arXiv subjects

Xian-Wei Kang

Publications and source records attributed to Xian-Wei Kang.

At least 37 records · Page 2Linked to original sources

arXiv2020

Pole analysis on the hadron spectroscopy of $Λ_b\to J/Ψp K^-$

In this paper we study the $J/Ψp$ spectroscopy in the process of $Λ_b\to J/Ψp K^-$. The final state interactions of coupled channel $J/Ψp$ ~-~ $\bar{D} Σ_c$~-~$\bar{D}^{*} Σ_c$ are constructed based on K-matrix with the Chew-Mandelstam function. We build the $Λ_b\to J/Ψp K^-$ amplitude according to the Au-Morgan-Pennington method. The event shape is fitted and the decay width of $Λ_b\to J/Ψp K^-$ is used to constrain the parameters, too. With the amplitudes we extract out the poles and their residues. Our amplitude and pole analysis suggest that the $P_c(4312)$ should be $\bar{D}Σ_c$ molecule, the $P_c(4440)$ could be an S-wave compact pentaquark state, and the structure around $P_c(4457)$ is caused by the cusp effect. The future experimental measurement of the decays of $Λ_b\to \bar{D}Σ_c K^-$ and $Λ_b\to \bar{D}^*Σ_c K^-$ would further help to study the nature of these resonances.

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arXiv2020

FCNC transitions of $Λ_b$ to neutron in Bethe-Salpeter equation approach

In a covariant quark-diquark model, we investigate the rare decay of $Λ_b \rightarrow n l^+ l^-$ and $Λ_b \rightarrow n γ$ in the Bethe-Salpeter equation approach. In this model the baryons are treated as bound states of a constituent quark and a diquark interacting via a gluon exchange and the linear confinement. We find that the ratio of form factors $R$ is varies from $-0.90$ to $-0.25$ and the branching ratios $Br(Λ_b \rightarrow n l^+ l^-)\times 10^{8}$ are $6.79(l=e),~4.08 ~ (l=μ),~2.9 ~(l=τ) $ and the branching ratio $Br(Λ_b \rightarrow γ)\times 10^{7} )=3.69$ in central values of parameters.

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arXiv2019

Nature of $X(3872)$ from the line shape

Using a general parameterization of two-body scattering amplitude, we systematically analyze the corresponding data on $X(3872)$, more explicitly, the CDF data on inclusive $p\bar{p}$ scattering to $J/ψπ^+π^-$, and the Belle and BaBar data on $B$ decays to $K\, J/ψπ^+π^-$ and $K D\bar{D}^{*0}$ around the $D^0\bar{D}^{*0}$ threshold. We achieve a good reproduction of data and find that the $X(3872)$ can be interpreted as a bound and/or virtual state, or even higher-order (double or triple) virtual sate pole. The latter point was not realized previously in the literature. % The latter point has not been realized in other literatures. As a result, the compositeness of the $X(3872)$ can vary largely from nearly 0 to 1. More higher-precision data is needed to discriminate its pole structure and nature.

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arXiv2019

Rare $Λ_b \rightarrow Λl^+ l^- $ decay in the Bethe-Salpeter equation approach

We study the rare decays $Λ_b \rightarrow Λl^+ l^-~(l=e,μ, τ)$ in the Bethe-Salpeter equation approach. We find that depending on the values of parameters in our model the branching ratio $Br(Λ_b \rightarrow Λμ^+ μ^-)\times 10^{6}$ varies from $0.812$ to $1.445$ when $κ= 0.050 \sim 0.060$ GeV$^3$ and the binding energy $E_0=-0.14$ GeV while $Br(Λ_b \rightarrow Λμ^+ μ^-)\times 10^{6}$ varies from $1.051$ to $1.098$ when $κ= 0.055$ Gev$^3$ and the binding energy $E_0$ changes from $-0.19$ to $-0.09$ GeV. These results agree with the experimental data. In the same parameter regions, we find that the branching ratio $Br(Λ_b \rightarrow Λe^+ e^-(τ^+ τ^-) )\times 10^{6}$ varies in the range $0.660-1.028$ ($0.252-0.392$) and $0.749-1.098$ ($0.286-0.489$), respectively.

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arXiv2019

Prospects for CP & P violation in $Λ_{c}^+$ decay at STCF

CP violation is an excellent tool for probing flavor dynamics as we learnt first with $K_L \to 2 π$ and later also with the weak decays of beauty mesons. LHCb 2019 data have shown CP violation for the first time in $D^0\to K^-K^+$ vs. $D^0\toπ^-π^+$. Searching for CP asymmetries is of great interest in charm quark sector in the Standard Model (SM) or even more beyond it. In charm hadron decays, lots of work had focused on two-body final states, and the measurements of CP asymmetries in three- or four-body final states are rare. Dalitz plots have shown an excellent record for three-body final states, and more results are desired for four-body ones. In this work we study CP asymmetries in the decays $Λ^+_c \to p K^-π^+π^0$/$Λπ^+π^+π^-$/$pK_Sπ^+π^-$, where the SM gives zero values for the first two channels, while $3.3 \times 10^{-3}$ for the last one due to $K^0 - \bar K^0$ oscillation. We performed a fast Monte Carlo simulation study by using electron-positron annihilation data of 1~$\textrm{ab}^{-1}$ at center-of-mass energy $\sqrt{s}\, =\, 4.64$ GeV. The data is expected to be available by the next generation Super Tau Charm Facility proposed by China and Russia with one year (or even less) data taking operation. The results indicate that a sensitivity at the level of 0.2$\sim$0.5% is accessible for these processes, which would be enough to measure nonzero CP-violating asymmetries as large as 1%.

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arXiv2019

Semileptonic decays of $D$ and $D_s$ mesons in the relativistic quark model

The form factors parameterizing the weak $D$ and $D_s$ transitions to light pseudoscalar and vector mesons are calculated in the framework of the relativistic quark model based on the quasipotential approach. The special attention is paid to the systematic account of the relativistic effects including transformation of the meson wave function from the rest to moving reference frame and contributions of the intermediate negative-energy states. The form factors are expressed through the overlap integrals of the meson wave functions, which are taken from previous studies of meson spectroscopy. They are calculated in the whole range of the transferred momentum $q^2$. Convenient parameterization of the form factors which accurately reproduces numerical results is given. The obtained values of the form factors and their ratios at $q^2=0$ agree well with the ones extracted form the experimental data. On the basis of these form factors and helicity formalism, differential and total semileptonic decay rates of $D$ and $D_s$ mesons as well as different asymmetries and polarization parameters are calculated. The detailed comparison of the obtained results with other theoretical calculations and experimental data is given.

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arXiv2019

Effective-range-expansion study of near threshold heavy-flavor resonances

In this work we study the resonances near the thresholds of the open heavy-flavor hadrons using the effective-range-expansion method. The unitarity, analyticity and compositeness coefficient are also taken into account in our theoretical formalism. We consider the $Z_c(3900)$, $X(4020)$, $χ_{c1}(4140)$, $ψ(4260)$ and $ψ(4660)$. The scattering lengths and effective ranges from the relevant elastic $S$-wave scattering amplitudes are determined. Tentative discussions on the inner structures of the aforementioned resonances are given.

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arXiv2019

Direct CP violation in multi-body $B$ decays with the $a^0_0(980)$--$f_0(980)$ mixing

We predict that the $a_0^0(980)$-$f_0(980)$ mixing would lead to large CP violation. We calculate the localized direct CP asymmetry in the decays $B^\pm \to f_0(980) [a_0^0(980)] π^\pm \to π^+ π^- π^\pm $ via the $a_0^0(980)$-$f_0(980)$ mixing mechanism based on the hypothetical $q\bar q$ structures of $a^0_0(980)$ and $f_0(980)$ in the QCD factorization. It is shown that there is a peak for CP violation, which could be as large as 58%, when the invariance mass of $ππ$ is near the masses of $a^0_0(980)$ and $f_0(980)$. Since the CP asymmetry is sensitive to the $a_0^0(980)$-$f_0(980)$ mixing, measuring the CP violating parameter in the aforementioned decays could provide a new way to verify the existence of the $a_0^0(980)$-$f_0(980)$ mixing and be helpful in clarifying the configuration nature of the light scalar mesons.

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arXiv2019

A study on the correlation between poles and cuts in $ππ$ scattering

In this paper we propose a dispersive method to describe two-body scattering with unitarity imposed. This approach is applied to elastic $ππ$ scattering. The amplitudes keep single-channel unitarity and describe the experimental data well, and the low-energy amplitudes are consistent with that of chiral perturbation theory. The pole locations of the $σ$, $f_0(980)$, $ρ(770)$ and $f_2(1270)$ and their couplings to $ππ$ are obtained. A virtual state appearing in the isospin-two S-wave is confirmed. The correlations between the left (and right) hand cut and the poles are discussed. Our results show that the poles are more sensitive to the right hand cut rather than the left hand cut. The proposed method could be used to study other two-body scattering processes.

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arXiv2018

Semileptonic $B$ and $B_s$ decays involving scalar and axial-vector mesons

We report our theoretical calculations on the branching fractions for the semileptonic $B$ and $B_s$ decays, i.e., $B (B_s) \to (P,\, V,\, S,\,A) \ell ν_\ell$, where $P$ and $V$ denote the pseudoscalar and vector mesons, respectively, while $S$ denotes the scalar meson with mass above 1 GeV and $A$ the axial-vector meson. The branching fractions for the semileptonic $B\to P$ and $V$ modes have been measured very well in experiment and our theoretical values are in good agreement with them. The ones for $B\to S$ and $A$ modes are our theoretical predictions. There is little experimental information on the semileptonic $B_s$ decays although much theoretical effort has been done. In addition, we predict the branching fractions of $B\to D^*_0(2400) \ell \barν_\ell$ and $B_s\to D^{*-}_{s0}(2317) \ell \barν_\ell$ as $(2.31\pm 0.25)\times 10^{-3}$ and $(3.07\pm0.34)\times 10^{-3}$, in order, assuming them as the conventional mesons with quark-antiquark configuration. The high luminosity $e^+e^-$ collider SuperKEKB/Belle-II is running, with the data sample enhanced by a factor of 40 compared to Belle, which will provide huge opportunity for the test of the theoretical predictions and further help understand the inner structure of these scalar and axial vector mesons, e.g., the glueball content of $f_0(1710)$ and the mixing angles for the axial-vector mesons. These decay channels can also be accessed by the LHCb experiment.

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arXiv2018

Test of semi-local duality in a large $N_C$ framework

In this paper we test the semi-local duality based on the method of Ref.[1] for calculating final-state interactions at varying number of colors ($N_C$). We compute the amplitudes by dispersion relations that respect analyticity and coupled channel unitarity, as well as accurately describing experiment. The $N_C$ dependence of the $ππ\toππ$ scattering amplitudes is obtained by comparing these amplitudes to the one of chiral perturbation theory. The semi-local duality is investigated by varying $N_C$. Our results show that the semi-local duality is not violated when $N_C$ is large. At large $N_C$, the contributions of the $f_2(1270)$, the $f_0(980)$ and the $f_0(1370)$ cancel that of the $ρ(770)$ in the finite energy sum rules, while the $f_0(500)$ has almost no effect. This gives further credit to the method developed in Ref.[1] for investigating the $N_C$ dependence of hadron-hadron scattering with final-state interactions. This study is also helpful to understand the structure of the scalar mesons.

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arXiv2018

Possible open-charmed pentaquark molecule $Ω_c(3188)$ --- the $D Ξ$ bound state --- in the Bethe-Salpeter formalism

We study the $S$-wave $DΞ$ bound state in the Bethe-Salpeter formalism in the ladder and instantaneous approximations. With the kernel generated by the hadronic effective Lagrangian, two open-charmed bound states, which quantum numbers are $I=0$, $J^P=(\frac{1}{2})^-$ and $I=1$, $J^P=(\frac{1}{2})^-$, respectively, are predicted as new candidates of hadronic pentaquark molecules in our formalism. If existing, they could contribute to the broad 3188 eV structure near the five new narrow $Ω_c$ states observed recently by the LHCb Collaboration.

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arXiv2018

Singly Cabibbo-suppressed hadronic decays of $Λ_c^+$

We study singly Cabibbo-suppressed two-body hadronic decays of the charmed baryon $Λ_c^+$, namely, $Λ_c^+\to ΛK^+, pπ^0, pη, nπ^+,Σ^0K^+,Σ^+ K^0$. We use the measured rate of $Λ_c^+\to pϕ$ to fix the effective Wilson coefficient $a_2$ for naive color-suppressed modes and the effective number of color $N_c^{\rm eff}$. We rely on the current-algebra approach to evaluate $W$-exchange and nonfactorizable internal $W$-emission amplitudes, that is, the commutator terms for the $S$-wave and the pole terms for the $P$-wave. Our prediction for $Λ_c^+\to pη$ is in excellent agreement with the BESIII measurement. The $pη$ ($pπ^0$) mode has a large (small) rate because of a large constructive (destructive) interference between the factorizable and nonfactorizable amplitudes for both $S$- and $P$-waves. Some of the SU(3) relations such as $M(Λ_c^+\to nπ^+)=\sqrt{2}M(Λ_c^+\to pπ^0)$ derived under the assumption of sextet dominance are not valid for decays with factorizable terms. Our calculation indicates that the branching fraction of $Λ_c^+\to nπ^+$ is about 3.5 times larger than that of $Λ_c^+\to pπ^0$. Decay asymmetries are found to be negative for all singly Cabibbo-suppressed modes and range from $-0.56$ to $-0.96$.

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arXiv2018

The semileptonic baryonic decay $D_s^+\to p\bar p e^+ ν_e$

The decay $D_s^+\to p \bar p e^+ν_e$ with a proton-antiproton pair in the final state is unique in the sense that it is the only semileptonic baryonic decay which is physically allowed in the charmed meson sector. Its measurement will test our basic knowledge on semileptonic $D_s^+$ decays and the low-energy $p\bar p$ interactions. Taking into account the major intermediate state contributions from $η, η', f_0(980)$ and $X(1835)$, we find that its branching fraction is at the level of $10^{-9} \sim 10^{-8}$. The location and the nature of $X(1835)$ state are crucial for the precise determination of the branching fraction. We wish to trigger a new round of a careful study with the upcoming more data in BESIII as well as the future super tau-charm factory.

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arXiv2018

Amplitude analysis of the anomalous decay $η'\toπ^+π^-γ$

In this paper we perform an amplitude analysis of $η'\toπ^+π^-γ$ and confront it with the latest BESIII data. Based on the final-state interaction theorem, we represent the amplitude in terms of an Omnés function multiplied by a form factor that corresponds to the contributions from left-hand cuts and right-hand cuts in the inelastic channels. We also take into account the isospin violation effect induced by $ρ-ω$ mixing. Our results show that the anomaly contribution is mandatory in order to explain the data. Its contribution to the decay width of $Γ(η'\toππγ)$ is larger than that induced by isospin violation. Finally we extract the pole positions of the $ρ$ and $ω$ as well as their corresponding residues.

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arXiv2017

CP Asymmetries in Strange Baryon Decays

While indirect & direct CP violations (CPV) had been established in the decays of strange & beauty mesons, none have been done for baryons. There are different "roads" for finding CP asymmetries in the decays of strange baryons; they are highly non-trivial ones. The HyperCP Collaboration had probed CPV in the decays of single $Ξ$ & $Λ$ [Phys.Rev.Lett 93 (2004) 262001]. We talk about future lessons from $e^+e^-$ collisions at BESIII/BEPCII: probing decays of pairs of strange baryons, namely $Λ$, $Σ$ & $Ξ$. Realistic goals are to learn about non-perturbative QCD. One can hope to find CPV in the decays of strange baryons; one can also dream to find impact of New Dynamics (ND). We point out that a new important era starts with the BESIII/BEPCII data accumulated by the end of 2018.

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arXiv2017

Branching fractions of semileptonic $D$ and $D_s$ decays from the covariant light-front quark model

Based on the predictions of the relevant form factors from the covariant light-front quark model, we show the branching fractions for the $D (D_s) \to (P,\,S,\,V,\,A)\,\ellν_\ell$ ($\ell=e$ or $μ$) decays, where $P$ denotes the pseudoscalar meson, $S$ the scalar meson with a mass above 1 GeV, $V$ the vector meson and $A$ the axial-vector one. Comparison with the available experimental results are made, and we find an excellent agreement. The predictions for other decay modes can be tested in a charm factory, e.g., the BESIII detector. The future measurements will definitely further enrich our knowledge on the hadronic transition form factor as well as the inner structure of the even-parity mesons ($S$ and $A$).

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arXiv2017

To the nature of $χ_{c2}(2P)$

We expect that $BR(χ_{c2}(2P)\to gluon\, gluon)\gtrsim 2 \%$ if Particle Data Group as well as BaBar and Belle collaboration correctly identified the state. In reality, this branching ratio corresponds to the one for $χ_{c2}(2P)$ decaying to the light hadrons. We also discuss the detection possibilities of these decays.

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