We will provide the theoretical description of $P_c$ states within coupled channel model. To provide information for the search of nucleon resonances with hidden charm $P_c$ for the on-going experiments at JLab, we make predictions by including the resonant amplitude of $\gamma p \to N^*_{c\bar{c}} \to J/\psi p$ calculated from all available theoretical models. The background is mainly from...
A continuum approach to the three valence-quark bound-state problem in quantum field theory is used to compute the spectrum and Poincar\'e-covariant wave functions for all flavour-$SU(3)$ octet and decuplet baryons and their first positive-parity excitations. Such analyses predict the existence of nonpointlike, dynamical quark-quark (diquark) correlations within all baryons; and a uniformly...
In this present work, we study the scattering of a pseudoscalar
meson off one ground state octet baryon in covariant baryon
chiral perturbation theory up to the next-to-next-to-leading order. We
remove the power counting breaking terms with the extended-on-mass-shell
scheme. We perform the fi?rst combined study of the pion-nucleon
and kaon-nucleon scattering data and show that the covariant...
We adopt a covariant version of the naive dimensional analysis and construct the two-nucleon contact Lagrangian constrained by Lorentz, parity, charge conjugation, and Hermitian conjugation symmetries.We show that at O(q^0), O(q^2), and O(q^4), where q denotes a generic small momentum, there are 4, 13, and 23 terms, respectively.We find that by performing 1/mN expansions, the covariant...
Radiative pion-photoproduction is studied in the framework of covariant SU(2) chiral perturbation theory up to loop order. The effects of the delta (1232) resonance are studied in the “$\epsilon$” power-counting scheme. Further, I will give an outlook how the magnetic dipole moment of the delta can be assessed with this reaction.
The nonleptonic weak decay of Lambda_c->K0bar eta p is analyzed from the viewpoint of probing the N(1535) resonance, which has a big decay branching ratio to eta N. Up to an arbitrary normalization, the invariant mass distribution of eta p is calculated with both the chiral unitary approach and an effective Lagrangian model. Within the chiral unitary approach, the N(1535) resonance is...
One of the greatest challenges within the Standard Model is to discover the source of visible mass. Indeed, this is the focus of a “Millennium Problem”, posed in 2000 by the Clay Mathematics Institute. The answer is hidden within quantum chromodynamics; and it is quite likely that revealing the origin of mass will also explain the nature of confinement. In addressing these issues, this...
High-precision nucleon-resonance electroproduction data on a large kinematic domain of energy and momentum transfer have proven crucial in revealing novel features of strong interactions within the Standard Model and unfolding structural details of baryon excited states. Thus, in anticipation of new data reaching to unprecedented photon virtuality, we employ a quark-diquark approximation to...
Investigation of double pion electroproduction channel is a very efficient tool for the study of nucleon resonances.
Many experiments have already provided a lot of data on the cross sections of the reaction $\gamma_{v} p \rightarrow p'\pi^{+}\pi^{-}$. Their subsequent interpretation within the phenomenological model delivered valuable information on nucleon resonances...
The study of electromagnetic transitions opens a window into the very nature of the strong interaction. And, indeed, such a study of how a ground-state nucleon transitions to an excited state, over a broad range of q$^2$, will provide keen insight into the evolution of how dynamically-generated masses emerge from the asymptotically-free, nearly massless quarks of perturbative QCD as well as...
A dedicated programme to study electromagnetic baryonic transitions in the time-like
region has started using the pion beam and the HADES (High Acceptance Di-Electron
Spectrometer) set-up at GSI [1].
First measurements have been performed in the second resonance region, at a center-of-mass
energy of 1.49 GeV, using carbon and polyethylene targets, allowing for an analysis
of the inclusive...
The CLAS experiments have achieved major advances in the study of the N∗
region of the electroproduction spectrum, and the ata on electrocouplings of the many baryon resonances in the mass range up to 1.8 GeV showed consistency between the different meson channels. We present our theoretical studies of structure functions in view of the CLAS12 experiments planned in the near future, which are...
The study of virtual photon polarisation in time-like baryon electromagnetic transitions allows for the extraction of crucial information about the nature of particles and interactions at a fundamental level. Recent research has considered the transition $\pi^-p\rightarrow n e^+ e^-$ with respect to the polarisation of the virtual photon, which has an impact on the angular distribution of the...
The precise determination of neutrino properties in current and future accelerator-based oscillation experiments requires a good understanding and realistic modeling of neutrino interactions in the detectors: it is crucial to distinguish signal from background, reconstruct the neutrino energy and minimize systematic uncertainties. A significant fraction of the inelastic-scattering...
The $\eta$/$\eta^{\prime}$-Meson is a unique tool to study low energy QCD phenomena and test models.
The isospin violating decay $\eta\rightarrow\pi^{+}\pi^{-}\pi^{0}$ is driven by the strong force and allows probing of the light quark masses, via measuring the corresponding decay amplitude. This amplitude is accessible either via a Dalitz-Plot or partial wave analysis. The latter one allows...
The A2 Collaboration performs a manifold research program using real photons in the Crystal Ball/TAPS experiment at the MAMI accelerator facility in Mainz. The experiments take advantage of high-intensity unpolarized, linearly or circularly polarized photon beams, and unpolarized or polarized targets. The detector setup provides almost complete coverage in solid angle and is well suited for...
Since the discovery of the $\Lambda(1405)$, it remains poorly described by conventional constituent quark models, and it is a candidate for having an "exotic" meson-baryon or "penta-quark" structure, similar to states recently reported in the hidden charm sector.
The $\Lambda(1405)$ can be produced in the reaction $\gamma p \rightarrow K^+ \Lambda(1405)$. The pure I=0 decay mode into...
An experimental program has been approved at the Thomas Jefferson National Accelerator Facility to measure the (ep,e’K+)Y reactions using the CLAS12 setup in Hall B.
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 an angle range of 2.5° to 4.5° by the...
We have investigated the cross section for the π−p→K0πΣ and pp→pK+πΣ reactions paying attention to a mechanism that develops a triangle singularity. The triangle diagram is realized by the decay of a N∗ to K∗Σ and the K∗ decay into πK, and the πΣ finally merges into Λ(1405). The mechanism is expected to produce a peak around 2140 MeV in the KΛ(1405) invariant mass. We found that a clear peak...
Recent theoretical results on spectroscopy, helicity amplitudes and strong decays will be reviewed.
We present calculations of the electromagnetic transitions of the nucleon,
to nucleon resonances $N^*$, namely the $\Delta(1232)\frac{3}{2}^+$,
$N(1520)\frac{3}{2}^-$ and $N(1535)\frac{1}{2}^-$.
Our results for these $\gamma^\ast N \to N^\ast$ reactions are
based on a covariant quark model. In this contribution, we focus
on the timelike regime --- where the square momentum transfer
is...
