Prediction of narrow N* and Λ* resonances with hidden charm above 4 GeV

Double-Strangeness Molecular-Type Pentaquarks from Coupled-Channel Dynamics

The existence of pentaquarks with strangeness content zero and one are major discoveries of the latest years in hadron physics. Most of these states can be understood as hadronic molecules and were predicted prior to their discovery within a model based on unitarized meson-baryon amplitudes obtained from vector-meson exchange interactions. Contrary to earlier statements, we show this model to also predict the existence of pentaquarks with double strangeness, at about 4500 and 4600 MeV, which are generated in a very specific and unique mechanism, via an attraction induced by a strong coupling between the two heaviest meson-baryon states.

An updated review of the new hadron states

The past decades witnessed the golden era of hadron physics. Many excited open heavy flavor mesons and baryons have been observed since 2017. We shall provide an updated review of the recent experimental and theoretical progresses in this active field. Besides the conventional heavy hadrons, we shall also review the recently observed open heavy flavor tetraquark statesX(2900) andTcc+(3875)as well as the hidden heavy flavor multiquark statesX(6900),Pcs(4459)0,Zcs(3985)-,Zcs(4000)+, andZcs(4220)+. We will also cover the recent progresses on the glueballs and light hybrid mesons, which are the direct manifestations of the non-AbelianSU(3) gauge interaction of the Quantum Chromodynamics in the low-energy region.

Molecular interpretation of the LHCb pentaquarks from an analysis of J/ψp spectrum

A coupled-channel approach including the ΛcD¯(*) and ηcp channels in addition to the Σc(*)D¯(*) and J/ψp channels, as required by unitarity and heavy quark spin symmetry (HQSS), is applied to the hidden-charm pentaquark Pc states, i.e., Pc(4312), Pc(4440) and Pc(4457), discovered by LHCb Collaboration. It is demonstrated that to obtain cutoff independent results, the one-pion exchange potential in the multichannel systems is to be supplemented with next-leading order counter terms responsible for the S-wave-to-D-wave transitions. We show that the experimental data for the J/ψp mass distributions are fully in line with the ΣcD¯ and ΣcD¯* hadronic molecular interpretation of the Pc(4312) and Pc(4440)/Pc(4457), respectively. A narrow Σc*D¯ molecule around 4.38 GeV is required by the HQSS with the evidence for its existence seen in the J/ψp spectrum. Moreover, we predict the line shapes for the elastic and inelastic channels.

Compositeness and several applications to exotic hadronic states with heavy quarks

Several methods for studying the nature of a resonance are applied to resonances recently discovered in the bottonomium and charmonium sectors. We employ the effective-range expansion, the saturation of the width and compositeness of a resonance, as well as direct fits to data. The latter stem from generic S -matrix parameterization that account for relevant dynamical features associated to channels that couple strongly in an energy region around the resonance masses, in which their thresholds also lie. We report on results obtained with these methods for the resonances Zb(10610), Zb(10650), Zcs(3985), Zc(3900), X(4020), X(6900), X(6825), and Pcs(4459).

The BGOOD experiment at ELSA Exotic structures in the strange quark sector?

The BGOOD photoproduction experiment accesses forward meson angles and low momentum exchange kinematics in the uds sector, which may be sensitive to molecular-like hadronic structure. Recent highlights are summarised in these proceedings.

Implications of the Zcs(3985) and Zcs(4000) as two different states

Recently, the hidden charm tetraquark states Z_cs(3985) and Z_cs(4000) with strangeness were observed by the BESIII and LHCb collaborations, respectively, which are great breakthroughs for exploring exotic quantum chromodynamics (QCD) structures. The first and foremost question is whether they are the same state. In this work, we explore the implications of the narrower state Z_cs(3985) in BESIII and the wider one Z_cs(4000) in LHCb as two different states. Within a solvable nonrelativistic effective field theory, we include the possible violations of heavy quark spin symmetry and SU(3) flavor symmetry in a comprehensive approach. If Z_cs(3985) and Z_cs(4000) are two different states, our results show that Z_cs(4000)/Z_cs(3985) is the pure (|D‾_s^∗D〉+/-|D‾_sD^∗〉)/2 state, and the SU(3) flavor partner of Z_c(3900) is Z_cs(4000) rather than the Z_cs(3985). Another two important consequences are the existence of a tensor D‾_s^∗D^∗ resonance with mass about 4126 MeV and width 13 MeV, and the suppression of the decay mode Z_cs(3985)→J/ψK. The two consequences can be tested in experiments and distinguish the two-state interpretation from the one-state scheme.

Evidence of a J/ψΛ structure and observation of excited Ξ- states in the Ξb-→J/ψΛK- decay

First evidence of a structure in the J/ψΛ invariant mass distribution is obtained from an amplitude analysis of Ξ_b^-→J/ψΛK^- decays. The observed structure is consistent with being due to a charmonium pentaquark with strangeness with a significance of 3.1σ including systematic uncertainties and look-elsewhere effect. Its mass and width are determined to be 4458.8±2.9_-1.1^+4.7MeV and 17.3±6.5_-5.7^+8.0MeV, respectively, where the quoted uncertainties are statistical and systematic. The structure is also consistent with being due to two resonances. In addition, the narrow excited Ξ^- states, Ξ1690^- and Ξ1820^-, are seen for the first time in a Ξ_b^- decay, and their masses and widths are measured with improved precision. The analysis is performed using pp collision data corresponding to a total integrated luminosity of 9 fb^-1, collected with the LHCb experiment at centre-of-mass energies of 7, 8 and 13 TeV.

Tetra- and Penta-Quark Structures in the Constituent Quark Model

With the development of high energy physics experiments, a large amount of exotic states in the hadronic sector have been observed. In order to shed some light on the nature of the tetraquark and pentaquark candidates, a constituent quark model, along with the Gaussian expansion method, has been employed systematically in real- and complex-range investigations. We review herein the double- and fully-heavy tetraquarks, but also the hidden-charm, hidden-bottom and doubly charmed pentaquarks. Several exotic hadrons observed experimentally were well reproduced within our approach; moreover, their possible compositeness and other properties, such as their decay widths and general patterns in the spectrum, are analyzed. Besides, we report also some theoretical predictions of tetra- and penta-quark states which have not seen by experiment yet.

Exploring Possible Triangle Singularities in the Ξ b − → K − J / ψ Λ Decay

We analyze possible singularities in the J/ψΛ invariant mass distribution of the Ξb−→K−J/ψΛ process via triangle loop diagrams. Triangle singularities in the physical region are found in 18 different triangle loop diagrams. Among those with Ξ*-charmonium-Λ intermediate states, the one from the χc1Ξ(2120)Λ loop, which is located around 4628 MeV, is found the most likely to cause observable effects. One needs S- and P-waves in χc1Λ and J/ψΛ systems, respectively, when the quantum numbers of these systems are 1/2+ or 3/2+. When the quantum numbers of the Ξ(2120) are JP=1/2+, 1/2− or 3/2+, the peak structure should be sharper than the other JP choices. This suggests that although the whole strength is unknown, we should pay attention to the contributions from the Ξ*-charmonium-Λ triangle diagram if structures are observed in the J/ψΛ invariant mass spectrum experimentally. In addition, a few triangle diagrams with the Ds1*(2700) as one of the intermediate particles can also produce singularities in the J/ψΛ distribution, but at higher energies above 4.9 GeV.

Strangeness Photoproduction at the BGO-OD experiment

The BGO-OD experiment at the ELSA accelerator facility uses an energy tagged bremsstrahlung photon beam to investigate the excitation structure of the nucleon. The setup consists of a highly segmented BGO calorimeter surrounding the target, with a particle tracking magnetic spectrometer at forward angles.

BGO-OD is ideal for investigating low momentum transfer processes due to the acceptance and high momentum resolution at forward angles. In particular, this enables the investigation of strangeness photoproduction where t-channel exchange mechanisms play an important role. This also allows access to low momentum exchange kinematics where extended, molecular structure may manifest in reaction mechanisms.

First key results at low t indicate a cusp-like structure in K+Σ0 photoproduction at W = 1900 MeV, line shapes and differential cross sections for K+Λ(1405)→ K+Σ0π0, and a peak structure in K0SΣ0 photoproduction. The peak in the K0SΣ0 channel appears consistent with meson-baryon generated states, where equivalent models have been used to describe the PC pentaquark candidates in the heavy charmed quark sector.

K0SΣ0 photoproduction at the BGO-OD experiment

The BGO-OD experiment at the ELSA accelerator facility uses an energy tagged bremsstrahlung photon beam to investigate the excitation structure of the nucleon via meson photoproduction.

The setup with a BGO calorimeter surrounding the target and an open dipole spectrometer covering the for ward region is ideally suited for investigating low momentum transfer processes, in particular in strangeness photoproduction.

The associated photoproduction of K0S and hyperons is essential to understand the role of K* exchange mech anisms. A cusp-like structure observed in the yp → K0SΣ+ reaction at the K* threshold is described by models including dynamically generated resonances from vector meson-baryon interactions. Such interactions are pre dicted to give a peak like structure in K0SΣ0 photoproduction off the neutron. A very preliminary cross section is determined and compared to the prediction, the results appear to support the model

Towards a theory of baryon resonances

In this talk, I discuss methods that allow for a systematic and model-independent calculation of the hadron spectrum. These are lattice QCD and/or its corresponding Effective Field Theories. Assorted results are shown and I take the opportunity to discuss some misconceptions often found in the literature.

Interpretation of the LHCb P_{c}(4312)^{+} Signal

We study the nature of the new signal reported by LHCb in the J/ψp spectrum. Based on the S-matrix principles, we perform a minimum-bias analysis of the underlying reaction amplitude, focusing on the analytic properties that can be related to the microscopic origin of the P_{c}(4312)^{+} peak. By exploring several amplitude parametrizations, we find evidence for the attractive effect of the Σ_{c}^{+}D[over ¯]^{0} channel, which is not strong enough, however, to form a bound state.

Emergence of a Complete Heavy-Quark Spin Symmetry Multiplet: Seven Molecular Pentaquarks in Light of the Latest LHCb Analysis

A recent analysis by the LHCb Collaboration suggests the existence of three narrow pentaquarklike states-the P_{c}(4312), P_{c}(4440), and P_{c}(4457)-instead of just one in the previous analysis [the P_{c}(4450)]. The closeness of the P_{c}(4312) to the D[over ¯]Σ_{c} threshold and the P_{c}(4440)  and  P_{c}(4457) to the D[over ¯]^{*}Σ_{c} threshold suggests a molecular interpretation of these resonances. We show that these three pentaquarklike resonances can be naturally accommodated in a contact-range effective field theory description that incorporates heavy-quark spin symmetry. This description leads to the prediction of all the seven possible S-wave heavy antimeson-baryon molecules [that is, there should be four additional molecular pentaquarks in addition to the P_{c}(4312), P_{c}(4440), and P_{c}(4457)], providing the first example of a heavy-quark spin symmetry molecular multiplet that is complete. If this is confirmed, it will not only give us an impressive example of the application of heavy-quark symmetries and effective field theories in hadron physics, it will also uncover a clear and powerful ordering principle for the molecular spectrum, reminiscent of the SU(3)-flavor multiplets to which the light hadron spectrum conforms.

Observation of a Narrow Pentaquark State, P_{c}(4312)^{+}, and of the Two-Peak Structure of the P_{c}(4450)^{+}

A narrow pentaquark state, P_{c}(4312)^{+}, decaying to J/ψp, is discovered with a statistical significance of 7.3σ in a data sample of Λ_{b}^{0}→J/ψpK^{-} decays, which is an order of magnitude larger than that previously analyzed by the LHCb Collaboration. The P_{c}(4450)^{+} pentaquark structure formerly reported by LHCb is confirmed and observed to consist of two narrow overlapping peaks, P_{c}(4440)^{+} and P_{c}(4457)^{+}, where the statistical significance of this two-peak interpretation is 5.4σ. The proximity of the Σ_{c}^{+}D[over ¯]^{0} and Σ_{c}^{+}D[over ¯]^{*0} thresholds to the observed narrow peaks suggests that they play an important role in the dynamics of these states.

Aspects of baryon spectroscopy at ELSA

A renaissance in hadron specroscopy in both meson and baryon sectors was triggered by the discovery of the enigmatic X, Y, Z states. Meanwhile, the discussion on unconventional quark-gluon compositions to understand their internal structure expanded to baryonic states in the charm sector, i.e. the pentaquark candidates observed at LHCb. Old problems and recent findings in the strange sector may suggest similar structures to exist there as well. In this light recent results and the ongoing new BGO-OD experiment at ELSA are discussed.

Charmonium-nucleon interactions from the time-dependent HAL QCD method

The charmonium-nucleon effective central interactions have been computed by the time-dependent HAL QCD method. This gives an updated result of a previous study based on the time-independent method, which is now known to be problematic because of the difficulty in achieving the ground-state saturation. We discuss that the result is consistent with the heavy quark symmetry. No bound state is observed from the analysis of the scattering phase shift; however, this shall lead to a future search of the hidden-charm pentaquarks by considering channel-coupling effects.

Compact pentaquark states

We investigated the lightest pentaquark state observed by the LHCb collaboration as a compact five-quark ground-state, with spin S = 3/2, and we showed that this state belongs to a SUf(3) flavor octet by means of a group theory approach. Moreover, we predicted in a parameter-free way the pentaquark state mass spectra for all the octet-pentaquark states. Finally, by means of an effective Lagrangian approach, we computed the octet-pentaquark partial decay widths in J/ψΛ, J/ψΣ and J/ψΞ channels.

Towards Exotic Hidden-Charm Pentaquarks in QCD

Inspired by P(c)(4380) and P(c)(4450) recently observed by LHCb, a QCD sum rule investigation is performed, by which they can be identified as exotic hidden-charm pentaquarks composed of an anticharmed meson and a charmed baryon. Our results suggest that P(c)(4380) and P(c)(4450) have quantum numbers J(P)=3/2(-) and 5/2(+), respectively. Furthermore, two extra hidden-charm pentaqurks with configurations D̅Σ(c)(*) and D̅(*)Σ(c)(*) are predicted, which have spin-parity quantum numbers J(P)=3/2(-) and J(P)=5/2(+), respectively. As an important extension, the mass predictions of hidden-bottom pentaquarks are also given. Searches for these partners of P(c)(4380) and P(c)(4450) are especially accessible at future experiments like LHCb and BelleII.

Identifying Exotic Hidden-Charm Pentaquarks

The LHCb Collaboration at the Large Hadron Collider at CERN discovered two pentaquark states P_{c}(4380) and P_{c}(4450). These two hidden-charm states are interpreted as the loosely bound Σ_{c}(2455)D^{*} and Σ_{c}^{*}(2520)D^{*} molecular states in the boson exchange interaction model, which provides an explanation for why the experimental width of P_{c}(4450) is much narrower than that of P_{c}(4380). The discovery of the new resonances P_{c}(4380) and P_{c}(4450), indeed, opens a new page for hadron physics. The partners of P_{c}(4380) and P_{c}(4450) should be pursued in future experiments.

Observation of J/ψp Resonances Consistent with Pentaquark States in Λ_{b}^{0}→J/ψK^{-}p Decays

Observations of exotic structures in the J/ψp channel, which we refer to as charmonium-pentaquark states, in Λ_{b}^{0}→J/ψK^{-}p decays are presented. The data sample corresponds to an integrated luminosity of 3 fb^{-1} acquired with the LHCb detector from 7 and 8 TeV pp collisions. An amplitude analysis of the three-body final state reproduces the two-body mass and angular distributions. To obtain a satisfactory fit of the structures seen in the J/ψp mass spectrum, it is necessary to include two Breit-Wigner amplitudes that each describe a resonant state. The significance of each of these resonances is more than 9 standard deviations. One has a mass of 4380±8±29 MeV and a width of 205±18±86 MeV, while the second is narrower, with a mass of 4449.8±1.7±2.5 MeV and a width of 39±5±19 MeV. The preferred J^{P} assignments are of opposite parity, with one state having spin 3/2 and the other 5/2.