Why nucleon resonance excitations beyond the photopoint can play a unique role in leading the path towards a comprehensive QCD theory will be laid out and illustrated by recent exclusive meson electroproduction cross sections off free and bound nucleons, new anticipated results, as well as potential upcoming opportunities.
In the early days of QCD phenomenology, resonances were thought to arise from single-particle constituent-quark-model-like states dressed by their decay channels to become short-lived resonances. The lowest lying resonances were of primary importance and sophisticated models were developed to accommodate them. Here the N*(1440) Roper resonance, its partner the Δ(1600) resonance and...
In this talk, we'll start by motivating the study of two meson photoproduction in association with a nucleon target. Then we'll review the formalism to describe these reactions before showing the latest results from the CLAS and GlueX experimental collaborations at the Jefferson Lab.
Understanding the strong interaction dynamics that underlie the emergence of hadron mass (EHM) represents one of the most challenging open problems in hadronic physics. The new opportunities for gaining insight into EHM from the experimental results on the evolution of the N->N electroexcitation amplitudes (the so-called gvpN electrocouplings) with photon virtuality Q^2 will be presented....
The electromagnetic form factors of the hadrons provide important information on the internal structure of hadrons. Perturbative QCD can be applied to calculate form factors of baryons at very high energies but at low and intermediate energies difficulty emerge due to the non-perturbative nature of QCD. In the first part of the talk, I will give an introduction to the dispersion theory, a...
e+e− annihilation provide a clean source of baryon excitations. With the large datasets
of J/psi and psi(3686) collected at BESIII, recent results of excited nucleon states as
well as excited hyperon states from BESIII will be reported, including studies of Xi in
psi(3686)-> K- Lambda Xi+ +c.c. , N in psi(3686) -> p pbar pi0/eta, Lambda and
Sigma in psi(3686)-->Lambda Sigma-bar pi0,...
Nucleons are the most fundamental bound three-body systems in Nature. With the CLAS12 spectrometer at Jefferson Lab, the spectrum and the structure of nucleon resonances is explored. This includes studies of exclusive $\pi N$, $\pi^+\pi^-p$, $K\Lambda$, and $K\Sigma^0$ electroproduction reactions and the evolution of the electrocouplings of resonances with photon virtuality $Q^2$. Such type of...
A key step to improve our understanding of nucleon structure in terms of Generalized Parton
Distributions (GPDs) is the measurement of Deeply Virtual Compton Scattering on the neutron (nDVCS;
ed → e'nγ(p)). This process provides mainly, in the kinematic range covered at Jefferson Lab, an access
to the GPD E of the neutron, which is the least known and constrained GPD as of today....
It is experimentally and theoretically challenging to determine the ex-
act number of exited nucleon states and their properties, since the short
lifetime of these exited states leads to strongly overlapping resonances.
Using a polarized beam, a polarized target or using the polarization
of the recoil nucleon helps to measure single or double polarization
observables, that are needed for...
Since the prediction of the bound states of a singlet of the color SU(3), the H-dibaryon (uuddss) in 1977[1], discussions regarding the H-dibaryon have persisted. An experimental result on the double-lambda hypernucleus [2] provided a lower limit of H-dibaryon mass very close to the $\Lambda\Lambda$ threshold. However, the possibility of resonant states near the threshold cannot be ruled out...
The first polarized target experiment of the CLAS12 program at JLab took place last year, scattering 10.5 GeV electrons on longitudinally polarized protons and neutrons in hydrogenated- and deuterated-ammonia targets. It is of high interest for Deeply Virtual Compton Scattering (DVCS) studies since using polarized electron beams and polarized nucleon targets is necessary for the complete...
The structure of the $N^*(1535)$ and $N^*(1650)$ remains puzzling. They strongly couple with $N\pi$, $N\eta$, $\Lambda K$ and $\Sigma K$. However, only the scattering amplitude of $N\pi \to N\pi$ has been measured in experiments. On the other hand, lattice QCD performs calculations from the first principles of QCD theory. The spectrum in the finite volume will provide us with additional...
Study of the spectrum of hadrons provides important insights into the interaction of the strong force. Photoproduction experiments can play a key role in these investigations and are used in the search for hadrons with conventional as well as exotic quantum numbers, such as mesons with gluonic degrees of freedom.
The GlueX experiment at Jefferson Lab features a 9 GeV linearly polarized photon...
Our current understanding of hadrons is through QCD, and confinement in QCD leads to a rich spectrum of hadrons. Experimentally, hadronic resonances can appear as peaks in the invariant mass distributions. However, universal parameters of hadronic resonances are encoded theoretically in the poles of the $S$-matrix. Still, not all observed peaks necessarily correspond to hadronic...
The proton has played a major role in the scientific endeavor. For instance, over a century ago, it exposed the substructure of the atom and, decades later, empirical indications about the existence of quarks. Its scrutiny is thus crucial in understanding the most complicated facets of quantum chromodynamics. In this talk we present a symmetry-preserving scheme, based upon continuum Schwinger...
We study the properties of the hadron-hadron potentials and quark-antiquark potentials from the viewpoint of the channel coupling[1]. We introduce the effective hadron-hadron potential with coupled to the quark channel.
As an application, we construct a coupled-channel model of $c\bar{c}$ and $D\bar{D}$ to describe exotic hadron $X(3872)$[2].
For the obtained nonlocal potentials, we apply...
As part of the N* program, the CLAS detector in Hall B was used in a series of photoproduction experiments with the intention of performing a complete and over-determined measurement of the polarisation observables associated with strangeness photoproduction. Although sufficient observables have now been measured to enable the associated reaction amplitudes to be determined, facilitating a...
The progress on the so-called proton radius puzzle has been impressive in recent years. Corresponding advances for unstable baryons such as hyperons are more challenging to achieve, but are eagerly awaited: they would reveal the role of flavour in the strong interaction dynamics governing the femtometer structure of hadrons. Due to the short hyperon life-time, most methods that have been...
The High Acceptance Di-Electron Spectrometer (HADES) [1], installed at GSI/FAIR Helmholtzzentrum in Darmstadt, was designed for spectroscopy of positron-electron pairs in heavy-ion reactions in the SIS-18 energy range (1-2 GeV/nucleon). The HADES collaboration has measured inclusive e+e- production in proton-nucleus and nucleus-nucleus systems at various...
Generalized Parton Distributions (GPDs) are a well-established tool for the exploration of the 3D nucleon structure. While extensive studies have been performed to unravel the 3D structure of the ground-state nucleon, little is known about the 3D structure of baryon resonances. The nucleon-to-resonance transition GPDs provide a unique tool for exploring the 3D structure and mechanical...
Visible matter is characterised by a single mass scale; namely, the proton mass. The proton's existence and structure are supposed to be described by quantum chromodynamics (QCD); yet, absent Higgs boson couplings, chromodynamics is scale invariant. Thus, if the Standard Model is truly a part of the theory of Nature, then the distinct qualities of the proton and all its excitations are...
The initial scientific case for upgrading the Continuous Electron Beam Accelerator Facility (CEBAF) at
Jefferson Lab (JLab) to 22 GeV will be presented. The proposed physics program encompasses a large
and diverse range of transforamtive investigations centered around the non-perturbative dynamics
inherent in hadron structure and the exploration of strongly interacting systems. It builds...
In recent years, a new generation of photoproduction experiments measuring not only cross sections but also single and double polarization asymmetries has helped the partial wave analysis groups to provide much more stringent information about the involed reaction multipoles and thus the contributing nucleon resonances. However, almost all existing measurements were obtained using proton...
In addition to conventional hadrons, such as baryons and mesons, quantum chromodynamics predict the existence of other hadronic states based on the principle of colour confinement. Among these, hybrid states are particularly intriguing. They arise from excitation in the gluonic field or, in a constituent approach, from the inclusion of a constituent gluon within the system. In recent years,...
The well-established $\Lambda(1405)$ hyperon with $J^\pi = \frac{1}{2}^-$ may be a dual structure consisting of two overlapping $I=0$ resonances. Each resonance may couple to $\Sigma\pi$ and $N\overline{K}$ final states, but a direct measurement of these two decays for each resonance has not previously been done. Using the GlueX detector system at Jefferson Lab we have obtained high...
Hadrons physics experiments enable us to obtain a better understanding of the strong force in the non-perturbative regime. Electromagnetic form factors quantify the location and motion of the building blocks of hadrons at the femtometer scale. For stable hadrons the space like form factors are accessible in electron scattering experiments. For short lived baryons like hyperons, these...
The BGOOD experiment at ELSA, with its linearly polarized γ beam and large solid angle detector, is a powerful tool for the investigation of the nucleon structure via meson photoproduction.
New results of Σ beam asymmetry for η photoproduction off the proton in the
energy range 1250-1730 MeV will be presented. The Σ beam asymmetry has been extracted with an original technique that allows to...
The nucleon resonance spectrum provides fundamental information about non-perturbative QCD. The precise data from both photoproduction and hadronic reactions are essential in order to separate the overlapping broad nucleon resonances using a partial-wave analysis (PWA). The J-PARC E45 experiment has been set up to accurately measure the nucleon resonance spectrum through the $\pi N \to \pi\pi...
The total and differential cross sections of elastic nucleon-nucleon scattering processes are studied in the framework of holographic QCD, considering the Pomeron and Reggeon exchange in the Regge regime. In our model setup, the Pomeron and Reggeon exchange are described by the Reggeized spin-2 glueball and vector meson propagator, respectively. How those contributions change with the energy...
The importance of transition form factors for a complete QCD theory will be experimentally and theoretically motivated and with an introduction of the extraction of consistent helicity-dependent electroexcitation couplings, the panelists strive to initiate an open discussion on the premise of this session.
Artificial Intelligence (AI) has dramatically transformed the landscape of computing and data processing, marking a paradigm shift in how machines interact with data and perform complex tasks. By leveraging algorithms that can learn from and adapt to data, AI has enabled computers to process and analyze vast amounts of information at speeds and accuracies that were previously unimaginable.
In...
Current studies of the hadron spectrum are limited by the accuracy and consistency of datasets. Information derived from theory models often requires fits to points at specific values of kinematic variables, which needs interpolation between measured points. In sparse data sets the quantification of uncertainties is problematic.
Machine Learning is a powerful tool that can be used to build an...
At high energies, the (transition) form factors of hadrons are most sensitive to the respective minimal quark content. At low energies, however, the form factors are dominated by universal features related to pion physics. Only these Goldstone bosons can carry information over large distances. Dispersion theory is used to obtain a model-independent representation of vector-isovector baryon...
The existence of exotic multi-quark states beyond the conventional valence three quark and quark-antiquark systems has been unambiguously confirmed in the heavy quark sectors. Such states could manifest as single colour bound objects, or evolve from meson-baryon and meson-meson interactions, creating molecular like systems and re-scattering effects near production thresholds. Equivalent...
The quest of unraveling the nature of excited hadrons necessarily involves determination of universal parameters of these states. Such determinations require input, either from experiment or theory. The challenge in answering these questions from theory arises from the very structure of the theory of strong interaction (QCD).
Lattice gauge theory is the only tool available to us to tackle...
I will give an overview of the recent activities of the Joint Physics Analysis Center and the plans for the future.
The quark model predicts exotic hadrons beyond the conventional quark-antiquark mesons and three quark baryons. Exotic candidates have since been observed in the early 2000's. Since then several exotic states have been discovered. LHCb has reported on tetraquark candidates such as the X(3872), the discovery of pentaquark resonances in 2015, and the first double charmed tetraquark. Many...
The talk will summarize progress in the field of complete-experiment analyses, for both the extraction of full spin-amplitudes and for truncated partial-wave analyses. The utility of the obtained results for future experiments will be discussed, in particular in view of photoproduction experiments for both 2-body and multi-particle final-states.
Inclusive electron scattering cross sections from a hydrogen target at a beam energy of 10.6~GeV have been measured with data
collected from the CLAS12 spectrometer at Jefferson Laboratory. These data cover a wide kinematic area in invariant mass $W$ of the
final state hadrons from the meson threshold up to 2.5~GeV and in virtual photon four-momentum squared $Q^2$ from 1 to 10~GeV$^2$.
...
The overarching goal in the realm of strong QCD physics is to gain a fundamental understanding of the nature of hadronic matter and its interactions. This involves exploring how Quantum Chromodynamics (QCD) manifests itself on the scales relevant to the formation of hadrons. Identifying the underlying symmetries and degrees of freedom that dictate the observed properties of hadrons is crucial...
The three narrow Pc states decaying to J/ψp observed by the LHCb experiment are consistent with earlier predictions for one $\bar D\Sigma_c$ and two $\bar D^*\Sigma_c$ bound states. Their strange partners are expected to exist. Here we present evidence for the production of these N resonances with hidden strangeness in $\gamma p$ reactions, such as γp → ϕp, γp → KΣ, γp → KΣ*, γp → KΣ,...
Hadrons are strongly interacting systems whose dynamics is driven by complex intercommunication between quarks and gluons. The theory of strong interaction, Quantum ChromoDynamics (QCD) , is supposed to describe all particles, however, due to numerical complexity we are still far away from reaching this goal. In such a situation, experimental knowledge about existing resonances becomes...
Experiments focusing on the structure of excited nucleons rely on sophisticated instrumentation, including wide spectrometers and large calorimeters equipped with a variety of detectors such as SiPMs, silicon microstrip trackers, plastic scintillators, drift tubes, resistive plate chambers and a new generation of position-sensitive detectors with accurate timing capabilities. To meet the...
Modern experimental facilities, new theoretical techniques for the continuum bound-state problem and progress with lattice-regularized QCD may have provided indications that soft quark+quark (diquark) correlations play a crucial role in hadron physics. For example, theory indicates that the appearance of such correlations is a necessary consequence of dynamical chiral symmetry breaking, viz. a...
Electroproduction reactions reveal the structure of light baryon resonances. Recent results of a simultaneous analysis of $\pi N$, $\eta N$, and $K\Lambda$ electroproduction data with the Juelich-Bonn-Washington (JBW) approach are presented. The extraction of multipoles and their uncertainties is discussed, and preliminary results for transition form factors at the resonance poles are shown.
Diquarks are often used as QCD effective degrees of freedom to describe nucleons and other baryons as well as exotic hadrons. However, even though they are successful in describing many of these low lying QCD states they and their properties have been difficult to pin down robustly. Here we present progress in studying diquarks in a gauge-invariant setup through embedding them in a parent...
The SPring-8 LEPS2 project explores the nature of hadrons through photoproduction processes by using a photon beam which is linear-polarized uniquely up to 2.4 GeV. One of the main subjects of LEPS2 is a light baryon spectroscopy in the s-channel of various meson photoproduction reactions. For this purpose, the BGOegg experiment was carried out with a detector setup where a liquid hydrogen...
Over the years, hadrons and their electromagnetic properties have been probed by a
variety of scattering experiments, with recent results rising compelling questions and
challenging the way we think about their structure.
In this presentation, I offer an overview of recent advancements in the precise
determination of the evolution of the electromagnetic couplings with squared 4-
momentum...
Baryon-baryon interactions are fundamental to understanding physics
across diverse length scales. Recent advancements in numerical studies, particularly from a lattice QCD perspective, have provided valuable insights into these interactions involving strange, charm, and bottom quarks. This presentation will discuss the latest developments in this field, emphasizing state-of-the-art...
The excited states of the Xi hyperons remain poorly understood due to limited experimental studies. In this presentation, we present our recent studies focusing on Xi and hyperon resonances at the Belle experiment. We aim to shed light on the properties of these states. Furthermore, we provide an overview of the current status of the Belle II experiment, and discuss the prospects for future...
In charm and beauty sectors a manyfold of exotic multiquark states of tetra- or pentaquark structure have been observed. Since they generally reside close to decay thresholds, they appear as narrow resonances due to the small available phasespace and the fact that the decay products are hadronically stable. In the unflavored sector, however, such multiquark states will appear as broad...
Pion photoproduction in the $\gamma p \to \pi^0 p$ reaction has been measured in the FROST experiment at the Thomas Jefferson National Accelerator Facility. In this experiment, circularly polarized photons with energies up to 3.082 GeV impinged on a transversely polarized frozen-spin target. Final-state protons were detected in the CEBAF Large Acceptance Spectrometer. Results of the...
The investigation of N and Δ excitations, as well as the quest for missing baryonic resonances, remains a central challenge in today’s hadron spectroscopy. Traditional approaches utilizing unpolarized γp cross section measurements are limited in their spectroscopic utility due to the broad width of baryonic intermediate states and their consequent overlap in the mass spectrum. An alternative...
Electric dipole moments (EDM) of fundamental particles serve as crucial probes for physics beyond the Standard Model. Similarly, magnetic dipole moments (MDM) of baryons provide information on their substructure and serve as experimental benchmarks for testing low-energy Quantum Chromodynamics (QCD) models, particularly those related to non-perturbative QCD dynamics. To expand upon the global...
I will present current efforts in describing the properties of dibaryons with functional methods. This work extends previous applications to mesons, baryons and four-quark states using Dyson-Schwinger and Bethe-Salpeter equations, where the spectrum and structure of the states is calculated using quark and gluon degrees of freedom. One particular focus is on the deuteron and its internal...
A theoretical interpretation of d*(2380)(Jp=3+), which was observed by WASA@COSY collaboration, is given [1]. This dibaryon structure is studied on the quark-gluon degrees of freedom with a SU(3) chiral constituent quark model and Resonating Group Method. Its mass and wave function are evaluated using a couple channel calculation with and C8C8 channels. It is found that the hidden-color...
New high-statistics total cross-section data for the $\gamma p \rightarrow J/\psi p$ reaction from GlueX experiment do not show direct evidence of the exotic $P_c(4312)^+$ state observed by the LHCb Collaboration. There is, however, a noticeable ``dip'' structure in the GlueX data near the energy corresponding to the mass of the observed LHCb state. We perform a fit to the GlueX data and find...
The focus of the session will be on the spectrum and structure of nucleon resonances (N), as revealed through N electroexcitation amplitudes. Such fundamental information on the mechanisms of strong-coupling QCD is crucial to validating any proposed solution to the theory and explaining the emergence of mass. Precise data from both electron and pion beams are necessary for developing robust...
The color dynamics of quarks and gluons favors attractive diquark correlations within color singlet hadrons. These dynamical correlations of finite spatial extent appear to play an important role in studying nucleon transition form factors within a quark-diquark picture. We review existing progress and present some new but partial preliminary results within a simple contact interaction model.
One of the most puzzling aspects of the Standard Model is that the overwhelming majority of the mass of hadronic systems arises from massless and nearly massless objects. From the little that we do understand, we know that mass generation is intricately connected to the internal structure of hadronic systems. Somewhat counter intuitively, it is some of the lightest hadronic objects, the...
We review the recent experimental and theoretical
advances in the study of the electromagnetic
structure of baryons and transitions between baryon states.
The main focus is in the study of the
$\gamma^\ast N \to N^\ast$ transition amplitudes and multipole form
factors in terms of the squared momentum transfer $Q^2$.
The status of the states...
Abstract
For the first time in the history of particle physics high intensity beam
of neutral long-lived kaons will be used at JLab to study strange hadron
spectroscopy. In this talk I will discuss the possibility to observe
dozens of missing hyperons predicted by LQCD and CQM, but not
yet observed. It will also allow to observe and measure with high accuracy
positions and widths...
The GlueX Experiment uses an intense photon beam of with energies up to 12 GeV and a large acceptance spectrometer to study many issues in hadron physics. These characteristics allow in particular for the study of comparatively rare photoproduction processes. The study of doubly strange baryons is particularly interesting for understanding the baryon spectrum, due to many states which are...
The first excited state of the nucleon dominates many nuclear phenomena at energies above the pion-production threshold and plays a prominent role in the physics of the strong interaction. The study of the N →Δ transition form factors (TFFs) allows to shed light on key aspects of the nucleonic structure that are essential for the complete understanding of the nucleon dynamics. An experimental...
The Apparatus for Mesons and Baryon Experimental Research (AMBER) is a high-energy physics project at the CERN’s M2 beam line of the Super Proton Synchrotron (SPS). The broad physics program for the upcoming years includes the measurement of the anti-proton production cross-section in pp, pHe and pD collisions, to provide unique information for astrophysics data interpretation, the measurement...
The term two-pole structure refers to the fact that particular single states in the hadron spec- trum as listed in the PDG tables are often two states. In this talk, I will review the status of this emerging field and its consequences for our understanding of bound states in QCD.
