Channel Nucleon Research Articles

Searching for strange hidden-charm pentaquark state Pcs(4459) in γp→K+Pcs(4459) reaction

We investigate the possibility of studying the strange hidden-charm pentaquark state $P_{cs}(4459)$ by photon-induced reactions on a proton target in an effective Lagrangian approach. The production process is described by the $t$-channel $K^{-}$ exchange, the $u$-channel $\Lambda$ exchange, the contract term, and the $s$- channel nucleon pole. Our theoretical approach is based on the assumption that $P_{cs}(4459)$ with $J^{P}=1/2^{-}$ or $J^{P}=3/2^{-}$ can be interpreted as a molecule composed of $\bar{D}^{*}\Xi_c$. Using the coupling constants of the $P^{J^P}_{cs}$ to $\gamma{}\Lambda$ and $K^{-}p$ channels obtained from molecule picture of the $P^{J^{P}}_{cs}(4459)$, the total cross-sections of the process $\gamma{}p\to{}P^{J^P}_{cs}K^{+}$ is evaluated. Our calculation indicates that the cross-section for $\gamma{}p\to{}P^{1/2^{-}}_{cs}K^{+}$ and $\gamma{}p\to{}P^{3/2^{-}}_{cs}K^{+}$ are of the order of 10.0 pb and 5.0 pb, respectively. In addition, we compute the cross-section by assuming $P_{cs}(4459)$ as a compact pentaquark and find it is quite different from the results of $\bar{D}^{*}\Xi_c$ molecule. Those results can be measured in future experiments, such as the Electron-Ion Collider in China and the United States. And can be used to test the nature of the $P_{cs}$.

An N/D study of the S 11 channel πN scattering amplitude * *Support in part by National Nature Science Foundations of China (11975028, 10925522), the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) (196253076 -TRR 110)

Extensive dynamical calculations are conducted in the study of channel low energy scatterings, based on various phenomenological model inputs of left cuts at the tree level. The subtleties of the singular behavior of the partial wave amplitude, at the origin of the complex plane, are analysed in detail. Furthermore, it is found that the dispersion representation for the phase shift, , must be modified in the case of scatterings. An additional contribution from the dispersion integral exists, which approximately cancels the contribution of the two virtual poles located near the end points of the segment cut, induced by channel nucleon exchanges. With limited reliance on the details of the dynamical inputs, the subthreshold resonance survives.

Photoproduction of possible pentaquark states Λb0(5912) and Λb0(5920) in the γp→Λb0(*)B+ reactions

In this work, we report on a theoretical study of possible pentaquark states $\Lambda^0_b(5912)$ and $\Lambda^0_b(5920)$ in the $\gamma{}p\to{}\Lambda_b^{0(*)}B^+$ reactions within an effective Lagrangian approach. In addition to the contributions from the $s$-channel nucleon pole and $t$-channel $\bar{B}^{{*}-}$ exchange, the contact term contribution are also included. Our theoretical approach is based on the chiral unitary theory where the $\Lambda^0_b(5912)$ and $\Lambda^0_b(5920)$ resonances are dynamically generated. Within the coupling constants of the $\Lambda^0_b(5912)$ and $\Lambda^0_b(5920)$ to $\bar{B}p$ and $\bar{B}^{*}p$ channels obtained from chiral unitary theory, the total and differential cross sections of the $\gamma{}p\to{}\Lambda_b^{0(*)}B^+$ are evaluated. Our calculation indicates that the cross section for $\gamma{}p\to{}\Lambda_b^{0}(5912)B^{+}$ and $\gamma{}p\to{}\Lambda_b^{0}(5920)B^{+}$ reactions are of the order of 0.0164 nb and 0.00527 nb,respectively. If measured in future experiments, such as Electron-Ion Collider in China (EicC) or US(US-EIC), the predicted total cross sections and specific features of the angular distributions can be used to test the (molecular) nature of the $\Lambda^0_b(5912)$ and $\Lambda^0_b(5920)$ that they may be pentaquark states.

Analysis of the differential cross section and photon beam asymmetry data for γp→η′p

The photoproduction reaction of $\gamma p \to \eta^\prime p$ is investigated based on an effective Lagrangian approach in the tree-level approximation, with the purpose being to understand the reaction mechanisms and to extract the resonance contents and the associated resonance parameters in this reaction. Apart from the $t$-channel $\rho$ and $\omega$ exchanges, $s$- and $u$-channel nucleon exchanges, and generalized contact term, the exchanges of a minimum number of nucleon resonances in the $s$ channel are taken into account in constructing the reaction amplitudes to describe the experimental data. It is found that a satisfactory description of the available data on both differential cross sections and photon beam asymmetries can be obtained by including in the $s$ channel the exchanges of the $N(1875)3/2^-$ and $N(2040)3/2^+$ resonances. The reaction mechanisms of $\gamma p \to \eta^\prime p$ are discussed and a prediction for the target nucleon asymmetries is presented.

Effects of N(2000)5/2+ on γp→K+Λ(1405)

The photoproduction reaction of $\ensuremath{\gamma}p\ensuremath{\rightarrow}{K}^{+}\mathrm{\ensuremath{\Lambda}}(1405)$ is investigated based on an effective Lagrangian approach at the tree-level approximation with the purpose of understanding the reaction mechanism and extracting the resonance contents and the associated resonance parameters in this reaction. Apart from the $t$-channel $K$ and ${K}^{*}$ exchanges, $s$-channel nucleon ($N$) exchange, $u$-channel $\mathrm{\ensuremath{\Sigma}}, \mathrm{\ensuremath{\Lambda}}$, and $\mathrm{\ensuremath{\Lambda}}(1405)$ exchanges, and generalized contact term, the exchanges of a minimum number of $N$ resonances in the $s$ channel are taken into account in constructing the reaction amplitudes to describe the experimental data. It is found that by introducing the $N(2000){5/2}^{+}$ resonance exchange in the $s$ channel, one can reproduce the most recent differential cross-section data from the CLAS Collaboration quite well. Further analysis shows that the cross sections of $\ensuremath{\gamma}p\ensuremath{\rightarrow}{K}^{+}\mathrm{\ensuremath{\Lambda}}(1405)$ at high energies are dominated by the $t$-channel $K$ exchange, while the contributions from the $s$-channel $N$ and $N(2000){5/2}^{+}$ exchanges are rather significant to the cross sections in the near-threshold energy region. Predictions for the beam and target asymmetries for $\ensuremath{\gamma}p\ensuremath{\rightarrow}{K}^{+}\mathrm{\ensuremath{\Lambda}}(1405)$ are given.

Photoproduction γp→K+Λ(1520) in an effective Lagrangian approach

The data on differential cross sections and photon-beam asymmetries for the $\gamma p \to K^+\Lambda(1520)$ reaction have been analyzed within a tree-level effective Lagrangian approach. In addition to the $t$-channel $K$ and $K^\ast$ exchanges, the $u$-channel $\Lambda$ exchange, the $s$-channel nucleon exchange, and the interaction current, a minimal number of nucleon resonances in the $s$ channel are introduced in constructing the reaction amplitudes to describe the data. The results show that the experimental data can be well reproduced by including either the $N(2060)5/2^-$ or the $N(2120)3/2^-$ resonance. In both cases, the contact term and the $K$ exchange are found to make significant contributions, while the contributions from the $K^\ast$ and $\Lambda$ exchanges are negligible in the former case and considerable in the latter case. Measurements of the data on target asymmetries are called on to further pin down the resonance contents and to clarify the roles of the $K^\ast$ and $\Lambda$ exchanges in this reaction.

Photon induced KΛ production on the proton in the low energy region

The associated photoproduction of [Formula: see text] from the proton in the low energy region is studied using an isobar model in which the nonresonant contributions are obtained from the nonlinear sigma model with chiral SU(3) symmetry which predicts, in a natural way, the contact term with its coupling strength along with the coupling strengths of the various Born terms predicted by the nonlinear sigma model. The present model is an extension of the nonlinear sigma model with chiral SU(2) symmetry, used earlier to study the photo, electro, and neutrino productions of pions. In the resonance sector, the contributions from the well established nucleon resonances ([Formula: see text]) in the [Formula: see text] channel, the hyperon resonances ([Formula: see text]) in the [Formula: see text] channel, and the kaon resonances ([Formula: see text] and [Formula: see text]) in the [Formula: see text] channel having spin [Formula: see text] and mass [Formula: see text][Formula: see text]GeV with a significant branching ratio in [Formula: see text] decay mode, have been considered. The strong and electromagnetic couplings of the [Formula: see text] channel nucleon resonances are taken from experiments while the couplings for the resonances in the [Formula: see text] and [Formula: see text] channels are fitted to reproduce the current data on the associated photoproduction of [Formula: see text] in this energy region. The numerical results are presented for the total and differential cross-sections and are compared with the available experimental data from CLAS and SAPHIR as well as with some of the recent theoretical models.

Nucleon and Δ resonances in γp→K+Σ0(1385) photoproduction

The photoproduction of $\gamma p \to K^+ \Sigma^0(1385)$ is investigated based on an effective Lagrangian approach using the tree-level Born approximation, with the purpose of understanding the reaction mechanisms and resonance contents and their associated parameters in this reaction. In addition to the $t$-channel $K$ and $K^\ast(892)$ exchanges, $s$-channel nucleon ($N$) exchange, $u$-channel $\Lambda$ exchange, and generalized contact term, the exchanges of a minimum number of $N$ and $\Delta$ resonances in the $s$ channel are taken into account in constructing the reaction amplitudes to describe the experimental data. It is found that the most recent differential cross-section data from the CLAS Collaboration can be well reproduced by including one of the $N(1895){1/2}^-$, $\Delta(1900){1/2}^-$, and $\Delta(1930){5/2}^-$ resonances. The reaction mechanisms of $\gamma p \to K^+ \Sigma^0(1385)$ are discussed in detail, and the predictions of the beam and target asymmetries for this reaction are given. The cross sections of $\gamma p \to K^0 \Sigma^+(1385)$ are shown to be able to further constrain the theoretical models and pin down the resonance contents for $\gamma p \to K^+ \Sigma^0(1385)$.

Nucleon resonances in γp→ωp reaction

The most recent high-precision data on spin observables $\Sigma$, $T$, $P'$, $E$, $F$ and $H$ reported by the CLAS Collaboration together with the previous data on differential cross sections and spin-density-matrix elements reported by the CLAS, A2, GRAAL, SAPHIR and CBELSA/TAPS Collaborations for the reaction $\gamma p \to \omega p$ are analyzed within an effective Lagrangian approach. The reaction amplitude is constructed by considering the $t$-channel $\pi$ and $\eta$ exchanges, the $s$-channel nucleon and nucleon resonances exchanges, the $u$-channel nucleon exchange and the generalized contact current. The latter accounts effectively for the interaction current and ensures that the full photoproduction amplitude is gauge invariant. It is shown that all the available CLAS data can be satisfactorily described by considering the $N(1520)3/2^-$, $N(1700)3/2^-$, $N(1720)3/2^+$, $N(1860)5/2^+$, $N(1875)3/2^-$, $N(1895)1/2^-$ and $N(2060)5/2^-$ resonances in the $s$-channel. The parameters of these resonances are extracted and compared with those quoted by PDG.

Features of ω photoproduction off proton target at backward angles: Role of nucleon Reggeon in u -channel with parton contributions

Backward photoproduction of $\omega$ off a proton target is investigated in a Reggeized model where the $u$-channel nucleon Reggeon is constructed from the nucleon Born terms in a gauge invariant way. The $t$-channel meson exchanges are considered as a background. While the $N_\alpha$ trajectory of the nucleon Reggeon reproduces the overall shape of NINA data measured at the Daresbury Laboratory in the range of $u$-channel momentum transfer squared $-1.7<u<0.02$ GeV$^2$ and energies at $E_\gamma=2.8$, 3.5 and 4.7 GeV, a possibility of parton contributions is searched for through the nucleon isoscalar form factor which is parameterized in terms of parton distributions at the $\omega NN$ vertex. Detailed analysis is presented for NINA data to understand the reaction mechanism that could fill up the deep dip from the nucleon Reggeon at momentum squared $u=-0.15$ GeV$^2$. The angle dependence of differential cross sections at the NINA energies above are reproduced in the overall range of $u$ including the CLAS data at forward angles in addition. The energy dependence of the differential cross section is investigated based on the NINA data and the recent LEPS data. A feature of the present approach that implicates parton contributions via nucleon form factor is illustrated in the total and differential cross sections provided by GRAAL and CB-ELSA Collaborations.

Ξ(1690)− production in the K−p→K+K−Λ reaction process near threshold

We investigate $\Xi(1690)^-$ production from the $K^-p\to K^+K^-\Lambda$ reaction within the effective Lagrangian approach at the tree-level Born approximation. We consider the $s$- and $u$-channel $\Sigma/\Lambda$ ground states and resonances for the $\Xi$-pole contributions, in addition to the $s$-channel $\Lambda$, $u$-channel nucleon pole, and $t$-channel $K^-$-exchange for the $\phi$-pole contributions. The $\Xi$-pole includes $\Xi(1320)$, $\Xi(1535)$, $\Xi(1690)(J^p=1/2^-)$,and $\Xi(1820)(J^p=3/2^-)$. We calculate the Dalitz plot density of $(d^2\sigma/dM_{K^+K^-}dM_{K^-\Lambda}$ at 4.2 GeV$/c$) and the total cross sections for the $K^-p\to K^+K^-\Lambda$ reaction near the threshold. The calculation results are in good agreement with previously acquired experimental data. Using the parameters from the fit, we present the total and differential cross sections for the two-body $K^-p\to K^+\Xi(1690)^-$ reaction near the threshold. In our calculation, a strong enhancement at backward $K^+$ angles is predicted because of the dominant $u$-channel contribution. We also demonstrate that the Dalitz plot analysis for $p_{K^-}=1.915 -- 2.065$ GeV/c enables us to access direct information regarding $\Xi(1690)^-$ production, which can be tested by future $K^-$ beam experiments. The possible spin-parity states of $\Xi(1690)^-$ are briefly discussed as well.

Photoproduction of f0(980) and f0(1500) resonances off a proton target

We study the $\gamma p \to p f_0$ [$f_0(980)$ and $f_0(1500)$] reaction close to threshold within an effective Lagrangian approach. The production process is described by $s$-channel nucleon pole or $t$-channel $\rho$ and $\omega$ exchange. The $K^0 \bar{K}^0$ invariant mass distributions of the $\gamma p\to f_0(980)p \to K^0 \bar{K}^0$ and $\gamma p\to f_0(1500)p \to K^0 \bar{K}^0 p$ reactions are investigated, where the two kaons have been separated in $S$ wave decaying from $f_0(980)$ and $f_0(1500)$. It is shown that the $s$-channel process is favored for the production of $f_0(980)$, while for the $f_0(1500)$ production, the experimental measurements can be described quite well by the $t$-channel process. It is expected that the theoretical results can be tested by further experiments at CLAS.

A Lattice QCD Study of Pion–Nucleon Scattering in the Roper Channel

We present a lattice QCD study of the puzzling positive-parity nucleon channel, where the Roper resonance $N^*(1440)$ resides in experiment. The study is based on an ensemble of gauge configurations with $N_f=2+1$ Wilson-clover fermions with a pion mass of $156$ MeV and lattice size $L=2.9$ fm. We use several $qqq$ interpolating fields combined with $N\pi$ and $N\sigma$ two-hadron operators in calculating the energy spectrum in the rest frame. Combining experimental $N\pi$ phase shifts with elastic approximation and the L\"uscher formalism suggests in the spectrum an additional energy level near the Roper mass $m_R=1.43$ GeV for our lattice. We do not observe any such additional energy level, which implies that $N\pi$ elastic scattering alone does not render a low-lying Roper resonance. The current status indicates that the $N^*(1440)$ might arise as dynamically generated resonance from coupling to other channels, most notably the $N\pi\pi$.

Nπ scattering in the Roper channel

We present results from our recent lattice QCD study of Nπ scattering in the positive-parity nucleon channel, where the puzzling Roper resonance N*(1440) resides in experiment. Using a variety of hadron operators, that include qqq-like, Nπ in p-wave and Nσ in s-wave, we systematically extract the excited lattice spectrum in the nucleon channel up to 1.65 GeV. Our lattice results indicate that Nπ scattering in the elastic approximation alone does not describe a low-lying Roper. Coupled channel effects between Nπ and Nππ seem to be crucial to render a low-lying Roper in experiment, reinforcing the notion that this state could be a dynamically generated resonance. After giving a brief motivation for studying the Roper channel and the relevant technical details to this study, we will discuss the results and the conclusions based on our lattice investigation and in comparison with other lattice calculations.

Nucleon resonances in γp→K*+Λ

The high-precision cross-section data for the reaction $\gamma p \to K^{*+}\Lambda$ reported by the CLAS Collaboration at the Thomas Jefferson National Accelerator Facility have been analyzed based on an effective Lagrangian approach in the tree-level approximation. Apart from the $t$-channel $K$, $\kappa$, $K^*$ exchanges, the $s$-channel nucleon ($N$) exchange, the $u$-channel $\Lambda$, $\Sigma$, $\Sigma^*(1385)$ exchanges, and the generalized contact term, the contributions from the near-threshold nucleon resonances in the $s$-channel are also taken into account in constructing the reaction amplitude. It is found that, to achieve a satisfactory description of the differential cross section data, at least two nucleon resonances should be included. By including the $N(2060){5/2}^-$ resonance, which is responsible for the shape of the angular distribution near the $K^*\Lambda$ threshold, and one of the $N(2000){5/2}^+$, $N(2040){3/2}^+$, $N(2100){1/2}^+$, $N(2120){3/2}^-$ and $N(2190){7/2}^-$ resonances, one can describe the cross-section data quite well, with the fitted resonance masses and widths compatible with those advocated by the Particle Data Group. The resulted predictions of the beam, target, and recoil asymmetries are found to be quite different from various fits, indicating the necessity of the spin observable data for $\gamma p \to K^{*+}\Lambda$ to further pin down the resonance contents and associated parameters in this reaction.

Study on the reaction of γp→f1(1285)p in Regge-effective Lagrangian approach

The production of the ${f}_{1}(1285)$ resonance in the reaction of $\ensuremath{\gamma}p\ensuremath{\rightarrow}{f}_{1}(1285)p$ is investigated within a Regge-effective Lagrangian approach. Besides the contributions of the $t$-channel $\ensuremath{\rho}$ and $\ensuremath{\omega}$ trajectories exchanges, we also take into account the contributions of $s\text{\ensuremath{-}}/u$-channel $N(2300)$ terms, $s\text{\ensuremath{-}}/u$-channel nucleon terms, and the contact term. By fitting to the CLAS data, we find that the $s$-channel $N(2300)$ term plays an important role in this reaction. We predict the total cross section for this reaction and find a clear bump structure around $W=2.3\text{ }\text{ }\mathrm{GeV}$, which is associated with the $N(2300)$ state. The reaction of $\ensuremath{\gamma}p\ensuremath{\rightarrow}{f}_{1}(1285)p$ could be useful to further study the $N(2300)$ experimentally.

Electric dipole moment of the deuteron in the standard model with NN − ΛN − ΣN coupling

We calculate the electric dipole moment (EDM) of the deuteron in the standard model with |ΔS|=1 interactions by taking into account the NN−ΛN−ΣN channel coupling, which is an important nuclear level systematics. The two-body problem is solved with the Gaussian Expansion Method using the realistic Argonne v18 nuclear force and the YN potential which can reproduce the binding energies of Λ3H, Λ3He, and Λ4He. The |ΔS|=1 interbaryon potential is modeled by the one-meson exchange process. It is found that the deuteron EDM is modified by less than 10%, and the main contribution to this deviation is due to the polarization of the hyperon–nucleon channels. The effect of the YN interaction is small, and treating ΛN and ΣN channels as free is a good approximation for the EDM of the deuteron.

Effects of a hyperonic many-body force on BΛ values of hypernuclei

The stiff equation of state (EoS) giving the neutron-star mass of $2M_{\odot}$ suggests the existence of strongly repulsive many-body effect (MBE) not only in nucleon channels but also in hyperonic ones. As a specific model for MBE, the repulsive multi-pomeron exchange potential (MPP) is added to the two-body interaction together with the phenomenological three-body attraction. For various versions of the Nijmegen interaction models, the MBE parts are determined so as to reproduce the observed data of $B_\Lambda$. The mass dependence of $B_\Lambda$ values is shown to be reproduced well by adding MBE with the strong MPP repulsion assuring the stiff EoS of hyperon-mixed neutron-star matter, when $P$-state components of the adopted interaction model lead to almost vanishing contributions. The nuclear matter $\Lambda\!N$ $G$-matrix interactions are derived and used in $\Lambda$ hypernuclei on the basis of the averaged-density approximation (ADA). The $B_\Lambda$ values of hypernuclei with $9 \le A \le 59$ are analyzed in the framework of Antisymmetrized Molecular Dynamics with use of the two types of $\Lambda\!N$ $G$-matrix interactions including strong and weak MPP repulsions. The calculated values of $B_\Lambda$ reproduce the experimental data finely within a few hundred keV. The values of $B_\Lambda$ in $p$-states also can be reproduced well, when ADA is modified to be suitable also to weakly-bound $\Lambda$ states.

Pion-nucleon scattering in the Roper channel from lattice QCD

We present a lattice QCD study of $N\pi$ scattering in the positive-parity nucleon channel, where the puzzling Roper resonance $N^*(1440)$ resides in experiment. The study is based on the PACS-CS ensemble of gauge configurations with $N_f=2+1$ Wilson-clover dynamical fermions, $m_\pi \simeq 156~$MeV and $L\simeq 2.9~$fm. In addition to a number of $qqq$ interpolating fields, we implement operators for $N\pi$ in $p$-wave and $N\sigma$ in $s$-wave. In the center-of-momentum frame we find three eigenstates below 1.65 GeV. They are dominated by $N(0)$, $N(0)\pi(0)\pi(0)$ (mixed with $N(0)\sigma(0)$) and $N(p)\pi(-p)$ with $p\simeq 2\pi/L$, where momenta are given in parentheses. This is the first simulation where the expected multi-hadron states are found in this channel. The experimental $N\pi$ phase-shift would -- in the approximation of purely elastic $N\pi$ scattering -- imply an additional eigenstate near the Roper mass $m_R\simeq 1.43~$GeV for our lattice size. We do not observe any such additional eigenstate, which indicates that $N\pi$ elastic scattering alone does not render a low-lying Roper. Coupling with other channels, most notably with $N\pi\pi$, seems to be important for generating the Roper resonance, reinforcing the notion that this state could be a dynamically generated resonance. Our results are in line with most of previous lattice studies based just on $qqq$ interpolators, that did not find a Roper eigenstate below $1.65~$GeV. The study of the coupled-channel scattering including a three-particle decay $N\pi\pi$ remains a challenge.

Effective theory of 3H and 3He

We present a new perturbative expansion for pionless effective field theory with Coulomb interactions in which at leading order (LO) the spin-singlet nucleon–nucleon channels are taken in the unitarity limit. Presenting results up to next-to-leading order for the Phillips line and the neutron–deuteron doublet-channel phase shift, we find that a perturbative expansion in the inverse scattering lengths converges rapidly. Using a new systematic treatment of the proton–proton sector that isolates the divergence due to one-photon exchange, we renormalize the corresponding contribution to the – binding energy splitting and demonstrate that the Coulomb force in pionless EFT is a completely perturbative effect in the trinucleon bound-state regime. In our new expansion, the LO is exactly isospin-symmetric. At next-to-leading order, we include isospin breaking via the Coulomb force and two-body scattering lengths, and find for the energy splitting .