arXiv subjects

Li-Sheng Geng

Publications and source records attributed to Li-Sheng Geng.

At least 199 records · Page 11Linked to original sources

arXiv2017

Role of the $N^*(1535)$ in the $Λ^+_c \to \bar{K}^0 ηp$ decay

The nonleptonic weak decay of $Λ^+_c \to \bar{K}^0 ηp$ is analyzed from the viewpoint of probing the $N^*(1535)$ resonance, which has a big decay branching ratio to $ηN$. Up to an arbitrary normalization, the invariant mass distribution of $ηp$ is calculated with both the chiral unitary approach and an effective Lagrangian model. Within the chiral unitary approach, the $N^*(1535)$ resonance is dynamically generated from the final state interaction of mesons and baryons in the strangeness zero sector. For the effective Lagrangian model, we take a Breit-Wigner formula to describe the distribution of the $N^*(1535)$ resonance. It is found that the behavior of the $N^*(1535)$ resonance in the $Λ^+_c \to \bar{K}^0 N^*(1535) \to \bar{K}^0 ηp$ decay within the two approaches is different. The proposed $Λ^+_c$ decay mechanism can provide valuable information on the properties of the $N^*(1535)$ and can in principle be tested by facilities such as BEPC II and SuperKEKB.

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arXiv2017

$Σ^*_{1/2^-}(1380)$ in the $Λ^+_c \to ηπ^+ Λ$ decay

A $Σ^*$ state with spin-parity $J^P = 1/2^-$ with mass and width around $1380$ MeV and $120$ MeV, refereed to as the $Σ^*_{1/2^-}(1380)$, has been predicted in several pentaquark models and inferred from the analysis of CLAS $γp$ data. In the present work, we discuss how one can employ the $Λ^+_c \to ηπ^+ Λ$ decay to test its existence, as well as to study the $Σ^*(1385)$ state with $J^P = 3/2^+$. Because the final $π^+ Λ$ system is in a pure isospin $I = 1$ combination, the $Λ^+_c \to ηπ^+ Λ$ decay can be an ideal process to study these $Σ^*$ resonances. In particular, we show that the decay angle and energy distributions of the $π^+$ are very different for $Σ^*(1385)$ and $Σ^*_{1/2^-}(1380)$. The proposed decay mechanism as well as the existence of the $Σ^*_{1/2^-}(1380)$ state can be checked by future BESIII and Belle experiments.

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arXiv2017

Hyperon-nucleon Scattering In A Covariant Chiral Effective Field Theory Approach

A recently proposed covariant chiral effective field theory approach is applied to study strangeness $S=-1$ hyperon-nucleon interactions at leading order. 12 low energy constants are introduced by Lorentz invariance, which is different from the heavy baryon approach, where only five appear. The Kadyshevsky equation is employed to iterate the chiral potentials. A quite satisfactory description of the 36 hyperon-nucleon scattering data is obtained with $χ^2\simeq 17$, which is comparable with the next-to-leading order heavy baryon approach. The results hint at a more efficient way to construct the chiral potentials.

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arXiv2017

$f_2(1810)$ as a triangle singularity

We perform calculations showing that a source producing $K^* \bar{K}^*$ in $J = 2$ and $L=0$ gives rise to a triangle singularity at $1810$ MeV with a width of about $200$ MeV from the mechanism $K^* \to πK$ and then $K\bar{K}^*$ merging into the $a_1(1260)$ resonance. We suggest that this is the origin of the present $f_2(1810)$ resonance and propose to look at the $πa_1(1260)$ mode in several reactions to clarify the issue.

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arXiv2017

$B_sπ$--$B\bar{K}$ interactions in finite volume and the $X(5568)$

The recent observation of $X(5568)$ by the D0 Collaboration has aroused a lot of interest both theoretically and experimentally. In the present work, we first point out that $X(5568)$ and $D_{s0}^*(2317)$ cannot simultaneously be of molecular nature, from the perspective of heavy-quark symmetry and chiral symmetry, based on a previous study of the lattice QCD scattering lengths of $DK$ and its coupled channels. Then we compute the discrete energy levels of the $B_sπ$ and $B\bar{K}$ system in finite volume using unitary chiral perturbation theory. The comparison with the latest lattice QCD simulation, which disfavors the existence of $X(5568)$, supports our picture where the $B_sπ$ and $B\bar{K}$ interactions are weak and $X(5568)$ cannot be a $B_sπ$ and $B\bar{K}$ molecular state. In addition, we show that the extended Weinberg compositeness condition also indicates that $X(5568)$ cannot be a molecular state made from $B_sπ$ and $B\bar{K}$ interactions.

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arXiv2017

Consistency between SU(3) and SU(2) chiral perturbation theory for the nucleon mass

Treating the strange quark mass as a heavy scale compared to the light quark mass, we perform a matching of the nucleon mass in the SU(3) sector to the two-flavor case in covariant baryon chiral perturbation theory. The validity of the $19$ low-energy constants appearing in the octet baryon masses up to next-to-next-to-next-to-leading order~\cite{Ren:2014vea} is supported by comparing the effective parameters (the combinations of the $19$ couplings) with the corresponding low-energy constants in the SU(2) sector~\cite{Alvarez-Ruso:2013fza}. In addition, it is shown that the dependence of the effective parameters and the pion-nucleon sigma term on the strange quark mass is relatively weak around its physical value, thus providing support to the assumption made in Ref.~\cite{Alvarez-Ruso:2013fza}.

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arXiv2016

Novel nonperturbative approach for radiative $\bar{B}^0(\bar{B}^0_s)\rightarrow J/ψγ$ decays

Radiative $\bar{B}^0(\bar{B}^0_s)\rightarrow J/ψγ$ decays provide an interesting case to test our understanding of (non)perturbative QCD and eventually to probe physics beyond the standard model. Recently, the LHCb Collaboration has reported an upper bound, updating the results of the BABAR Collaboration. Previous theoretical predictions based on QCD factorization or perturbative QCD have shown large variations due to different treatment of nonfactorizable contributions and meson-photon transitions. In this paper, we report on a novel approach to estimate the decay rates, which is based on a recently proposed model for $B$ decays and the vector meson dominance hypothesis, widely tested in the relevant energy regions. The predicted branching ratios are $\mathrm{Br}[\bar{B}^0\rightarrow J/ψγ]=\left(3.50\pm0.34^{+1.12}_{-0.63}\right)\times10^{-8}$ and $\mathrm{Br}[\bar{B}^0_s\rightarrow J/ψγ]=\left(7.20\pm0.68^{+2.31}_{-1.30}\right)\times10^{-7}$. The first uncertainty is systematic and the second is statistical, originating from the experimental $\bar{B}^0_s\rightarrow J/ψϕ$ branching ratio.

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arXiv2016

Strangeness $S=-1$ hyperon-nucleon scattering in covariant chiral effective field theory

Motivated by the successes of covariant baryon chiral perturbation theory in one-baryon systems and in heavy-light systems, we study relevance of relativistic effects in hyperon-nucleon interactions with strangeness $S=-1$. In this exploratory work, we follow the covariant framework developed by Epelbaum and Gegelia to calculate the $YN$ scattering amplitude at leading order. By fitting the five low-energy constants to the experimental data, we find that the cutoff dependence is mitigated, compared with the heavy-baryon approach. Nevertheless, the description of the experimental data remains quantitatively similar at leading order.

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arXiv2016

A hidden-charm pentaquark state in $Λ^0_b \to J/ψp π^-$ decay

We study here the $Λ_b^0 \to J/ψp π^-$ reaction in analogy to the $Λ^0_b \to J/ψp K^-$ one, and we note that in both decays there is a sharp structure (dip or peak) in the $J/ψp$ mass distribution around $4450$ MeV, which is associated in the $Λ^0_b \to J/ψp K^-$ experiment to an exotic pentaquark baryonic state, although in $Λ_b^0 \to J/ψp π^-$ it shows up with relatively low statistics. We analyze the $Λ^0_b \to J/ψp π^-$ interaction along the same lines as the $Λ^0_b \to J/ψp K^-$ one, with the main difference stemming from the reduced Cabibbo strength in the former and the consideration of the $π^-p$ final state interaction instead of the $K^-p$ one. We find that with a minimal input, introducing the $π^-p$ and $J/ψp$ interaction in $S$-wave with realistic interactions, and the empirical $P$-wave and $D$-wave contributions, one can accomplish a qualitative description of the $π^-p$ and $J/ψp$ mass distributions. More importantly, the peak structure followed by a dip of the experimental $J/ψp$ mass distribution is reproduced with the same input as used to describe the data of $Λ^0_b\rightarrow J/ψp K^-$ reaction. The repercussion for the triangular singularity mechanism, invoked in some works to explain the pentaquark peak, is discussed.

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arXiv2016

The $a_0(980)$ and $Λ(1670)$ in the $Λ^+_c \to π^+ ηΛ$ decay

We propose to study the $a_0(980)$ and the $Λ(1670)$ resonances in the $Λ^+_c \to π^+ ηΛ$ decay via the final state interactions of the $π^+ η$ and $ηΛ$ pairs. The weak interaction part proceeds through the $c$ quark decay process: $c(ud) \to (s + u + \bar d)(ud)$, while the hadronization part takes place in two different mechanisms. In the first mechanism, the $sud$ cluster picks up a $q\bar{q}$ pair from the vacuum to form the $ηΛ$ meson-baryon pair while the $u\bar{d}$ pair from the weak decay hadronizes into a $π^+$. In the second, the $sud$ cluster turns into a $Λ$, while the $u\bar{d}$ pair from the $c$ decay picks up a $q\bar{q}$ pair and hadronizes into a meson-meson pair ($πη$ or $K\bar{K}$). Because the final $π^+ η$ and $ηΛ$ states are in pure isospin $I = 1$ and $I=0$ combinations, the $Λ^+_c \to π^+ ηΛ$ decay can be an ideal process to study the $a_0(980)$ and $Λ(1670)$ resonances. Describing the final state interaction in the chiral unitary approach, we find that the $π^+ η$ and $ηΛ$ invariant mass distributions, up to an arbitrary normalization, show clear cusp and peak structures, which can be associated with the $a_0(980)$ and $Λ(1670)$ resonances, respectively. The proposed mechanism can provide valuable information on the nature of these resonances and can in principle be test by facilities such as BEPCII.

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arXiv2016

The $Λ_{b}\rightarrow J/ψK^{0}Λ$ reaction and a hidden-charm pentaquark state with strangeness

We study the $Λ_{b}\rightarrow J/ψK^{0}Λ$ reaction considering both the $K^{0}Λ$ interaction with its coupled channels and the $J/ψΛ$ interaction. The latter is described by taking into account the fact that there are predictions for a hidden-charm state with strangeness that couples to $J/ψΛ$. By using the coupling of the resonance to $J/ψΛ$ from these predictions we show that a neat peak can be observed in the $J/ψΛ$ invariant mass distribution, rather stable under changes of unknown magnitudes. In some cases, one finds a dip structure associated to that state, but a signal of the state shows up in the $J/ψ$ spectrum.

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arXiv2016

The $Λ_c(2595)$ resonance as a dynamically generated state: the compositeness condition and the large $N_c$ evolution

Recent studies have shown that the well established $Λ_c(2595)$ resonance contains a large meson-baryon component, which can vary depending on the specific formalism. In this work, we examine such a picture by utilizing the compositeness condition and the large number of colors ($N_c$) expansion. We examine three different models fulfilling two body unitarity in coupled-channels, and adopting renormalization schemes where the mass of the $Λ_c(2595)$ resonance is well described, but not necessarily its width, since we do not consider three body channels and work at the isospin symmetric limit. Both approximations might have an effect larger on the width than on the mass. In this context, our studies show that the compositeness of the $Λ_c(2595)$ depends on the number of considered coupled channels, and on the particular regularization scheme adopted in the unitary approaches and, therefore, is model dependent. In addition, we perform an exploratory study of the $Λ_c(2595)$ in the large $N_c$ expansion, within a scheme involving only the $πΣ_c$ and $KΞ'_c$ channels, whose dynamics is mostly fixed by chiral symmetry. In this context and formulating the leading-order interaction as a function of $N_c$, we show that for moderate $N_c> 3$ values, the mass and width of the $Λ_c(2595)$ deviate from those of a genuine $qqq$ baryon, implying the relevance of meson-baryon components in its wave function. Furthermore, we study the properties of the $Λ_c(2595)$, in the strict $N_c \to \infty $ limit, using an extension of the chiral Weinberg-Tomozawa interaction to an arbitrary number of flavors and colors. This latter study hints at the possible existence of a (perhaps) sub-dominant $qqq$ component in the $Λ_c(2595)$ resonance wave function, which would become dominant when the number of colors gets sufficiently large.

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arXiv2016

Octet baryon masses and sigma terms in covariant baryon chiral perturbation theory

We report on a recent study of the ground-state octet baryon masses and sigma terms in covariant baryon chiral perturbation theory with the extended-on-mass-shell scheme up to next-to-next-to-next-to-leading order. To take into account lattice QCD artifacts, the finite-volume corrections and finite lattice spacing discretization effects are carefully examined. We performed a simultaneous fit of all the $n_f = 2+1$ lattice octet baryon masses and found that the various lattice simulations are consistent with each other. Although the finite lattice spacing discretization effects up to $\mathcal{O}(a^2)$ can be safely ignored, but the finite volume corrections cannot even for configurations with $M_ϕL>4$. As an application, we predicted the octet baryon sigma terms using the Feynman-Hellmann theorem. In particular, the pion- and strangeness-nucleon sigma terms are found to be $σ_{πN} = 55(1)(4)$ MeV and $σ_{sN} = 27(27)(4)$ MeV, respectively.

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arXiv2015

F-wave heavy-light meson spectroscopy in QCD sum rules and heavy quark effective theory

We study the F-wave c_bar s heavy meson doublets (2+,3+) and (3+,4+). They have large orbital excitations L=3, and may be good challenges (tests) for theoretical studies. To study them we use the method of QCD sum rule in the framework of heavy quark effective theory. Their masses are predicted to be m_{(2+,3+)} = (3.45 \pm 0.25, 3.50 \pm 0.26) GeV and m_{(3+,4+)} = (3.20 \pm 0.22, 3.26 \pm 0.23) GeV, with mass splittings Delta m_{(2+,3+)} = m_{3+} - m_{2+} = 0.046 \pm 0.030 GeV and Delta m_{(3+,4+)} = 0.053 \pm 0.044 GeV, respectively. We note that this is a pioneering work and these results are provisional.

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arXiv2015

Looking for a hidden-charm pentaquark state with strangeness $S=-1$ from $Ξ^-_b$ decay into $J/ψK^- Λ$

Assuming that the recently observed hidden-charm pentaquark state, $P_c(4450)$, is of molecular nature as predicted in the unitary approach, we propose to study the decay of $Ξ^-_b\rightarrow J/ψK^- Λ$ to search for the strangeness counterpart of the $P_c(4450)$. There are three ingredients in the decay mechanism: the weak decay mechanism, the hadronization mechanism, and the finite state interactions in the meson-baryon system of strangeness $S=-2$ and isospin $I=1/2$ and of the $J/ψΛ$. All these have been tested extensively. As a result, we provide a genuine prediction of the differential cross section where a strangeness hidden-charm pentaquark state, the counterpart of the $P_c(4450)$, can be clearly seen. The decay rate is estimated to be of similar magnitude as the $Λ_b^0\rightarrow J/ψK^- p$ observed by the LHCb collaboration.

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arXiv2015

Photoproduction of the $f'_2(1525)$ and $K^*_2(1430)$

Assuming that the $f'_2(1525)$ and $K^*_2(1430)$ resonances are dynamically generated states from the vector meson-vector meson interactions in $S$-wave with spin $S=2$, we study the $γp \to f'_2(1525) p$ and $γp \to K^*_2(1430) Λ(Σ)$ reactions. These reactions proceed in the following way: the incoming photon first mutates into a $ρ^0$, $ω$, or $ϕ$ meson via vector meson dominance, which then interacts with the $ρ^0$, $ω$ or $K^*$ emitted by the incoming proton to form the tensor mesons $f'_2(1525)$ and $K^*_2(1430)$. The picture is simple and has no free parameters, as all the parameters of the mechanism have been fixed in previous studies. We predict the differential and total cross sections of these reactions. The results can be tested in future experiments and therefore offer new clues on the nature of these tensor states.

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arXiv2015

Dynamically generated $J^P=1/2^-(3/2^-)$ singly charmed and bottom heavy baryons

Approximate heavy-quark spin and flavor symmetry and chiral symmetry play an important role in our understanding of the nonperturbative regime of strong interactions. In this work, utilizing the unitarized chiral perturbation theory, we explore the consequences of these symmetries in the description of the interactions between the ground-state singly charmed (bottom) baryons and the pseudo-Nambu-Goldstone bosons. In particular, at leading order in the chiral expansion, by fixing the only parameter in the theory to reproduce the $Λ_b(5912)$ [$Λ_b^*(5920)$] or the $Λ_c(2595)$ [$Λ_c^*(2625)$], we predict a number of dynamically generated states, which are contrasted with those of other approaches and available experimental data. In anticipation of future lattice QCD simulations, we calculate the corresponding scattering lengths and compare them to the existing predictions from a $\mathcal{O}(p^3)$ chiral perturbation theory study. In addition, we estimate the effects of the next-to-leading-order potentials by adopting heavy-meson Lagrangians and fixing the relevant low-energy constants using either symmetry or naturalness arguments. It is shown that higher-order potentials play a relatively important role in many channels, indicating that further studies are needed once more experimental or lattice QCD data become available.

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arXiv2015

$S$-wave $KK^*$ interaction in a finite volume and the $f_1(1285)$

Lattice QCD simulations provide a promising way to disentangle different interpretations of hadronic resonances, which might be of particular relevance to understand the nature of the so-called $XYZ$ particles. Recent studies have shown that in addition to the well-established naive quark model picture, the axial-vector meson $f_1(1285)$ can also be understood as a dynamically generated state built upon the $KK^*$ interaction. In this work, we calculate the energy levels of the $KK^*$ system in the $f_1(1285)$ channel in finite volume using the chiral unitary approach. We propose to calculate the loop function in the dimensional regularization scheme, which is equivalent to the hybrid approach adopted in previous studies. We also study the inverse problem of extracting the bound state information from synthetic lattice QCD data and comment on the difference between our approach and the L{\" u}scher method.

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