Baryon Resonances Research Articles

Radiative decays of dynamically generated charmed baryons

In this work we study the radiative decay of dynamically generated ${J}^{P}=\frac{{1}^{\ensuremath{-}}}{2}$ charm baryons into the ground state ${J}^{P}=\frac{{1}^{+}}{2}$ baryons. Since different theoretical interpretations of these baryonic resonances and, in particular, of the ${\ensuremath{\Lambda}}_{c}(2595)$, give different predictions, a precise experimental measurement of these decays would be an important step for understanding their nature.

LEADING MODES OF 3π0 PRODUCTION IN PROTON-PROTON COLLISIONS AT INCIDENT PROTON MOMENTUM 3.35 GeV/c

For the first time pp → pp3π0 has been measured at an incident proton momentum of Pb = 3.35 GeV / c . The total cross section has been determined. The reaction mechanism is studied by a Dalitz plot analyses, which indicate that the leading production and decay mechanism is closely related to the simultaneous excitation of Δ(1232) and N*(1440) baryon resonances.

DOUBLE PION PRODUCTION IN NN AND $\bar NN$ COLLISIONS

With an effective Lagrangian approach, we give a full analysis on the NN → NNππ and [Formula: see text] reactions by exploring the roles of various resonances with mass up to 1.72 GeV. We find large contributions from Δ, N*(1440), Δ(1600) and Δ(1620) resonances. Our calculations also indicate sizeable contributions from nucleon poles for the energies close to the threshold. A good description to the existing data of different isospin channels of NN → NNππ and [Formula: see text] for beam energies up to 2.2 GeV is reached. Our results provide important implications to the ABC effect and guildlines to the future experimental projects at COSY, HADES and HIRFL-CSR. We point out that the [Formula: see text] at FAIR could be an essential place for studying the properties of baryon resonances and the data with baryon and anti-baryon in final states are worth analyzing.

SPECTROSCOPY OF BARYON RESONANCES AT ELSA

Current and upcoming experiments at the ELectron Stretcher Accelerator (ELSA) facility will determine polarization (or spin) observables for photoproduction processes involving baryon resonances. Differences between the predictions for these observables can be large, and so conversely they provide strong constraints in the analyses that aim at studying the properties of known resonances and at searching for hitherto unobserved states. The current effort with the Crystal Barrel/TAPS detector at ELSA is to utilize highly-polarized frozen-spin (butanol) and deuterium targets in combination with polarized photon beams. I will discuss recent spectroscopy results and present a brief status of the polarization program.

MESON PRODUCTION AND BARYON RESONANCES AT CLAS

I give a brief overview of the exploration of baryon properties in meson photo- and electroproduction. These processes provide ample information for the study of electromagnetic couplings of baryon resonances and to search for states, yet to be discovered. The CLAS detector, combined with the use of energy-tagged polarized photons and polarized electrons, as well as polarized targets and the measurement of recoil polarization, provide the tools for a comprehensive nucleon resonance program. I briefly present the status of this program, prospects for the next few years, and plans for the Jefferson Lab 12 GeV upgrade.

INVESTIGATION OF B-MESON DECAYS INTO BARYONS WITH THE BABAR DETECTOR

We report on investigations of B-meson decays into baryons with the BABAR detector. The comparison of different decay channels reveals that higher multiplicities are preferred for these decays. Furthermore, an enhancement in the invariant baryon-antibaryon mass distribution can be observed in several baryonic decay modes. In addition, the study of baryon resonances seen in baryonic B-meson decays is presented.

Dilepton production in proton-proton and quasifree proton-neutron reactions at 1.25 GeV

We investigate the pp --> pp e+e- and quasifree pn --> pn e+e- reactions within an effective Lagrangian model at the laboratory kinetic energy of 1.25 GeV for which experimental data have recently been reported by the HADES Collaboration. The model uses a meson-exchange approximation to describe the initial nucleon-nucleon (NN) scattering. Contributions to the reaction amplitudes are included from the NN bremsstrahlung as well as from the excitation, propagation and radiative decay of the Delta(1230) isobar state. It is found that the HADES data on the e+e- invariant mass distribution in the pp --> pp e+e- reaction are reproduced excellently by our model where the Delta isobar term dominates the spectrum. However, the quasifree pn --> pn e+e- cross sections are underpredicted in the invariant mass region of 0.40 - 0.55 GeV/c^2 even after including contributions of the eta Dalitz decay and the subthreshold production and decay of the rho^0 meson via the baryonic resonance N*(1520). In the case of the quasifree pn --> pn e+e- reaction, a strong sensitivity to the pion electromagnetic form factor is observed which helps to bring the calculated cross sections closer to the data in the higher dilepton mass region.

Three Body Systems with Strangeness and Exotic Systems

We report on four Σ’s and three Λ’s, in the 1500–1800 MeV region, as two meson—one baryon S-wave (1/2)+ resonances found by solving the Faddeev equations in the coupled channel approach, which can be associated to the existing S = −1, J P = 1/2+ low lying baryon resonances. On the other hand we also report on a new, hidden strangeness N * state, mostly made of \({K \bar{K} N}\), with mass around 1920 MeV, which we think could be responsible for the peak seen in the γp → K + Λ around this energy. Finally we address a very novel topic in which we show how few body systems of several ρ mesons can be produced, with their spins aligned up to J = 6, and how these states found theoretically can be associated to several known mesons with spins J = 2, 3, 4, 5, 6.

Analysis of recent $ \eta$ photoproduction data

Recent data on eta-meson photoproduction off a proton target in the energy range 2 < sqrt{s} < 3 GeV are analyzed with regard to their overall consistency. Results from the ELSA and CLAS measurements are compared with predictions of a Regge model whose reaction amplitude was fixed via a global fit to pre-2000 measurements of differential cross sections and polarization observables for gamma p -> eta p at higher energies. We find that all recent experimental results on differential cross sections for eta-meson photoproduction are in good agreement with each other, except for the CLAS data from 2009. However, the latter can be made consistent with the other data at the expense of introducing an energy-dependent renormalization factor. We point out that there indications in the data for a possible excitation of baryon resonances with masses around 2.1 and 2.4 GeV.

Theoretical Study of Formation Rates of η-, η′- and ω-Mesic Nuclei Induced by the Pion Beam

We present the theoretical study on formation rates of the η-, η′and ω-meson-nucleus systems induced by the (π,N) reactions on nuclear targets. For the η-mesic nuclei, we can study the in-medium properties of the N∗(1535) baryon resonance. As for the η′(958) mesonnucleus system, the in-medium UA(1) anomaly effect might be observed. We can also know the in-medium behavior of the ω meson by the (π,N) reaction with nuclear targets. We conclude that valuable information on mesons in the medium can be extracted from global structures of the missing mass spectra in the (π,N) reaction.

Chiral Quark Model Approach for the Study of Baryon Resonances

We report the chiral quark model approach for the study of baryon resonances in meson photoproduction and meson-nucleon scattering processes. Focussing on the $\pi N$ and $K N$ scatterings, we show that the cross sections near threshold can be well accounted for by the chiral quark model with only few parameters. The $S$-wave dominance in both $\pi^- p\to \eta n$ and $K^- p\to \Sigma^0\pi^0$ can be well understood in the quark model framework. In particular, the quark model provides a constraint on the relative signs for resonance coupling form factors, which seems to be consistent with results from isobaric models.

Three-body hadronic molecules

In this talk, I discuss our recent studies of three-hadron systems and the resonances found therein. The studies consist of solving Faddeev equations with the input two body interactions obtained from the chiral Lagrangians. The systems which we study are either made of two mesons and a baryon or of three mesons. The motivation for these studies comes from the data on many baryon resonances, especially the ones with Jπ = 1/2+, which show a large branching ratio to the two meson-one baryon decay channels. In addition to this, several new studies at BES, BELLE, BABAR etc., claim the existence of new meson resonances which seem to couple strongly to three-meson systems, where mostly two out of the three mesons appear as a known resonance. Hitherto, we have studied two meson-one baryon systems with strangeness = −1, 0 and 1 and three-meson systems made of two-pseudoscalars and a vector meson. As we will show in this manuscript, we find many resonances which couple to three-hadrons.

Charmed hadrons in nuclear medium

We study the properties of charmed hadrons in dense matter within a coupled-channel approach which accounts for Pauli blocking effects and meson self-energies in a self-consistent manner. We analyze the behaviour in this dense environment of dynamically-generated baryonic resonances as well as the open-charm meson spectral functions. We discuss the implications of the in-medium properties of open-charm mesons on the Ds0(2317) and the predicted X(3700) scalar resonances.

Exotic pentaquarks as Gamov–Teller resonances

If the number of colors Nc is taken large, baryons and their excitations can be considered in a mean-field approach. We argue that the mean field in baryons breaks spontaneously the spherical and SU(3) flavor symmetries, but retains the SU(2) symmetry of simultaneous rotations in space and isospace. The one-quark and quark-hole excitations in the mean field, together with the SU(3) rotational bands about them determine the spectrum of baryon resonances, which turns out to be in good accordance with reality when one puts Nc = 3. A by-product of this scheme is a confirmation of the light pentaquark Θ+ baryon uudds̄ as a typical Gamov–Teller resonance long known in nuclear physics. An extension of the same large-Nc logic to charmed baryons leads to a prediction of a anti-decapenta (1̄5̄)-plet of charmed pentaquarks, two of which, Bc++ = cuuds̄ and Bc+ = cudds̄, may be light and stable with respect to strong decays.

Resonances as a possible observable of hot and dense nuclear matter

One of the most fundamental questions in the field of relativistic heavy-ion physics is how to reach and explore densities which are needed to cross the chiral and/or the deconfinement phase transition. In this analysis we investigate the information we can gather by analyzing baryonic and mesonic resonances on the hot and dense phases in such nuclear reactions. The decay products of these resonances carry information on the properties of the resonances at the spacetime point of their decay. We especially investigate the percentage of reconstructable resonances as a function of density for heavy-ion collisions in the energy range between Elab = 30 A GeV and = 200 A GeV, the energy domain between the future FAIR facility and the present RHIC collider.

Differential cross sections and recoil polarizations for the reactionγp→K+Σ0

High-statistics measurements of differential cross sections and recoil polarizations for the reaction $\gamma p \rightarrow K^+ \Sigma^0$ have been obtained using the CLAS detector at Jefferson Lab. We cover center-of-mass energies ($\sqrt{s}$) from 1.69 to 2.84 GeV, with an extensive coverage in the $K^+$ production angle. Independent measurements were made using the $K^{+}p\pi^{-}$($\gamma$) and $K^{+}p$($\pi^-, \gamma$) final-state topologies, and were found to exhibit good agreement. Our differential cross sections show good agreement with earlier CLAS, SAPHIR and LEPS results, while offering better statistical precision and a 300-MeV increase in $\sqrt{s}$ coverage. Above $\sqrt{s} \approx 2.5$ GeV, $t$- and $u$-channel Regge scaling behavior can be seen at forward- and backward-angles, respectively. Our recoil polarization ($P_\Sigma$) measurements represent a substantial increase in kinematic coverage and enhanced precision over previous world data. At forward angles we find that $P_\Sigma$ is of the same magnitude but opposite sign as $P_\Lambda$, in agreement with the static SU(6) quark model prediction of $P_\Sigma \approx -P_\Lambda$. This expectation is violated in some mid- and backward-angle kinematic regimes, where $P_\Sigma$ and $P_\Lambda$ are of similar magnitudes but also have the same signs. In conjunction with several other meson photoproduction results recently published by CLAS, the present data will help constrain the partial wave analyses being performed to search for missing baryon resonances.

Partial wave analysis of Ψ′ → γχc0 → γpK− λ̄ used for searching for baryon resonance

Abundant Ψ′ events have been collected at the Beijing Electron Positron Collider- II (BEPCII) that could undoubtedly provide us with a great opportunity to study the more attractive charmonium decays. As has been noticed before, in the process of J/Ψ decaying to the baryonic final states, pK−λ̄, the evident Λ* and N* bands have been observed. Similarly, by using the product of χcJ from Ψ′ radiative decay, we may confirm this or find some extra new resonances. χc0's data samples will be more than χc1,2, taking into account the larger branching ratio of Ψ′ → γχc0. Here, we provide explicit partial wave analysis formulae for the very interesting channel Ψ′ → γχc0 → γpK−λ̄.

High-pTresonances as a possibility to explore hot and dense nuclear matter

One of the fundamental objectives of experiments with ultrarelativistic heavy ions is to explore strongly interacting matter at high baryon density and high temperature. In this investigation we apply a hadronic transport approach to study in particular the information that can be obtained by analyzing baryonic and mesonic resonances. The decay products of these resonances carry information on the resonances properties at the space-time point of their decay. We especially investigate the percentage of reconstructable resonances as a function of baryon density for heavy-ion collisions in the energy range between ${E}_{\mathrm{lab}}=30$ A GeV and $\sqrt{s}=200$ A GeV, the energy domain between the future GSI Facility for Antiproton and Ion Research and the present BNL Relativistic Heavy Ion Collider. It is shown that a transverse-momentum-dependent analysis of resonances might be beneficial for investigating the high-baryon-density phase of heavy-ion collisions.

Chiral dynamics and baryon resonances

The structure of baryon resonance in coupled-channel meson-baryon scattering is studied from the viewpoint of chiral dynamics. The meson-baryon scattering amplitude can be successfully described together with the properties of the resonance in the scattering, by implementing the unitarity condition for the amplitude whose low energy structure is constrained by chiral theorem. Recently, there have been a major progress in the study of the structure of the resonance in chiral dynamics. We review the methods to clarify the structure of the resonance by focusing on the Λ ( 1405 ) resonance.

Formation of a narrow baryon resonance with positive strangeness in K + collisions with Xe nuclei

The data on the charge-exchange reaction K^+Xe --> K^0 p Xe, obtained with the bubble chamber DIANA, are reanalyzed using increased statistics and updated selections. Our previous evidence for formation of a narrow pK^0 resonance with mass near 1538 MeV is confirmed and reinforced. The statistical significance of the signal reaches some 8\sigma (6\sigma) when estimated as S/\sqrt{B} (S/\sqrt{B+S}). The mass and intrinsic width of the \Theta^+ baryon are measured as m = (1538+-2) MeV and \Gamma = (0.39+-0.10) MeV.