Search

We study the $J/\psi$ photoproduction $\gamma p\to J/\psi p$ near threshold to investigate the role played by the open charm channels and possible signals from the hidden charm $P_c$ pentaquark states. With the diffractive mechanism described by a Pomeron exchange model extrapolated from high energies to the lower energy region, it shows that the differential cross sections compared with the recent results from the GlueX Collaboration have apparent deficits in the large scattering angles. The inclusion of the open charm channels and intermediate $P_c$ states can significantly improve the descriptions of the differential cross section data, in particular, at the energy regions of the $\Lambda_c\bar{D}^{(*)}$ thresholds. This can explain the structures observed by the GlueX Collaboration at the $\Lambda_c\bar{D}^{(*)}$ thresholds as the open charm CUSP effects. Given that these $P_c$ pentaquark states are hadronic molecules dynamically generated by the $\Sigma_c\bar{D}^{(*)}$, we find that the production of these $P_c$ states should be suppressed at leading order since their couplings to both $\gamma p$ and $J/\psi p$ are through loop transitions. This can explain why no obvious signals for the $P_c$ states are observed by the present datasets. In order to further disentangling the role played by $s$-channel mechanisms, we also investigate the polarized beam asymmetry which shows sensitivities to the open charm threshold effects and interferences from the $P_c$ productions. Experimental measurement of this observable at the Jefferson Laboratory is strongly encouraged., Comment: 10 pages, 6 figures

In this study, we analyze the cross-section data from the $e^+e^-\to \gamma J/\psi\omega$ process to explore both short-distance and long-distance interactions for the radiative transition $Y(4200)\to \gamma X(3872)$. We investigate the short-distance effects through the E1 transition among the $c\bar{c}$ components, and the long-distance effects via hadronic loop diagrams. Our numerical analysis reveals that short-distance interactions play a significantly larger role in the radiative transition than that of the long-distance interactions. This finding underscores the importance of the compact $c\bar{c}$ components in both the initial and final states for accurately understanding the cross-section $\sigma[e^+e^-\to \gamma J/\psi\omega]$. Furthermore, with the help of relative branch ratio $\mathcal{R}$ we estimate the $\Gamma[Y(4200)\to\gamma X(3872)]$ implied in the the experimental study. Finally, we also discuss the possible existence of $\psi(4040)$ signal within the cross-section data.

We demonstrate that triangle singularity (TS) and box singularity (BS) mechanisms can produce unique narrow enhancements at the $\Lambda_c\bar{D}$ and $\Lambda_c\bar{D}^*$ thresholds in the invariant mass spectra of $J/\psi p$ and $J/\psi p\pi$, respectively. Taking into account that such mechanisms only depend on the initial $\Sigma_c^{(*)}\bar{D}^{(*)}$ interactions near threshold within the TS or BS kinematic regimes, the $\Lambda_c\bar{D}$ and $\Lambda_c\bar{D}^*$ threshold enhancements can be regarded as a feed-down phenomenon originated from both the heavier pentaquark decays and the $\Sigma_c^{(*)}\bar{D}^{(*)}$ scatterings from the continuum. A search for these structures in the $J/\psi p$ and $J/\psi p\pi$ spectra in both exclusive and semi-inclusive processes will provide a smoking-gun evidence for the hadronic molecule nature of those observed pentaquarks and clarify the role played by the TS and BS in the near-threshold dynamics., Comment: Revtex, 6 pages, 5 figures; Comments are welcome

How to hunt for higher $P$-wave states of charmonium is still an open topic when $2P$ charmonia were identified. {In this work, we present an unquenched quark model calculation to illustrate the spectroscopy behavior of these $3P$, $4P$ and $5P$ states in charmonium family.} For the $3P$ charmonia, the predicted masses are around 4.2 GeV and their two-body open-charm decay behaviors were given, by which we propose that searching for these $3P$ states via their open-charm decay channels from $\gamma\gamma$ fusion and $B$ decay can be accessible at future experiment like LHCb and Belle II. We continue to calculate the masses of these $4P$ and $5P$ charmonia. Combing with these calculated results of higher $P$-wave states of charmonium, we find that the coupled-channel effect becomes more obvious with increasing the radial quantum number, which can be understood well by the modified Godfrey-Isgur model with screened potential., Comment: 8 pages, 4 figures and 7 tables. Accepted for publication in PRD

In this work, the branching ratio $\mathcal{B}[B\to K\chi_{c0}(2P)]$ is extracted for the first time through the fit fractions in the newly measured $B\to KD\bar{D}$ process by LHCb. With the rescattering mechanism, this extracted branching ratio is reproduced well. Our study further enforces the role of the newly measured $B\to KD\bar{D}$ process to establish the $\chi_{c0}(2P)$ charmonium state, which is a crucial step when constructing charmonium family., Comment: 9 figures, 2 figures and 2 tables. Version for publication in Phys. Rev. D

In this work, we seriously discuss whether $X(3915)$ can be treated as a $\chi_{c0}(2P)$ state. Based on an unquenched quark model, we give the mass spectrum of the $\chi_{cJ}(2P)$ states, where there are no free input parameters in our calculation. Our result shows that the mass gap between $\chi_{c0}(2P)$ and $\chi_{c2}(2P)$ can reach 13 MeV, which can reproduce the mass difference between $Z(3930)$ and $X(3915)$. Additionally, the calculated masses of $\chi_{c0}(2P)$ and $\chi_{c2}(2P)$ are consistent with experimental values of $X(3915)$ and $Z(3930)$, respectively. Besides, giving the mass spectrum analysis to support $X(3915)$ as $\chi_{c0}(2P)$, we also calculate the width of $\chi_{c0}(2P)$ with the same framework, which is also consistent with the experimental data of $X(3915)$. Thus, the possibility of charmoniumlike state $X(3915)$ as $\chi_{c0}(2P)$ state is further enforced., Comment: 12 pages, 9 figures and 6 tables. More discussions added. Accepted by PRD for publication

The gamma-ray burst GRB 180720B is very peculiar. On one hand, some interesting features have been found by performing the detailed time-resolved spectral analysis in the prompt phase. First, the `flux-tracking' pattern is exhibited both for the low energy spectral index $\alpha$ and the peak energy $E_{p}$ in the Band function. Second, some parameter relations show strong monotonous positive correlations, include $E_{p}-F$, $\alpha-F$, $E_{p}-\alpha$, and $E_{p}-L_{\gamma,iso}$ for all time-resolved spectra. Lastly, it should be noted that the values of $\alpha$ do not exceed the synchrotron limits (from $-\frac{3}{2}$ to $-\frac{2}{3}$). On the other hand, the photons with the energy of $\gtrsim$ 100 MeV were detected by LAT both in the prompt phase and afterglow. Notably, the 5 GeV photon was observed at 142 s after the GBM trigger. The spectrum of this burst in the LAT range can be described as $F_{\nu}\propto \nu^{-1.3} t^{-1.54\pm0.02}$ in the afterglow phase. And there are six GeV photons during the X-ray flare when the lower energy emission is fading to a weaker level. We try to give reasonable interpretations of the mechanism for prompt emission and the high energy emission (100 MeV to GeV) in the afterglow. The interpretations suggesting that synchrotron origin can account for the prompt emission and synchrotron self-Compton radiation can account for both the spectrum and temporal behavior of the 100 MeV to GeV afterglow emission that have been accepted by us., Comment: published by ApJ

The prompt emission of gamma-ray bursts remains mysterious since the mechanism is difficult to understand even though there are much more observations with the development of detection technology. But most of the gamma-ray bursts spectra show the Band shape, which consists of the low energy spectral index $\alpha$, the high energy spectral index $\beta$, the peak energy $E_{p}$ and the normalization of the spectrum. We present a systematic analysis of the spectral properties of 36 GRBs, which were detected by the Gamma-ray Burst Monitor (GBM), simultaneously, were also observed by the Large Area Telescope (LAT) and the LAT Low Energy (LLE) detector on the $Fermi$ satellite. We performed the detailed time-resolved spectral analysis for all of the bursts in our sample. We found that the time-resolved spectrum at peak flux can be well fitted by the empirical Band function for each burst in our sample. Moreover, the evolution patterns of $\alpha$ and $E_{p}$ have been carried for statistical analysis, and the parameter correlations have been obtained such as $E_{p}-F$, $\alpha-F$, and $E_{p}- \alpha$, all of them are presented by performing the detailed time-resolved spectral analysis. We also demonstrated that the two strong positive correlations $\alpha-F$ and $E_{p}-\alpha$ for some bursts originate from a non-physical selection effects through simulation., Comment: accepted for publication in The Astrophysical Journal