Search

Two-pole structures refer to the fact that two dynamically generated states are located close to each other between two coupled channels and have a mass difference smaller than the sum of their widths. Thus, the two poles overlap in the invariant mass distribution of their decay products, creating the impression that only one state exists. This phenomenon was first noticed for the Λ(1405) and the K1(1270), and then for several other states. This report explicitly shows how the two-pole structures emerge from the underlying universal chiral dynamics describing the coupled-channel interactions between a heavy matter particle and a pseudo-Nambu-Goldstone boson. Furthermore, we predict similar two-pole structures in other systems dictated by chiral symmetry, such as the isospin 1/2 K¯∑c − πΞ′c coupled channel, awaiting experimental discoveries.

In this work, we interpret the newly observed η 1 (1855) resonance with exotic J P C = 1 − + quantum numbers in the I = 0 sector, reported by the BESIII Collaboration, as a dynamically generated state from the interaction between the lightest pseudoscalar mesons and axial-vector mesons. The interaction is derived from the lowest order chiral Lagrangian from which the Weinberg–Tomozawa term is obtained, describing the transition amplitudes among the relevant channels, which are then unitarized using the Bethe–Salpeter equation, according to the chiral unitary approach. We evaluate the η 1 (1855) decays into the η η ′ and K K ¯ * π channels and find that the latter has a larger branching fraction. We also investigate its SU(3) partners, and according to our findings, the π 1 (1400) and π 1 (1600) structures may correspond to dynamically generated states, with the former one coupled mostly to the b 1 π component and the latter one coupled to the K 1 (1270) K ¯ channel. In particular, our result for the ratio Γ (π 1 (1600) → f 1 (1285) π) / Γ (π 1 (1600) → η ′ π) is consistent with the measured value, which supports our interpretation for the higher π 1 state. We also report two poles with a mass about 1.7 GeV in the I = 1 / 2 sector, which may be responsible for the K * (1680) . We suggest searching for two additional η 1 exotic mesons with masses around 1.4 and 1.7 GeV. In particular, the predicted η 1 (1700) is expected to have a width around 0.1 GeV and can decay easily into K K ¯ π π . [ABSTRACT FROM AUTHOR]

An exotic state with JPC = 1−+, denoted by η1(1855), was observed by BESIII Collaboration recently in J/ψ → γηη′. The fact that its mass is just below the threshold of KK̄1(1400) stimulates us to investigate whether this exotic state can be interpreted as a KK̄1(1400) + c.c. molecule or not. Using the one boson exchange model, we show that it is possible for KK̄1(1400) with JPC = 1−+ to bind together by taking the momentum cutoff Λ ≳ 2 GeV and yield the same binding energy as the experimental value when Λ ≈ 2.5 GeV. In this molecular picture, the predicted branch ratio Br(η1(1855) → ηη′) ≈ 15% is consistent with the experimental results, which again supports the molecular explanation of η1(1855). Relevant systems, namely KK̄1(1400) with JPC = 1−− and KK̄1(1270) with JPC = 1−±, are also investigated, some of which can be searched for in the future experiments. [ABSTRACT FROM AUTHOR]

Many efforts have been made to reveal the nature of the overabundant resonant structures observed by the worldwide experiments in the last two decades. Hadronic molecules attract special attention because many of these seemingly unconventional resonances are located close to the threshold of a pair of hadrons. To give an overall feature of the spectrum of hadronic molecules composed of a pair of heavy-antiheavy hadrons, namely, which pairs are possible to form molecular states, we take charmed hadrons for example to investigate the interaction between them and search for poles by solving the Bethe-Salpeter equation. We consider all possible combinations of hadron pairs of the S-wave singly-charmed mesons and baryons as well as the narrow P-wave charmed mesons. The interactions, which are assumed to be meson-exchange saturated, are described by constant contact terms which are resummed to generate poles. It turns out that if a system is attractive near threshold by the light meson exchange, there is a pole close to threshold corresponding to a bound state or a virtual state, depending on the strength of interaction and the cutoff. In total, 229 molecular states are predicted. The observed near-threshold structures with hidden-charm, like the famous X(3872) and Pc states, fit into the spectrum we obtain. We also highlight a Λc ¯Λc bound state that has a pole consistent with the cross section of the e+e- → ...c...c precisely measured by the BESIII Collaboration. [ABSTRACT FROM AUTHOR]

Abstract: The resonances () contribution to two-photon exchange (TPE) effects in is calculated in a simple hadronic model. The calculation shows the TPE contributions by resonance , which are dependent on the unknown phases of protonʼs time-like form factors , are much larger than the TPE contributions by non-resonance and are comparable with measurement precision of coming PANDA detector at for most . [Copyright &y& Elsevier]

Abstract: We extend our recent phenomenological study of reactions to the reactions for anti-proton beam momenta up to 3.0 GeV within an effective Lagrangian approach. The contribution of with its Nσ decay mode is found to be dominant at the energies close to threshold for and channels. At higher energies or for and channels where mode cannot contribute, large contributions from double-Δ, , and are found. In the near-threshold region, sizeable contributions from , , and nucleon pole are also indicated. Although these results are similar to those for reactions, the antinucleon–nucleon collisions are shown to be complementary to the nucleon–nucleon collisions and may even have advantages in some aspects. The PANDA/FAIR experiment is suggested to be an excellent place for studying the properties of relevant and resonances. [Copyright &y& Elsevier]

With an effective Lagrangian approach, we give a full analysis on the NN → NNππ and $\bar NN\, \to \,\bar NN\pi \pi $ 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 $\bar NN\, \to \,\bar NN\pi \pi $ 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 ${\rm {\bar PANDA}}$ 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. [ABSTRACT FROM AUTHOR]

Abstract: Evidence has been accumulating for the existence of significant intrinsic non-perturbative five-quark components in various baryons. The inclusion of the five-quark components gives a natural explanation of the excess of over , significant quark orbital angular momentum in the proton, the problematic mass and decay pattern of the lowest baryon nonet, etc.. A breathing mode of is suggested for the lowest baryon octet. Evidence of a predicted member of the new scheme, around 1380 MeV, is introduced. [Copyright &y& Elsevier]

The following sections are included: Introduction Conventional Meson Spectrum Glueball Spectrum Hybrid Mesons Multiquarks Molecular States [ABSTRACT FROM AUTHOR]

The following sections are included: Baryons as qqq States Outstanding Problems in Baryon Spectroscopy Baryon Spectroscopy at BESI and BESII Prospects for Baryon Spectroscopy at BESIII [ABSTRACT FROM AUTHOR]

The following sections are included: Partially Conserved Vector Current (PCAC) and Soft Pions Beyond the Breit–Wigner Description of a Broad Resonance Final State Interaction Theorem and Omnés Solution On the Nature of the Lightest Scalar Resonances [ABSTRACT FROM AUTHOR]

The following sections are included: Introduction Experimental Status of Two-Photon Processes Measurement of Two-Photon Processes at BES-III Summary [ABSTRACT FROM AUTHOR]

The strangeness production in heavy ion collisions was proposed to be probes of the nuclear equation of state, Kaon potential in nuclear medium, strange quark matter and quark-gluon plasma, etc. However, to act as reliable probes, proper understanding of the basic ingredients for the strangeness production, such as pp → pK+Λ, pp → ppϕ and pp → nK+Σ+ is necessary. Recent study of these reactions clearly shows that previously ignored contributions from the spin-parity 1/2- resonances, N*(1535) and Δ*(1620), are in fact very important for these reactions, especially for near-threshold energies. It is necessary to include these contributions for getting reliable calculation for the strangeness production in heavy ion collisions. [ABSTRACT FROM AUTHOR]

Abstract: The reaction is a very good isospin 3/2 filter for studying decaying to . With an effective Lagrangian approach, contributions from a previous ignored sub--threshold resonance are fully included in addition to those already considered in previous calculations. It is found that the resonance gives an overwhelmingly dominant contribution for energies very close to threshold, with a very important contribution from the t-channel ρ exchange. This solves the problem that all previous calculations seriously underestimate the near-threshold cross section by order(s) of magnitude. Many important implications of the results are discussed. [Copyright &y& Elsevier]

Abstract: We investigate the correlations between the scalar meson configurations and Okuba–Zweig–Iizuka (OZI) rule violations in the hadronic decays of heavy quarkonia, e.g., and ϒ, into isoscalar vector meson (ϕ and ω) and scalar mesons (, , and ). It shows that the dramatic change of the values of the branching ratio fraction of from low (e.g., in decays) to high energies (e.g., in ϒ decays) will not only test the glueball- mixings, but also provide important information about the mysterious OZI-rule violations within the scalars. [Copyright &y& Elsevier]

With accumulation of high statistics data at BES and CLEO-c, many new interesting channels can get enough statistics for partial-wave analysis (PWA). Among them, ψ↦γ p¯,γΛ¯,γΣ¯,γΞ¯ channels provide a good place for studying baryon-antibaryon interactions; the double radiative decays ψ↦γγ V with V ≡ ρ,ω,φ have a potential to provide information on the flavor content of any meson resonances (R) with positive charge parity ( C = +) and mass above 1 GeV through ψ↦γ R↦γγ V; ψ(2 s)↦γχc0,1,2 with χc0,1,2↦ K¯π+π- and 2π+2π- decays are good processes to study χcJ charmonium decays. Using the covariant tensor formalism, here we provide theoretical PWA formulae for these channels. [ABSTRACT FROM AUTHOR]

Taking proton as an ensemble of quark–gluon Fock states and using the principle of detailed balance, we construct a simple statistical model for parton distribution of proton. The recent observed Bjorken-x dependent light flavor sea quark asymmetry d¯(x)−u¯(x) can be well reproduced by Monte Carlo simulation as a pure statistical effect. [Copyright &y& Elsevier]

Abstract We extend our previous study on the decay behavior of P c hadronic molecules to their strange and beauty partners. While P c (4380) and P c (4450) locate just below the D ¯ Σ c ⁎ and D ¯ ⁎ Σ c thresholds, respectively, their proposed strange partners N (1875) and N (2080) sit just below the K Σ ⁎ and K ⁎ Σ thresholds, respectively. Using the effective Lagrangian approach as the same as for the study of P c hadronic molecular states and with the couplings determined by the SU (3) flavor symmetry, the decay patterns of N (1875) and N (2080) are obtained assuming them to be the S -wave K Σ ⁎ and K ⁎ Σ molecules, respectively. It is found that the measured decay properties of N (1875) and N (2080) are reproduced well. Our results suggest that both N (1875) and N (2080) can be described as the hadronic molecular pentaquark states in the hidden strangeness sector with quantum number I (J P) = 1 / 2 (3 / 2 −). Further checks on their hadronic molecule nature by various experiments are proposed. With the same approach, we also give our predictions for the decay behavior of the possible beauty partners of the P c hadronic molecular states. The B ⁎ Λ b is found to be the largest decay mode for both B Σ b ⁎ and B ⁎ Σ b hadronic molecules, hence can be used to look for the hidden beauty pentaquark states in forthcoming experiments. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses various reports within the issue that were written based on presentations at the Seventh International Symposium on Chiral Symmetry in Hadron and Nuclei with subtopics including chiral dynamics of few-body hadron systems, mesonic atoms and nuclei, and exotic hadrons.

Abstract: The study of the strangeness production from pp collisions plays important roles in two aspects: exploring the properties of baryon resonances involved and understanding the strangeness production from heavy ion collisions to explore the properties of high energy and high density nuclear matter. Here we review our recent studies on several most important channels for the strangeness production from pp collisions. The previously ignored contributions from and resonances are found to play dominant role for the , and reactions near-thresholds. These contributions should be included for further studies on the strangeness production from both pp collisions and heavy ion collisions. [Copyright &y& Elsevier]

Abstract: From recent studies of strangeness in the proton and properties of the lowest spin-parity 1/2− baryons, N*(1535) and , new pictures for the internal structure of the five-quark components in the proton and the lowest 1/2− baryon resonances are emerging. While the proton and the lowest 1/2− baryon nonet may have large diquark-diquark-antiquark components, the lowest 1/2− baryon decuplet is proposed to have vector-meson-baryon components. [Copyright &y& Elsevier]

Abstract: New measurement by CELSIUS-WASA Collaboration on the reaction reveals clear evidence for the presence of the Roper resonance which has been ignored in previous theoretical calculations. In this article, based on an effective Lagrangian approach and available knowledge on the Roper resonance, we investigate the role of the Roper resonance for the reaction. It is found that the contribution from the Roper resonance becomes significant for kinetic energy above 1.1 GeV, consistent with the new experimental observation. The t-channel σ-meson exchange is dominant for the production of the Roper resonance. [Copyright &y& Elsevier]