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Register a new userPion-induced production of hidden-charm pentaquarks $P_{c}(4312),P_{c}(4440)$, and $P_{c}(4457)$
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The production of the hidden-charm pentaquarks $P_{c}$ via pion-induced reaction on a proton target is investigated within an effective Lagrangian approach. Three experimentally observed states, $P_c(4312)$, $P_c(4440)$, and $P_c(4457)$, are considered in the calculation, and the Reggeized $t$-channel meson exchange is considered as main background for the reaction $pi ^{-}prightarrow J/psi n$. The numerical results show that the experimental data of the total cross section of the reaction $pi^{-}prightarrow J/psi n$ at $Wsimeq 5$ GeV can be well explained by contribution of the Reggeized $t$ channel with reasonable cutoff. If the branching ratios $Br[P_{c}rightarrow J/psi N]simeq 3%$ and $Br[P_{c}rightarrow pi N]simeq 0.05%$ are taken, the average value of the cross section from the $P_{c}(4312)$ contribution is about 1.2 nb/100 MeV, which is consistent with existing rude data at near-threshold energies. The results indicate that the branching ratios of the $P_{c}$ states to the $J/psi N$ and $pi N$ should be small. The shape of differential cross sections shows that the Reggeized $t$-channel provides a sharp increase at extreme forward angles, while the differential cross sections from the $P_{c}$ states contributions are relatively flat. High-precision experimental measurements on the reaction $pi ^{-}prightarrow J/psi n$ at near-threshold energies are suggested to confirm the LHCb hidden-charm pentaquarks as genuine states, and such experiments are also helpful to understand the origin of these resonance structures.
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The three pentaquark states, $P_{c}(4312)$, $P_{c}(4440)$, and $P_{c}(4457)$, discovered by the LHCb Collaboration in 2019, can be nicely arranged into a multiplet of $bar{D}^{(ast)}Sigma_{c}^{(ast)}$ of seven molecules dictated by heavy quark spin symmetry. In this work we employ the effective Lagrangian approach to investigate the two decay modes of $P_{c}(4457)$, $P_{c}(4457) to P_{c}(4312) pi$ and $P_{c}(4457) to P_{c}(4312) gamma$, via the triangle mechanism, assuming that $P_{c}(4457)$ and $P_{c}(4312)$ are $bar{D}^{ast}Sigma_{c}$ and $bar{D}Sigma_{c}$ bound states but the spin of $P_{c}(4457)$ can be either 1/2 or 3/2. Our results show that the spin of $P_{c}(4457)$ can not be discriminated through these two decay modes. The decay widths of $P_{c}(4457) to P_{c}(4312) pi$ and $P_{c}(4457) to P_{c}(4312) gamma$ are estimated to be of order of 100 keV and 1 keV, respectively. The ratio of the partial decay widths of $P_{c}(4457) to P_{c}(4312) pi$ to $P_{c}(4457) to P_{c}(4312) gamma$ is similar to the ratio of $D^{ast}to Dpi$ to $D^{ast}to Dgamma$, which could be used to check the molecular nature of $P_{c}(4457)$ and $P_{c}(4312)$ if they can be observed in the future.
We investigate the production of the hidden-charm pentaquark $P_{cs}^0(4459)$ with strangeness in the $K^- p to J/psi Lambda$ reaction, employing two different theoretical frameworks, i.e., the effective Lagrangian method and the Regge approach. Having determined all relevant coupling constants, we are able to compute the total and differential cross sections for the $K^- p to J/psi Lambda$ reaction. We examine the contributions of $P_{cs}$ with different sets of spin-parity quantum number assigned. The present results may give a guide for possible future experiments.
Motivated by the recent discovery of the first hidden charm pentaquark state with strangeness $P_{cs}(4459)$ by the LHCb Collaboration, we study the likely existence of a three-body $Sigma_{c}bar{D}bar{K}$ bound state, which shares the same minimal quark content as $P_{cs}(4459)$. The $Sigma_{c}bar{D}$ and $DK$ interactions are determined by reproducing $P_c(4312)$ and $D_{s0}^*(2317)$ as $Sigma_cbar{D}$ and $bar{D}bar{K}$ molecules, respectively, while the $Sigma_cbar{K}$ interaction is constrained by chiral effective theory. We indeed find a three-body bound state by solving the Schrodinger equation using the Gaussian Expansion Method, which can be viewed as an excited hidden charm pentaquark state with strangeness, $P_{cs}^*(4739)$, with $I(J^P)=1(1/2^+)$ and a binding energy of $77.8^{+25}_{-10.3}$ MeV. We further study its strong decays via triangle diagrams and show that its partial decay widths into $DXi_c$ and $D_s^*Sigma_c$ are of a few tens MeV, with the former being dominant.
In a chromomagnetic model, we analyse the properties of the newly observed $P_c(4457)^+$, $P_c(4440)^+$, and $P_c(4312)^+$ states. We estimate the masses of the $(uud)_{8_c}(cbar{c})_{8_c}$ and $(uds)_{8_c}(cbar{c})_{8_c}$ pentaquark states by considering the isospin breaking effects. Their values are determined by calculating mass distances from the $Sigma_c^{++}D^-$ and $Xi_c^{prime+}D^-$ thresholds, respectively. It is found that the isospin breaking effects on the spectrum are small. From the uncertainty consideration and the rearrangement decay properties in a simple model, we find that it is possible to assign the $P_c(4457)^+$, $P_c(4440)^+$, and $P_c(4312)^+$ as $J^P=3/2^-$, $1/2^-$, and $3/2^-$ pentaquark states, respectively. The assignment in the molecule picture can be different, in particular for the $P_c(4312)^+$. The information from open-charm channels, e.g. ${cal B}[P_ctoSigma_c^{++}D^-]/{cal B}[P_cto J/psi p]$, will play an important role in distinguishing the inner structures of the $P_c$ states. Discussions and predictions based on the calculations are also given.
The cross section of the $ep to e p gamma$ reaction has been measured at $Q^2 = 0.33$ (GeV/c)$^2$. The experiment was performed using the electron beam of the MAMI accelerator and the standard detector setup of the A1 Collaboration. The cross section is analyzed using the low-energy theorem for virtual Compton scattering, yielding a new determination of the two structure functions $P_LL}-P_{TT}/epsilon$ and $P_{LT}$ which are linear combinations of the generalized polarizabilities of the proton. We find somewhat larger values than in the previous investigation at the same $Q^2$. This difference, however, is purely due to our more refined analysis of the data. The results tend to confirm the non-trivial $Q^2$-evolution of the generalized polarizabilities and call for more measurements in the low-$Q^2$ region ($le$ 1 (GeV/c)$^2$).
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