Baryon Exchange Research Articles

Exploration of the LHCb Pc\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$P_c$$\\end{document} states and possible resonances in a unitary coupled-channel model

We extend our previous study of the interactions of D¯(∗)Λc-D¯(∗)Σc(∗)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\bar{D}^{(*)} \\Lambda _c - \\bar{D}^{(*)}\\Sigma _c^{(*)}$$\\end{document} within an analytic, unitary, coupled-channel approach by including the J/ψp\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$J/\\psi p$$\\end{document} channel and performing fits to the J/ψp\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$J/\\psi p$$\\end{document} invariant mass distributions in the Λb0→J/ψpK-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Lambda _b^0 \\rightarrow J/\\psi p K^-$$\\end{document} decay by the LHCb Collaboration. We take into account the contributions of t-channel pseudoscalar and vector meson exchanges and u-channel baryon exchanges in this work, and a series of bound states and resonances with different spin-parities are dynamically generated. According to the results, four states have a significant impact on the physical observables, with two having a spin-parity of 1/2-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1/2^-$$\\end{document} and the other two having 3/2-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$3/2^-$$\\end{document}. These states can be associated with the LHCb hidden-charm pentaquarks. We further provide the coupling strength between each pole and different channels, which provides some insights on how to search for them in future experiments. Moreover, we also search for poles in higher partial waves up to J=7/2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$J=7/2$$\\end{document} and find indications for the existence of several states with larger widths.

Photoproduction γp→K*+Λ in a Reggeized model

The high-precision differential cross-section data for the reaction $\gamma p \to K^{*+}\Lambda$ are reanalyzed within a Regge-inspired effective Lagrangian approach. The model adopts Regge phenomenology to constrain the $t$-channel contributions from the $\kappa$, $K$, and $K^*$ exchanges. A minimal number of resonances in the $s$ channel are introduced in constructing the reaction amplitudes in order to describe the data. It is shown that the differential cross-section data for $\gamma p \to K^{*+}\Lambda$ can be satisfactorily described by introducing the only $N(2060){5/2}^-$ resonance in the $s$ channel, which is quite different from our earlier work performed in an effective Lagrangian approach [A. C. Wang {\it et al.}, Phys. Rev. C 96, 035206 (2017)], where the amplitudes are computed by evaluating Feynman diagrams and it is found that introducing at least one additional resonance apart from the $N(2060){5/2}^-$ is indispensable for reproducing the data. The roles of individual contributions from meson and baryon exchanges on the angular distributions are found to be highly model dependent. The extracted mass of $N(2060){5/2}^-$ turns out to be well determined, independent of how the $t$-channel amplitudes are constructed, whereas the width does not.

Resonances in forward π+π− photoproduction on hydrogen

We show that the cross section of the Δ(1230) production in the γp → pπ+ π− reaction at forward angles and with unpolarized photons can be described in terms of gauge invariant one pion t-channel exchange amplitudes. Proper description of the polarized cross sections requires, however, the inclusion of contributions from the baryon exchanges.

Study of multipion production in np-interaction at intermediate energies

The reactions of the multipion production in np-interactions were studied at the momenta of incident neutrons from 1.73 to 5.20 GeV/c. The pions multiplicity of the studied reactions was from 2 to 6. It was shown that the characteristics of the reactions were satisfactory described within the framework of OPER-model (One Pion Reggeizied Exchange). Additionally the diagrams of one baryon exchange (OBE) were used for a better description of the data at the momenta of incident neutrons below 3 GeV/c.

P¯pannihilation intoD¯Dmeson pair within an effective Lagrangian model

We study the charmed meson pair (${\bar D}^0 D^0$ and $D^- D^+$) production in ${\bar p}p$ annihilation within an effective Lagrangian model that has only the baryon-meson degrees of freedom and involves the physical hadron masses. The reaction amplitudes include terms corresponding to the t-channel $\Lambda_c^+$, $\Sigma_c^+$ and $\Sigma_c^{++}$ baryon exchanges and the s-channel excitation, propagation and decay of the $\Psi$(3770) resonance into the charmed mesons. The initial- and final-state distortion effects have been accounted for by using a simple eikonal approximation-based procedure in the same way as was done in our previous study of the ${\bar p}p \to {\bar \Lambda}_c^-\Lambda_c^+$ reaction within a similar model. The ${\bar D}^0 D^0$ production reaction is dominated by the $\Lambda_c^+$ baryon exchange process, and the corresponding total cross sections are predicted to be in the range of 0.18 - 0.7 $\mu$b for antiproton beam momenta varying between threshold and 20 $GeV/c$. The $\Psi$(3770) resonance contributions have a large influence on the differential cross sections of the $D^- D^+$ production reaction.

Study of the reaction npπ → npπ+π− at 1.0 and 1.5 GeV

The np → npπ + π − reaction has been studied at the incident neutron energies of 1.0 GeV and 1.5 GeV in 4π-geometry using the neutron beam produced by the breakup of the relativistic deuterons at the JINR Synchrophasotron. The np → npπ + π − data obtained at 1.5 GeV demonstrate the dominance of the ΔΔ excitation process with a significant contribution of the higher-lying baryonic resonances, while the data at 1.0 GeV show a non-resonant behavior. The angular and mass distributions are compared with the predictions of different models suggested for the double pion production in the NN collisions. The calculations performed within the model based on the reggeized π-exchange taking one baryon exchange into account are in good agreement with the experimental data obtained at both energies.

ψ(3770)resonance and its production inp¯p→DD¯

The production of a $D\bar D$ meson-pair in antiproton-proton ($\bar p p$) annihilation close to the production threshold is investigated, with special emphasis on the role played by the $\psi$(3770) resonance. The study is performed in a meson-baryon model where the elementary charm production process is described by baryon exchange. Effects of the interactions in the initial and final states are taken into account rigorously, where the latter involves also those due to the $\psi$(3770). The predictions for the $D\bar D$ production cross section are in the range of 30 -- 250 nb, the contribution from the $\psi$(3770) resonance itself amounts to roughly 20 -- 80 nb.

Production of charmed pseudoscalar mesons in antiproton-proton annihilation

We study the production of charmed mesons (D, D_s) in antiproton-proton annihilation close to the reaction thresholds. The elementary charm production process is described by baryon exchange and in the constituent quark model, respectively. Effects of the interactions in the initial and final states are taken into account rigorously. The calculations are performed in close analogy to our earlier study on pbarp to KbarK by connecting the processes via SU(4) flavor symmetry. Our predictions for the DDbar production cross section are in the order of 10^{-2} -- 10^{-1} mu b. They turned out to be comparable to those obtained in other studies. The cross section for a D_sD_s pair is found to be of the same order of magnitude despite the fact that its production in pbarp scattering requires a two-step process.

Vector- and Pseudoscalar-baryon coupled channel systems

In this manuscript, I will report the details of our recent work on the vector meson-baryon (VB) interaction, which we studied with the motivation of finding dynamical generation of resonances in the corresponding systems. We started our study by building a formalism based on the hidden local symmetry and calculating the leading order contributions to the scattering equations by summing the diagrams with: (a) a vector meson exchange in the t-channel (b) an octet baryon exchange in the s-, u-channels and (c) a contact interaction arising from the part of the vector meson-baryon Lagrangian which is related to the anomalous magnetic moment of the baryons. We find the contribution from all these sources, except the s-channel, to be important. The amplitudes obtained by solving the coupled channel Bethe-Salpeter equations for the systems with total strangeness zero, show generation of one isospin 3/2, spin 1/2 resonance and three isospin 1/2 resonances: two with spin 3/2 and one with spin 1/2. We identify these resonances with Δ (1900) S31, N*(2080) D13, N*(1700) D13, and N*(2090) S11, respectively.We have further extended our study by including pseudoscalar meson-baryon (PB) as the coupled channels of VB systems. For this, we obtain the PB → VB amplitudes by using the Kroll-Ruddermann term where, considering the vector meson dominance phenomena, the photon is replaced by a vector meson. The calculations done within this formalism reveal a very strong coupling of the VB channels to the low-lying resonances like Λ(1405) and Λ(1670), which can have important implications on certain reactions producing them. In addition to this, we find that the effect of coupling the higher mass states to the lighter channels is not restricted to increasing the width of those states, it can be far more strong.

Negative parityΛandΣresonances coupled to pseudoscalar and vector mesons

An exploration of the dynamically generated $\ensuremath{\Lambda}$ and $\ensuremath{\Sigma}$ resonances has been made in the vector meson-baryon (VB) systems coupled to pseudoscalar meson-baryon (PB) channels. The VB interactions are obtained from the Lagrangians written within the hidden local symmetry which, in addition to Yukawa-type vector-baryon-baryon (VBB) vertices, naturally gives rise to a contact interaction. Using the VBB vertices, we calculate the $t$-, $s$-, and $u$-channel diagrams considering the octet baryon exchange in the latter two cases. For the PB channels we rely on the the Weinberg-Tomozawa interactions and calculate the $\mathrm{PB}\ensuremath{\leftrightarrow}\mathrm{VB}$ transition amplitudes extending the Kroll-Ruderman theorem by replacing the photon by the vector mesons. In addition to the low-lying $\ensuremath{\Lambda}(1405)$, $\ensuremath{\Lambda}(1670)$ found in previous works, we find resonances which coincide well with $\ensuremath{\Lambda}(2000)$, $\ensuremath{\Sigma}(1750){S}_{11}$, $\ensuremath{\Sigma}(1940){D}_{13}$, $\ensuremath{\Sigma}(2000){S}_{11}$ and predict three ${\ensuremath{\Lambda}}^{*}$'s with ${J}^{\ensuremath{\pi}}=3/{2}^{\ensuremath{-}}$ and masses $1754\ensuremath{-}i2\text{ }\text{ }\mathrm{MeV}$, $1862\ensuremath{-}i33\text{ }\text{ }\mathrm{MeV}$, $2139\ensuremath{-}i14\text{ }\text{ }\mathrm{MeV}$ together with a broad $1/{2}^{\ensuremath{-}}$ ${\ensuremath{\Sigma}}^{*}$ with mass $\ensuremath{\sim}1430\text{ }\text{ }\mathrm{MeV}$. We find that most of these next-to-low-lying states couple weakly with the pseudoscalar mesons, which implies that it is important to study the reactions with VB final states in order to obtain reliable information on the properties of such resonances.

Polarized pK- scattering in Unitary Baryon Chiral Perturbation Theory

We study $pK^-$ scattering in the energy range from threshold through the $\Lambda(1520)$ peak in UBChPT, taking into account $\mathcal{O}(q)$ vertices from meson-baryon contact interactions and $s$- and $u$-channel ground-state baryon exchange, $s$- and $u$-channel decuplet- and nonet-baryon exchange and $t$-channel vector-meson exchange, as well as $\mathcal{O}(q^2)$ flavor-breaking vertices. Detailed fits to data are presented, including a substantial body of differential cross-section data with meson momentum $q_\mathrm{lab} > 300$ MeV not considered in previous treatments.

Pion-nucleon scattering in Kadyshevsky formalism. II. Baryon exchange sector

In this article, which is the second part in a series of two, we construct tree-level baryon exchange and resonance amplitudes for $\ensuremath{\pi}N/\mathit{MB}$ scattering in the framework of the Kadyshevsky formalism. We use this formalism to formally implement absolute pair suppression, where we make use of the method of Takahashi and Umezawa. The resulting amplitudes are Lorentz invariant and causal. We continue studying the frame dependence of the Kadyshevsky integral equation using the method of Gross and Jackiw. The invariant amplitudes, including those for meson exchange, are linked to the phase shifts using the partial-wave basis.

SYNCHRONISATION OF RESONANCES WITH THRESHOLDS

The mechanism by which a resonance may be attracted to a sharp threshold is described with several examples. It involves a threshold cusp interfering constructively with either or both (i) a resonance produced via confinement, (ii) attractive t- and u-channel exchanges. More generally, it is suggested that resonances are eigenstates generated by mixing between confined states and long-range meson and baryon exchanges.

Exclusive charm production inp¯pcollisions ats≲15GeV

We discuss the open charm production in the peripheral reactions $\overline{p}p\ensuremath{\rightarrow}{\overline{Y}}_{c}{Y}_{c}$ and $\overline{p}p\ensuremath{\rightarrow}{M}_{c}{\overline{M}}_{c}$, where ${Y}_{c}$ and ${M}_{c}$ stand for ${\ensuremath{\Lambda}}_{c}^{+},{\ensuremath{\Sigma}}_{c}^{+}$ and $D,{D}^{*}$, respectively, at $\sqrt{s}\ensuremath{\lesssim}15$ GeV, which corresponds to the energy range of FAIR. Our consideration is based on the topological decomposition of the planar quark and diquark diagrams, which allows us to estimate consistently meson and baryon exchange trajectories and energy scale parameters as well. The spin dependance is determined by the effective interaction of the lowest exchanged resonance. Unknown parameters are fixed by an independent analysis of open strangeness production in $\overline{p}p\ensuremath{\rightarrow}\overline{Y}Y$ and $\overline{p}p\ensuremath{\rightarrow}\overline{K}K$ reactions and of SU(4) symmetry. We present the corresponding cross sections and longitudinal double-spin asymmetries for exclusive binary reactions with open charm mesons and baryons in the final state. The polarization observables have a nontrivial $t$ and $s$ dependence that is sensitive to details of the open charm production mechanism.

The narrow width of the Θ+—a possible explanation

The narrow width of the exotic narrow baryon resonance Θ+ might be explained by mixing between the two nearly degenerate states that arise in models with two diquarks and an antiquark. The only open Θ+ decay channel is KN. When two states both coupled to a single dominant decay mode are mixed by the loop diagram via this decay mode, diagonalization of the loop diagram decouples one mass eigenstate from this decay mode as in some treatments of the ρ–π decay from the mixed singlet–octet ω–φ system, the K∗–π decay of the strange axial vector mesons and the NK couplings of some baryons. This mechanism can explain the narrow width and weak coupling of Θ+→KN while allowing a relatively large production cross section from K∗ exchange. Interesting tests are suggested in K−p reactions where backward kaon production must go by exotic baryon exchange.

Associative photoproduction of Roper resonance and ω meson

Associative photoproduction of $\ensuremath{\omega}$ meson and ${N}^{*}(1440)$ on nucleons, $\ensuremath{\gamma}+\stackrel{\ensuremath{\rightarrow}}{N}\ensuremath{\omega}{+N}^{*}(1440),$ in the near threshold region is investigated in a framework employing effective Lagrangians. Besides $\ensuremath{\pi}$ exchange in the t channel, baryon exchanges, i.e., N and ${N}^{*}$ exchanges, in the s and u channels are also taken into account in calculations of differential cross section and beam asymmetry. Important inputs of this model are the vector and tensor coupling constants of $\ensuremath{\omega}{\mathrm{NN}}^{*}(1440)$ vertex, which are assumed to be equal to the values of these couplings for $\ensuremath{\omega}\mathrm{NN}$ vertex. Using our previous estimation of $\ensuremath{\omega}\mathrm{NN}$ coupling constants obtained from a fit to available experimental data on photoproduction of $\ensuremath{\omega}$ meson in the near threshold region, we produce the necessary numerical predictions for different observables in $\ensuremath{\gamma}+\stackrel{\ensuremath{\rightarrow}}{N}\ensuremath{\omega}{+N}^{*}(1440).$ Numerical results show that at low $|t|$ dominant contribution comes from t channel $\ensuremath{\pi}$ exchange while the effects of nucleon and ${N}^{*}(1440)$ pole terms can be seen at large $|t|.$ Our predictions for the differential cross section and beam asymmetry for the processes $\ensuremath{\gamma}+\stackrel{\ensuremath{\rightarrow}}{N}\ensuremath{\omega}{+N}^{*}(1440),$ where N is proton and neutron, at ${E}_{\ensuremath{\gamma}}=2.5\mathrm{GeV}$ are presented with zero width approximation and also with the inclusion of width effects of ${N}^{*}(1440).$

Role of Δ exchange for p annihilation into two-pion and three-pion channels

p annihilation into two pions and three pions is studied in a baryon exchange model. Annihilation diagrams involving nucleon as well as Δ-resonance exchanges are included consistently in the two- and three-pion channels. Effects from the initial-state interaction are fully taken into account. A comparison of the influence of the Δ exchange on the considered annihilation channels is made and reveals that its importance for three-pion annihilation is strongly reduced as compared to two-pion annihilation. It is found that annihilation into three uncorrelated pions can yield up to 10% of the total experimentally observed three-pion annihilation cross-section.

Spin effects in backward deuteron scattering and baryonic degrees of freedom in the deuteron

The effect of the baryon-resonance admixture to the deuteron wave function on the momentum dependences of the differential cross section, the tensor analyzing power T20, and the polarization-transfer coefficient κ0 for backward elastic deuteron-proton scattering at high energies is investigated. The reaction in question is assumed to proceed predominantly through nucleon and nucleon-resonance exchanges. The formalism used in this study is based on light-front dynamics. The effect of various parameters of the problem on the results of the calculations is analyzed, and it is shown that, even at a 1% level of the total admixture of nucleon resonances to the deuteron wave function, a description of experimental data that is superior to that within the one-nucleon-exchange approximation can be achieved by appropriately choosing the contributions of various resonances. For qualitative agreement between the results of the calculations and experimental data to be attained, it is sufficient to take into account the contributions of the lightest negative-parity baryon resonances. Upon taking into account baryon exchanges, results computed for observables with different deuteron wave functions show a smaller scatter than analogous results obtained within the one-nucleon-exchange approximation.

Comprehensive evidence for a narrow ${\mathrm{p}}\overline{\mathrm{p}}$ state of mass 2.02 GeV $/c^2$

We review earlier results, and add new evidence, on the existence of a narrow \({\mathrm{p}}\overline{\mathrm{p}}\) state at a mass of 2.02 GeV\(/c^2\), which is seen in six different final states, produced via baryon exchange in \(\pi^+{\mathrm{p}}\)\((\pi^-{\mathrm{p}})\) interactions at 20 (12) GeV\(/c\). The data come from a new analysis of the WA56 experiment done at the CERN Omega spectrometer. The 2020 peak is produced near mid-rapidity, in a kinematic region not explored before in baryon exchange processes. Agreement is found with an earlier observation of this state, and its absence in a series of unsuccessful searches is explained. Very low upper limits on mesonic decays of this state favor its interpretation as a baryonium candidate.

Comprehensive evidence for a narrow

We review earlier results, and add new evidence, on the existence of a narrow ${\mathrm{p}}\overline{\mathrm{p}}$ state at a mass of 2.02 GeV $/c^2$ , which is seen in six different final states, produced via baryon exchange in $\pi^+{\mathrm{p}}$ $(\pi^-{\mathrm{p}})$ interactions at 20 (12) GeV $/c$ . The data come from a new analysis of the WA56 experiment done at the CERN Omega spectrometer. The 2020 peak is produced near mid-rapidity, in a kinematic region not explored before in baryon exchange processes. Agreement is found with an earlier observation of this state, and its absence in a series of unsuccessful searches is explained. Very low upper limits on mesonic decays of this state favor its interpretation as a baryonium candidate.