Search

A sample including 935 blazars with 415 Flat Spectrum Radio Quasars (FSRQs) and 520 BL Lac objects (BL Lacs) (233 HBLs (High synchrotron peak frequency BL Lacs), 144 IBLs (Intermediate synchrotron peak frequency BL Lacs), and 143 LBLs (Low synchrotron peak frequency BL Lacs)) is selected in Fermi 3FGL catalogue. The correlations between two flux densities of the radio 1.4 GHz and γ -ray at 0.1, 0.3, 1, 3, and 10 GeV are investigated for the samples of all blazars, FSRQs, BL Lacs, and subclasses of HBLs and LBLs, respectively. Results show that there are strong positive correlations between the two flux densities, with the correlation coefficients r = 0.48 ∼ 0.81 , and the chance probabilities p all less than 10 − 4 . The correlation coefficient has different trends with the change of γ -ray emission frequency for different blazar samples, and the average correlation coefficients for all the samples at five respective bands decrease with the increase of γ -ray frequency. Therefore, with the increase of γ -ray frequency, the dominant mechanism of γ -ray radiation of blazar is changing, and at the same frequency the dominant mechanism is different for different samples. The γ -ray emission of HBLs may be mainly dominated by the synchrotron self-Compton, while the other mechanisms are responsible for the γ -ray emissions of LBLs. The origin of γ -ray in FSRQs is more complex than that of BL Lacs.

In this paper, the flux densities at the radio (R) 1.4 GHz, optical (O) 4.68 × 10 14 Hz, X-ray (X) 1 keV, and γ -ray ( γ ) 1 GeV are obtained from the available literature for a Fermi blazar sample. The 6 effective spectral indices ( α RO , α RX , α R γ , α OX , α O γ , and α X γ ) between any two of above bands are calculated. The correlations between any two spectral indices are investigated for the whole blazar sample and the subclass samples of FSRQs (Flat Spectral Radio Quasars) and BL Lacs including High synchrotron peak frequency BL Lacs (HBLs) and Low synchrotron peak frequency BL Lacs (LBLs). Results show that: (1) There are close correlations between any two spectral indices for all samples, except for the sample of HBLs and the correlation between α OX and α R γ . This kind of correlations can be explained by the structures of energy spectral distributions at four bands. (2) In the scatter plots of effective spectral index correlations, FSRQs and LBLs are distributed in the same area, but HBLs and FSRQs (LBLs) are distributed in the different areas. (3) The separation degree (discrimination) between the distributions of FSRQs (LBLs) and HBLs differs with the scatter plot of effective spectral index correlations, and the discrimination is related to the frequencies to determine two effective spectral indices.

We investigate the $B^+\to J/\psi \phi K^+$ decay via various rescattering diagrams. Without introducing genuine exotic resonances, it is shown that the $Z_{cs}(4000)$, $Z_{cs}(4220)$ and $X(4700)$ reported by the LHCb collaboration can be simulated by the $J/\psi K^{*+}$, $\psi^\prime K^+$ and $\psi^\prime \phi$ threshold cusps, respectively. These cusps are enhanced by some nearby triangle singularities. The $X(4685)$ with $J^P=1^+$ cannot be well simulated by the threshold effects in our model, which implies that it may be a genuine resonance., Comment: 7 pages, 6 figures, 2 tables

Recently LHCb declared a new structure $X(6900)$ in the final state di-$J/\psi$ which is popularly regarded as a $cc$-$\bar c\bar c$ tetraquark state. %popularly. Within the Bethe-Salpeter (B-S) frame we study the possible $cc$-$\bar c\bar c$ bound states and the interaction between diquark ($cc$) and antidiquark ($\bar c\bar c$). In this work $cc$ ($\bar c\bar c$) is treated as a color anti-triplet (triplet) axial-vector so the quantum numbers of $cc$-$\bar c\bar c$ bound state are $0^+$, $1^+$ and $2^+$. Learning from the interaction in meson case and using the effective coupling we suggest the interaction kernel for diquark and antidiquark system. Then we deduce the B-S equations for different quantum numbers. Solving these equations numerically we find the spectra of some excited states can be close to the mass of $X(6900)$ when we assign appropriate values for parameter $\kappa$ introduced in the interaction (kernel).We also briefly calculate the spectra of $bb$-$\bar b\bar b$ bound states. Future measurement of $bb$-$\bar b\bar b$ state will help us to determine the exact form of effective interaction., Comment: 14 pages, two figures

The LHCb collaboration reported the observation of a narrow peak in the $D^- K^+$ invariant mass distributions from the $B^+\to D^+ D^- K^+$ decay. The peak is parameterized in terms of two resonances $X_0(2900)$ and $X_1(2900)$ with the quark contents $\bar{c}\bar{s}ud$, and their spin-parity quantum numbers are $0^+$ and $1^-$, respectively. We investigate the rescattering processes which may contribute to the $B^+\to D^+ D^- K^+$ decays. It is shown that the $D^{*-}K^{*+}$ rescattering via the $\chi_{c1}K^{*+}D^{*-}$ loop or the $\bar{D}_{1}^{0}K^{0}$ rescattering via the $D_{sJ}^{+}\bar{D}_{1}^{0}K^{0}$ loop simulate the $X_0(2900)$ and $X_1(2900)$ structures. Such phenomena are due to the analytical property of the scattering amplitudes with the triangle singularities located to the vicinity of the physical boundary., Comment: 6 pages, 3 figures

The $P_c(4312)$, $P_c(4440)$, and $P_c(4457)$ observed by the LHCb Collaboration are very likely to be $S$-wave $\Sigma_c\bar{D}^{(*)}$ molecular candidates due to their near-threshold character. In this work, we study the hidden-charm decay modes of these $P_c$ states, $P_c\to J/\psi p(\eta_cp)$, using a quark interchange model. The decay mechanism for the $P_c\to J/\psi p(\eta_cp)$ processes arises from the quark-quark interactions, where all parameters are determined by the mass spectra of mesons. We present our results in two scenarios. In scenario I, we perform the dynamical calculations and treat the $P_c$ states as pure $\Sigma_c \bar D^{(*)}$ molecules. In scenario II, after considering the coupled channel effect between different flavor configurations $\Sigma^{(*)}_c\bar D^{(*)}$, we calculate these partial decay widths again. The decay patterns in these two scenarios can help us to explore the molecular assignment and the inner flavor configurations for the $P_c$ states. In particular, the decay widths of $\Gamma(P_c(4312)\to\eta_cp)$ are comparable to the $J/\psi p$ decay widths in both of these two scenarios. Future experiments like LHCb may confirm the existence of the $P_c(4312)$ in the $\eta_cp$ channel., Comment: 13 pages, 7 figures, version published in PRD

A resonance-like structure as narrow as 10 MeV is observed in the K−p invariant mass distributions in Λc+→pK−π+. This precise measurement is based on a data sample of about 1.5 million events, and the bin width of K−p invariant mass is only 1 MeV. The narrow peak precisely lies on the Λη threshold, because of which it is natural to identify it as a threshold cusp. Being different from the common two-body unitary cusp, we find that the narrowness of this cusp can be induced by a nearby triangle singularity of the Λa0(980) or ηΣ(1660) rescattering process.

In this work we study the weak decays of $$\Xi _{cc}\rightarrow \Xi _c$$Ξcc→Ξc and $$\Xi _{cc}\rightarrow \Xi '_c$$Ξcc→Ξc′ in the light-front quark model. Generally, a naive, but reasonable conjecture suggests that the cc subsystem in $$\Xi _{cc}$$Ξcc ( us pair in $$\Xi ^{(')}_c$$Ξc(′)) stands as a diquark with definite spin and color assignments. During the concerned processes, the diquark of the initial state is not a spectator, namely must be broken. A Racah transformation would decompose the original (cc)q into a combination of c(cq) components. Thus we may deal with the decaying c quark alone while keeping the (cq) subsystem as a spectator. With the re-arrangement of the inner structure we calculate the form factors numerically and then obtain the rates of semi-leptonic decays and non-leptonic decays, which will be measured in the future.

$P_c(4312)$ observed by the LHCb collaboration is confirmed as a pentaquark and its structure, production, and decay behaviors attract great attention from theorists and experimentalists. Since its mass is very close to sum of $\Sigma_c$ and $\bar D$ masses, it is naturally tempted to be considered as a molecular state composed of $\Sigma_c$ and $\bar D$. Moreover, $P_c(4312)$ is observed in the channel with $J/\psi p$ final state, requiring that isospin conservation $P_c(4312)$ is an isospin-1/2 eigenstate. In literature, several groups used various models to estimate its spectrum. We systematically study the pentaquarks within the framework of the Bethe-Salpeter equation; thus $P_c(4312)$ is an excellent target because of the available data. We calculate the spectrum of $P_c(4312)$ in terms of the Bethe-Salpter equations and further study its decay modes. Some predictions on other possible pentaquark states that can be tested in future experiments are made.

We study the $P_{cs}(4459)^0$ recently observed by LHCb using the method of QCD sum rules. Our results support its interpretation as the $\bar D^* \Xi_c$ hadronic molecular state of either $J^P=1/2^-$ or $3/2^-$. Within the hadronic molecular picture, the three LHCb experiments observing $P_c$ and $P_{cs}$ states \cite{lhcb,Aaij:2015tga,Aaij:2019vzc} can be well understood as a whole. This strongly supports the existence of hadronic molecules, whose studies can significantly improve our understanding on the construction of the subatomic world. To verify this picture, we propose to further investigate the $P_{cs}(4459)^0$ to examine whether it can be separated into two states, and to search for the $\bar D \Xi_c$ molecular state of $J^P=1/2^-$., Comment: 8 pages, 3 figure, 1 table, revised version to be published in EPJC

Without contamination from the final state interactions, the calculation of the branching ratios of semileptonic decays \begin{document}$ \Xi^{(')}_{c}\to\Xi+e^+\nu_e $\end{document} may provide further information about the inner structure of charmed baryons. Moreover, by studying such processes, one can better determine the form factors of \begin{document}$ \Xi_c\to\Xi $\end{document} that can be further applied to relevant estimates. In this study, we used the light-front quark model to carry out computations where the three-body vertex functions for \begin{document}$ \Xi_c $\end{document} and \begin{document}$ \Xi $\end{document} are employed. To fit the new data of the Belle II, we re-adjusted the model parameters to obtain \begin{document}$ \beta_{s[sq]} = 1.07 $\end{document} GeV, which is 2.9 times larger than \begin{document}$ \beta_{s\bar s} = 0.366 $\end{document} GeV. This value may imply that the \begin{document}$ ss $\end{document} pair in \begin{document}$ \Xi $\end{document} constitutes a more compact subsystem. Furthermore, we investigated the non-leptonic decays of \begin{document}$ \Xi^{(')}_c\to \Xi $\end{document} , which will be experimentally measured soon. Thus, our model will be tested in terms of consistency with the new data.

A resonance-like structure as narrow as 10 MeV is observed in the ${K}^{\ensuremath{-}}p$ invariant mass distributions in ${\mathrm{\ensuremath{\Lambda}}}_{c}^{+}\ensuremath{\rightarrow}p{K}^{\ensuremath{-}}{\ensuremath{\pi}}^{+}$ 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 ${K}^{\ensuremath{-}}p$ invariant mass spectrum, the narrow peak is found precisely lying at the $\mathrm{\ensuremath{\Lambda}}\ensuremath{\eta}$ 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 $\mathrm{\ensuremath{\Lambda}}\text{\ensuremath{-}}{a}_{0}(980{)}^{+}$ or $\ensuremath{\eta}\text{\ensuremath{-}}\mathrm{\ensuremath{\Sigma}}(1660{)}^{+}$ rescatterings.

Within a picture of the $f_1(1285)$ being a dynamically generated resonance from the $ K^*\bar K$ interactions, we estimate the rates for the radiative transitions of the $f_1(1285)$ meson to the vector mesons $\rho^0$,$\omega$ and $\phi$. These radiative decays proceed via the kaon loop diagrams. The calculated results are in fair agreement with the experimental measurements. Some predictions can be tested by experiments and their implementation and comparison with these predictions will be valuable to decode the nature of the $f_1(1285)$ state., Comment: 5 pages, 3 figures

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 $\Lambda_b\to J/\psi K^- p$. 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 $\Sigma_c^{(*)}$ can be produced at leading order in $\Lambda_b$ 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., Comment: 9 pages, 6 figures, 4 tables; published version in PLB

Recently, a vector charmonium-like state was observed in the portal of . This intrigues an active discussion on the structure of the resonance because it has obvious significance for gaining a better understanding on its hadronic structure that contains suitable inner constituents. Therefore, this observation concerns the general theoretical framework about possible structures of exotic states. Since the mass of is slightly above the production threshold of whereas it is below that of with the same quark contents as that of , it is natural to conjecture that is a molecular state of , as suggested in the literature. Confirming or negating this allegation would shed light on the goal we are concerned with. We calculate the mass spectrum of a system composed of a vector meson and an axial vector i.e., within the framework of the Bethe-Salpeter equations. Our numerical results show that the dimensionless parameter in the form factor, which is phenomenologically introduced to every vertex, is far beyond the reasonable range for inducing even a very small binding energy . It implies that the system cannot exist in the nature as a hadronic molecule in this model. Therefore, we may not be able to assume the resonance to be a bound state of and instead, it could be attributed to something else, such as a tetraquark.

The spectrum of hadrons is the manifestation of color confinement of quantum chromodynamics. Hadronic resonances correspond to poles of the S-matrix. Since 2003, lots of new hadron resonant structures were discovered in the mass regions from light mesons to hadrons containing a pair of a heavy quark and an antiquark. Many of them are candidates of exotic hadrons, and they are usually observed as peaks in invariant mass distributions. However, the S-matrix also has kinematical singularities due to the on-shellness of intermediate particles for a process, such as two-body thresholds and triangle singularities, and they can produce peaks as well. On the one hand, such singularities may be misidentified as resonances; on the other hand, they can be used as tools for precision measurements. In this paper, we review the threshold cusps and various triangle singularities in hadronic reactions, paying attention to their manifestations in phenomena related to exotic hadron candidates., Comment: Version accepted for publication in Prog. Part. Nucl. Phys.; 84 pages, 34 figures

We study the phase structure of QCD matter in the framework of a multiphase transport model by implementing a strong local parton density fluctuation scenario. Our calculations on the beam energy dependence of net-proton high moment show that local parton density fluctuation only has a small effect. But it becomes important when all baryons are included. We then study the effect on elliptic flow and find that an enhanced local parton density fluctuation leads to a significant effect on protons but a small effect on pions. Our study provides a reference of transport dynamics on QCD phase transition phenomena and will be relevant for the upcoming phase II of the beam energy scan program at RHIC.

The discovery of $\Xi_{cc}^{++}$ 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 $J^P=1/2^-$ $\Omega_{cc}^P$, which very likely decay into $\Omega_{cc}\pi^0$ breaking isospin symmetry. In the isospin-1/2 $\Xi_{cc}^P$ 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 $\Xi_{cc}^{P}$ states in the $\Xi_{cc}^{++}\pi^-$ mode. Searching for them and their analogues are helpful to establish the hadron spectrum., Comment: 6 pages, 3 figures; accepted for publication as a Rapid Communication in Physical Review D

The Ω and ϕ production in relativistic heavy-ion collisions is studied in a dynamical quark coalescence model using the phase space information of strange quarks from a multiphase transport (AMPT) model. Enhanced local parton density fluctuation is implemented in the AMPT to simulate the QCD phase transition dynamics. By studying the transverse momentum $$p_{\rm T}$$ spectra and the elliptic flow of the multi-strangeness particles, such as Ω and ϕ, and the $$\Omega /\phi $$ ratio as a function of $$p_{\rm T}$$ in the AMPT, we find that the new development improves the description of experimental data. The study motivates further experimental investigations of Ω and ϕ production in phase II of the Beam Energy Scan program at RHIC.

A prototype thick-GEM-based cooling storage ring external-target experiment (CEE) time projection chamber (TPC) is constructed and tested with the pulsed ultraviolet laser beams. The results indicate that the prototype TPC has a good performance in three-dimensional track resolution. In X direction the position resolution is about 0.2 mm, and in Y direction the position resolution is about 0.5 mm. The results also determine that the energy resolution is about 5.4%, which achieve the requirements of the CEE experiment and can be used to study the nuclear state equation and the quantum chromo dynamics.

Employing the relativized quark model and the quark-interchange model, we investigate the decay of the charged heavy quarkonium-like states $Z_c(3900)$, $Z_c(4020)$, $Z_c(4430)$, $Z_b(10610)$ and $Z_b(10650)$ into the ground and radially excited heavy quarkonia via emitting a pion meson. The $Z_c$ and $Z_b$ states are assumed to be hadronic molecules composed of open-flavor heavy mesons. The calculated decay ratios can be compared with the experimental data, which are useful in judging whether the molecule state assignment for the corresponding $Z_c$ or $Z_b$ state is reasonable or not. The theoretical framework constructed in this work will be helpful in revealing the underlying structures of some exotic hadrons., Comment: 19 pages, 4 figures, version published in EPJC

We investigate the process $$B_c^+\rightarrow B_s^0\pi ^+\pi ^0$$ 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 X(5777), is predicted to be present in the invariant mass distribution of $$B_s^0 \pi ^+$$ . Because the relative weak $$B\bar{K}$$ $$(I=1)$$ interaction does not support the existence of a dynamically generated hadronic molecule, 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.

This study focuses on the bistatic high range resolution profiles (HRRPs) of precessing targets and considers how to utilise bistatic HRRPs for feature extraction. The movement model of the slippery bistatic scattering centres of precessing targets and the wideband bistatic echo model are introduced firstly. The dynamic simulation method of the bistatic HRRPs of the precessing target is presented using the bistatic scattering coefficients obtained via electromagnetic calculations, and the simulation results validate the theoretical analysis. Furthermore, the characteristics of the bistatic HRRP are analysed and show that the bistatic HRRP generally reflects the projection of the target onto the bisector of the bistatic angle, except that the bistatic angle is so wide that the bistatic HRRP is quite different from the monostatic HRRP. This research is helpful for imaging, and identifying precessing targets in the bistatic radar.

The bistatic scattering centres are commonly modeled as the fixed scattering centres for imaging; however, the location of the bistatic scattering centre changes with the bistatic geometry in some real scenes. This paper focuses on the bistatic scattering centres of cone-shaped targets and considers how to utilize the length of the bistatic high-resolution range profile (HRRP) for target identification. Firstly, the locations of the bistatic scattering centres on the edge of a cone-shaped target are deduced with the method of equivalent currents, which are the intersection points of the edge and the plane constructed by the symmetry axis and the bisector of the bistatic angle. Then, based on the above conclusion, the wideband echo model and bistatic HRRP of a cone-shaped target is deduced. Then, the relation between the length of the bistatic HRRP and target length is deduced, which is useful for target identification. Finally, the bistatic HRRPs of cone-shaped targets are calculated via the Feko software and the calculated results validate the theoretical analysis. This research provides an exact mathematics model for the echo simulation, imaging, feature extraction and identification of cone-shaped targets in the bistatic radar.

We investigate the invariant mass distributions of $$B_s\pi $$ via different rescattering processes. The triangle singularity which appears in the rescattering amplitude may simulate the resonance-like bump around 5568 MeV. However, because the scattering $$B_s^*\pi \rightarrow B_s\pi $$ is supposed to be weak, if the pertinent background is much larger, it would be hard to ascribe the observation of X(5568) to rescattering effects.

We investigate the processes ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\ensuremath{\gamma}J/\ensuremath{\psi}\ensuremath{\phi}$, $\ensuremath{\gamma}J/\ensuremath{\psi}\ensuremath{\omega}$, and ${\ensuremath{\pi}}^{0}J/\ensuremath{\psi}\ensuremath{\eta}$ to search for the charmoniumlike states with hidden $s\overline{s}$, such as $Y(4140)$, $Y(4274)$, $X(4350)$, and $X(3915)$. These processes receive contributions from the charmed-strange meson rescatterings. When the center-of-mass energies of ${e}^{+}{e}^{\ensuremath{-}}$ 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 nonresonance explanation about the resonancelike 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.

We discuss that the kinematic effects from the anomalous triangle singularity (ATS) can contribute to the enhancements of the newly observed heavy pentaquark candidates Pc+(4380) and Pc+(4450) in Λb → J/ψK− p. This may bring ambiguities on our understanding of the nature of these two enhancements. In order to distinguish the cases that the threshold enhancements are either produced by genuine states or by the nearby anomalous thresholds of the ATS, we propose to look for the pentaquark candidates in J/ψ photoproduction where the ATS cannot play a role. We show that if Pc+(4380) and Pc+(4450) are genuine states, their production via the s-channel process can be directly measured in the angular distribution at large scattering angles. It benefits from the feature that in the vector meson photoproduction the s-channel resonance excitations can be easily separated from the background t-channel diffractive process.

We investigate the reaction $\pi^- p \to \pi^- J/\psi p$ 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 $J/\psi p$ 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., Comment: 15 pages, 3 figures, 4 tables

We investigate the possible rescattering effects which may contribute to the process $B^+\to J/\psi\phi K^+$. It is shown that the $D_{s}^{*+}D_{s}^-$ rescattering via the open-charmed meson loops, and $\psi^\prime \phi$ rescattering via the $\psi^\prime K_1$ 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 $\chi_{c1}(3P)$., Comment: 14 pages, 5 figures, 1 table

We re-investigate the exclusive decays of eta(c) and eta'(c) to a pair of light vector mesons, i.e. eta(c)(eta'(c)) -> V V. The long-distance intermediate meson loop (IML) effects are evaluated as a non-perturbative mechanism in addition to the short-distance c (c) over bar. annihilation contributions. We show that both processes can be reasonably well constrained with the help of the available experimental data. Since eta(c) and eta'(c) are the spin-0 partners of J/psi and psi', respectively, our study is useful for gaining insights into the pQCD helicity selection rule violations in charmonium decays and the long-standing "rho pi puzzle". (c) 2012 Elsevier B.V. All rights reserved.

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., Comment: 13 pages, 5 figures, 1 table, version to appear in Phys. Lett. B

We propose to search for a tetraquark candidate [Formula: see text] in [Formula: see text] or ΛΛKK*. The existence of tetraquark state [Formula: see text] was predicted in the literature due to specific diquark effective degrees of freedom inside hadrons. In order to understand the underlying dynamics for exotic hadrons, a search for the tetraquark [Formula: see text] is strongly recommended. We make an estimate of the production rate of [Formula: see text] in an effective lagrangian theory. The proposed reaction involves two Λ production, of which the narrow widths make it a great advantage in the analysis of the final state missing mass spectrum.

We report a study of the process e(+)e(-) -> (D*(D) over bar*)(0)pi(0) using e(+)e(-) collision data samples with integrated luminosities of 1092 pb(-1) at root s = 4.23 GeV and 826 pb(-1) at root s = 4.26 GeV collected with the BESIII detector at the BEPCII storage ring. We observe a new neutral structure near the (D*(D) over bar*)(0) mass threshold in the pi(0) recoil mass spectrum, which we denote as Z(c)(4025)(0). Assuming a Breit-Wigner line shape, its pole mass and pole width are determined to be (4025.5(-4.7)(+2.0) +/- 3.1) MeV/c(2) and (23.0 +/- 6.0 +/- 1.0) MeV, respectively. The Born cross sections of e(+)e(-) -> Z(c)(4025)(0)pi(0) -> (D*(D) over bar*)(0)pi(0) are measured to be (61.6 +/- 8.2 +/- 9.0) pb at root s = 4.23 GeV and (43.4 +/- 8.0 +/- 5.4) pb at root s = 4.26 GeV. The first uncertainties are statistical and the second are systematic.

Using a data sample collected with the BESIII detector operating at the BEPCII storage ring, we observe a new neutral state Z(c)(3900)(0) with a significance of 10.4 sigma. The mass and width are measured to be 3894.8 +/- 2.3 +/- 3.2 MeV/c(2) and 29.6 +/- 8.2 +/- 8.2 MeV, respectively, where the first error is statistical and the second systematic. The Born cross section for e(+)e(-) -> pi(0)pi(0) J/Psi and the fraction of it attributable to pi(0)Z(c)(3900)(0) -> pi(0)pi(0) J/Psi in the range E-c.m. = 4.19-4.42 GeV are also determined. We interpret this state as the neutral partner of the four-quark candidate Z(c)(3900)(+/-).

The decay ${Z}_{c}(3900{)}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}\ensuremath{\omega}{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}$ is searched for using data samples collected with the BESIII detector operating at the BEPCII storage ring at center-of-mass energies $\sqrt{s}=4.23$ and 4.26 GeV. No significant signal for the ${Z}_{c}(3900{)}^{\ifmmode\pm\else\textpm\fi{}}$ is found, and upper limits at the 90% confidence level on the Born cross section for the process ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{Z}_{c}(3900{)}^{\ifmmode\pm\else\textpm\fi{}}{\ensuremath{\pi}}^{\ensuremath{\mp}}\ensuremath{\rightarrow}\ensuremath{\omega}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ are determined to be 0.26 and 0.18 pb at $\sqrt{s}=4.23$ and 4.26 GeV, respectively.

We report an observation of the process J/psi -> gamma X(1835) -> gamma(KSKS0)-K-0 eta at low (KSKS0)-K-0 mass with a statistical significance larger than 12.9s using a data sample of 1.31 x 109 J/psi events collected with the BESIII detector. In this region of phase space the (KSKS0)-K-0 system is dominantly produced through the f (0)(980). By performing a partial wave analysis, we determine the spin parity of the Xd1835_ to be J(PC) = 0(-+). The mass and width of the observed X(1835) are 1844 +/- 9(stat)(-25)(+16)(syst) MeV/c(2) and 192(-17)(+20)(sta)(-43)(+62)(syst) MeV, respectively, which are consistent with the results obtained by BESIII in the channel J/psi -> gamma pi(+)pi(-)eta'.

We propose to study the pentaquark candidates of P-c(+) (4380) and P-c(+) (4450) in J/psi 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/psi photoproduction would conclude that they should be genuine states and provide further evidence for their existence.

Based on a sample of 1.31×109 J/ψ events collected with the BESIII detector at the BEPCII collider, Dalitz plot analyses of selected 79,625 η→π+π-π0 events, 33,908 η→π0π0π0 events, and 1,888 η′→π0π0π0 events are performed. The measured matrix elements of η→π+π-π0 are in reasonable agreement with previous measurements. The Dalitz plot slope parameters of η→π0π0π0 and η′→π0π0π0 are determined to be -0.055±0.014±0.004 and -0.640±0.046±0.047, respectively, where the first uncertainties are statistical and the second systematic. Both values are consistent with previous measurements, while the precision of the latter one is improved by a factor of 3. Final state interactions are found to have an important role in those decays.

Using a sample of 1.31 x 10(9) J/psi events collected with the BESIII detector at the BEPCII collider, the decays J/psi -> phi pi(+)pi(-)pi(0) and J/psi -> phi pi(0)pi(0)pi(0) are investigated. The isospin- violating decay J/psi -> phi pi(0)f(0)(980) with f(0)(980)-> pi pi is observed for the first time. The width of the f(0)(980) obtained from the dipion mass spectrum is found to be much smaller than the world average value. In the pi(0)f(0)(980) mass spectrum, there is evidence of f(1)(1285) production. By studying the decay J/psi ->eta', the branching fractions of eta' -> pi(+)pi(-)pi(0) and eta' -> pi(0)pi(0)pi(0), as well as their ratio, are also measured.