleon weak vector form factors to electromagnetic form factors. Adding the axial vector current contribution, we find $B^0\to ρ^-p\bar{n}$ and $B^+\to ρ^0p\bar{n}$ to be at $10^{-5}$ order. The three-body modes appear to dominate over the two-body modes such as $B\to p\bar{p}$, $p\bar Λ$.

hep-ph↗

arXiv2001

Understanding $B\to D^{*-}N\bar{N}$ and Its Implications

The CLEO Collaboration recently reported the observation of the $B^0\to D^{*-}p\bar{n}$ mode at a rate only a factor of 4--5 lower than $B^0\to D^{*-}ρ^+$ and $D^{*-}π^+$. We try to understand this with a factorization approach of current produced nucleon pairs. The baryon weak vector current form factors are related by isospin rotation to nucleon electromagnetic form factors. By using $G^{p,n}_M$ measured from $e^+e^-\to \bar{N}N$ and $p\bar{p}\to e^+e^-$ processes, assuming factorization of the $B^0\to D^{*-}$ transition and the $p\bar n$ pair production, we are able to account for up to 60% of the observed rate. The remainder is argued to arise from the axial current. The model is then applied to B decays to other mesons plus $p\bar{n}$ modes and $D^{*-}$ plus strange baryon pairs.

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