Search

In this work, we investigate the resonance production in $\Lambda^+_c \to \gamma \pi^+ \Lambda$ decay through the triangle singularity (TS) mechanism, within an effective Lagrangian approach. We find that the appropriate loop decay process could develop a triangle singularity in the invariant mass $M_{\pi\Lambda}$ around $1.35$ GeV, with the shape depending on the quantum numbers of $\Sigma^*$ states that couple to the final $\pi\Lambda$ system. Especially, the $\Sigma(1380)1/2^-$ state newly predicted in the pentaquark model, if exists, significantly enhances the TS contribution and sharpens the TS peak due to the $S$-wave $\Sigma^*\pi\Sigma$ vertex in the loop. Therefore, the existence of the $\Sigma(1380)1/2^-$ state can be examined by measuring the TS signal in $\Lambda^+_c \to \gamma \pi^+ \Lambda$. Considering also possible tree-level diagrams, we additionally obtain the branching ratio ${\rm Br}(\Lambda^+_c \to \gamma \pi^+ \Lambda)\simeq 1.5\times 10^{-5}$. We suggest the investigation of this reaction by future BESIII, LHCb, and Belle experiments., Comment: 8 pages, 6 figures

In this work, we study the role of triangle singularity in the $J/\psi \to \gamma \bar{p} \Delta$ decay. We find that through a triangle mechanism, involving a triangle loop composed by $\omega$, $\pi$ and $p$, this decay may develop a triangle singularity and produce a visible peak in the invariant mass $M_{\gamma\Delta}$ around 1.73 GeV with a width of 0.02 GeV. Such a triangle mechanism may also cause significant spin effects on the final $\Delta$, which can be detected by measuring its spin density matrix elements. Our calculations show that the branching ratios due to the triangle mechanism is Br($J/\psi\to \gamma \bar p\Delta,\Delta\to \pi p$)=$1.058\times 10^{-6}$. Hopefully, this reaction can be investigated at BESIII and future experiments, e.g. Super Tau-Charm Facility, and the narrow width of the induced structure, the moving TS position and the distinct features of the spin density matrix elements of the $\Delta$ may serve as signals for the triangle singularity mechanism., Comment: 7 pages, 5 figures

In this work, we study the spin density matrix element $\rho_{00}$ of the $\phi$ in the decay $J/\psi \rightarrow \eta \pi \phi$. In previous studies, a band around 1.4 GeV on the $\pi^0\phi$ distribution in Dalitz plot was reported by the BESIII Collaboration. This structure may be caused by the production of a resonance or the triangle singularity mechanism. We find that the predictions of the spin density matrix elements of the final $\phi$ based on these mechanisms show distinct features. Thus the measurement of the spin density matrix elements of the $\phi$ in this reaction may offer an alternative way to study the triangle singularity and to clarify the reaction mechanisms, i.e. resonance production or kinematic effects. This work also shows the potential of spin observables in studying kinematic singularities., Comment: 7 pages and 5 figures. Replaced with the published version. Added more calculations and discussions

Generation of arbitrarily spin polarized muon pairs is investigated via polarized $e^-e^+$ collision. We calculate the fully spin-resolved cross section ${\rm d}\sigma_{e^-e^+\rightarrow \mu^-\mu^+}$ and utilize the Monte Carlo method of binary collision to describe the production and polarization processes of muon pairs. We find that, due to the dependence of mixed helicities on the scattering angle, arbitrarily polarized muon pairs with both of the longitudinal and transverse spin components can be produced. The collision of tightly collimated electron and positron beams with highly longitudinal polarization and nC charge can generate about $40\%$ muon pairs with longitudinal polarization and about $60\%$ muon pairs with transverse polarization. The compact high-flux $e^-e^+\rightarrow\mu^-\mu^+$ muon source could be implemented through the next-generation laser-plasma linear collider, and would be essential to facilitate the investigation of fundamental physics and the measurement technology in broad areas.

Laser-driven brilliant controllable polarized $\gamma$-photon sources open the way for designing compact $\gamma\gamma$ collider, which enable the large yield of linear Breit-Wheeler (LBW) pairs in a single shot and thus provide an opportunity for the investigation of polarized LBW process. In this work we investigate the polarization characteristics of LBW pair production via our developed spin-resolved binary collision simulation method. Polarization of $\gamma$-photons modifies the kinematics of scattering particles and induces the correlated energy-angle shift of LBW pairs, and the latter's polarization characteristic depends on the helicity configures of scattering particles. Our method confirms that the polarized $\gamma\gamma$ collider with an asymmetric setup can be performed with currently achievable laser facilities to produce abundant polarized LBW pairs, fulfilling the detection power of polarimetries. The precise knowledge of polarized LBW process is in favor of the calibration and monitor of polarized $\gamma\gamma$ collider, and could enhance the opacity of $\gamma$-photons in high-energy astrophysical objects to exacerbate the inconsistency between some observations and standard models.

In this paper, we study the polarization of the $\Lambda(1405)$ in the $\gamma p \rightarrow K^+ \pi \Sigma$ reaction within an effective Lagrangian approach and isobar model. In our model, the $\Lambda(1405)$ is excited through the t-channel $K/K^*$ exchanges and u-channel hyperon exchange. Compared to previous studies, we also include the contribution from a contact term, which is necessary for our model to interpret the polarization of the $\Lambda(1405)$. In addition, we also discuss the possibility to verify the proposed two-pole structure of the $\Lambda(1405)$ using the polarization data. We find that the polarization of the $\Lambda(1405)$ or the polarization of the final $\Sigma$ in this reaction is sensitive to the invariant mass $M_{\pi\Sigma}$. Thus the measurement of the dependence of the $\Lambda(1405)$ polarization on the $M_{\pi\Sigma}$ can offer valuable information about the pole structure of the $\Lambda(1405)$., Comment: 8 pages, 7 figures. Version accepted by PLB

In this work, we make a theoretical study on the $p \bar p \rightarrow \Lambda \bar\Lambda \eta$ reaction for antiproton beam energy from threshold to 4GeV within an effective Lagrangian approach and isobar model. By assuming this reaction is dominated by the excitation of $\Lambda$ and $\bar \Lambda$ resonances in intermediate states, we calculate the total cross sections and give the predictions of the angular distribution and invariant mass spectrum of final particles. In particular, we discuss the possibility to verify the existence of a narrow $\Lambda$ resonance found in the process of $K^- p\to \eta \Lambda$ in the present reaction. It shows that the $p \bar p \rightarrow \bar \Lambda \Lambda \eta$ reaction can provide us with valuable information about the $\Lambda$ resonances having significant couplings to $\bar K N$ and $\Lambda\eta$ channels. Thus the experimental data of this reaction will be a good supplement to the $\bar K N\to\eta \Lambda$ scattering data for studying $\Lambda$ resonances., Comment: 8 pages, 5 figures

In this work, we perform a study of nucleon resonance production in the $\gamma p \to p\eta\phi$ reaction within an effective Lagrangian approach. In our model, we consider the excitation of the $N^*(1535)$, $N^*(1650)$, $N^*(1710)$ and $N^*(1720)$ in the intermediate state and the background term. We find that this reaction is dominated by the excitation of the $N^*(1535)$ in the near threshold region. Especially, we study the possible role of the scalar meson exchange in this reaction. It is found that the $f_0(980)$ exchange may give a significant contribution and the parity asymmetry can be used to identify its role in this reaction., Comment: 6 pages, 4 figures, Accepted for publication in Phys. Rev. C

The associate $K\Lambda(1520)$ photon and hadronic production in the $\gamma p \to K^+\Lambda(1520)$, $p p \to p K^+ \Lambda(1520)$ and $\pi^- p \to K^0 \Lambda(1520)$ reactions are investigated within the effective Lagrangian approach and the isobar model. We are interested in the contribution from the $N^*(2120)$ (previously called $N^*(2080)$) resonance, which has a significant coupling to the $K\Lambda(1520)$ channel. The theoretical results show that the current experimental data for the $\gamma p \to K^+\Lambda(1520)$ reaction favor the existence of the $N^*(2120)$ resonance, and that these measurements can be used to further constrain its properties. We present results, including the $N^*(2120)$ contribution, for total cross sections of the $\gamma p \to K^+\Lambda(1520)$, $\pi^- p \to K^0 \Lambda(1520)$, and $p p \to p K^+ \Lambda(1520)$ reactions. For this latter one, we also calculate invariant mass and Dalitz plot distributions., Comment: Talk given at the workshop on Hadron Nuclear Physics, Zhangjiajie, China, July 18 to 22, 2013

The value of the $\Lambda(1405){\bar K}N$ coupling constant $g_{\Lambda(1405)\bar{K}N}$ is obtained by fitting it to the experimental data on the total cross sections of the $K^-p \to \pi^0\Sigma^0$ reaction. On the basis of an effective Lagrangian approach and isobar model, we show that the value $|g_{\Lambda(1405)\bar{K}N}| = 1.51 \pm 0.10$ could be extracted from the available experimental data by assuming that the $s-$channel $\Lambda(1405)$ resonance plays a dominant role, whereas, the background contributions from the $s-$channel $\Lambda(1115)$, $t-$channel $K^*$ and $u-$channel nucleon pole processes are small and can be neglected. However, the $u-$channel nucleon pole diagram may also give an important contribution in the present calculations. After the background contributions are taken into account, the above value of $g_{\Lambda(1405)\bar{K}N}$ is reduced to $|g_{\Lambda(1405)\bar{K}N}| = 0.77 \pm 0.07$, which is not supported by the previous calculations and the recent CLAS measurements. The theoretical calculations on differential cross sections are also presented, which can be checked by future experiments., Comment: To be published on Phys. Rev. C

In this work, we discuss the possibility of studying nucleon resonances in the $K^+N$ interactions. Based on our model calculations, it is found that the hyperon exchange plays an important role for the excitation of nucleon resonances in the $K^+N$ interactions. Therefore, the studies on nucleon resonance production in the $K^+N$ interactions can offer us valuable information about the couplings of nucleon resonances with strange particles. By selecting suitable decay channels of nucleon resonances, some reactions are also suitable to look for missing resonances., Comment: Talk presented at XI International Conference on Hypernuclear and Strange Particle Physics (HYP2012), Oct.1-5, 2012, Barcelona (Spain)

We investigate the $\Lambda(1520)$ hadronic production in the $p p \to p K^+ \Lambda(1520)$ and $\pi^- p \to K^0 \Lambda(1520)$ reactions within the effective Lagrangian method. For $\pi^- p \to K^0 \Lambda(1520)$ reaction, in addition to the "background" contributions from $t-$channel $K^*$ exchange, $u-$channel $\Sigma^+$ exchange, and $s-$channel nucleon pole terms, we also consider the contribution from the nucleon resonance $N^*(2080)$ (spin-parity $J^P = 3/2^-$), which has significant coupling to $K\Lambda(1520)$ channel. We show that the inclusion of the nucleon resonance $N^*(2080)$ leads to a fairly good description of the low energy experimental total cross section data of $\pi^- p \to K^0 \Lambda(1520)$ reaction. From fitting to the experimental data, we get the $N^*(2080)N\pi$ coupling constant $g_{N^*(2080)N \pi} = 0.14 \pm 0.04$. By using this value and with the assumption that the excitation of $N^*(2080)$ is due to the $\pi^0$-meson exchanges, we calculate the total and differential cross sections of $p p \to p K^+ \Lambda(1520)$ reaction. We also demonstrate that the invariant mass distribution and the Dalitz Plot provide direct information of the $\Lambda(1520)$ production, which can be tested by future experiments., Comment: 9 pages, 7 figures

Within an effective Lagrangian approach, we investigate the reaction mechanism of $K^- p\to \eta\Lambda$ near threshold. It is found that a new $D_{03}$ resonance, with mass $M=1668.5\pm 0.5$MeV and width $\Gamma=1.5\pm0.5$MeV, is needed to interpret the experimental data reported by the Crystal Ball collaboration. To verify our results, remeasurements on the differential cross sections and $\Lambda$ polarization in this reaction will be helpful. Furthermore, we also show that the reaction $p\bar p\to \Lambda\bar \Lambda \eta$ is a good place to look for this new resonance if it exists., Comment: Presented at the 20th International IUPAP Conference on Few-Body Problems in Physics, 20 - 25 August, 2012, Fukuoka, Japan

Recently, we reported a theoretical study on the $K^- p \to \eta \Lambda$ reaction near threshold by using an effective Lagrangian approach. It was found that the description of angular distribution data measured by the Crystal Ball Collaboration needs a $D_{03}$ resonance with mass $M=1668.5\pm 0.5$ MeV and total decay width $\Gamma=1.5\pm 0.5$ MeV, which is not the conventional $\Lambda$(1690) or other $\Lambda$ state listed in the Particle Data Group book. In the present work, we study the $\Lambda$ polarization in the $K^- p \to \eta \Lambda$ reaction within the same framework. The results show that the existence of this narrow $D_{03}$ state is also compatible with current $\Lambda$ polarization data and that the more accurate $\Lambda$ polarization data at $P_{K^-}=735$MeV can offer further evidence for the existence of this resonance. Furthermore, the role of the $\Lambda(1690)$ resonance in this reaction is also discussed., Comment: 7 pages, 7 figures

By using resonance model, we investigate $K^+ N \rightarrow K N \eta$ reactions with the assumption that these reactions are dominated by the excitation of $N^*(1535)$ near threshold. It is found that the hyperon and $\rho$ exchange diagrams give the most important contributions to these reactions. Thus these reactions may be a good place to study the coupling of $N^*(1535)$ with $K\Lambda$, $K\Sigma$ and $N\rho$ channels. We demonstrate that the angular distributions of final particles provide useful information about the different mechanisms of the $N^*(1535)$ excitations, which could be useful for future experimental analysis on these reactions., Comment: 10 pages, 4 figures

We report on a theoretical study of the $K^- p \to \eta \Lambda$ reaction near threshold by using an effective Lagrangian approach. The role of $s-$channel $\Lambda(1670)$, $t-$channel $K^*$ and $u-$channel proton pole diagrams are considered. We show that the total cross sections data are well reproduced. However, only including the $s-$wave $\Lambda(1670)$ state and the background contribution from $t-$ and $u-$channel are not enough to describe the bowl structures in the angular distribution of $K^- p \to \eta \Lambda$ reaction, which indicates that there should be higher partial waves contributing to this reaction in some energy region. Indeed, if we considered the contributions from a $D_{03}$ resonance, we can describe the bowl structures, however, a rather small width ($\sim 2$ MeV) of this resonance is needed., Comment: Published version