XVIII International Conference on Hadron Spectroscopy and Structure (HADRON2019)

Modern hadron-spectroscopy experiments such as COMPASS collect data samples of unprecedented size, so that novel analysis techniques become possible and necessary. One such technique is the freed-isobar partial-wave analysis (PWA). In this approach, fixed parametrizations for the amplitudes of intermediate states–commonly modeled using Breit-Wigner shapes–are replaced by sets of...

The light-meson spectrum can be studied by analyzing data from diffractive dissociation of pion or kaon beams. The contributions of the various different states that are produced in these reactions are disentangled by the means of partial-wave analysis. A challenge in these analyses is that the partial-wave expansion has to be truncated, i.e. that only a finite subset...

We study the effects of the $\Delta$(1232) resonance as an effective degree of freedom in a global analysis of the pion photo-production off nucleons. Cross sections and polarization observables have been calculated for charged and neutral pion channels in relativistic chiral perturbation theory up to third order in the δ counting. We compare our model with a large database containing the ...

PAWIAN is a powerful, user-friendly and highly modular partial wave analysis software package with the aim to support analyses for a multitude of different physics cases at hadron physics experiments. Real data originating from the pbar p annihilation process and from e+ e- reactions are currently under investigation with PAWIAN. The software is written in C++ and follows an object-oriented...

Physical models can suffer from systematic deficiencies due to omitted physics, which can bias parameter estimates and predictions. Such simplifications may be unavoidable, but physicists often have some idea of what is missing from their models. I discuss how physical knowledge of model discrepancy can be encoded into the language of Bayesian statistics, and how the inclusion of this...

Hamiltonian effective field theory has been used for explaining Lattice data. We develop it within partial waves mixing in the rest frame. The dimension of the Hamiltonian can be highly reduced with the partial wave cut-off and rotation symmetry. We apply this method to extract the Pion-Pion s-, d- and f-wave phase shifts within Isospin=2 case.

Lattice QCD calculations provide an ab initial access to hadronic process. These calculations are usually performed in a small cubic volume with periodic boundary conditions. The infinite volume extrapolations for three-body systems are indispensable to understand many systems of high current interest. We derive the three-body quantization condition in a finite volume using an effective field...

The vector-vector approach is revisited. In the original formalism, some approximations are made, considering the vector meson to have small momenta comparing to its mass. In the $\rho-\rho$ scattering, and for Isospin$=0$, the potential obtained is much more attractive in $J=2$ than for $J=0$, and thus, two bound states are found, where the one with $J=2$ is more bound. These are identified...

I will review recent results on hadron spectroscopy analyses from JPAC

We investigate the Schmid theorem, which states that if one has a tree level mechanism with a particle decaying to two particles and one of them decaying posteriorly to two other particles, the possible triangle singularity developed by the mechanism of elastic rescattering of two of the three decay particles does not change the cross section provided by the tree level. We investigate the...

BESIII Collaboration has reported the observation of $a_0^0(980)-f_0(980)$ mixing. From the Dalitz plot of BESIII's paper for the decay $\eta \rightarrow \gamma \gamma$, one can see that there is a peak around $1.4$ GeV on $\pi^0 \phi$ distribution. In general, this peak can be interpreted as a dynamically resonance state or a kinematic effect. In this paper, by using the effective Lagrangian...

Recent experimental observations of charged charmonium- and bottomonium-like structures have brought lots of excitements in the field of hadron spectroscopy. If these structures are associated with the existence of the corresponding hadrons, these states includes minimally two quarks and two antiquarks, being objects clearly beyond the conventional quark model picture. Such charged...

We study the J/ψ to K K f0(980) reaction and find that the mechanism to produce this decay develops a triangle singularity at K f0 invariant mass around 1515 MeV. We find the branching ratio obtained for this decay to be of the order of 10^{−5}, accessible in present facilities.

In my talk, I will present our recent dispersive analysis of the gamma* gamma* -> pipi/ pieta processes from the threshold up to 1.4 GeV in the two-photon invariant mass. These amplitudes serve as an important input to constrain the hadronic piece of light-by-light scattering contribution to (g-2) and support the current experimental program at BESIII.

A resonance-like structure as narrow as 10 MeV is observed in the $K^-p$ invariant mass distributions in $\Lambda_c^+\to p K^- \pi^+$. This precise measurement is based on a data sample of about 1.5 million events, and the bin width of $K^-p$ invariant mass is only 1 MeV. The narrow peak precisely lies on the $\Lambda\eta$ threshold, because of which it is natural to identify it as a threshold...

In this work we study the effects of a triangle singularity in the cross sections of the πp → K⁰πΣ and pp → pK⁺πΣ reactions. The triangle mechanism is generated the following way: the initial scattering creates the N* resonance that decays into K*Σ, then, the K* decays into πK and the π fuses with Σ to create the Λ(1405). From this mechanism, a peak associated with the triangle singularity is...

In this talk I will discuss the triangle mechanism in Lambda_c decay and isospin-violating Lambda(1405).This process is prohibited by the isospin symmetry, but the decay into this channel is enhanced by the contribution of the triangle diagram, which is sensitive to the mass of the internal particles. Interestingly, a first narrow peak was observed in the pi0 Sigma0 invariant mass ...