The current status of the $\eta$ photoproduction analysis within the Jülich-Bonn framework is presented. A structure in production on the proton at around $W\sim 1.68$ GeV is discussed. Furthermore, the extraction of resonance helicity couplings and their correlations from $\eta$ photoproduction is outlined, and how new experiment could help to further disentangle these quantities. Also, a...
We present the result of the combined analysis of the eta and eta-prime photoproduction data measured by A2,CB-ELSA and CLAS collaborations. The analysis confirms the existence of the N(1895)1/2- state and allowed us to define its properties with a good presicion.
Results of the phenomenological analysis of $\eta$ and $\eta'$
photoproduction on the protons and the neutrons with updated version of
EtaMAID model are presented.The model includes 23 nucleon resonances parameterized with Breit-Wigner shapes, $t$-channel exchange of vector and axial-vector mesons with Regge cuts,and Born terms in $s$ and $u$ channels.
A new approach is discussed to avoid...
Important insights into the excitation spectra of baryons are provided by measure-
ments of polarization observables in reactions that involve particles with spin. The
photoproduction of a single pseudoscalar meson constitutes an example-reaction that
has been under intense investigation recently.
In this talk, we present the basic method of moment-analysis for pseudoscalar...
We carried out exclusive measurements of photo-production of an eta meson from a proton target with an egg-shape BGO calorimeter (BGOegg) and forward charged particle detectors at LEPS2/SPring-8, Japan. The differential cross-section at extreme backward angles were obtained and compared with the prediction from etaMAID2018. Possible evidence for a high spin N* resonance with a mass of 2.2 ~2.3...
Pole parameters, as the minimally model dependent link between measurements and QCD approaches, were always extracted from experiment through procedures notably relying on elaborated microscopic theories. Partial waves were obtained by fitting free parameters of a microscopic model to experimental data, and poles were extracted by performing the analytic continuation of the result into the...
The research work of Nuclear and Particle Physics group at University of Basel is centered around Hadron Physics sector. Photoproduction of Mesons provides an efficient tool for the study of decays of nucleon resonances and the excitation spectrum of hadrons tells us about the internal degrees of freedom. Thus to know the internal structural details of nucleons and mesons, investigation of...
We present calculations of $\gamma^\ast N \to N^\ast$
transition form factors, where $N$ is the nucleon
and $N^\ast$ and $N^\ast$ is a nucleon resonance,
based on a covariant quark model.
At high photon virtualities (large $Q^2$)
it is expected that the valence quark degrees of freedom
dominate the contributions to the transition form factors.
In these conditions, the quark model estimates...
The nucleon excitation spectrum has traditionally been at the heart of strong interaction studies. Nucleon resonances and their transition form factors are interesting in a variety of processes: In addition to nucleon-pion scattering and meson photo- and electroproduction, from where they are experimentally extracted, nucleon resonances also appear as intermediate states in nucleon Compton...
The \pi^+\pi^-p photo- and electroproduction off proton channel is sensitive to the contributions from most excited nucleon states, offering an effective tool for the exploration of the nucleon resonance spectrum and structure. The data on nine independent one-fold differential \pi^+\pi^-p photo- and electroproduction cross sections have become available for the first time from the...
One important step in understanding the baryon spectrum is a precise knowledge of the excited states and their decays. In order to extract the contributing resonances from experimental data a partial wave analysis needs to be performed. To resolve ambiguities, the measurement of polarization observables is indispensable. In the regime of high mass baryon resonances multi-meson final states are...
Understanding of the non-trivial pattern of excited states of QCD at low energies is one of the main goals of the modern nuclear physics. One of the most interesting states is the so-called Lambda 1405, which is widely accepted as a dynamically generated state from the meson-baryon interaction.
Recently, high precision data on the energy shift and width of the Kaonic-hydrogen as well as the...
Low-energy data on the three charge states in $\gamma p \to K^+(\Sigma\pi)$ from CLAS at JLab, on $K^-p\to \pi^0\pi^0\Lambda$ and $\pi^0\pi^0\Sigma$ from the Crystal Ball at BNL, bubble chamber data on $K^-p\to\pi^-\pi^+\pi^{\pm}\Sigma^{\mp}$, low-energy $K^-p$ differential cross sections for elastic and charge exchange scattering, total cross sections on $K^-$ induced reactions, and data on...
A Σ∗ resonance with spin-parity JP=1/2− and mass in the vicinity of the K¯N threshold has been predicted in the unitary chiral approach and inferred from the analysis of CLAS data on the γp→K+π0Σ0 reaction. In this work, based on the dominant Cabibbo favored weak decay mechanism, we perform a study of Λ+c→π+π0Σ∗ with the possible Σ∗ state decaying into π−Σ+ through a triangle diagram. This...
The study of baryonic excited states provides fundamental information on the internal structure of the nucleon and on the degrees of freedom that are relevant for QCD at low energies. N* are composite states and are sensitive to details of the how quark are confined.
A program has been approved at JLAB to search for new excited baryon states in the mass range from 1.8 GeV to 3 GeV with...
In the past decade, lots of hadrons were discovered especially in the heavy quarkonium mass ranges that cannot be fit into the level scheme provided by the traditional quark models. In the talk I will review some of the most popular proposals for the nature of these so-called XYZ states, including hadronic molecules, hadro-quarkonia and tetraquarks, as well as the non-trivial predictions that...
We explore the photo-production of possible exotic $N^*$, which are narrow pentaquark candidates containing light quarks or Charm or Beauty. The latter two are also known as $P_c$ and $P_b$ states in literatures. We analyzed the Compton scattering off the proton in the third resonance region in a coupled-channel effective Lagrangian model with K-matrix approximation. The evidence of exotic...
The spectroscopy of charmonium-like states together with the spectroscopy of charmed and strange baryons is discussed. It is a good testing tool for the theories of strong interactions, including: QCD in both the perturbative and non-perturbative regimes, LQCD, potential models and phenomenological models [1, 2, 3]. An understanding of the baryon spectrum is one of the primary goals of...
