arXiv subjects

Chia-Wei Liu

Publications and source records attributed to Chia-Wei Liu.

66 records · Page 4Linked to original sources

arXiv2020

Mixing effects of $Σ^0-Λ^0$ in $Λ_c^+$ decays

We analyze the mixing between $Σ^0$ and $Λ^0$ based on the baryon masses. We distinguish the contributions from QCD and QED in the baryon mass splittings. We find that the mixing angle between $Σ^0$ and $Λ^0$ is $(2.07\pm 0.03)\times 10^{-2} $, which leads to the decay branching fraction and up-down asymmetry of $Λ_c^+ \to Σ^0 e^+ ν_e$ to be ${\cal B}(Λ_c^+ \to Σ^0 e^+ ν_e)=(1.5\pm 0.2)\times 10^{-5}$ and $α(Λ_c^+ \to Σ^0 e^+ ν_e)=-0.86\pm 0.04$, respectively. Moreover, we obtain that $Δ{\cal B}\equiv {\cal B}(Λ_c^+\to Σ^0 π^+) - {\cal B}(Λ_c^+\to Σ^+π^0)=(3.8\pm 0.5)\times 10^{-4}$ and $Δα\equivα(Λ_c^+\to Σ^0 π^+) -α(Λ_c^+\to Σ^+π^0)=(-1.6\pm 0.7)\times10^{-2}$, which should vanish without the mixing.

hep-ph↗

arXiv2020

Charmed Baryon Weak Decays with Vector Mesons

We give a systematic study of ${\bf B}_c\to {\bf B}_n V$ decays, where ${\bf B}_c$ and $ {\bf B}_n$ correspond to the anti-triplet charmed and octet baryons, respectively, while $V$ stand for the vector mesons. We calculate the color-symmetric contributions to the decays from the effective Hamiltonian with the factorization approach and extract the anti-symmetric ones based on the experimental measurements and $SU(3)_F$ flavor symmetry. We find that most of the existing experimental data for ${\bf B}_c\to {\bf B}_n V$ are consistent with our fitting results. We present all the branching ratios of the Cabbibo allowed, singly Cabbibo suppressed and doubly Cabbibo suppressed decays of ${\bf B}_c\to {\bf B}_n V$. The decay parameters for the daughter baryons and mesons in ${\bf B}_c\to {\bf B}_n V$ are also evaluated. In particular, we point out that the Cabbibo allowed decays of $Λ_c^+ \to Λ^0 ρ^+$ and $ Ξ_c^0 \to Ξ^- ρ^+$ as well as the singly Cabbibo suppressed ones of $Λ_c^+ \to Λ^0 K^{*+}$, $Ξ_c^+ \to Σ^+ ϕ$ and $Ξ_c^0\to Ξ^- K^{*+}$ have large branching ratios and decay parameters with small uncertainties, which can be tested by the experimental searches at the charm facilities.

hep-ph↗

arXiv2019

Up-down asymmetries of charmed baryon three-body decays

We study the up-down asymmetries in the three-body anti-triplet charmed baryon decays of ${\bf B_c}\to{\bf B_n}MM' $ with the $SU(3)_f$ flavor symmetry, where ${\bf B_c}$ presents the anti-triplet charmed baryon of $(Ξ_c^0,-Ξ_c^+,Λ_c^+)$, while ${\bf B_n}$ and $M^{(')}$ denote octet baryon and meson states, respectively. By assuming the s-wave meson-pairs to be the dominant constituents in final state configurations, we can write the spin-dependent decay amplitude into parity-conserving and parity-violating parts, parametrized by 6 real parameters under $SU(3)_f$, respectively. Fitting these parameters by 16 experimental data points with the minimum $χ^2$ method, we obtain that $χ^2/d.o.f=2.4$. With the fitted parameters, we evaluate the up-down asymmetries along with the decay branching ratios of ${\bf B_c}\to{\bf B_n}MM' $. Some of these up-down asymmetries are accessible to the experiments at BESIII, BELLE-II and LHCb.

hep-ph↗

arXiv2019

Charmed Baryon Weak Decays with Decuplet Baryon and SU(3) Flavor Symmetry

We study the branching ratios and up-down asymmetries in the charmed baryon weak decays of ${\bf B}_c\to {\bf B}_DM$ with ${\bf B}_{c(D)}$ anti-triplet charmed (decuplet) baryon and $M$ pseudo-scalar meson states based on the flavor symmetry of $SU(3)_F$. We propose equal and physical-mass schemes for the hadronic states to deal with the large variations of the decuplet baryon momenta in the decays in order to fit with the current experimental data. We find that our fitting results of ${\cal B}({\bf B}_c\to {\bf B}_DM) $ are consistent with the current experimental data in both schemes, while the up-down asymmetries in all decays are found to be sizable, consistent with the current experimental data, but different from zero predicted in the literature. We also examine the processes of $Ξ_c^0 \to Σ^{\prime 0}K_S/K_L$ and derive the asymmetry between the $K_L/K_S$ modes being a constant.

hep-ph↗

arXiv2019

Asymmetries of anti-triplet charmed baryon decays

We analyze the decay processes of ${\bf B}_c \to {\bf B}_n M$ with the $SU(3)_F$ flavor symmetry and spin-dependent amplitudes, where ${\bf B}_c({\bf B}_n)$ and $M$ are the anti-triplet charmed (octet) baryon and nonet meson states, respectively. In the $SU(3)_F$ approach, it is the first time that the decay rates and up-down asymmetries are fully and systematically studied without neglecting the ${\cal O}(\overline{15})$ contributions of the color anti-symmetric parts in the effective Hamiltonian. Our results of the up-down asymmetries based on $SU(3)_F$ are quite different from the previous theoretical values in the literature. In particular, we find that the up-down symmetry of $ α(Λ_c^+\to Ξ^0 K^+)_{SU(3)} = 0.94^{+0.06}_{-0.11}$, which is consistent with the recent experimental data of $0.77\pm0.78$ by the BESIII Collaboration, but predicted to be zero in the literature. We also examine the $K_S^0-K_L^0$ asymmetries between the decays of ${\bf B}_c \to {\bf B}_n K_S^0$ and ${\bf B}_c \to {\bf B}_n K_L^0$ with both Cabibbo-allowed and doubly Cabibbo-suppressed transitions.

hep-ph↗

arXiv2019

Semileptonic decays of anti-triplet charmed baryons

We study the semileptonic decays ${\bf B_c} \to {\bf B_n} \ell^+ ν_{\ell}$ where ${\bf B_{c(n)}}$ is the anti-triplet-charmed (octet) baryon with the $SU(3)_f$ flavor symmetry and helicity formalism. In particular, we present the decay branching ratios of $ {\bf B_c} \to {\bf B_n}\ell^+ ν_\ell$ in three scenarios: (a) an exact $SU(3)_f$ symmetry with equal masses for the anti-triplet-charmed (octet) baryon states of ${\bf B_c}$ (${\bf B_n}$), (b) $SU(3)_f$ parameters without the baryonic momentum-transfer dependence, and (c) $SU(3)_f$ with baryonic transition form factors in the heavy quark limit. We show that our results are all consistent with the existing data. Explicitly, we predict that ${\cal B}( Ξ_c^+ \to Ξ^0 e^+ ν_{e})=(11.9\pm1.3, 9.8\pm 1.1, 10.7\pm 0.9)\times 10^{-2}$ and ${\cal B}( Ξ_c^0 \to Ξ^- e^+ ν_{e})=(3.0\pm0.3, 2.4\pm 0.3, 2.7\pm 0.2)\times 10^{-2}$ in the scenarios (a), (b) and (c) agree with the data of $(14.0^{+8.3}_{-8.7})\times 10^{-2}$ and $(5.6\pm2.6)\times 10^{-2}$ from the CLEO Collaboration, respectively. In addition, we obtain that ${\cal B}(Λ_c^+\to n e^+ ν_e)=(2.8\pm 0.4, 4.9\pm0.4, 5.1\pm0.4)\times 10^{-3}$ in (a), (b) and (c). We also examine the longitudinal asymmetry parameters of $α({\bf B_c} \to {\bf B_n} \ell^+ ν_{\ell})$, which are sensitive to the different scenarios with $SU(3)_f$. Some of the decay branching ratios and asymmetries can be observed by the ongoing experiments at BESIII and LHCb as well as the future searches by BELLEII.

hep-ph↗

arXiv2019

Three-body charmed baryon Decays with SU(3) flavor symmetry

We study the three-body anti-triplet ${\bf B_c}\to {\bf B_n}MM'$ decays with the $SU(3)$ flavor ($SU(3)_f$) symmetry, where ${\bf B_c}$ denotes the charmed baryon anti-triplet of $(Ξ_c^0,-Ξ_c^+,Λ_c^+)$, and ${\bf B_n}$ and $M(M')$ represent baryon and meson octets, respectively. By considering only the S-wave $MM'$-pair contributions without resonance effects, the decays of ${\bf B_c}\to {\bf B_n}MM'$ can be decomposed into irreducible forms with 11 parameters under $SU(3)_f$, which are fitted by the 14 existing data, resulting in a reasonable value of $χ^2/d.o.f=2.8$ for the fit. Consequently, we find that the triangle sum rule of ${\cal A}(Λ_c^+\to n\bar K^0 π^+)-{\cal A}(Λ_c^+\to pK^- π^+)-\sqrt 2 {\cal A}(Λ_c^+\to p\bar K^0 π^0)=0$ given by the isospin symmetry holds under $SU(3)_f$, where ${\cal A}$ stands for the decay amplitude. In addition, we predict that ${\cal B}(Λ_c^+\to n π^{+} \bar{K}^{0})=(0.9\pm 0.8)\times 10^{-2}$, which is $3-4$ times smaller than the BESIII observation, indicating the existence of the resonant states. For the to-be-observed ${\bf B_c}\to {\bf B_n}MM'$ decays, we compute the branching fractions with the $SU(3)_f$ amplitudes to be compared to the BESIII and LHCb measurements in the future.

hep-ph↗

arXiv2019

Singly Cabibbo suppressed decays of $Λ_{c}^+$ with SU(3) flavor symmetry

We analyze the weak processes of anti-triplet charmed baryons decaying to octet baryons and mesons with the SU(3) flavor symmetry and topological quark diagram scheme. We study the decay branching ratios without neglecting the contributions from ${\cal O}(\overline{15})$ for the first time in the SU(3) flavor symmetry approach. The fitting results for the Cabibbo allowed and suppressed decays of $Λ_{c}^+$ are all consistent with the experimental data. We predict all singly Cabibbo suppressed decays. In particular, we find that ${\cal B}(Λ_c^+\to p π^0)=(1.3\pm0.7)\times 10^{-4}$, which is slightly below the current experimental upper limit of $2.7\times 10^{-4}$ and can be tested by the ongoing experiment at BESIII as well as the future one at Belle-II.

hep-ph↗

arXiv2018

SU(3) symmetry breaking in charmed baryon decays

We explore the breaking effects of the $SU(3)$ flavor symmetry in the singly Cabibbo-suppressed anti-triplet charmed baryon decays of ${\bf B}_c\to {\bf B}_n M$, with ${\bf B}_c=(Ξ_c^0,Ξ_c^+,Λ_c^+)$ and ${\bf B}_n(M)$ the baryon (pseudo-scalar) octets. We find that these breaking effects can be used to account for the experimental data on the decay branching ratios of ${\cal B}(Λ_c^+\to Σ^{0} K^{+},Λ^{0} K^{+})$ and $R'_{K/π}$=${\cal B}(Ξ^0_c \to Ξ^- K^+)$/${\cal B}(Ξ^0_c \to Ξ^- π^+)$. In addition, we obtain that ${\cal B}(Ξ_{c}^{0} \to Ξ^{-} K^{+},Σ^{-} π^{+})=(4.6 \pm 1.7,12.8 \pm 3.1)\times 10^{-4}$, ${\cal B}(Ξ_c^0\to pK^-,Σ^+π^-)=(3.0 \pm 1.0, 5.2 \pm 1.6)\times 10^{-4}$ and ${\cal B}(Ξ_c^+\to Σ^{0(+)} π^{+(0)})=(10.3 \pm 1.7)\times 10^{-4}$, which all receive significant contributions from the breaking effects, and can be tested by the BESIII and LHCb experiments.

hep-ph↗

arXiv2018

Charmed Baryon Weak Decays with SU(3) Flavor Symmetry

We study the semileptonic and non-leptonic charmed baryon decays with $SU(3)$ flavor symmetry, where the charmed baryons can be ${\bf B}_{c}=(Ξ_c^0,Ξ_c^+,Λ_c^+)$, ${\bf B}'_{c}=(Σ_c^{(++,+,0)},Ξ_{c}^{\prime(+,0)},Ω_c^0)$, ${\bf B}_{cc}=(Ξ_{cc}^{++},Ξ_{cc}^+,Ω_{cc}^+)$, or ${\bf B}_{ccc}=Ω^{++}_{ccc}$. With ${\bf B}_n^{(\prime)}$ denoted as the baryon octet (decuplet), we find that the ${\bf B}_{c}\to {\bf B}'_n\ell^+ν_\ell$ decays are forbidden, while the $Ω_c^0\to Ω^-\ell^+ν_\ell$, $Ω_{cc}^+\toΩ_c^0\ell^+ν_\ell$, and $Ω_{ccc}^{++}\to Ω_{cc}^+\ell^+ν_\ell$ decays are the only existing Cabibbo-allowed modes for ${\bf B}'_{c}\to {\bf B}'_n\ell^+ν_\ell$, ${\bf B}_{cc}\to {\bf B}'_c\ell^+ν_\ell$, and ${\bf B}_{ccc}\to {\bf B}_{cc}^{(\prime)}\ell^+ν_\ell$, respectively. We predict the rarely studied ${\bf B}_{c}\to {\bf B}_n^{(\prime)}M$ decays, such as ${\cal B}(Ξ_c^0\toΛ^0\bar K^0,\,Ξ_c^+\toΞ^0π^+)=(8.3\pm 0.9,8.0\pm 4.1)\times 10^{-3}$ and ${\cal B}(Λ_c^+\to Δ^{++}π^-,\,Ξ_c^0\toΩ^- K^+)=(5.5\pm 1.3,4.8\pm 0.5)\times 10^{-3}$. For the observation, the doubly and triply charmed baryon decays of $Ω_{cc}^{+}\to Ξ_c^+\bar K^0$, $Ξ_{cc}^{++}\to (Ξ_c^+π^+$, $Σ_c^{++}\bar K^0)$, and $Ω_{ccc}^{++}\to (Ξ_{cc}^{++}\bar K^0,Ω_{cc}^+π^+,Ξ_c^+ D^+)$ are the favored Cabibbo-allowed decays, which are accessible to the BESIII and LHCb experiments.

hep-ph↗

arXiv2018

Anti-triplet charmed baryon decays with SU(3) Flavor Symmetry

We study the decays of the anti-triplet charmed baryon state $(Ξ_c^0,Ξ_c^+,Λ_c^+)$ based on the $SU(3)$ flavor symmetry. In particular, after predicting ${\cal B}(Ξ_c^0\to Ξ^-π^+)=(15.7 \pm 0.7)\times 10^{-3}$ and ${\cal B}(Ξ_c^+\toΞ^-π^+π^+)=(14.7\pm 8.4)\times 10^{-3}$, we extract that ${\cal B}(Ξ_c^0\toΛK^-π^+,ΛK^+K^-,Ξ^- e^+ν_e)=(16.8\pm 2.3,0.45\pm 0.11,48.7\pm 17.4)\times 10^{-3}$ and ${\cal B}(Ξ_c^+\to p K_s^0 K_s^0,Σ^+ K^-π^+,Ξ^0π^+π^0,Ξ^0 e^+ν_e)=(1.3\pm 0.8,13.8\pm 8.0,33.8\pm 21.9,33.8^{+21.9}_{-22.6})\times 10^{-3}$. We also find that ${\cal B}(Ξ_c^0\to Ξ^{0} η,Ξ^{0} η')=(1.7 ^{+ 1.0 }_{- 1.7 },8.6 ^{+ 11.0 }_{-\;\,6.3 })\times 10^{-3}$, ${\cal B}(Ξ_c^0\to Λ^{0} η,Λ^{0} η')=(1.6 ^{+ 1.2 }_{- 0.8 },9.4 ^{+ 11.6 }_{-\;\,6.8 })\times 10^{-4}$ and ${\cal B}(Ξ_c^+\to Σ^{+} η,Σ^{+} η')=(28.4 ^{+ 8.2 }_{- 6.9 },13.2 ^{+ 24.0 }_{- 11.9 })\times 10^{-4}$. These $Ξ_c$ decays with the branching ratios of $O(10^{-4}-10^{-3})$ are clearly promising to be observed by the BESIII and LHCb experiments.

hep-ph↗

arXiv2017

How NOT To Evaluate Your Dialogue System: An Empirical Study of Unsupervised Evaluation Metrics for Dialogue Response Generation

We investigate evaluation metrics for dialogue response generation systems where supervised labels, such as task completion, are not available. Recent works in response generation have adopted metrics from machine translation to compare a model's generated response to a single target response. We show that these metrics correlate very weakly with human judgements in the non-technical Twitter domain, and not at all in the technical Ubuntu domain. We provide quantitative and qualitative results highlighting specific weaknesses in existing metrics, and provide recommendations for future development of better automatic evaluation metrics for dialogue systems.

cs.CL↗