arXiv subjects

Xiao-Hai Liu

Publications and source records attributed to Xiao-Hai Liu.

At least 55 records · Page 3Linked to original sources

arXiv2019

Visible narrow cusp structure in $Λ_c^+\to p K^- π^+$ enhanced by triangle singularity

A resonance-like structure as narrow as 10 MeV is observed in the $K^-p$ invariant mass distributions in $Λ_c^+\to p K^- π^+$ at Belle. Based on the large data sample of about 1.5 million events and the small bin width of just 1 MeV for the $K^-p$ invariant mass spectrum, the narrow peak is found precisely lying at the $Λη$ threshold. While lacking evidence for a quark model state with such a narrow width at this mass region, we find that this narrow structure can be naturally identified as a threshold cusp but enhanced by the nearby triangle singularity via the $Λ$-$a_0(980)^+$ or $η$-$Σ(1660)^+$ rescatterings.

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arXiv2018

New spectrum of negative-parity doubly charmed baryons: Possibility of two quasistable states

The discovery of $Ξ_{cc}^{++}$ by the LHCb Collaboration triggers predictions of more doubly charmed baryons. By taking into account both the $P$-wave excitations between the two charm quarks and the scattering of light pseudoscalar mesons off the ground state doubly charmed baryons, a set of negative-parity spin-1/2 doubly charmed baryons are predicted already from a unitarized version of leading order chiral perturbation theory. Moreover, employing heavy antiquark-diquark symmetry the relevant low-energy constants in the next-to-leading order are connected with those describing light pseudoscalar mesons scattering off charmed mesons, which have been well determined from lattice calculations and experimental data. Our calculations result in a spectrum richer than that of heavy mesons. We find two very narrow $J^P=1/2^-$ $Ω_{cc}^P$, which very likely decay into $Ω_{cc}π^0$ breaking isospin symmetry. In the isospin-1/2 $Ξ_{cc}^P$ sector, three states are predicted to exist below 4.2~GeV with the lowest one being narrow and the other two rather broad. We suggest to search for the $Ξ_{cc}^{P}$ states in the $Ξ_{cc}^{++}π^-$ mode. Searching for them and their analogues are helpful to establish the hadron spectrum.

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arXiv2017

Influence of threshold effects induced by charmed meson rescattering

We investigate the processes $e^+e^-$ annihilating to $J/ψππ$, $ψ^\primeππ$ and $h_cππ$. The coupled-channel effects induced by the couplings between the widely accepted $D$-wave charmonium $ψ(4160)$ and $D_1D$, $D_1D^*$ and $D_2D^*$ charmed meson pairs in the $S$-wave state with couplings given by heavy quark spin symmetry are analyzed. The line shapes show the presence of cusps that result from the singularities of the rescattering loops, which could be helpful in understanding the nature of $Y(4260)$, $Y(4360)$, $Z_c(3900)$/$Z_c(3885)$ and $Z_c(4020)$/$Z_c(4025)$.

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arXiv2017

Generating a resonance-like structure in the reaction $B_c\to B_s ππ$

We investigate the process $B_c^+\to B_s^0π^+π^0$ via $B\bar{K}^*$ rescattering. The kinematic conditions for triangle singularities are perfectly satisfied in the rescattering diagrams. A resonance-like structure around the $B\bar{K}$ threshold, which we denote as $X(5777)$, is predicted to be present in the invariant mass distribution of $B_s^0 π^+$. Because the relative weak $B\bar{K}$ $(I=1)$ interaction does not support the existence of a dynamically generated hadronic molecule, the $X(5777)$ can be identified as a pure kinematical effect due to the triangle singularity. Its observation may help to establish a non-resonance interpretation for some $XYZ$ particles.

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arXiv2016

How to understand the underlying structures of $X(4140)$, $X(4274)$, $X(4500)$ and $X(4700)$

We investigate the possible rescattering effects which may contribute to the process $B^+\to J/ψϕK^+$. It is shown that the $D_{s}^{*+}D_{s}^-$ rescattering via the open-charmed meson loops, and $ψ^\prime ϕ$ rescattering via the $ψ^\prime K_1$ loops may simulate the structures of $X(4140)$ and $X(4700)$, respectively. However, if the quantum numbers of $X(4274)$ ($X(4500)$) are $1^{++}$ ($0^{++}$), it is hard to to ascribe the observation of $X(4274)$ and $X(4500)$ to the $P$-wave threshold rescattering effects, which implies that $X(4274)$ and $X(4500)$ could be genuine resonances. We also suggest that $X(4274)$ may be the conventional orbitally excited state $χ_{c1}(3P)$.

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arXiv2016

Understanding the newly observed heavy pentaquark candidates

We find that several thresholds can contribute to the enhancements of the newly observed heavy pentaquark candidates $P_c^+(4380)$ and $P_c^+(4450)$ via the anomalous triangle singularity (ATS) transitions in the specific kinematics of $Λ_b\to J/ψK^- p$. Apart from the observed two peaks we find that another peaks around 4.5 GeV can also be produced by the ATS. We also show that the $Σ_c^{(*)}$ can be produced at leading order in $Λ_b$ decay. This process is different from the triangle diagram and its threshold enhancement only appears as CUSP effects if there is no pole structure or the ATS involved. The threshold interaction associated with the presence of the ATS turns out to be a general phenomenon and plays a crucial role in the understanding of candidates for exotic states.

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arXiv2016

Could the observation of $X(5568)$ be resulted by the near threshold rescattering effects?

We investigate the invariant mass distributions of $B_sπ$ via different rescattering processes. Because the triangle singularity (TS) could be present for a very broad incident energy region, it can be expected that the TS peaks may simulate the resonance-like bump $X(5568)$ observed by the D0 collaboration. The highly process-dependent characteristic of TS mechanism offers a criterion to distinguish it from other dynamic mechanisms.

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arXiv2016

Understanding the nature of the heavy pentaquarks and searching for them in pion-induced reactions

We investigate the reaction $π^- p \to π^- J/ψp$ via the open-charm hadron rescattering diagrams. Due to the presence of the triangle singularity (TS) in the rescattering amplitudes, the TS peaks can simulate the pentaquark-like resonances arising in the $J/ψp$ invariant mass distributions, which may bring ambiguities on our understanding of the nature of the exotic states. Searching for the heavy pentaquark in different processes may help us to clarify the ambiguities, because of the highly process-dependent characteristic of the TS mechanism.

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arXiv2015

Searching for charmoniumlike states with hidden $s\bar{s}$

We investigate the processes $e^+e^-$$\to$$γJ/ψϕ$, $γJ/ψω$ and $π^0 J/ψη$ to search for the charmnium-like states with hidden $s\bar{s}$, such as $Y(4140)$, $Y(4274)$, $X(4350)$ and $X(3915)$. These processes will receive contributions from the charmed-strange meson rescatterings. When the center-of-mass energies of the $e^+e^-$ scatterings are taken around the $D_{s0}(2317)D_s^{*}$, $D_{s1}(2460)D_s$ or $D_{s1}(2460)D_s^{*}$ threshold, the anomalous triangle singularities can be present in the rescattering amplitudes, which implies a non-resonance explanation about the resonance-like structures. The positions of the anomalous triangle singularities are sensitive to the kinematics, which offers us a criterion to distinguish the kinematic singularities from genuine particles.

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arXiv2015

Searching for observable effects induced by anomalous triangle singularities

We investigate the anomalous triangle singularity (ATS) and its possible manifestations in various processes. We show that the ATS should have important impact on our understanding of the nature of some newly observed threshold states. Discussions on how to distinguish the ATS phenomena from genuine dynamic pole structures are presented.

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arXiv2015

Photoproduction of hidden charm pentaquark states $P_c^+(4380)$ and $P_c^+(4450)$

We propose to study the pentaquark candidates of $P_c^+(4380)$ and $P_c^+(4450)$ in $J/ψ$ photoproduction and look for further experimental evidence for their nature. Since the photoproduction process does not satisfy the so-called "anomalous triangle singularity" condition their presence in $J/ψ$ photoproduction would conclude that they should be genuine states and provide further evidence for their existence.

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arXiv2014

Exotic Four Quark Matter: $Z_1(4475)$

Motivated by the LHCb's recent confirmation of $Z_1(4475)$ as the $J^P=1^+$ resonance, we investigate various exotic interpretations of $Z_1(4475)$, which may be an axial vector tetraquark state, the P-wave excitation of the S-wave $D_1 {\bar D}^\ast$ or $D_2 {\bar D}^\ast$ molecule, the S-wave molecule composed of a $D$ or $D^*$ meson and a D-wave vector $D$ meson, or the cousin molecular state of $Z_c(3900)$ and $Z_c(4020)$ composed of a $D$ or $D^*$ meson and their radial excitations. With the help of the heavy quark symmetry, we predict the typical radiative and hidden-charm and open-charm strong decay patterns of $Z_1(4475)$, which are crucial to further identify the molecular state assignment of $Z_1(4475)$.

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arXiv2014

Probing the $XYZ$ states through radiative decays

In this work, we have adopted the spin rearrangement scheme in the heavy quark limit and extensively investigated three classes of the radiative decays: $\mathfrak{M}\to (b\bar{b})+γ$, $(b\bar{b})\to \mathfrak{M}+γ$, $ \mathfrak{M} \to \mathfrak{M}^\prime+γ$, corresponding to the electromagnetic transitions between one molecular state and bottomonium, one bottomonium and molecular state, and two molecular states respectively. We also extend the same formalism to study the radiative decays of the molecular states with hidden charm. We have derived some model independent ratios when the initial or final states belong to the same spin flavor multiplet. Future experimental measurement of these ratios will test the molecular picture and explore the underlying structures of the $XYZ$ states.

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arXiv2014

Resolving the puzzling decay patterns of charged $Z_c$ and $Z_b$ states

We investigate the ratio of the branching fractions of the molecular candidates decaying into the ground and radially excited states within the quark interchange model. Our numerical results suggest that these molecular candidates are more likely to decay into the radially excited states than into ground states. Especially, the ratio $Γ[Z_c(4430)\to πψ(2S)]$/$Γ[Z_c(4430)\to πJ/ψ]\sim 9.8$ is close to the experimental measurement, which supports the interpretation of $Z_c(4430)$ as the $\bar{D}D^*(2S)$ molecular state. The ratios of the branching fractions of $Z_b(10610)$ and $Z_b(10650)$ to $πΥ(2S, 3S)$ and $πΥ(1S)$ agrees very well with Belle's measurement. We also predict the similar ratios for $Z_c(3900)$, $Z_c(4020)$, $R_{Z_c(3900)}$$\approx$1.3 and $R_{Z_c(4020)}$$\approx$$4.7$. Hopefully the $πψ(2S)$ mode, and ratios $R_{Z_c(3900)}$ and $R_{Z_c(4020)}$ will be measured by the BESIII and Belle collaborations in the near future, which shall be very helpful to understand the underlying dynamics of these exotic states.

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arXiv2014

Strong decays of the $XYZ$ states

Through the spin rearrangement scheme in the heavy quark limit, we have performed a comprehensive investigation of the decay pattern and production mechanism of the hidden beauty di-meson states, which are either composed of a P-wave bottom meson and an S-wave bottom meson or two S-wave bottom mesons. We further extend the corresponding formula to discuss the decay behavior of some charmonium-like states by combining the experimental information with our numerical results. The typical ratios presented in this work can be measured by future experiments like BESIII, Belle, LHCb and the forthcoming BelleII, which shall provide important clues to the inner structures of the exotic states.

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arXiv2013

Investigating possible decay modes of $Y(4260)$ under the $D_1(2420)\bar D +c.c$ molecular state ansatz

By assuming that $Y(4260)$ is a $D_1\bar D$ molecular state, we investigate some hidden-charm and charmed pair decay channels of $Y(4260)$ via intermediate $D_1\bar D$ meson loops with an effective Lagrangian approach. Through investigating the $α$-dependence of branching ratios and ratios between different decay channels, we show that the intermediate $D_1 \bar D$ meson loops are crucial for driving these transitions of $Y(4260)$ studied here. The coupled channel effects turn out to be more important in $Y(4260) \to D^{*}\bar{D}^{*}$, which can be tested in the future experiments.

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arXiv2013

Exploring the threshold behavior and implications on the nature of Y(4260) and $Z_c(3900)$

By assuming that Y(4260) either is a $D_1\bar{D}$ molecular state, or has sizeable couplings with $D_0 \bar{D}^*$ and $D_1^\prime \bar{D}$, we investigate several decay modes of Y(4260). Under the special kinematic configurations, triangle singularity (TS) may occur in the rescattering amplitude, which will significantly change the threshold behavior. Obvious threshold enhancements or narrow cusp structures appear quite naturally without introducing a genuine resonance. We emphasize that the radiative decay modes may be useful for studying $D^{(*)}\bar{D}$ $S$-wave scattering.

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arXiv2012

Extracting $ππ$ $S$-wave scattering lengths from cusp effect in heavy quarkonium dipion transitions

Charge-exchange rescattering $π^+π^-\to π^0π^0$ leads to a cusp effect in the $π^0π^0$ invariant mass spectrum of processes with $π^0π^0$ in the final state which can be used to measure $ππ$ $S$-wave scattering lengths. Employing a non-relativistic effective field theory, we discuss the possibility of extracting the scattering lengths in heavy quarkonium $π^0π^0$ transitions. The transition $Υ(3S)\toΥ(2S)π^0π^0$ is studied in details. We discuss the precision that can be reached in such an extraction for a certain number of events.

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