Exotic multi-quark states and baryon spectroscopy workshop

25 Jun 2024, 09:00 → 27 Jun 2024, 18:00 Europe/Berlin

Wolfgang Paul Hörsaal (Universitätsclub Bonn, the University of Bonn)

Hartmut Schmieden (uni-bonn), Thomas Jude (The University of Bonn)

The final workshop of the Strong-2020 transnational access for FTD-Hadron/ELSA

 

We wish to bring together theory and experiment to discuss baryon spectroscopy across the quark flavour and mass range.  In particular, we will focus on the role of exotic multi-quark states in the baryon sector and candidates beyond three valence quark systems.

The research and results achieved with the projects supported at the FTD-Hadron/ELSA infrastructure will be highlighted, which were predominantly part of the BGOOD and CBELSA/TAPS meson photoproduction experiments.  The science case will be discussed along with results from other facilities worldwide and recent theoretical developments.  The workshop is open for contributions across the hadron physics community.  Registration will be open from March 1st.

The FTD-Hadron/ELSA transnational access project is part of the Strong-2020 consortium and has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement STRONG-2020 - No. 824093.

Maps.pdf

Tuesday, 25 June

1 Welcome

Speaker: Hartmut Schmieden

WELCOME_HS.pdf

2 Single meson photoproduction at CBELSA/TAPS

Speaker: Annika Thiel

Talk_AThiel.pdf

10:30 Coffee break

3 Multi-meson photoproduction off the proton - recent results from the CBELSA/TAPS experiment

A good understanding of the spectrum and the properties of baryon resonances requires a detailed study of the excited states and their decays. To extract contributing resonances from data, cross sections and polarization observables must be determined and further investigated by partial wave analysis.
Multi-meson final states are particularly important at high energies, where still resonances are predicted which remained so far unobserved. They also allow the interesting investigation of sequential decay chains, where a high mass resonance decays via an intermediate excited state down into the ground state.

The Crystal Barrel/TAPS experiment is ideally suited to measure the photoproduction of neutral mesons decaying into photons due to its good energy resolution, high detection efficiency for photons, and the nearly complete solid angle coverage. A longitudinally or transversely polarized target and a linearly or circularly polarized photon beam allow extensive measurements of polarization observables.

Recent results are presented, giving a particular emphasis to $\gamma p \rightarrow p \pi^0\pi^0$.

Speaker: Nils Stausberg (HISKP)

Stausberg_STRONG_2020.pdf

4 QCD Exotics and where to find them

Speaker: Meike Küßner

MeikeKuessner.pdf

12:30 Lunch break

5 $\eta$ and $\eta'$ photoproduction on nucleons

The most interesting experimental data for η and η′ photoproduction on nucleons are presented. Besides, results of the phenomenological analysis of these reactions with updated version of EtaMAID model are discussed. The model well describes both differential cross sections and polarization observables at photon beam energies from the threshold upto 9 GeV. The nature of some interesting specifics in the data is discussed.

Speaker: Victor Kashevarov

Kashevarov_Bonn-2024.pdf

6 Results of JRA7 - light and heavy quark hadron spectroscopy

Speaker: Juan Miguel Nieves Pamplona

NievesBonn.June25.pdf

16:00 Coffee

7 The Bonn polarised target

Speaker: Victoria Lagerquist

Victoria_June 2024 Talk.pdf

8 The Research and Technology Centre for Detector Physics (FTD) and ELSA test beam line

Speaker: Bernhard Ketzer

Wednesday, 26 June

9 Exotic hadrons: tetraquarks, pentaquarks and hadronic molecules

Recently the LHCb Collaboration announced the discovery of a new type of
exotic hadron -- a doubly-charmed tetraquark $T_{cc}^+$, whose mass agrees
precisely with a 2017 theoretical prediction. I will discuss the recent
related experimental and theoretical developments regarding new types of
hadrons: tetraquark and pentaquark hadronic molecules, doubly heavy baryons,
stable tetraquarks and others.

Speaker: Marek Karliner

karliner_bonn_june_26_2024.pdf

10:00 Coffee break

10 Pc states at LHCb

Speaker: Sebastian Neubert

11 The study of exotic baryon structure via strangeness photoproduction at BGOOD

Speaker: Thomas Jude (The University of Bonn)

Strangeness_BGOOD_Jude.pdf

12:30 Lunch break

12 The LHCb Pentaquarks as hadronic molecules

In the talk the concept of hadronic molecules is introduced and the implications of this structure illustrated on three examples: The nature of the Y(4230), the Zb states and finally the LHCb pentaquarks. In particular, it is described which features of the LHCb pentaquarks point at their possible molecular nature and what further predictions can be deduced from that property.

Speaker: Christoph Hanhart (Forschungszentrum Juelich)

hanhart_spectroscopyWorkshopBonn2024.pdf

13 Two-pole structures in QCD

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 discuss in some detail the cases of the two Λ(1405) and the two $D^{0⋆}$(2300) states. I further discuss the consequences for our understanding of bound states in QCD and point out some sins committed in the current literature.

Speaker: Ulf-G Meißner

Ulf_EMC24pp4.pdf

16:00 Coffee break

14 Three methods to search for the two $\Xi(1820)$ states

The chiral unitary approach produces two states from the pseudoscalar-baryon decuplet interaction in the region of the $ \Xi(1820)$. A recent BESIII experiment on the $ \Psi(3868) \to \bar \Xi K^- \Lambda$ showed a clean peak that had an abnormally large width and was interpreted in [1] in terms of the two $\Xi(1820)$. In view of this, we propose to look at the $\Omega_c \to \pi^+ \, (\pi^0,\, \eta)\, \pi \Xi^*$ reaction [2], where the $\pi \Xi^*$ invariant mass shows an interference pattern of the two resonances. A third reaction $\Psi(3686) \to \bar Ξ^+ \bar K^0 Σ^{∗−}$ [3] looks at the $\bar K^0 Σ^∗$ invariant mass distribution, where due to phase space restrictions, the lower mass $ \Xi(1820)$ is suppressed and the higher mass around 1875 MeV with a larger width shows up clearly.

[1] R.~Molina, W.~H.~Liang, C.~W.~Xiao, Z.~F.~Sun and E.~Oset,
%``Two states for the $\Xi(1820)$ resonance,''
[arXiv:2309.03618 [hep-ph]].

[2] W.~H.~Liang, R.~Molina and E.~Oset,
%``The $\Omega_c \to \pi^+ \, (\pi^0,\, \eta)\, \pi \Xi^*$ reactions and the two $\Xi(1820)$ states,''
[arXiv:2404.18882 [hep-ph]].

[3] Man-Yu Duan, Jing Song, Wei-Hong Liang and E. Oset

Searching for the two poles of the Ξ(1820) in the $\Psi(3686) \to \bar Ξ^+ \bar K^0 Σ^{∗−}$ decay

to be submitted.

Speaker: Prof. Eulogio Oset (IFIC, Universidad de Valencia)

Eulogio_Bonn24.pdf

15 Low-energy kaon-nuclei interaction studies at the DAFNE collider: a strangeness Odyssey

The low-energy QCD, the theory within the Standard Model describing the strong interaction, is still missing fundamental experimental results to achieve a breakthrough in its understanding. Among these, the low-energy kaon-nucleon/nuclei interaction studies are playing a key-role.
Combining the excellent quality of the low-energy kaon beam delivered by the DAFNE collider of INFN-LNF with new experimental techniques, like high-precision spectroscopic Silicon Drift Detectors, we performed unprecedented measurements in the low-energy strangeness sector in the framework of the SIDDHARTA Collaboration and are presently running the SIDDHARTA-2 experiment for very challenging kaonic atoms measurements, such as kaonic deuterium first measurement.
I shall introduce the physics of kaonic atoms, the experiment, the first exciting results, and discuss future plans. I shall also present AMADEUS collaboration results on studies of low-energy kaons interacting with various nuclei.
The experiments at DAFNE represent a unique opportunity to unlock QCD secrets in the strangeness sector and contribute to better understand the role of strangeness in the Universe, from nuclei to the stars.

Speaker: Catalina Oana Curceanu (INFN-LNF)

Catalina-Exotic-Bonn-june2024.pdf

Thursday, 27 June

16 Hadronic resonances from lattice QCD

Speaker: Carsten Urbach

urbach-exoticWS.pdf

10:00 Coffee break

17 Coherent neutral-pion and eta-meson photoproduction on the deuteron studied at ELPH

We have studied the interaction between the eta meson and deuteron from measurement of cross sections for coherent neutral-pion and eta-meson photoproduction on the deuteron. We have found a narrow resonance-like bump in the eta-deuteron subsystem at the vicinity of the threshold, suggesting strong eta-deuteron attraction. The sharp backward-peaking angular dependence of deuteron emission, predicted by the existing theoretical calculations, does not appear. We discuss the possibilities of using coherent neutral-pion and eta-meson photoproduction on a nucleus to study the eta-nuclear interaction.

References:
Phys. Rev. C 104, L052201 (2021); Phys. Rev. C 105, 045201 (2022).

Speaker: Takatsugu Ishikawa (Research Center for Nuclear Physics (RCNP), Osaka University)

ishikawa20240627f.pdf

18 Coherent meson photoproduction off the deuteron at forward angles at BGOOD

Speaker: Thomas Jude

Coherent_BGOOD_Jude.pdf

12:30 Lunch break

19 Σ beam asymmetry for η photoproduction on the proton at BGOOD

The Σ beam asymmetry in meson photoproduction off the nucleon is a very sensitive observable in the investigation of the nucleon structure. The BGOOD experiment at ELSA, with its linearly polarized γ beam and large solid angle detector, is an ideal facility for the detection of charged and neutral particle final states.
New results of Σ beam asymmetry will be presented for η photoproduction off the proton in the energy range 1250-1730 MeV; these results have been obtained analyzing at the same time all the available statistics from the main η decay channels with an original technique that allows to treat simultaneously periods with different efficiencies and polarization degrees.

Speaker: Alessia Fantini (INFN (sez "Tor <vergata"), University of Rome "Tor Vergata")

Fantini_EXOTIC.pdf

20 N* studies using KY electroproduction at CLAS12

Speaker: Lucilla Lanza

Lanza_Exotic_062724.pdf

15:30 Coffee break

21 New results from GlueX

Speaker: Farah Afzal

22 The future experiment at ELSA

Speaker: Ulrike Thoma

23 STRONG-2020 status and prospects

STRONG-2020 succeeded in gathering a large community in Europe and beyond that focuses on all aspects of the strong interaction.
It encompasses both fundamental research and applications using top-level infrastructures as a backbone, with the ambition of pushing further the frontier of knowledge in hadron physics.
We present at this workshop a general summary of the project which is about to reach its termination as well as several achievements including some from FTD/ELSA.
Prospects beyond STRONG-2020 in the framework of Horizon Europe will also be discussed.

Speaker: Boris Hippolyte

Boris_Strong2020.pdf

24 Closing remarks and discussion