Baryon resonance state with strangeness $S = +1$ observed in systems $p K^0$ and $n K^+$ is interpreted as a result of the decay $N^{*+} \to p η$ of the well-known resonance $N^*(1535)$ (with spin-parity $j^P = {1/2}^-$ and mass $m \approx 1.54$ GeV) and the subsequent oscillation $η\rightleftarrows K^0$. It is argued that the latter is noticeably enhanced by the neighbourhood of the $η$ and $K^0$ levels and the gluon exchanges of the "penguin" form.
The pion nucleon sigma-term is extracted on the basis of the soliton picture of the nucleon from the mass spectrum of usual and the recently observed exotic baryons, assuming that they have positive parity. The value found is consistent with that inferred by means of conventional methods from pion nucleon scattering data. The study can also be considered as a phenomenological consistency check of the soliton picture of baryons.
We study heavy baryons with an exotic flavor quantum number formed by a heavy meson and a nucleon (Dbar-N and B-N) through a long range one pion exchange interaction. The bound state found previously in the (I,JP) =(0,1/2-) channel survives when short range interaction is included. In addition, we find a resonant state with (I,JP)=(0,3/2-) as a Feshbach resonance predominated by a heavy vector meson and a nucleon (Dbar*-N and B*-N). We find that these exotic states exist for the charm and heavier flavor region.
The light-mass exotics with J^{PC}=1^{-+} observed at BNL and CERN may have a simple explanation as dynamically generated resonances in eta-prime pi rescattering in the final state interaction. This dynamics is mediated by the same anomalous glue which also generates the large mass of the eta-prime. OZI violating processes are also potentially important to eta-prime production in proton-proton collisions close to threshold.
We investigate the potential of near-future neutrino telescopes like NESTOR for searches for exotic processes in ultrahigh energy neutrino-quark scattering. (NESTOR is the acronym for NEutrinos, from Supernovae and TeV sources, Ocean Range ... a water Cherenkov detector to be constructed in the Mediterranean off the coast of Greece). We consider signatures such as muon bundles and/or contained cascades from the nonperturbative production of multiple weak gauge bosons in the Standard Model, compositeness and leptoquark production.
The QCD sum rule approach is employed in order to study chiral properties of positive- and negative-parity nucleon resonances. It is pointed out that nucleons with an ``exotic'' chiral property, which can be represented by local five-quark operators, can be paired with a standard nucleon forming a single chiral multiplet. The sum rules of the five-quark operators, however, are shown not to couple strongly to chirally-``exotic'' nucleon resonances at the mass region of less than 2 GeV.
We classify the meson and baryon long lived resonances considering quarks with electric charge 5/3 and $-4/3$ (in units of $\vert e\vert$) predicted by some 3-3-1 models. Some of these exotic resonances have the usual electric charges $0,\pm1$, others have $\pm(3,4,5)$, and the lightest ones decaying only into leptons plus known resonances. We propose another heavy $SU(3)_H$ global symmetry under which hadrons involving only exotic quarks can be constructed.
Using large $N_c$ counting rule, it is argued that tetra-quark resonances do not exist. Also it is pointed out that there exists the violation of exchange degeneracy in the exotic $KN$ scattering channel. It implies either the failure of resonance saturation assumption or it suggests the existence of exotic baryon resonances in such a channel.
The exotic J^{PC}= 1^{-+} resonance π_{1}(1600)is examined in the framework of the Quark Model with Constituent Gluon (QMCG). We report the possibility of interpreting that resonance as quark-antiquark-gluon hybrid meson, with a masse = 1.65+0.05-0.04 GeV and a rho-pi decay width = 0.28+0.14-0.09 GeV.
We investigate the possibility that the light-mass exotic mesons with J^PC=1^-+ observed at BNL and CERN may be resonances in the eta-pi and eta'-pi systems associated with the anomalous glue which generates the eta' mass in QCD.
The K+ nucleon elastic scattering process has been reexamined in light of recent measurements which have found a narrow exotic S=+1 resonance in their KN invariant mass distributions. We have analyzed the existing database in order to consider the effect of a narrow state on fits to K+ nucleon observables.
A behavior of the nucleon structure functions in the resonance region is investigated. Expressions for resonance production form factors, dependent on photon virtuality $Q^2$, which have correct threshold behavior and take into account available data on resonance decays, are obtained. Contributions of resonances to nucleon structure functions are calculated. Obtained expressions are used to investigate the quark-hadron duality in the electron-nucleon scattering processes with the structure function $F_2$ as an example.
We study heavy baryons with exotic flavor quantum numbers formed by a heavy meson and a nucleon (DbarN and BN) with positive parity. One pion exchange interaction, providing a tensor force, dominates as a long range force to bind the DbarN and BN ystems. In the heavy quark mass limit, pseudoscalar meson and vector meson are degenerate and the binding mechanism by the tensor force analogous to that in the nuclear systems becomes important. As a result, we obtain the DbarN and BN resonant states in the J^P=1/2^+, 3/2^+ and 5/2^+ channels with I=0.
We investigate the electric form factors of the nucleon and Roper resonance using a quark-diquark model. We find that the charge radii of the nucleon and Roper resonance are almost the same in size.
We present a study of electroexcitation of nucleon resonances with higher spins, in a soft-wall AdS/QCD model, comparing our results with existing data from the CLAS Collaboration at JLab, from MAMI, and other experiments.
A Goldstone boson with a mass of 35 MeV is derived from the dibaryon masses found in the experimental data of B. Tatischeff et al. The existence of quantized vibrations is utilized to explain narrow width nucleon resonances below the pion-nucleon threshold. The quantum of 35 MeV is found between nucleon states with like spins and parities. Evidence of the 35 MeV quantum is in agreement with the mass operator method of the Fil'kov model for low-mass baryons and with the "light" pion concept of the Walcher particle-hole model. Azimov's idea of a low-lying baryon octet is revived with evidence fr…
The physics of electromagnetic excitation of nucleon resonances and of their relevance in nucleon structure studies are discussed. Preliminary data from the CLAS detector on the N-Delta(1232) transition multipoles, the helicity amplitudes of the N*(1535), and the search for so-called "missing resonances" at Jefferson Lab are presented.
Highlights in the search for nonconventional (non qqbar) meson states are the pi_1(1400) and pi_1(1600) exotic candidates. Should they exist, mounting theoretical arguments suggest that they are tetraquark molecular resonances excitable by meson rescattering. We report a new tetraquark calculation within a model field theory approximation to Quantum Chromodynamics in the Coulomb gauge supporting this conjecture. We also strengthen this claim by consistently contrasting results with exotic state predictions for hybrid (q qbar g) mesons within the same theoretical framework. Our findings confirm…
Many new states in the charmonium and bottomonium mass region were recently discovered by the BaBar, Belle and CDF Collaborations. We use the QCD Sum Rule approach to study the possible structure of some of these states. In particular we identify the recently observed bottomonium-like resonance $Z_b^+(10610)$ with the first excitation of the tetraquark $X_b(1^{++})$, the analogue of the X(3872) state in the charm sector.
We evaluate a hadronic molecule formed by a heavy meson and a nucleon respecting heavy quark symmetry. The tensor force of pion exchange potential plays a dominate role to produce an strong attraction in this system. Solving coupled channel Schrödinger equations for PN and P* N, we find many bound and resonant states with isospin I=0 while there are few resonances in I=1 state. The rich structures with I=0 indicate that the spectrum of heavy baryons near the threshold is influenced by the contributions from such hadron composite structures.
We outline how one can understand the Skyrme model from the modern perspective. We review the quantization of the SU(3) rotations of the Skyrmion, leading to the exotic baryons that cannot be made of three quarks. It is shown that in the limit of large number of colours the lowest-mass exotic baryons can be studied from the kaon-Skyrmion scattering amplitudes, an approach known after Callan and Klebanov. We follow this approach and find, both analytically and numerically, a strong Theta+ resonance in the scattering amplitude that is traced to the rotational mode. The Skyrme model does predict …
I study the very recently discovered S=-2 resonance Xi--(1886) by the NA49 collaboration at the CERN SPS. This resonance was already predicted, with a mass close to 1.9 GeV, in a recent publication mostly dedicated to the S=1 resonance Theta+(1540). To confirm this recent prediction, I apply the same standard quark model with a quark-antiquark annihilation constrained by chiral symmetry. This method also explained with success the repulsive hard core of nucleon-nucleon, kaon-nucleon exotic scattering, and the short range attraction present in pion-nucleon and pion-pion non-exotic scattering. I…
We develop a generalized version of heavy-baryon chiral perturbation theory to describe pion-nucleon scattering in a kinematic domain that extends continuously from threshold to the delta-isobar peak. The $P$-wave phase shifts are used to illustrate this framework.
The strongly repulsive core of the short-range nucleon-nucleon interaction leads to the existence of high-momentum nucleons in nuclei. Inclusive electron scattering can be used to probe these high-momentum nucleons and study the nature of the corresponding short-range correlations in nuclei. With recent data from Jefferson Lab we have begun to map out the strength of two-nucleon correlations in nuclei, while upcoming experiments should allow us to isolate the presence of multi-nucleon correlations. In addition to their importance in describing nuclear structure, these configurations of correla…
A description of the nucleon and Roper resonance in a quark-diquark approach is presented. We show that two states with the quantum number of the nucleon can appear in the ground state of the spatial configuration, when there are two types of diquarks: scalar-isoscalar and axial-vector-isovector diquarks. The mass difference between the two states is generated by the mass difference between the two diquarks, which is due to the spin-spin interaction between the two quarks in the diquarks. The two states are then identified with the nucleon and Roper resonance.
In this work, we study the interaction between a nucleon and a $P$-wave charmed meson in the $T$ doublet by exchanging a pion. Our calculations indicate that a nucleon and a $P$-wave charmed meson with $J^P=0^+$ or $J^P=1^+$ in the $T$ doublet can form bound states. We propose the experimental search for these exotic molecular states near the $D_1(2420)N$ and $D_2^*(2460)N$ thresholds, where Belle, LHCb and the forthcoming Belle II have the discovery potential for them.
We discuss the relations between Generalized Parton Distributions (GPDs) and nucleon resonances. We first briefly introduce the concept of "transition" GPDs. Then we discuss a straightforward application to the modelization of the N-$Δ$ magnetic transition form factor. Finally, we discuss the experimental aspects of the subject and present first preliminary experimental investigations in this field.
Influence of the effects of the pion-nucleon and nucleon-nucleon re-scattering on the polarization observables of the reaction gamma + d = p + p + pi- in Delta - isobar region is investigated. Pion-nucleon and nucleon-nucleon re-scattering are studied in the diagrammatic approach. Relativistic-invariant forms of the pion photoproduction and pion-nucleon scattering operators are used. The unitarization procedure in K-matrix approach is applied for the resonance partial amplitudes. It is shown a considerable influence of the re-scattering effects on the polarization observables of this reaction …
We study the very recently discovered $Θ^+$ (1540) at SPring-8, at ITEP and at CLAS-Thomas Jefferson Lab. We apply the same RGM techniques that already explained with success the repulsive hard core of nucleon-nucleon, kaon-nucleon exotic scattering, and the attractive hard core present in pion-nucleon and pion-pion non-exotic scattering. We find that the K-N repulsion excludes the Theta+ as a K-N s-wave pentaquark. We explore the Theta+ as heptaquark, equivalent to a N+pi+K borromean boundstate, with positive parity and total isospin I=0. We find that the kaon-nucleon repulsion is cancelled b…
We present a detailed analysis of resonance contributions in the context of higher twist effects in the moments of the proton spin structure function g_1. For each of these moments, it is found that there exists a characteristic Q^2 region in which (perturbative) higher twist corrections coexist with (non-perturbative) resonance contribution of comparable magnitude.
We study the very recently discovered Theta+ (1540) at SPring-8, at ITEP and at CLAS-Thomas Jefferson Lab. We apply the same RGM techniques that already explained with success the repulsive hard core of nucleon-nucleon, kaon-nucleon exotic scattering, and the attractive hard core present in pion-nucleon and pion-pion non-exotic scattering. We find that the K-N repulsion excludes the Theta+ as a K-N s-wave pentaquark. We explore the Theta+ as a heptaquark, equivalent to a N+pi+K borromean bound-state, with positive parity and total isospin I=0. We find that the kaon-nucleon repulsion is cancell…
In this talk we show how it is possible to apply the general scheme of effective scattering theory to the description of hadronic processes. We perform the numerical tests of the tree level bootstrap constraints for renormalization prescriptions in the case of elastic kaon-nucleon scattering process.
The axial charges of the nucleon and the well-established N* resonances are studied within a consistent framework. For the first time the axial charges of the N* resonances are produced for the relativistic constituent quark model. The axial charge of the nucleon is predicted close to experiment, and the ones of N*(1535) and N*(1650), the only cases where such a comparison is possible, agree well with results from quantum chromodynamics on the lattice that have recently become available. The relevance of the magnitudes of the N* axial charges for the low-energy behavior of quantum chromodynami…
We describe the electroproduction of the N(1440) Roper resonance in soft-wall AdS/QCD. The Roper resonance is identified as the first radially excited state of the nucleon, where higher-Fock states in addition to the three-quark component are included. The main conclusion is that the leading 3q component plays the dominant role in the description of electroproduction properties of this resonance: form factors, helicity amplitudes and charge densities. The obtained results are in good agreement with the recent results of the CLAS Collaboration at JLab.
The resonances, containing $c\bar c$ plus $s\bar s$ (or light $q\bar q$) quarks in the mass region $(3900-4700)$ MeV, are analyzed in the relativistic strong coupling theory, with and without channel coupling phenomena. The conventional charmonium spectrum is presented, being calculated with the relativistic string Hamiltonian, which does not contain fitting parameters, while for high excitations the universal flattened confining potential is used. It is shown that $X(4274),X(4500),X(4700)$ can be identified as $3\,^3P_1, 4\,^3P_0, 5\,^3P_0$ states. The exotic states are considered using the c…
We discuss the target and beam normal spin asymmetries in elastic electron-nucleon scattering which depend on the imaginary part of two-photon exchange processes between electron and nucleon. We express this imaginary part as a phase space integral over the doubly virtual Compton scattering tensor on the nucleon. We use unitarity to model the doubly virtual Compton scattering tensor in the resonance region in terms of $γ^* N \to πN$ electroabsorption amplitudes. Taking those amplitudes from a phenomenological analysis of pion electroproduction observables, we present results for beam and targe…
A relativistic light-front quark model is used to describe both the elastic nucleon and nucleon-Roper transition form factors in a large Q2 range, up to 35 GeV2 for the elastic and up to 12 GeV2 for the resonance case. Relativistic three-quark configurations satisfying the Pauli exclusion principle on the light-front are used for the derivation of the current matrix elements. The Roper resonance is considered as a mixed state of a three-quark core configuration and a molecular N+sigma hadron component. Based on this ansatz we obtain a realistic description of both processes, elastic and inelas…
In this talk we demonstrate the results of application of the perturbative effective theory formalism developed in recent papers to the calculation of $πN$ elastic scattering amplitude. Restrictions on the contributing resonance parameters are obtained and the low energy coefficients are calculated.
The (π^{-}Δ^{++}) production on the nucleon by real and virtual photons is discussed as initial step in a simple model approach for the two pion photo- and electroproduction on the nucleon, with emphasis on nucleon resonance excitation which is of interest for new facilities like TJNAF. A calculation for (π^{-}Δ^{++}) channel in resonance excitation region is presented and compared to existing experimental data along with a discussion of physical effects that we find to be of relevance. The calculation is proposed as a starting basis for the investigation of (N^{*}) electromagnetic form factor…
Vertex operators for photo- and electro-production of baryon states with arbitrary spin-parity, $ γ+ N\to B(J^P)$, are constructed. The operators obey gauge invariance and analyticity constraints. Analyticity is realized as a requirement of the generalized Siegert theorem for vertex form factors.
Nucleon and $Δ$ resonances in the fourth resonance region are studied in a multichannel partial-wave analysis which includes nearly all available data on pion- and photo-induced reactions off protons. In the high-mass range, above 1850\,MeV, several alternative solutions yield a good description of the data. For these solutions, masses, widths, pole residues and photo-couplings are given. In particular, we find evidence for nucleon resonances with spin-parities $J^P=1/2^+...7/2^+$. For one set of solutions, there are four resonances forming naturally a spin-quartet of resonances with orbital a…
A pedagogical review of the past 50 years of study of resonances, leading to our understanding of the quark content of baryons and mesons. The level of this review is intended for undergraduates or first-year graduate students. Topics covered include: the quark structure of the proton as revealed through deep inelastic scattering; structure functions and what they reveal about proton structure; and prospects for further studies with new and upgraded facilities, particularly a proposed electron-ion collider.
Recently several experimental groups analysed data on $π^- p \to ηπ^- p$ and $π^- p \to ηπ^0 n$ reactions with exotic $1^{-+}$ $P$-wave and found a conflicting evidence for an exotic meson $I=1 1^{-+} (1405)$. High statistics data on these reactions are presently analysed by BNL E852 Collaboration. All these analyses are based on the crucial assumption that the production amplitudes do not depend on nucleon spin. This assumption is in sharp conflict with the results of measurements of $π^- p \to π^- π^+ n$, $π^+ n \to π^+ π^- p$ and $K^+ n \to K^+ π^- p$ on polarized targets at CERN which find…
The mass and meson-current coupling constant of the resonance $X(5568)$, as well as the width of the decay $X(5568)\to B_s^{\ast}π$ are calculated by modeling the exotic $X(5568)$ resonance as a diquark-antidiquark state $% X_b=[su][bd]$ with quantum numbers $J^{P}=1^{+}$. The calculations are made employing QCD two-point sum rule method, where the quark, gluon and mixed vacuum condensates up to dimension eight are taken into account. The sum rule approach on the light-cone in its soft-meson approximation is used to explore the vertex $X_bB_{s}^{\ast}π$ and extract the strong coupling $% g_{X_…
The photo-production of nucleon resonances is calculated based on a chiral constituent quark model including both relativistic corrections H{rel} and two-body exchange currents, and it is shown that these effects play an important role. We also calculate the first moment of the nucleon spin structure function g1 (x,Q^2) in the resonance region, and obtain a sign-changing point around Q^2 ~ 0.27 {GeV}^2 for the proton.
Compound states manifest themselves as bound states, resonances, or primitives, and their character is determined by their interaction with the continuum. If the interaction experiences a perturbation, a compound state can change its manifestation. Phase analysis of nucleon-nucleon scattering indicates the existence of primitives in the 3S1, 1S0, and 3P0 channels. Electromagnetic interaction can shift primitives from the unitary cut, turning them into narrow resonances. We evaluate this effect on the 1S0 proton-proton scattering channel within the framework of the Simonov-Dyson model. We show …
Spin-$\ffh$ resonance contributions in pion-nucleon scattering are investigated within the coupled channel $K$-matrix approach for c.m. energies up to $\sqrt s=$ 2 GeV. All previously studied $πN$, $2πN$, $ηN$, $K Λ$, $K Σ$, and $ωN$ final states are included. We find a significant improvement of $χ^2$ in almost all channels by inclusion of the spin-$\ffh$ states. The obtained coupling parameters are discussed.
Inspired by the recent results of the WASA-at-COSY Collaboration, in which they found a resonance pole in the coupled $^{3}D_{3}$ - $^{3}G_{3}$ partial waves as expected from the $d^{*}$ resonance hypothesis, we calculated the resonance structure in the coupled $^{3}D_{3}$ - $^{3}G_{3}$ partial wave phase shifts of nucleon-nucleon scattering in the framework of two constituent quark models: the quark delocalization color screening model and the chiral quark model. Our results show that there is a resonance $^{7}S_{3}^{ΔΔ}$ in the coupled $^{3}D_{3}^{NN}$ and $^{3}G_{3}^{NN}$ partial waves in b…
Recent progress on the extraction of electromagnetic properties of nucleon resonance excitation through pion photo- and electroproduction is reviewed. Cross section data measured at MAMI, ELSA, and CEBAF are analyzed and compared to the analysis of other groups. On this basis, we derive longitudinal and transverse transition form factors for most of the four-star nucleon resonances. Furthermore, we discuss how the transition form factors can be used to obtain empirical transverse charge densities. Contour plots of the thus derived densities are shown for the Delta, Roper, S11, and D13 nucleon …
We have calculated coupling constants of a neutral pion with the lowest two nucleon resonances. This includes both the diagonal as well as non-diagonal coupling constants involving a nucleon resonance and a nucleon. For this, we first calculate vacuum-to-pion correlation function of the interpolating fields of two nucleons and then take its matrix elements with respect to a nucleon spinor and/or a nucleon resonance spinor(s). Using different QCD sum rules obtained from different matrix elements we eliminate unwanted coupling constants and solve for the desired ones. This is a simple extension …
In this work, we discuss the possibility of studying nucleon resonances in the $K^+N$ interactions. Based on our model calculations, it is found that the hyperon exchange plays an important role for the excitation of nucleon resonances in the $K^+N$ interactions. Therefore, the studies on nucleon resonance production in the $K^+N$ interactions can offer us valuable information about the couplings of nucleon resonances with strange particles. By selecting suitable decay channels of nucleon resonances, some reactions are also suitable to look for missing resonances.
We study the deeply-virtual Compton scattering (DVCS) process $e^- N \to e^- γπN$ involving the transition between a nucleon and a nucleon resonance in the $πN$ system, within the framework of generalized parton distributions (GPDs). For the four lowest-lying nucleon resonances, $Δ(1232)$, $P_{11}(1440)$, $D_{13}(1520)$, and $S_{11}(1535)$, we express the DVCS amplitude in the Bjorken limit in terms of corresponding nucleon-to-resonance GPDs. Building upon the knowledge of the well studied electromagnetic nucleon-to-resonance transition form factors, which map the quark charge densities in tra…
The role of the nucleon resonances ($N^*$) in $ω$ photoproduction is investigated by using the resonance parameters predicted by Capstick and Roberts. The contributions from the nucleon resonances are found to be significant in various spin asymmetries. In particular, we found that a crucial test of our predictions can be made by measuring the parity asymmetry and beam-target double asymmetry at forward scattering angles.
We review some results obtained by the Coimbra-Ljubljana collaboration that reveal the important role of the pion cloud in the low- and intermediate-energy nucleon and delta resonances.
Status, open questions, and future prospects of the physics of excited nucleons are discussed. Emphasis is on the study of the structure of nucleons via measurements of their electromagnetic transition form factors, the search for "missing" resonances, the spin structure of the nucleon in the resonance region, and connections between the resonance and the deep-inelastic regimes.
The negative-parity baryons are studied by a novel approach in the QCD sum rule. It is found that the parity of the ground-state nucleon is determined by the sign of the quark condensate. We predict the mass of negative-parity nucleon.
We study the strong couplings of the nucleon and delta resonances in a collective model. In the ensuing algebraic treatment we derive closed expressions for decay widths which are used to analyze the experimental data for strong decays into the pion and eta channels.
We utilize a light-front relativistic quark model (LF RQM) to predict the 3q core contribution to the electroexcitation amplitudes for the Delta(1232)P33, N(1440)P11, N(1520)D13, and N(1535)S11 up to Q2= 12GeV2. The parameters of the model have been specified via description of the nucleon electromagnetic form factors in the approach that combines 3q and pion-cloud contributions in the LF dynamics.
