arXiv subjects

Chia-Wei Liu

Publications and source records attributed to Chia-Wei Liu.

At least 55 records · Page 3Linked to original sources

arXiv2022

Time-reversal asymmetries in $Λ_b \to Λ(\to p π^-)\ell^+\ell^-$

We study the decays of $Λ_b \to Λ(\to p π^-) \ell ^+ \ell^-$ with $\ell = (e, μ, τ)$. In particular, we examine the full angular distributions with polarized $Λ_b$ and identify the time-reversal asymmetries or T-odd observables. By using the homogeneous bag model, we find that the decay branching fractions of $Λ_b \to Λ\ell^+\ell^-$ are $(9.1\pm 2.5,7.9\pm 1.8, 2.1\pm 0.2)\times 10^{-7}$ for $\ell =(e, μ,τ)$, respectively. In addition, we obtain that $A_{FB}^{\ell} = -0.369\pm 0.007$ and $A_{FB}^{h}=-0.333\pm 0.004$, averaged in the range of $15 \leq q^2 \leq 20~ \text{GeV}^2$. These results are well consistent with the current experimental data. We also explore the T-odd observables in $Λ_b \to Λ(\to p π^-) μ^+ μ^-$, which are sensitive to new physics~(NP). Explicitly, we illustrate that the current experimental measurement from one of the T-odd observables favors the existence of NP, such as the extra $Z$-boson model.

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arXiv2022

Semileptonic decays of doubly charmed baryons with $Ξ_c-Ξ_c'$ mixing

We study the $Ξ_c- Ξ_c'$ mixing effects in the semileptonic decays the doubly charm baryons of $Ξ_{cc}$. We focus on the ratio of ${\cal R}(θ_c) \equiv {\cal B}( Ξ_{cc} \to Ξ_c' e^+ ν_e)/ {\cal B}( Ξ_{cc} \to Ξ_c e^+ ν_e) $ and find that $({\cal R}(θ_0),{\cal R}(- θ_0)) =(0.46 \pm 0.01,7.33 \pm 0.23)$ with $θ_0 = 0.137π$, which are in sharp contrast to ${\cal R}(0)=2.15\pm0.11$ without the mixing. The ratio is enhanced~(suppressed) by a factor of four for a negative~(positive) $θ_c$. In addition, the polarization asymmetries of $Ξ_c^{(\prime)}$ are found to be $α(-θ_0) = 0.32 ~(-0.76)$ and $α(θ_0) = -0.82~(-0.38)$. As ${\cal R}$ and $α$ are highly sensitive to $θ_c$ and unaffected by the $W$-exchange contributions, they provide excellent opportunities to determine $θ_c$ in the ongoing experiments.

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arXiv2022

Semileptonic decays of doubly charmed baryons with bag model

We study the semileptonic decays of $B_{cc}$ ${\rightarrow}$ $B_c\ell^+ν_\ell$ with the bag model, where $\ell$ = $(e, μ)$, $B_{cc}$ = $(Ξ_{cc}^{++}$, $Ξ_{cc}^+$, $Ω_{cc}^+$), and $ B_c$ are the singly charmed baryons with $J^P= 1/2^+$. We obtain the decay widths of $Γ(Ξ_{cc}^{++}{\rightarrow}Ξ_c^+e^+ν_e, Ξ_c^{\prime+}e^+ν_e, Λ_c^+e^+ν_e, Ω_c^+ e^+ν_e) =(5.1\pm 0.1 , 11\pm 1, 0.34\pm 0.06, 0.76\pm 0.06)\times 10^{-14}$~GeV, $Γ(Ξ_{cc}^+\rightarrow Ξ_c^0e^+ν_e, Ξ_c^{\prime0}e^+ν_e , Σ_c^0e^+ν_e) = (5.1\pm 0.6, 11\pm 1, 1.5\pm 0.1) \times 10^{-14}$~GeV, and $Γ(Ω_{cc}^+\rightarrow Ω_c^0 e^+ν_e, Ξ_c^0e^+ν_e , Ξ_c^{\prime0} e^+ν_e) = (22\pm 2, 0.32 \pm 0.04, 0.77\pm 0.06)\times 10^{-14}$~GeV. We also get that $Γ$($B_{cc}$ ${\rightarrow}$ $B_cμ^+ν_μ$)/$Γ$($B_{cc}$ ${\rightarrow}$ $B_ce^+ν_e$) = $0.97\sim 1.00$. In addition, we discuss the $SU(3)$ flavor breaking effects, classified into three aspects: phase space differences, spectator quarks, and overlappings of the transited quarks. In particular, we show that the breaking effects are dominated by the phase space differences, which can be as large as 25\%. Explicitly, we find that $Γ(Ξ_{cc}^{++} \to Λ_c ^+ e^+ ν_e) V_{cs}^2/Γ(Ξ_{cc}^{++} \to Ξ_c ^+ e^+ ν_e )V_{cd}^2 = 1.24$, which is expected as $1$ under the exact $SU(3)$ flavor symmetry.

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arXiv2022

Center of mass motion in bag model

Despite the great success on the mass spectra, the reputation of the bag model has been closely followed by the embarrassment from the center of mass motion. It leads to severe theoretical inconsistencies. For instance, the masses and the decay constants would no longer be independent of the momentum. In this work, we provide a systematical approach to resolve this problem. The meson decay constants as well as the baryon transition form factors can be computed consistently in our framework. Notably, the form factors in the neutron $β$ decays do not depend on any free parameters, and are determined to be $F^V_1 =1 $ and $F^A_1 = 1.31$ or $F_1^A/F_1^V= 1.31$, which is close the experimental value of $F^A_1/F^V_1 = 1.27$. In addition, we find that ${\cal B} (Λ_b \to Λγ) = (6.8 \pm 3.3 ) \times 10^{-6} $, which agrees to the experimental value of $(7.1\pm 1.7)\times 10^{-6}$.

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arXiv2022

Time-reversal asymmetries in $Λ_b$ semileptonic decays

We study the decays of $Λ_b \to Λ_c(\to B_n f) \ell ^- \overlineν$ with $\ell = e, μ, τ$, where $B_n$ and $f$ are the daughter baryons and the rest of the particles in $Λ_c$ cascade decays, respectively. In particular, we examine the full angular distributions with polarized $Λ_b$ and lepton mass effects, in which the time-reversal asymmetries are identified. We concentrate on the decay modes of $Λ_b \to Λ_c(\to p K^- π^+) \ell ^- \overlineν$ to demonstrate their experimental feasibility. We show that the observables associated with the time-reversal asymmetries are useful to search for new physics as they vanish in the standard model. Explicitly, we find that they are sensitive to the right-handed current from new physics, and possible to be observed at LHCb.

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arXiv2022

New extraction of CP violation in b-baryon decays

We study CP violation in b-baryon decays of $Ξ_b^- \to Ξ^- D$ with $D = D^0, \bar{D}^0$ and $D_i~(i=1,2)$. We find that these baryonic decay processes provide an ideal opportunity to measure the weak phase due to the absence of the relative strong phase. Explicitly, we relate $\barρ$ and $\barη$ the CKM elements with the decay rate ratios of $R_i= Γ(Ξ_b^- \to Ξ^-D_{i} ) / Γ( Ξ_b^- \to Ξ^-D^0 )$ without the charge conjugate states. As a complementary, we also examine the decay distributions of $Λ_b \to Λ(\to p π^- ) D$. There are in total 32 decay observables, which can be parameterized by 9 real parameters, allowing the experiments to extract the angle $γ\equiv \arg(-V_{ud}V_{ub}^*/V_{cd}V_{cb}^*)$ in the CKM unitarity triangle. In addition, the feasibilities of the experimental measurements are discussed. We find that $\barρ$ and $\barη$ can be extracted at LHCb Run3 from $Ξ_b^- \to Ξ^- D$, and a full analysis of $Λ_b \to Λ(\to p π^-)D$ is available at LHCb Run4.

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arXiv2022

Heavy-Flavor-Conserving Hadronic Weak Decays of Charmed and Bottom Baryons: an Update

This paper serves as an update of the previous work entitled ``Heavy-Flavor-Conserving Hadronic Weak Decays of Charmed and Bottom Baryons". We make an improvement on the bag wave functions by removing the center-of-mass motion of the bag. All the baryon matrix elements are now calculated under the same framework without introducing new parameters. The matrix elements of 4-quark operators are found to be nearly twice larger than the previous ones. The calculated branching fractions of $ Ξ_c ^0 \to Λ_c ^+π^-$ and $Ξ_b^- \to Λ^0_b π^-$ are both in agreement with current experimental results. For the yet-to-be-measured heavy-flavor-conserving decays, we find ${\cal B}( Ξ_c ^+ \to Λ_c ^+π^0) = (13.8 \pm 1.4)\times 10^{-3}$, ${\cal B}( Ξ_b^0 \to Λ^0_b π^0) = (2.6 \pm 0.3)\times 10^{-3}$, ${\cal B}( Ω_c ^0 \to Ξ_c^+π^-) = (2.0 \pm 0.2)\times 10^{-3}$ and ${\cal B}( Ω_c ^0 \to Ξ_c^0π^0)= (1.1 \pm 0.1)\times 10^{-3}$. They are all accessible to LHCb, Belle and Belle II and can be tested in the near future.

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arXiv2022

Searching $B_c^\ast$ via conservation laws

To distinguish $B_c^{\ast +}(1^3S_1)$ and $B_c^+(1^1S_0)$ in the experiments, we propose two methods based on the conservation laws. I. From the angular momentum conservation, a nonzero helicity of $J/ψ$ of $B_c^{(\ast)+ } \to J/ψπ^+$ would be an evidence of $B_c^{\ast +}$. II. Since $B_c^+ \to B^+ ϕ$ is kinematically forbidden, $ B_c^{\ast +} \to B^+ ϕ$ provides a clean channel to probe $B_c^{\ast +}$\,. Particularly, our results show that $B_c^{\ast +}$ is promising to be observed at LHC via $B_c^{(\ast)+} \to J/ψπ^+$. On the other hand, we find that ${\cal B} ( B_c^{\ast+} \to B^+ ϕ) = ( 7.0 \pm 3.0 ) \times 10 ^{-9} $, which is also feasible to be measured at the forthcoming experiments at HL-LHC and FCC-hh.

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arXiv2022

Weak Radiative Decays of Anti-triplet Bottomed Baryons in Light-Front Quark Model

We study the weak radiative decays of ${\bf B}_b \to {\bf B}_n γ$ with ${\bf B}_{b(n)} $ the anti-triplet-bottom (octet) baryons in the light front quark model. We obtain that ${\cal B}(Λ_b \to Λγ)= (7.1 \pm 0.3 )\times 10 ^{-6}$, which agrees well with the current experimental value of $(7.1 \pm 1.7 )\times 10 ^{-6}$. We predict that ${\cal B}(Ξ_b^0 \to Ξ^0 γ)= (1.0 \pm 0.1 )\times 10 ^{-5}$ and ${\cal B}(Ξ_b^- \to Ξ^- γ) = (1.1 \pm 0.1) \times 10^{-5}$, which are consistent with the latest upper limits set by the LHCb collaboration. In addition, we find that the $SU(3)_F$ flavor symmetry breaking effects for the modes related to the $b\to d γ$ transition can be as large as $20\%$.

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arXiv2022

Study of charmless two-body baryonic $B$ decays

We study the charmless two-body decays of $B\to {\bf B}_n \overline{\bf B}_n^\prime$ with $B = ( B^+ , B^0 , B^0_s)$ and ${\bf B}_n^{(\prime)}$ the low-lying octet baryons. The factorizable amplitudes are calculated by the modified bag model, while the nonfactorizable ones are extracted from the experimental data with the $SU(3)_F$ flavor symmetry. We are able to explain all current experimental measurements and provide predictions on the decay branching ratios in $B\to {\bf B}_n \overline{\bf B}_n^\prime$. Particularly, we find that ${\cal B}(B_s^0 \to Ξ^0 \overlineΞ^0) = (19.3\pm 2.7 )\times 10^{-7}$ and ${\cal B}(B_s^0 \to Ξ^- \overlineΞ^-) = (19.4\pm 2.7 )\times 10^{-7}$, which are sizable and able to be observed in the ongoing experiments at LHCb and BELLE-II. Furthermore, the decay branching ratios of $B_s^0 \to (p\overline{p}, n\overline{n})$ and $B^0 \to (Ξ^0 \overlineΞ^0 ,Σ^+\overlineΣ^+)$ are expected to be $O(10^{-10})$, which are suppressed due to the angular momentum conservation and chiral symmetry.

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arXiv2022

Sizable Time-reversal violating effects in bottom baryon decays

We study time-reversal~(T) asymmetries in the charmless two-body decays of antitriplet bottom baryons. We find that in ${\bf B}_b \to {\bf B}_n P$ with ${\bf B}_b = (Ξ_b ^- , \,Ξ_b^0, \,Λ_b)$ and ${\bf B}_n(P)$ a octet baryon (pseudoscalar meson), the positive and negative helicity amplitudes are both sizable, resulting in the large T-violating effects. Particularly, the T-odd parameters, $β_w$, for the color-enhanced channels are expected to be around $40\%$ and $-25\%$ in $b\to s $ and $b\to d $ transitions for the standard model, which can be measured by the experiments at LHCb, respectively. On the other hand, in ${\bf B}_b \to {\bf B}_n V(γ)$ with $V(γ)$ a vector meson~(photon), the decays are predominated by a single helicity amplitude, and the T violating effects by the correlations among spins are suppressed. We also explore the T violating observables for the $Ξ_b$ decays based on the angular distributions.

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arXiv2022

Searching for possible evidences of new physics in $B\to V_1 V_2$

We explore the decays of $B\to V_1V_2$ ($V_{1,2}= (ρ, ω,K^*, ϕ)$ and $B= (B^0, B^+,B_s)$) with transverse polarizations. We explicitly evaluate the eigenstates of T-odd scalar operators involving spins for the first time, which offer physical insight among the T violating observables. Based on the helicity suppression of tree operators for transverse polarizations in the standard model (SM), we deduce that $Δϕ_p= Δϕ_\parallel - Δϕ_\perp=0$ with $Δϕ_{\perp,\parallel}$ the weak phases of the transverse amplitudes. In contrast, the experiments show that $Δϕ_p (B^0 \to K^{*0} ω)= -0.84\pm 0.54$, which could be a signal of new physics. There is also a discrepancy between our result in the SM and the experimental data for the transverse polarized branching ratio in $B^0 \to K^{*0} ω$. In addition, by counting the helicity flips, we argue that $\sin(ϕ_\parallel - ϕ_\perp ) \approx 0$, which meets well with most of the experiments except for the ones with $B^0\to K^{*0}ω$, where $ϕ_{\parallel,\perp}$ are the strong phases in the transverse amplitudes.

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arXiv2021

Revisiting semileptonic $B^-\to p\bar{p} \ell^- \barν_{\ell}$ decays

We systematically revisit the baryonic four-body semileptonic decays of $B^- \to {\bf B}\bar{\bf B}'\ell^- \barν_{\ell}$ by the perturbative QCD counting rules with ${\bf B}$ representing octet baryons and $\ell=e,μ$. We study the transition form factors of $B^- \to {\bf B} \bar{\bf B}'$ in the limit of $(p_{\bf B}+p_{\bar{\bf B}'})^2 \to \infty $ with the three-body $\bar{B}\to {\bf B}\bar{\bf B}' M$ and $B^- \to p\bar{p} μ^- \barν_μ$ data along with $SU(3)_f$ flavor symmetry. We calculate the decay branching ratios and angular asymmetries as well as the differential decay branching fractions of $B^- \to p \bar{p} \ell^- \barν_{\ell}$. In particular, we find that our new result of ${\cal B}( B^- \to p \bar{p} \ell^- \barν_{\ell})=(5.21\pm0.34)\times 10^{-6}$, which is about one order of magnitude lower than the previous theoretical prediction of $(10.4\pm2.9)\times 10^{-5}$, agrees well with both experimental measurements of $(5.8^{+2.6}_{-2.3})\times 10^{-6}$ and $(5.3\pm0.4)\times 10^{-6}$ by the Belle and LHCb Collaborations, respectively. We also evaluate the branching ratios and angular asymmetries in other channels of $B^- \to {\bf B}\bar{\bf B}\ell^- \barν_{\ell}$, which can be tested by the ongoing experiments at LHCb and BelleII.

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arXiv2021

Time-reversal asymmetries and angular distributions in $Λ_b \to ΛV$

We study the spin correlations to probe time-reversal~(T) asymmetries in the decays of $Λ_b \to ΛV ~(V=ϕ, ρ^0, ω, K^{*0})$. The eigenstates of the T-odd operators are obtained along with definite angular momenta. We obtain the T-odd spin correlations from the complex phases among the helicity amplitudes. We give the angular distributions of $Λ_b \to Λ(\to p π^-)V(\to PP')$ and show the corresponding spin correlations, where $P^{(\prime)}$ are the pseudoscalar mesons. Due to the helicity conservation of the $s$ quark in $Λ$, we deduce that the polarization asymmetries of $Λ$ are close to $-1$. Since the decay of $Λ_b \to Λϕ$ in the standard model~(SM) is dictated by the single weak phase from the product of CKM elements, $V_{tb}V_{ts}^*$, the true T and CP asymmetries are suppressed, providing a clean background to test the SM and search for new physics. In the factorization approach, as the helicity amplitudes in the SM share the same complex phase, T-violating effects are absent. Nonetheless, the experimental branching ratio of $Br(Λ_b \to Λϕ) = (5.18\pm 1.29 )\times 10^{-6}$ suggests that the nonfactorizable effects or some new physics play an important role. By parametrizing the nonfactorizable contributions with the effective color number, we calculate the branching ratios and direct CP asymmetries. We also explore the possible T-violating effects from new physics.

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arXiv2021

Semileptonic weak decays of anti-triplet charmed baryons in the light-front formalism

We systematically study the semileptonic decays of ${\bf B_c} \to {\bf B_n}\ell^+ ν_{\ell}$ in the light-front constituent quark model, where ${\bf B_c}$ represent the anti-triplet charmed baryons of $(Ξ_c^0,Ξ_c^+,Λ_c^+)$ and ${\bf B_n}$ correspond to the octet ones. We determine the spin-flavor structures of the constituents in the baryons with the Fermi statistics and calculate the decay branching ratios (${\cal B}$s) and averaged asymmetry parameters ($α$s) with the helicity formalism. In particular, we find that ${\cal B}( Λ_c^+ \to Λe^+ ν_{e}, ne^+ ν_{e})=(3.55\pm1.04, 0.36\pm0.15)\%$, ${\cal B}( Ξ_c^+ \to Ξ^0 e^+ ν_{e},Σ^0 e^+ ν_{e},Λe^+ ν_{e})=(11.3\pm3.35), 0.33\pm0.09,0.12\pm0.04\%$ and ${\cal B}( Ξ_c^0 \to Ξ^- e^+ ν_{e},Σ^- e^+ ν_{e})=(3.49\pm0.95,0.22\pm0.06)\%$. Our results agree with the current experimental data. Our prediction for ${\cal B}( Λ_c^+ \to n e^+ ν_{e})$ is consistent with those in the literature, which can be measured by the charm-facilities, such as BESIII and BELLE. Some of our results for the $Ξ_c^{+(0)}$ semileptonic channels can be tested by the experiments at BELLE as well as the ongoing ones at LHCb and BELLEII.

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arXiv2021

Non-leptonic two-body decays of $Λ_b^0$ in light-front quark model

We study the non-leptonic two-body weak decays of $Λ_b^0 \to p M$ with $ M=(π^-,K^-)$ and $(ρ^-,K^{*-})$ in the light-front quark model under the generalized factorization ansatz. By considering the Fermi statistic between quarks and determining spin-flavor structures in baryons, we calculate the branching ratios (${\cal B}$s) and CP-violating rate asymmetries ($\mathcal{A}_{CP}$s) in the decays. Explicitly, we find that ${\cal B}( Λ_b^0 \to p π^- ,pK^-)=(4.18\pm0.15\pm0.30, 5.76\pm0.88\pm0.23)\times10^{-6}$ and ${\mathcal{A}_{CP}}( Λ_b^0 \to p π^- ,\,pK^-)=(-3.60\pm0.14\pm0.14, 6.36\pm0.21\pm0.18)\%$ in comparison with the data of ${\cal B}( Λ_b^0 \to p π^- ,pK^-)=(4.5\pm0.8, 5.4\pm1.0)\times10^{-6}$ and ${\mathcal{A}_{CP}}( Λ_b^0 \to p π^- ,pK^-)=(-2.5\pm 2.9, -2.5\pm2.2)\%$ given by the Particle Data Group, respectively. We also predict that ${\cal B}( Λ_b^0 \to p ρ^-,pK^{*-} )=(12.13\pm3.27\pm0.91, 2.58\pm0.87\pm0.13)\times 10^{-6}$ and ${\mathcal{A}_{CP}}( Λ_b^0 \to p ρ^-,pK^{*-} )=(-3.32\pm0.00\pm0.14,19.25\pm0.00\pm0.80)\%$, which could be observed by the experiments at LHCb.

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arXiv2020

Nonleptonic two-body weak decays of $Λ_b$ in modified MIT bag model

We study the nonleptonic two-body weak decays of $Λ_b$ by modifying the MIT bag model without introducing new parameters to construct the momentum eigenstates of the baryons. We find that the branching ratios of $Λ_b^0 \to Λ_c^+ π^-$, $Λ_c^+ K^-$, $p π^-$ and $pK^-$ are $(4.5\pm0.2)\times 10^{-3}$, $(3.4\pm 0.1)\times 10^{-4}$, $(5.0\pm 0.5)\times 10^{-6}$ and $(6.0\pm 0.7) \times 10^{-6}$, which are all well consistent with the current experimental data, respectively. We also explore P and CP asymmetries for the decays of $Λ_b^0 \to p (π^-,K^-)$. In particular, we obtain that the direct CP-violating rate asymmetries in $Λ_b^0 \to p π^-$ and $Λ_b^0 \to p K^-$ are around $-4.4\%$ and $6.7\%$, in comparison with $(-2.5\pm2.9)\%$ and $(-2.5\pm2.2)\%$ from the Particle Data Group in 2020, respectively.

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arXiv2020

Semileptonic decays of $Λ_c^+$ in dynamical approaches

We study the semileptonic decays of $Λ_c^+ \to Λ(n)\ell^+ ν_{\ell}$ in two relativistic dynamical approaches of the light-front constituent quark model (LFCQM) and MIT bag model (MBM). By considering the Fermi statistic between quarks and determining spin-flavor structures in baryons along with the helicity formalism in the two different dynamical models, we calculate the branching ratios (${\cal B}$s) and averaged asymmetry parameters ($α$s) in the decays. Explicitly, we find that ${\cal B}( Λ_c^+ \to Λe^+ ν_{e})=(3.36\pm0.87,3.48)\%$ and $α( Λ_c^+ \to Λe^+ ν_{e})=(-0.97\pm0.03,-0.83)$ in (LFCQM, MBM), in comparison with the data of ${\cal B}( Λ_c^+ \to Λe^+ ν_{e})=(3.6\pm0.4)\%$ and $α( Λ_c^+ \to Λe^+ ν_{e})=-0.86\pm 0.04$ given by the Particle Data Group, respectively. We also predict that ${\cal B}( Λ_c^+ \to n e^+ ν_{e})=(0.57\pm0.15, 3.6\pm1.5)\times 10^{-3}$ and $α( Λ_c^+ \to n e^+ ν_{e})=(-0.98\pm0.02,-0.96\pm0.04)$ in LFCQM with two different scenarios for the momentum distributions of quarks in the neutron, and ${\cal B}( Λ_c^+ \to n e^+ ν_{e})= 0.279\times 10^{-2}$ and $α( Λ_c^+ \to n e^+ ν_{e})=-0.87$ in MBM, which could be tested by the ongoing experiments at BESIII, LHCb and BELLEII.

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