One of the open challenges in subnuclear physics is to understand the
non-perturbative regime of Quantum Chromodynamics, including the world
of the nucleon and its excitations.
A necessary step towards this aim is a precise knowledge
of the experimental spectrum and the properties of baryon resonances.
Recently, large progress has been made especially based on photoproduction
experiments providing not only differential cross section
measurements but also high quality single and double polarization
observables.
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 the Λ(1405) all captured the attention of model builders. However, through the consideration of coupled-channel scattering, it is well known that resonances can also arise through nonperturbative rescattering processes without any resort to a quark-model-like state. Remarkably, experimental data alone is unable to resolve these two very different interpretations of the physical structure of baryon resonances.
The important development that is enabling the resolution of resonance structure is the ability to bring the coupled-channel analysis of experimental scattering data to the finite-volume of lattice QCD where predictions can be confronted with lattice-QCD calculations. This combination of experiment and lattice QCD demands that we reevaluate our notions of baryon resonance structure.
In this presentation, the infinite-volume world of experiment and the finite-volume world of lattice QCD are bridged by Hamiltonian effective field theory (HEFT), a nonperturbative extension of effective field theory incorporating the Luescher formalism. We'll discuss the model (in)dependence of the HEFT approach and then apply it to the Nucleon, Delta and Lambda spectra with an emphasis on resolving the physical structure of these spectra. New results for the Δ(1600) and Λ(1670) will be highlighted. We'll confront state of the art lattice QCD calculations of low-lying scattering states in these channels and examine the extent to which these lattice calculations are in accord with experiment. Finally, the impact these findings have on the missing baryon resonances problem will be summarised.
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 CLAS results on the electrocouplings of the Delta(1232)3/2+ and N(1440)1/2+ were successfully reproduced within the continuum Schwinger method (CSM) for Q2 from 1-5 GeV^2 by employing the same momentum dependence of the dressed quark mass inferred from the QCD Lagrangian that was used in the successful description of the pion and nucleon elastic electromagnetic form factors and supported in independent LQCD evaluations. The CSM predictions for the Delta(1600)3/2+ electrocouplings made in 2019 have been confirmed in analysis of the CLAS pi+pi-p electroproduction data published in 2023. This successful description of a broad array of observables within the CSM-framework offers sound evidence for insight into EHM from studies of the N electroexcitation amplitudes. New results on electrocouplings of Ns in the third resonance region will be available soon from analysis of pi+pi-p electroproduction data that will shed light on the connection between dynamical chiral symmetry breaking and EHM. Experiments of the 6-GeV era with CLAS allow us to explore the range of distances where <30% of hadron mass is expected to be generated while data from CLAS12 for Q^2 <10 GeV^2 will significantly extend this range. A further increase of the CEBAF energy to 22 GeV and pushing the capabilities of CLAS12 to measure exclusive meson electroproduction at luminosities up to 5-10^35 cm^-2s^-1 will offer the only foreseen opportunity to explore the full range of distances where the dominant part of hadron mass and N structure emerge from QCD
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 model-independent tool based on the first principles of QFT. I will show how dispersion relations relate space-like and time-like regions from the first principles. I will then present the dispersive formalism that we have constructed in the Uppsala group to study the form factors in the non-perturbative region. Some latest results in the nucleon sector will be presented. Our predictions can be tested in experiments such as Jlab, HADES+PANDA, Belle and BES. In the second part of the talk, I will talk about an ongoing project where we are studying how to combine both the dispersion theory and functional methods.
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. The
measurement of E, together with H, yields information on the quark total angular momentum – via the
Ji's sum rule – the missing ingredient to understand the nucleon spin composition. The GPD E is
accessed in nDVCS by measuring the Beam Spin Asymmetry (BSA). The measurement of the BSA of
nDVCS, combined with other nDVCS observables and from those obtained in pDVCS measurements,
will allow to perform the quark-flavor separation of the GPDs. This talk will report results for nDVCS
obtained at Jefferson Lab with a 10.5-GeV polarized electron beam, the Hall-B CLAS12 detector, and a
liquid deuterium target. The CLAS12 nDVCS beam-spin asymmetries provide unparalleled constraints
on the imaginary part of E, and, combined to proton-DVCS CLAS12 data, allow to extract its quark-
flavor dependence. An overview of the recent experiment on nDVCS carried out with CLAS12 and a
longitudinally polarized target will also be provided.
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 extraction of Generalized Partons Distributions (GPDs). These structure functions allow to describe the 3D structure of the nucleon, the origin of its spin, and the forces at play within it.
This experiment will allow the measurement of the DVCS target-spin and double-spin asymmetries on neutrons for the first time. From these observables, integrals of GPDs over the momentum fraction x (Compton Form Factors) will be extracted, giving access to the H and E GPDs for the neutron in particular. Combining results on the proton and the neutron will allow for the flavor decomposition of GPDs.
An overview of the experiment and the analysis will be presented, highlighting the tools specifically developed to work with a polarized nuclear target and preliminary results for DVCS asymmetries.
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 studies with CLAS have revealed a complex interplay between a core of dressed quarks and an external meson-baryon cloud inside of the excited nucleon states.
With CLAS12, also measurements of $N \to N^*$ transitions in the DIS region have been performed, addressing the three-dimensional structure of nucleon resonances through their transition GPDs (generalized parton distributions).
In the future, the increase of the CEBAF energy and the upgrade of the CLAS12 spectrometer to study exclusive electroproduction channels at higher luminosities and photon virtualities will offer a unique opportunity to study the nucleon excitation mechanisms.
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 an unambiguous partial wave analysis
solution.
The CBELSA/TAPS experiment in Bonn provides a polarized pho-
ton beam as well as a longitudinally or transversely polarized target,
allowing for the determination of single and double polarization ob-
servables. The Crystal Barrel (CB) calorimeter, together with the
MiniTAPS calorimeter in forward direction, give the opportunity for
close to 4$\pi$ coverage for the measurements.
This talk will present preliminary results of the determination of
the polarization observables T, P and H, for energies between 600MeV
and 3200MeV, using data collected after the recent upgrade of the
CB calorimeters readout electronics and these results are compared to
previous data and model predictions
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 information on the scattering amplitude of these coupled channels through the bridge between finite and infinite volumes. These new constraints will help us understand the structure of the $N^*(1535)$ and $N^*(1650)$. In this presentation, we will introduce recent work based on Hamiltonian Effective Field Theory (HEFT) for the N(1535) and N(1650) by analyzing the $N\pi \to N\pi$ scattering amplitudes and lattice energy levels simultaneously.
The statistical hadronization model is known to describe very well the yields of particles produced in heavy-ion collisions at LHC, RHIC, and SPS over many orders of magnitude. Recently, we have shown [1,2] that at lower energies, not just yields but also spectra of the most abundant particles containing u and d quarks can be reproduced in the thermal model.
Strangeness, heavy compared to the temperature and rarely produced, is not expected to thermalize at low energies. Instead, further insights can be gained by studying baryonic resonances, which are excited in large amounts in the system at high net-baryon density (high baryochemical potential).
In this talk, we will discuss Delta(1232) production using the thermal Monte Carlo event generator THERMINATOR 2, where we have implemented a finite width of the resonance based on the S-matrix theory [3]. Model predictions will be confronted with the unique set of experimental results published by the HADES collaboration [4].
References
[1] S. Harabasz et al., Phys.Rev.C 102 (2020) 5, 054903
[2] S. Harabasz et. al., Phys.Rev.C 107 (2023) 3, 034917
[3] P. M. Lo et al., Phys.Rev.C 96 (2017) 1, 015207
[4] J. Adamczewski-Musch et al. (HADES), Phys.Lett.B 819 (2021) 136421
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, etc. Recent results of baryon
spectroscopy at Belle will be reported as well.
Furthermore, multi-dimensional analyses making use of polarization and
entanglement can shed new light on the production and decay properties hyperon-
antihyperon pairs. In a series of recent studies performed at BESIII, significant
transverse polarization of the (anti)hyperons has been observed in 𝐽/𝜓 or 𝜓(3686) to
ΛΣ-bar , ΣΣ-bar , ΞΞ-bar .The decay parameters for the most common hadronic weak
decay modes were measured, and due to the non-zero polarization, the parameters
of hyperon and antihyperon decays could be determined independently of each other
for the first time. Comparing the hyperon and antihyperon decay parameters yields
precise tests of direct, Δ𝑆 = 1 CP-violation that complement studies performed in the
kaon sector.
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 at this time.
Recently, an experiment aimed at exploring the H-dibaryon has been conducted at J-PARC (E42 experiment) [3]. This experiment utilized a Hyperon Spectrometer, which consists of a superconducting magnet (HS magnet) and a gas electron multiplier (GEM)-based time projection chamber (HypTPC). This unique system, which incorporates the experimental target and operates even with beam injection, allows for unprecedented detection capabilities, enabling the identification of decay particles over a large acceptance. Consequently, it provides access not only to H-dibaryon exploration but also to various other hadron physics topics. Currently, analyses are simultaneously progressing on the following topics.
In this presentation, I will overview the distinguished experiment and also report the recent status of these analyses and preliminary results.
Ref.
[1] R. L. Jaffe, Phys. Rev. Lett. 38, 195 (1977)
[2] H. Takahashi et al., Phys. Rev. Lett. 87, 212502 (2001)
[3] J.K. Ahn et al, the proposal of J-PARC E42 experiment, Search for H-Dibaryon with a Large Acceptance Hyperon Spectrometer
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 resonances.
For example, the kinematical singularities, that correspond to intermediate particles going on shell and producing a peak in the invariant mass distributions, without any correspondance to a pole in the $S$-matrix. This was originally identified by Landau, and has been recently used to explain the $a_1(1420)$. We re-examine this scenario in the full three-body unitary approach, utilising a recent approach, and extending it to the relevant coupled-channel system. We show the pattern and mechanism leading to the triangle singularity to all orders in exchange diagrams.
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 methods, to calculate the electromagnetic transitions of the nucleon to its excited states, emphasizing those that produce a change in parity. Among other things, this allows us to inquire on how one of the corollaries of the Emergent Hadronic Mass, namely Dynamical Chiral Symmetry Breaking, manifests itself in changes in the hadron substructure; in particular, leading to the formation of non point-like dynamical diquarks.
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 two methods of the local approximation proposed previously, the formal derivative expansion and the derivative expansion in the HAL QCD method, by carefully examining the energy dependence of the potential.
We confirm that the local approximation by the HAL QCD method works better than the formal derivative expansion also for the energy-dependent potential. At the same time, we show that, in the HAL QCD method, the resulting phase shift is sensitive to the choice of the wavefunction to construct the local potential when the system has a shallow bound state such as $X(3872)$.
To investigate the internal structure of the $X(3872)$, we introduce the direct 4-point interaction of the hadron channel, in addition to the contribution of the coupling to the quark channel. We study the dominant component of the $X(3872)$ by analyzing the wavefunctions, compositeness, and pole trajectories.
[1] I. Terashima and T. Hyodo, Phys. Rev. C 108, 035204 (2023).
[2] M. Takizawa and S. Takeuchi, PTEP 2013, 093D01 (2013).
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 beam incident on a LH2 target, which is surrounded by an almost hermetic detector system. This makes GlueX an ideal tool to search for hadrons in a wide variety of final states with both charged and neutral final state particles, including strange hadrons decaying into kaons.
This talk presents results from our initial campaign of data taking.
Theory models [1] predict a total of 44 cascade states below 2.5 GeV. Currently, there are only six Ξ states that have at least a three-star rating in the PDG [2], with the production mechanism of these states still remaining mostly elusive. The goal of the “Very Strange” [3] project is to study the quasi-real photoproduction of cascades to search for missing and new states. This work focuses on the analysis of CLAS12 data collected at Jefferson Lab to study the production mechanisms and decays of excited Ξ- states that are not well established, with the possibility of determining their quantum numbers. The new data would make it possible to measure for the first time the beam polarisation transfer and induced polarisation of the Ξ- baryon as a kinematical variable function. Additionally, cascade studies look promising as a tool to differentiate genuine quark states from hadronic molecule states, for which the Ξ(1620) resonance has been proposed as a candidate [4]. Extracting more information about the cascade baryons could also allow us to begin unravelling the composition of the core of neutron stars [5], exploring the hyperon puzzle.
[1] S. Capstick and N. Isgur, “Baryons in a relativized quark model with chromodynamics”, (1986).
[2] J. Beringer et al. (Particle Data Group), “Review of Particle Physics”, (2012).
[3] A. Afanasev et al. (Very Strange Collaboration and CLAS collaboration at JLab), “Photoproduction of the Very Strangest Baryons on a Proton Target in CLAS12”, (2013).
[4] E.Oset, A.Ramos, C. Bernhold, “On the spin, parity and nature of the Ξ(1620) resonance”, (2018).
[5] A. Clevinger et al., “Hybrid equations of state for neutron stars with hyperons and deltas”, (2022).
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 near model-independent partial wave analysis, global data in strangeness channels is a couple of orders of magnitude smaller than pion photoproduction, so some ambiguities remain.
These ambiguities can be resolved by measuring observables spanning combinations of beam, target and recoil polarisation, all of which is possible with the CLAS data due to the self-analysing property of the hyperon and experiments involving polarised beams and targets. Studies on strangeness photoproduction reactions may provide evidence of previously undetermined resonances, due to the different coupling strengths of these states to other reaction channels.
This talk will focus on recent measurements of beam-target double polarisation observables on strangeness photoproduction channels being led by the York group on data from the FROST polarised target experiment, outline prospects for measuring target-recoil observables on this data, and highlight the “unfinished business” in strangeness photoproduction that awaits completion.
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 developed and utilized successfully for structure studies of nucleons, are not applicable. However, hyperons being unstable is not only a challenge but also a blessing: in weak, parity violating decays, features such as spin polarization and quantum correlations become experimentally accessible. This is in contrast to nucleons, for which dedicated polarimeter detectors are needed for this purpose. From the experimentally accessible spin properties, the full, complex time-like form factors can be extracted, which in turn give information about space-like quantities such as the charge radius.
The BESIII experiment at the electron-positron collider BEPC-II in Beijing, China, has performed a series of pioneering hyperon structure measurements through dedicated energy-scan campaigns. In my talk, I will present the results that have emerged from BESIII in the recent years, and discuss the next steps in our journey towards a more coherent understanding of hadron structure.
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 energies providing information on a contribution from baryonic matter which manifests itself as an excess radiation with respect to a nucleon-nucleon reference. The radiation is mediated by the rho vector meson, which properties (spectral function) are strongly modified in the cold or dense nuclear matter. These modifications are due to vector meson-baryon couplings and can also be studied in decays of baryonic resonances R → Ne+e- (Dalitz decays) providing information on the electromagnetic baryon-resonance transition form factors (eTFF) in the time-like region.
The elementary collisions, especially those with pion beams, offer a great opportunity to study eTFF in a direct way. The HADES collaboration has measured the $\Delta$(1232) Dalitz decay in pp collisions [2] delivering, for the first time, the $\Delta$ → pe+e- branching ratio. In the next step, using combined measurements of hadronic and dielectron final states in $\pi$-N collisions and Partial Wave Analysis (PWA) developed by the Bonn-Gatchina group [3], the contributions of N(1440), N(1520) and N(1535) to two pion and dielectron final states have been studied. As a result cross sections for $\Delta$$\pi$, N$\rho$, N$\sigma$ isobar contributions have been extracted. In dielectron channel the off-shell $\rho$ meson contribution to the Dalitz decays of N(1520) and N(1535) have been obtained and allowed for extraction of the mass dependence of the effective time-like eTFF [4]. Studies of angular distributions of emitted electrons have delivered information on hadronic spin density matrix elements (the helicity structure of baryon eTFF) [5]. The recent upgrade of the HADES detector [6] made possible to study also electromagnetic decays of hyperons. First measurements at HADES on both virtual and real photon decays, Y → Y e+e and Y* → Y $\gamma$ , have been performed in p+p collisions at 4.5 GeV [7].
The results of the HADES collaboration obtained with proton and pion beams will be presented. The eTFF will be compared to various versions of the Vector Dominance Model, to quark-constituent model [8] and Lagrangian microscopic calculations [5]. In addition the Dalitz decay will provide valuable information about eTFF of hyperon resonances. Prospects for HADES measurements at SIS-18 in the near future within the FAIR-Phase0 programme will also be discussed.
[1] G. Agakichiev et al. (HADES), Eur. Phys. J. A 41, 243 (2009).
[2] J. Adamczewski-Musch et al. (HADES), Phys. Rev. C95, 06520 (2017).
[3] J. Adamczewski-Musch et al. (HADES), Phys. Rev. C 102, 024001 (2020).
[4] R. Abou Yassine et al. (HADES), arXiv:2205.15914 [nucl-ex]
[5] M. Zétényi et al., Phys. Rev. C 104, 015201 (2021).
[6] J. Adamczewski-Musch et al. (HADES), Eur. Phys. J. A 57, 138 (2021).
[7] J. Rieger (HADES, PANDA@ HADES), EPJ Web of Conferences 291, 05005 (2024).
[8] G. Ramalho, M. T. Pena, Phys. Rev. D 95, 014003 (2017).
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 properties of such resonances, reaching beyond the 2D picture provided by the widely studied transition form factors and opening the way towards a deeper understanding of baryon resonances on the partonic level. Transition GPDs can be measured in exclusive processes with nucleon to resonance transitions, like N to N deeply virtual Compton scattering and N to N deeply virtual meson production, but also formalisms for a measurement with hadronic beams, especially meson beams, exist. The talk will provide an introduction to transition GPDs and the related higher-level observables. First experimental data from the $ep \to e \Delta^{++} \pi^{-}$ deeply virtual meson production process and from the $ep \to e \Delta^{++} \gamma$ deeply virtual Compton scattering process, available from the CLAS12 experiment at Jefferson Laboratory, will be presented, and further opportunities with other channels and different target polarizations will be discussed. In addition, future opportunities to measure transition GPDs at JLAB, J-PARC, COMPASS, and the EIC will be reviewed.
*The work is partly supported by Deutsche Forschungsgemeinschaft (Project No. 508107918).
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 emergent features of QCD. Indeed, baryons are the most fundamental three-body systems in Nature and the science challenge is to explain how QCD, a Poincare'-invariant quantum non-Abelian gauge theory, builds each of the baryons in the complete spectrum. Meeting this challenge must begin with an elucidation of the impacts of nonperturbatively-generated running-couplings and -masses on baryon properties and interactions. So, this presentation will give special emphasis to the three pillars of EHM -- namely, the running gluon mass, process-independent effective charge, and running quark mass; their role in stabilising QCD; and their measurable expressions in a diverse array of nucleon and resonance observables.
Author & Speaker: Prof. Craig Roberts, Nanjing University, cdroberts@nju.edu.cn
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 upon the unique
capabilities of CEBAF high-luminosity operations, the availability of existing or planned Hall equipment,
and recent advancements in accelerator technology. Highlights and some key measurements will be
discussed, with emphasis on the significant physics outcomes and unique aspects of these programs
that distinguish them from other existing or planned facilities.
Physicists investigate the subatomic world by bombarding their subject of study with a hail of tiny subatomic “bullets”. From the way these “bullets” bounce off their target one can infer a wealth of detailed information about the target’s structure. Different kinds of subatomic “bullets” probe different aspects of the target, certain important aspects of the force holding atomic nuclei together can only be investigated by shooting particles called antineutrons and hyperons, which are believed to be very difficult to produce and control. However these usually rare particles can be produced in copious amounts and easily launched as a spinoff of a “super J/ψ factory”. This opens fresh research opportunities in particle and nuclear physics, as well as in astrophysics and medical physics, requiring no additional infrastructure.
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 experiments are not feasible, giving the need for alternative approaches. In electromagnetic Dalitz decays of hyperons, the time-like structure can be accessed in terms of transition form factors. My special interest lies here in the $\Sigma^0$ to $\Lambda$ transition, the only electromagnetic transition between ground state hyperons.
Electromagnetic hyperon Dalitz decays have never been measured before but are predicted by theory. The FAIR Phase-0 experiment PANDA@HADES gives us the unique opportunity to measure this type of decays since it enables the reconstruction of the hadronic decay products of the hyperons as well as the electrons from the Dalitz decay. We are performing a differential measurement of the $\Sigma^0$ to $\Lambda$ Dalitz decay with the aim to provide a first estimate of the magnetization radius of the $\Sigma^0$ hyperon and the branching ratio of the $\Sigma^0$ Dalitz decay.
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 targets. Data on reactions off the neutron are scarce and mostly limited to unpolarized cross sections and only a few single polarization asymmetries.
New experiments at the electron stretcher accelerator ELSA in Bonn, with the Crystal Barrel/TAPS detector setup and a transversely polarized deuterated butanol target, allowed for the simultaneous measurement of the polarization observables $\Sigma$, T, P, and H off protons and neutrons. The data are of particular relevance for clarifying the origin of the narrow structure in the $\eta n$ system at W = 1.66 GeV.
In this talk, recent results on exclusive $\pi^0$ and $\eta$ photoproduction off quasi-free neutrons and their interpretation within the BnGa PWA are discussed.
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 statistics samples for the $\Lambda(1405)$ structure decaying to both final states. The photoproduction measurement in the beam energy range $6.5 - 11.6$ GeV used a liquid hydrogen target together with a large-acceptance charged particle tracking and electromagnetic calorimeter system. The experiment obtained the differential cross sections $d\sigma/dM_{\Sigma^{0}\pi^{0}}$ and $d\sigma/dM_{p K^-}$ in the $-(t-t_{min})$ range $0.0 - 1.5$~(GeV/c)$^2$ from analyzing the reaction $\gamma p \to K^{+}\Lambda^*$, collected during the first phase of GlueX running. The $\Sigma^{0}\pi^{0}$ data exhibited both the dual $\Lambda(1405)$ states and the $\Lambda(1520)$ hyperon. The $p K^-$ data were dominated by the $\Lambda(1520)$ hyperon sitting atop the tails of the $\Lambda(1405)$ states decaying to the $p K^-$ final state.
The data were subjected to $K$-matrix fits to both final state channels from one or two $\Lambda(1405)$ plus the $\Lambda(1520)$ resonances. The two-resonance hypothesis for the $\Lambda(1405)$ region resulted in much better matching to the experimental results. The complex $T$-matrix pole positions of the dual $\Lambda(1405)$ resonances as well as the $\Lambda(1520)$ were extracted, and the results will be presented. The results also include first-time measurements of the mass- and beam-energy- integrated photoproduction cross sections in the stated energy range for the dual $\Lambda(1405)$ and the $\Lambda(1520)$ states. Within the framework of the $K$-matrix fits to the $\Lambda(1405)$ states, the branching ratio and branching fractions to the $N\overline{K}$ and $\Sigma\pi$ final states were obtained for the first time and will also be presented.
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 simultaneously analyze all the available statistics from different η decay channels and periods with different efficiencies and polarization degrees.
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 $\pi N \to \pi\pi N$ hadronic reactions across an energy range from 1.5 to 2.15 GeV. The E45 detector system features a large-acceptance Superconducting Hyperon Spectrometer, equipped with a GEM-based time projection chamber (HypTPC). This spectrometer was designed for high-precision measurements with a high-rate capability up to 1 MHz beam at J-PARC. This presentation will discuss the current status of preparations and the anticipated outcomes of the E45 experiment.
In this talk I discuss the current status of the extraction of Low-energy constants (LEC) in the chiral Lagrangian with three light flavours from current Lattice QCD data. The LEC are adjusted to describe the baryon octet and decuplet masses from a large set of lattice ensembles, where finite-box and discretization effects are considered. Accurate results require an analysis at N^3LO.
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, both theoretical and experimental efforts have been dedicated to the study of hybrid mesons. Their identification seems, at first sight, easier since some $J^{PC}$ quantum numbers are forbidden in a $q\bar{q}$ configuration but allowed for $q\bar{q}g$. On the other hand, hybrid baryons do not have such ``smoking gun'' signature since all quantum numbers $J^P$ can be populated by conventional $qqq$ configuration. On the theory side, hybrid baryons have been studied within the framework of the MIT bag model, flux tube model, QCD sum rules, large-$N$ QCD and lattice QCD. Although these models predict the existence of hybrid baryons, their predictions for the masses and structures differ considerably from each other. On the experimental side, significant efforts are underway at the Jefferson Laboratory to identify these particles.
In this presentation, we propose a constituent model for describing hybrid baryons with heavy quarks. First, the flavour-spin-colour wavefunctions of the core of quarks are computed based on the Pauli exclusion principle. Then, the spin of the core of quarks is coupled to the helicity of the gluon by using the two-body helicity formalism of Jacob and Wick, leading to a series of helicity states with fixed $J^P$ quantum numbers. Eventually, the spectrum of the system is computed by the help of the method of the envelope theory, which was already used in the past for studying conventional baryons and hybrid mesons, with conclusive results.
We summarise recent theoretical results on the spectrum of three-
and four-quark states with strange and charm-quark content obtained
from functional QCD using Dyson-Schwinger and Bethe-Salpeter equations.
We discuss differences and similarities in the spectra of light and strange baryons
and address the flavour dependence and the internal structure of four-quark
states with open and hidden charm and bottom content.
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 is discussed in detail, focusing on the contribution ratios. The adjustable parameters involved in the model are determined with the experimental data, and it is presented that the resulting total and differential cross sections are consistent with the data in a wide kinematic region.
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.
A(i)DAPT is a program aiming to utilize AI techniques, in particular
generative modeling, to support Nuclear and High Energy Physics
experiments. Its purpose is to extract physics directly from data in the
most complete manner possible. Generative models such GANs and
Normalizing Flows are employed to capture the full correlations between
particles in the final state of nuclear reactions. This many-fold
program will allow us to to achieve various goals including accurately
fitting data in a multidimensional space and unfolding detector effects
to minimize their impact on the relevant physics. Moreover, it will
enable us to store a large amount of realistic-like data in an extremely
compact format and to extract reaction amplitudes in an alternative way.
We aim at incorporating universality of scattering amplitudes, training
networks with different kinematics of the same final state or different
final states to recover the underlying physics. As of today, we've
conducted a positive closure test on inclusive electron scattering,
demonstrating that generative models are able to reproduce $2\pi$
photoproduction data. We also showed that GANs are a viable tool to
unfold detector smearing, ensuring the preservation of initial correlations.
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 this talk the developments in CLAS12 tracking are presented leveraging machine learning techniques to achieve increased tracking efficiency, resulting in a 50%-75% increase in statistics in different physics reactions. The novel methods in track parameter reconstruction using artificial intelligence in CLAS12 allow physics reaction identification in real-time, leading to a significant reduction in data processing times (3 to 6 times) for experiments. The methods discussed can be applicable for future experiments running in streaming mode for data reduction and partial data processing in real time.
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 interpolated dataset, with quantification of uncertainties. The primary focus here is one type of machine learning called a Gaussian Process (GP). By calculating the covariance between known datapoints, the GP can predict the mean and standard deviation of other, unknown, datapoints. The model built here is checked and tested using Legendre polynomials to ensure it is unbiased and gives accurate predictions. This is then demonstrated on two datasets; one sparsely and one densely populated.
Whilst this model is only demonstrated on polarisation observables, it could easily be adapted to provide information on other measured quantities, such as cross-sections.
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 (transition) form factors at low energies. The ingredients are pion-baryon scattering amplitudes and the well-measured pion vector form factor. The latter is related to the p-wave pion phase shift, which contains as its most prominent feature the information about the rho meson. As a consequence, the dispersive framework leads to a model-independent version of vector-meson dominance. In the present scheme, motivated by chiral perturbation theory, the pion-baryon amplitudes are constructed from baryon-exchange diagrams providing the long-range aspects and subtraction constants for the short-distance physics. Also here the measured p-wave pion phase shift is utilized to account for the strong interactions between the pions. The baryon exchange diagrams are typically not included in models of vector-meson dominance and also not in quark models, in clear distinction to the scheme presented here. Up to now, the subtraction constants constitute free parameters and are determined by fits to experimental or lattice data. We apply this dispersive low-energy scheme to
1. the form factors of the nucleon, with focus on the dependence on both the virtuality and the pion mass [1,2];
2. the transition form factors of nucleon to Delta(1232) [3];
3. the transition form factors of nucleon to N*(1520) [4].
An outlook is provided how to improve the pion-baryon scattering amplitudes and how to tackle the determination of the subtraction constants.
[1] Stefan Leupold, Eur.Phys.J.A 54 (2018) 1, 1
[2] Fernando Alvarado, Di An, Luis Alvarez-Ruso, Stefan Leupold, Phys.Rev.D 108 (2023) 11, 114021
[3] Moh Moh Aung, Stefan Leupold, Elisabetta Perotti, Yupeng Yan, arXiv 2401.17756 [hep-ph]
[4] Di An, Stefan Leupold, in preparation
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 structures may be evidenced in the light, uds sector. The BGOOD photoproduction experiment at ELSA is ideal to study spatially extended, molecular-like structure which may manifest in strangeness photoproduction reaction mechanisms. BGOOD is comprised of a central calorimeter for neutral meson momentum reconstruction and complemented by a magnetic spectrometer in forward directions for charged particle identification.
Our published results in the strangeness sector may suggest a dominant role of meson-baryon dynamics which has an equivalence to the $P_c$ states in the charmed sector. This includes structure in $K^0\Sigma^0$ and $K^+(\Lambda(1405)\rightarrow \pi^0\Sigma^0)$ photoproduction at the $K^*Y$ thresholds having a direct analogue to the $P_c(4457)$ at the $\Sigma_C\bar{D}^*$ threshold.
In the non-strange baryon-baryon sector, coherent meson photoproduction off the deuteron enables access to proposed dibaryon states, including the recently discovered candidate, $d^*(2380)$. Our measured differential cross sections at forward angles challenge conventional descriptions of coherent photoproduction, which should be suppressed due to the large momentum transferred to the deuteron.
Supported by DFG projects 388979758/405882627 and the European Union’s Horizon 2020 programme, grant 824093.
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 the non-perturbative dynamics of QCD encoded in the determined finite-volume interaction spectra. Many insights have been gained on resonant two-body systems in the past by studying such spectra. Now -- with the advent of the three-body finite-volume methods -- advances are being made towards more complex systems. This progress will be discussed in the talk, including theoretical developments and applications to phenomenologically interesting systems.
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 theoretical approaches, including hadronic molecules and tightly bound tetra- and penta-quarks, aim to describe the nature and properties (mass/quantum numbers) of these states, also predicting that these exotic candidates may be part of a larger multiplet of exotic states. The discovery of further exotic hadrons and measurement of their properties will help to scrutinize these theoretical models and determine the internal structure of these states. LHCb is in a unique position to study a wide range of decay modes for multiple b-hadron species. The latest results of these studies from LHCb are presented and discussed.
Experimental investigations of the structure of excited nucleon states ($N^*$s) from different exclusive channels in terms of their $\gamma_vpN^*$ electrocouplings over a broad range of $Q^2$ are providing essential insights into the nature of the non-perturbative strong interaction responsible for their generation. Extraction of electrocouplings from analyses of $\pi N$, $\eta N$, and $\pi\pi N$ data from CLAS at JLab have been completed for most $N^*$ states up to 1.8~GeV and $Q^2 < 5$~GeV$^2$ with electron beams up to 6~GeV. Recent analyses of these results within QCD-connected approaches and quark models have shown remarkable agreement with data, leading to improved insights into the dynamical origins for the emergent part of hadron mass. New experiments with CLAS12 at beam energies up to 11~GeV extend $Q^2$ to $\approx$10~GeV$^2$, which will allow for the exploration of strong interaction dynamics at distance scales where the transition between quark-gluon confinement and pQCD is expected. Further advances in understanding $N^*$ structure, especially for states above 1.8~GeV, will rely on data from the $KY$ exclusive channels from CLAS and CLAS12 since some $N^*$s decay preferentially to $\pi \pi N$ final states. The $KY$ data are necessary to provide independent cross-checks for the extracted electrocouplings to those from other channels. In this regard, development of reaction models for $KY$ electroproduction are of particular importance. This presentation will highlight results from ongoing analyses of $KY$ final states from CLAS12 data. Future studies at a possible 22~GeV energy-upgraded JLab are also now being considered to approach the pQCD regime with studies of exclusive processes and will be discussed.
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$^2$.
Owing to the nearly $4\pi$ acceptance of the CLAS12 detector, the data cover a broad $W$-range in each $Q^2$ bin. For the first time,
the inclusive electron scattering cross sections in the resonance region have become available for $Q^2$ up to 10~GeV$^2$ with a broad
$W$-coverage in each bin of $Q^2$. Comparison with the resonant contributions computed from the CLAS results on the $Q^2$-evolution of
the nucleon resonance electroexcitation amplitudes has demonstrated a promising opportunity to extend the information on their
$Q^2$-evolution up to 10~GeV$^2$. Together these results from CLAS and CLAS12 offer the prospect for insight into the nucleon parton
distributions at large fractional parton momenta $x$ for $W < 2.5$~GeV, covering the range of distances where the transition from
the strongly coupled to pQCD regimes is expected. In this talk, I will discuss the current status of the analysis and the future plan.
An experimental program has been approved at the Thomas Jefferson National Accelerator Facility to measure the (ep,e’K+)Y reactions to search for new excited baryon states in the mass range from 1.8 GeV to 3 GeV with CLAS12.
Data have been obtained using electron beams with energies of 6.5, 7.5, and 10.2 GeV, impinging upon a liquid hydrogen target in the CLAS12 center. Scattered electrons have been detected in a polar angle range of 2.5° to 4.5° by the Forward Tagger (FT) and at angles greater than 6° in the CLAS12 Forward Detector, allowing to measure the KY electro-production differential cross section and to probe the Q2 evolution of the nucleon resonances electro-couplings in the Q2 range from 0.05 GeV2 to 3 GeV2. By studying the Q2 evolution of electroexcitation amplitudes it will be possible to distinguish between regular N states and possible additional hybrid baryon states in the mass range of 2.0 GeV < W < 2.5 GeV where the lightest hybrid baryons are expected to be located based on LQCD studies of the N* spectrum. Preliminary results for KY electroproduction will be reported and prospects for future studies will be discussed.
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.
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, etc., which give clear supports of the existence of the strange molecular partners of Pc states. More production processes of these N resonances with hidden strangeness are proposed to further test the hadronic molecular picture.
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 crucial. Over the last decade photoproduction proved to be a very valuable tool in extraction of resonance properties - all 6 new three/four-star N* resonances accepted by the Particle Data Group in 2004-2020 years originated from a clean and controlled photoproduction environment. One of the main features which allows photoproduction to be such a superior technique is the ability to access very sensitive polarisation observables. Single and double polarisation observables are a lot more sensitive in resonance searches compared to trivial bump-hunting technique. Due to technical limitations most groups are concentrated on polarisation observables which involve beam and/or target polarisation. In this research we present new data on the so-called spin-transfer variable Cx, which describes polarisation dependence of the recoil nucleon from photon helicity. The talk will present the world first results of neutron Cx for single-pion photoproduction on the proton, obtained with the Crystal Ball at MAMI with linearly and circularly polarised photon beams. It will be shown that these new types of data have very different sensitivity on PWA amplitudes. Inclusion of the new data in the database of the SAID partial wave analysis shifted the solution to a new global minima which, not only gives better agreement with the current data, but also improves the description of a range of other single and double polarisation observables for charged pion photoproduction. It will be shown that incorporations of other types of observables, beyond beam-target, is essential to unbiased extractions of the nuclear resonances properties.
The J-PARC Hadron Experimental Facility was constructed with an aim to explore the origin and evolution of matter in the universe through the experiments with intense particle beams. Over the past decade, many results in particle and nuclear physics have been obtained at the present facility. In order to expand the physics programs to unexplored regions that have never been reached, the extension project of the Hadron Experimental Facility has been extensively discussed. We will discuss the physics of the current and the extended Hadron Experimental Facility for solving the issues in the fields of the strangeness nuclear physics, hadron physics, and flavor physics.
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 to this pursuit. Experimentally, the focus is on exploiting the diverse spectrum of beams ranging from heavy ions to more elementary hadronic and electromagnetic probes. The accelerator facility GSI in Darmstadt, Germany, and its future extension, FAIR, are particularly unique since they offer pion, proton and anti-proton beams at various energies and with high intensities. Combined with versatile instruments (HADES, CBM, PANDA), GSI and FAIR provide a rich program addressing and connecting various topics within the fields of heavy-ion, nuclear, and hadron physics. In this talk, I will give an overview of the physics potential that is presently pursued at GSI and planned for FAIR in the context of strong QCD and its applications.
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 demand for precise spectroscopy and ToF measurements, waveform digitizers and ASICs have become standard tools for building robust readout systems capable of handling the vast amount of data generated by these detectors.
The FERS-5200 by CAEN addresses the challenge of providing flexibility and cost-effectiveness in the readout of large detector arrays. This distributed and easily scalable platform integrates the entire readout chain, from detector frontend to DAQ. Based on compact ASIC-based cards integrating A/D conversion and data processing, the FERS-5200 ensures optimal performance across extensive detector volumes without compromising readout efficiency. Synchronization, event building, and DAQ operations are efficiently managed by a single Concentrator board, capable of sustaining thousands of readout channels.
With its compatibility spanning a wide range of detectors such as SiPMs, multianode PMTs, GEMs, Silicon Strip detectors, Wire Chambers, and Gas Tubes, the FERS-5200 meets the diverse requirements in the field of nuclear and particle physics.
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 corollary of emergent hadronic mass that is responsible for almost all visible mass in the universe; experiment has uncovered signals for such correlations in, for instance, the flavour-separation of the proton's electromagnetic form factors; and phenomenology suggests that diquark correlations might be critical to the formation of exotic multiquark hadrons. A broad spectrum of such information is evaluated in this talk, with a view to consolidating the facts and therefrom moving toward a coherent, unified picture of hadron structure and the role that diquark correlations might play.
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.
The speaker will discuss the new structures reported by the CMS collaboration recently. Three structures are found in the J/ψJ/ψ mass spectrum in pp collisions at 13 TeV, and a model with quantum interference among these structures provides a good description of the data. Among them, a new structure with mass around 6.6 GeV is observed with a local significance > 5σ. Another structure with even higher significance is consistent with the X(6900) resonance reported by LHCb and confirmed by ATLAS. Evidence for another new structure, with a local significance of 4.7σ, is found at a mass around 7.1 GeV. Results are also reported for a model without interference, which does not fit the data as well and shows mass shifts relative to the model with interference.
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 hadron containing a spectactor quark using lattice QCD calculations.
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 target was covered by a large-acceptance and high-resolution electromagnetic calorimeter. Recent results on the baryon spectroscopy in the BGOegg experiment will be mainly discussed with plans by using the phase-2 upgraded setup. In addition, other recent results of the LEPS2 project will be mentioned as the related topics toward the understanding of hadron structures.
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 transfer, across both spacelike and timelike kinematic domains. I also
introduce the experimental revelation of long-anticipated yet previously elusive baryon
states, alongside the detection of exotic multiquark states.
Theoretical frameworks, driven by these new data, have witnessed significant progress,
enhancing consistency, refining uncertainty control, and broadening their applicability.
Beyond phenomenological quark models and sophisticated data analyses, I illustrate
that contemporary QCD calculations and continuum-based QCD functional methods,
such as Dyson-Schwinger-Bethe-Salpeter methods, are converging towards a unified
spectroscopic picture.
I particularly emphasize our current understanding of light baryons, which have
undergone meticulous scrutiny and precision analysis, thanks to detectors in the
acceptance frontier in facilities worldwide. These investigations have unveiled the rich
diversity in their internal composition.
Furthermore, I introduce the interpretation of various dynamic baryonic properties,
underscoring the importance of integrating independent theoretical methodologies. For
instance, the combination of chiral effective field theory with lattice QCD extrapolations
and large NC limit relations incorporating quark-antiquark degrees of freedom, plays a
crucial role in controlling uncertainties.
Measurements of the magnetic and electric dipole moments of particles are pivotal for understanding both Standard Model physics and its potential extensions. However, measuring these properties for short-lived particles presents inherent challenges. This study proposes innovative techniques for directly measuring the electromagnetic dipole moments of charm baryons at the Large Hadron Collider (LHC). We outline plans for a dedicated fixed-target experiment, detailing expected sensitivities from simulated detector setups. An experimental validation is foreseen for 2025 at LHC insertion region 3, utilising bent crystals. This test aims to confirm the feasibility of our approach, crucial for the future fixed-target experiment for charm baryon dipole moments.
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 effort in experimental electromagnetic dipole moment measurements, we propose an innovative approach focusing on $\Lambda$ baryons. This approach aims to significantly improve the existing measurements, which have remained unchanged for over four decades, performing the measurement for the first time with a collider experiment. Our proposed technique leverages the spin precession within the LHCb dipole magnet. The feasibility of reconstructing $\Lambda$ baryons using the tracking stations downstream of the LHCb dipole magnet will be outlined, highlighting the challenges and the advancements in the experimental technique. The resolution on the reconstructed quantities needed for the EMD and MDM measurement has been evaluated on data collected with the LHCb detector during the Run 2 of the LHC and compared with simulations. Additionally, we will discuss sensitivity studies and provide insights into the potential of dipole moment measurements during LHC Run3 and beyond.
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 studies of Xi resonances at Belle II and other facilities.
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 polarization observables $T$ and $F$ have been extracted. The data generally agree with predictions of present partial-wave analyses, but also show marked differences. By incorporating the present data into the databases, the SAID fits have been improved with relatively small $\chi^2$ and significant changes in the parameters of the $\Delta(1910)1/2^+$ and $N(2190)7/2^-$ have been found with the JüBo model.
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 avenue for exploration lies in the study of polarization variables, which are intimately linked to partial wave amplitudes, offering valuable insights into amplitude interference. This pursuit is significantly enhanced by experimental setups featuring both polarized beams and targets, which provide measurements of cross section asymmetries in different relative polarization states. The g14 experiment, conducted at CLAS (Jefferson Lab, USA) during 2011-2012, provided such conditions, employing a circularly polarized photon beam (momentum range: 0.6-2.3 GeV/c) interacting with a longitudinally polarized HD target. This presentation will discuss the results of beam-helicity and target-spin asymmetry measurements in two-pion photoproduction from these data. The two-pion channel, being the primary contributor to the total cross section, can potentially provide useful information for the investigation of intermediate states; in particular, about those located in the second resonance mass region, whose decay lead to an exclusive final state comprising two pions and a nucleon. The latest findings will be showcased and compared against previous results from CLAS and other experiments.
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 that the dip could be the result of destructive interference between the $P_c(4312)^+$ resonance and an associated non-resonant background. There are other possible explanations for this structure, including effects related to open charm thresholds; however the LHCb state is still compatible with the GlueX results. Further study will require additional statistics beyound the approximately 320 pb$^{-1}$ of the GlueX data set. One exciting new opportunity will b the the High-p Experiment at J-PARC, which is capable of measuring the $\pi^- p \rightarrow J/\psi n$ reaction. This will dramatically improve our understanding of the dynamics of $c\bar{c}$ production at the threshold and offer a new way to confirm the LHCb Pc states. Additionally, it will allow a high-precision determination of the $J/\psi$-$p$ scattering length independent from any assumptions of vector meson dominance.
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 methodologies employed in lattice investigations and their potential implications for future research.
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 resonances in general, since the decay products themselves constitute already very broad resonances. This complicates enormeously their unambiguous detection.
In this contribution the focus is on dibaryonic multiquark states, which may exist as loosely bound molecular systems or as deeply bound hexaquarks. The history of such objects has been paved with reams of pros and cons, until recently the d*(2380) has been detected - a quite narrow dibaryonic state with I(JP) = 0(3+) and deeply bound relative to the ΔΔ threshold [1,2].
Though this is the only unambigously identified dibaryon resonance so far, in view of the many recently discovered threshold states in the flavored sectors also the longstanding discussion about further unflavored dibaryon resonances near thresholds appears in a new light. There are a number of well-known states with definite spin-parity at the ΔN threshold. Since they appear as broad overlapping resonances in elastic scattering and single-pion production, sophisticated partial-wave analyses had to be utilized for their identification.
Very recently also evidence for dibaryonic states near the N*(1440)N threshold have been reported [3]. WASA-at-COSY data for the isoscalar single-pion production show that its cross section does not grow above threshold as expected conventionally, but rather exhibits a Lorerentzian shape suggesting isoscalar states with JP = 1+ and 1-.
Interestingly, a sophisticated NN-interaction model with intermediate dibaryon formation can account for all these states leading thus to a quantitative description of the corresponding experimental NN-phase-shifts in the range from 0 up to 1 GeV[4].
For the flavored sector many model predictions including LQCD [5] have been published with partly controversial results. Experimentally the search for the H-dibaryon is still going on. Very recently a deeply bound H-dibaryon, the socalled sexaquark has been proposed - being possibly even a dark matter candidate [6]. Possibly it could be searched for at the future K_long beamline of JLab.
[1] for a review see, e.g., H.Clement and T. Skorodko, Chin. Phys. C 45 (2021) 022001 and references therein
[2] M.Bashkanov and H. Clement, Nucl. Phys. A 1037 (2023) 122698
[3] H. Clement et al., Phys. Rev. C 106 (2022) 065204
[4] V. I. Kukulin et al., Chin. Phys. C 46 (2022) 114116
[5] HAL QCD, Phys. Rev. Lett. 127 (2021) 072003
[6] G. R. Farrar and N. Wintergerst, JHEP 12 (2023) 099 and references therein
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 structure, but in principle the approach can be extended to other dibaryons in the light, strange and charm region.
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 component C8C8 is dominant in its wave function. Moreover, its partial widths of almost all possible strong decays are also computed and the obtained results agree with the data well. Our study suggests that d(2380) may be assigned as a compact hexaquark system with significant hidden-color component. In addition, the electromagnetic characteristics of this 3+ dibaryon state, such as the charge distribution, charge radius, multipole moments, and etc. are further studied. We believe that those observables can be used as additional physical quantities to distinguish the different interpretations. Finally, the production of d*(2380) at forthcomingPanda is also estimated.
[1] Yubing Dong, Pengnian Shen, and Zongye Zhang, “d*(2380) in a chiral constituent quark model”, Prog. Part. Ncul. Phys. 131 (2023), 104045.
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 approaches for amplitude analyses, capable of delivering sound results for N quantum numbers and excitation amplitudes over a broad range of q2 to be interpreted starting from the QCD Lagrangian. Our workshop will foster the synergies necessary to move this effort forward in a timely way. (Context for this proposal is provided in Exploring the production of Ns with pion and electron beams [1], published December 2022 in the quarterly online journal The Innovation Platform.) We will focus on how to coordinate the physics of performing dynamical coupled-channel analyses on the reaction data of πN and g()N->ππN and KY. This will require a full amplitude and partial-wave analysis to constrain the pion- and electron-induced N production. We will also discuss spanning the gap of the space-like (q2 < 0) and time-like (q2 > 0) divide anchored by the photoproduction data at q2 = 0. There will be a short presentation on exploring the production of N*s with pion and electron beams, followed by a panel discussion and open forum.
[1] https://edition.pagesuite.com/html5/reader/production/default.aspx?pubname=&edid=34216959-80ec-4ce6-af9a-b90be9d71c84&pnum=288
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 charged pion and kaon, that may be able to fill in the missing piece of the puzzle. One potential window into the internal structure of the charged pion and kaon is their elastic electromagnetic form factors, $F_{\pi}(Q^{2})$ and $F_{K}(Q^{2})$. Electromagnetic form factors are fundamental quantities which describe the spatial distribution of partons within a hadron. Determining these form factors, as well as how they vary with $Q^{2}$, is an important step on our road to understanding the internal structure of these objects.
Recently measured data at JLab has the potential to push the $Q^{2}$ reach of these measurements is deep into unexplored territory. These cutting edge measurements could help disentangle the mass generation puzzle of QCD. In this talk, I will outline the current progress on these pion and kaon form factor measurements. I will also discuss the opportunities and challenges of further pion and kaon form factor measurements at future facilities, such as the EIC.
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 $\Delta(1232)\frac{3}{2}^+$,
$N(1440)\frac{1}{2}^+$, $N(1520)\frac{3}{2}^-$ and $N(1535)\frac{1}{2}^-$
is discussed in detail, but higher mass $N^\ast$ states
are also mentioned.
The results are interpreted using theoretical models
based on quark degrees of freedom, meson cloud excitations
of baryon cores, and others.
We also look for the analytic structure
of the helicity transition amplitudes and multipole form
factors in terms of the $N^\ast$ spin.
We will emphasize both the low-$Q^2$ and large-$Q^2$
regions to reinforce crucial physical constraints on observables that
hold in these limits.
Hypernuclei have been studied since the 1950's for understanding the fundamental baryon interaction under the flavored-SU(3) symmetry. We have been experimental investigating hypernuclei with induced reaction of heavy ion beams in the fixed nuclear target, and we recently conducted the WASA-FRS experiment at GSI (FAIR Phase 0). Furthermore, we have been analyzing nuclear emulsion data taken in the E07 experiment at J-PARC, and we study single- and double-strangeness hypernuclei. For the both experimental activities, we develop specific machine learning models. Details of these projects and our future plans will be discussed.
The proposed STCF is a symmetric electron-positron beam collider designed to provide e+e− interactions at a centerof-mass energy from 2.0 to 7.0 GeV. The peaking luminosity is expected to be 0.5×10^35 cm−2s−1. STCF is expected to deliver more than 1 ab−1 of integrated luminosity per year. The huge samples could be used to make precision measurements of the properties of XYZ particles; search for new sources of CP violation in the strange-hyperon and tau−lepton sectors; make precise independent mea-surements of the Cabibbo angle (theta)c) to test the unitarity of the CKM matrix; search for anomalous decays with sensitivities extending down to the level of SM-model expectations and so on. In this talk, the physics interests will be introduced as well as the the recent progress on the project R&D.
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 of strange mesons.
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 poorly known or unidentified that are expected to be narrow. The GlueX data has allowed for the identification of several of these states, opening a new window to the study of the cascade baryon spectrum. Additionally, the photoproduction of charmonium states near threshold is expected to proceed dominantly through the exchange of gluons with a target nucleus, therefore providing information on the gluonic structure of the nucleon. GlueX has collected the world's largest sample of photoproduced J/psi near threshold, and has identified higher excited charmonium states such as the chi_cJ(1P) and psi(2S) states in photoproduction.
The status and prospects of both of these efforts will be reviewed.