Higlights
  • New insights on low energy πN scattering amplitudes: comprehensive analyses at ${{{\cal{O}}\left(p^3\right)}}$ level
    A production representation of partial-wave S matrix is utilized to construct low-energy elastic pion-nucleon scattering amplitudes from cuts and poles on complex Riemann sheets. Among them, the contribution of left-hand cuts is estimated using the ${\cal{O}}\left( {{p^3}} \right)$ results obtained in covariant baryon chiral perturbation theory within the extended-on-nass-shell scheme. By fitting to data on partial-wave phase shifts, it is indicated that the existences of hidden poles in S11 and P11 channels, as conjectured in our previous paper [Eur. Phys. J. C, 78(7): 543 (2018)], are firmly established. Specifically, the pole mass of the S11 hidden resonance is determined to be (895±81)−(164±23)i MeV, whereas, the virtual pole in the P11 channel locates at (966±18) MeV. It is found that analyses at the ${\cal{O}}\left( {{p^3}} \right)$ level improves significantly the fit quality, comparing with the previous ${\cal{O}}\left( {{p^2}} \right)$ one. Quantitative studies with cautious physical discussions are also conducted for the other S- and P-wave channels.
  • Study of the $ {{a_1}}$(1260) resonance in the $ {{\gamma p \to \pi^+\pi^+\pi^- n}} $ reaction
    Within an effective Lagrangian approach and resonance model, we study the $ \gamma p \to a_1(1260)^+ n $ and $ \gamma p \to \pi^+\pi^+\pi^- n $ reactions via the $ \pi $-exchange mechanism. For the $ \gamma p \to \pi^+\pi^+\pi^- n $ reaction, we perform a calculation of the differential and total cross-sections by considering the contributions of the $ a_1(1260) $ intermediate resonance decaying into $ \rho \pi $ and then into $ \pi^+\pi^+\pi^- $. Besides, the non-resonance process is also considered. With a lower mass of $ a_1(1260) $, the experimental data for the invariant $ \pi^+\pi^+\pi^- $ mass distributions can be fairly well reproduced. For the $ \gamma p \to a_1(1260)^+ n $ reaction, with the model parameters, the total cross-section is of the order of 10 μb at the photon beam energy $ E_{\gamma} $~2.5 GeV. It is expected that the model calculations in this work could be tested by future experiments.
  • Structure, formation, and decay of ${{\bar{K}NN}}$ system by Faddeev-AGS calculations
    The Faddeev AGS equations for the coupled-channels $\bar{K}NN-\pi\Sigma{N}$ system with quantum numbers I = 1/2 and S = 0 are solved. Using separable potentials for the $\bar{K}N-\pi\Sigma$ interaction, we calculate the transition probability for the $(Y_{K})_{I=0}+N\rightarrow\pi\Sigma{N}$ reaction. The possibility to observe the trace of the $K^{-}pp$ quasi-bound state in $\pi\Sigma{N}$ mass spectra was studied. Various types of chiral-based and phenomenological potentials are used to describe the $\bar{K}N-\pi\Sigma$ interaction. Finally, we show that we can observe the signature of the $K^{-}pp$ quasi-bound state in the mass spectra, as well as the trace of branch points in the observables.
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  • Search for decay modes of heavy and superheavy nuclei
    Published: 2019-05-22, doi: 10.1088/1674-1137/43/7/074102
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    Spontaneous fission (SF) with a new formula based on a liquid drop model is proposed and used in the calculation of the SF half-lives of heavy and superheavy nuclei (Z = 90–120). The predicted half-lives are in agreement with the experimental SF half-lives. The half-lives of $ \alpha $ decay (AD) for the same nuclei are obtained by using the Wentzel-Kramers-Brillouin (WKB) method together with Bohr-Sommerfeld (BS) quantization condition considering the isospin-dependent effects for the cosh potential. The decay modes and branching ratios of superheavy nuclei (Z = 104-118) with experimental decay modes are obtained, and the modes are compared with the experimental ones and with the predictions found in the literature. Although some nuclei have predicted decay modes that are different from their experimental decay modes, decay modes same as the experimental ones are predicted for many nuclei. The SF and AD half-lives, branching ratios, and decay modes are obtained for superheavy nuclei (Z = 119–120) with unknown decay modes and compared with the predictions obtained in a previous study. The present results provide useful information for future experimental studies performed on both the AD and SF of superheavy nuclei.
  • Expected energy spectrum of cosmic ray protons and helium below 4 PeV measured by LHAASO
    Published: 2019-05-21, doi: 10.1088/1674-1137/43/7/075001
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    The Large High Altitude Air Shower Observatory (LHAASO) is a composite cosmic ray observatory consisting of three detector arrays: kilometer square array (KM2A), which includes the electromagnetic detector array and muon detector array, water Cherenkov detector array (WCDA) and wide field-of-view Cherenkov telescope array (WFCTA). One of the main scientific objectives of LHAASO is to precisely measure the cosmic rays energy spectrum of individual components from $ 10^{14} $ eV to $ 10^{18} $ eV. The hybrid observation will be employed by the LHAASO experiment, in which the lateral and longitudinal distributions of extensive air shower can be observed simultaneously. Thus, many kinds of parameters can be used for primary nuclei identification. In this paper, high purity cosmic ray simulation samples of the light nuclei component are obtained using multi-variable analysis. The apertures of 1/4 LHAASO array for pure proton and mixed proton and helium (H&He) samples are $ 900 \rm\ m^{2}Sr $ and $ 1800 \rm\ m^{2}Sr $ , respectively. Prospect of obtaining proton and H&He spectra from 100 TeV to 4 PeV is discussed.
  • Non-parametric reconstruction of dark energy and cosmic expansion from the Pantheon compilation of type Ia supernovae
    Published: 2019-05-20, doi: 10.1088/1674-1137/43/7/075101
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    The equation of state (EoS) of dark energy plays an important role in the evolution of the universe and has attracted considerable interest in the recent years. With the progress in observational technique, a precise constraint on the EoS of dark energy can be obtained. In this study, we reconstruct the EoS of dark energy and cosmic expansion using Gaussian processes (GP) from the most up-to-date Pantheon compilation of type Ia supernovae (SNe Ia), which consists of 1048 finely calibrated SNe Ia. The reconstructed EoS of dark energy has a large uncertainty owing to its dependence on the second-order derivative of the construction. Adding the direct measurements of Hubble parameters $H(z)$ as an additional constraint on the first-order derivative can partially reduce the uncertainty; however, it is still not sufficiently precise to distinguish between the evolving and the constant dark energy. Moreover, the results heavily rely on the prior of the Hubble constant $H_0$. The $H_0$ value inferred from SNe+$H(z)$ without prior is $H_0=70.5\pm 0.5~{\rm km~s^{-1}~Mpc^{-1}}$. Moreover, the matter density $\Omega_M$ has a non-negligible effect on the reconstruction of dark energy. Therefore, more accurate determinations on $H_0$ and $\Omega_M$ are required to tightly constrain the EoS of dark energy.
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