K+Λ(1405) photoproduction at the BGO-OD experiment

Since the discovery of the Λ(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 Λ(1405) can be produced in the reaction γp K+Λ(1405). The pure I=0 decay mode into Σ0π0 is prohibited for the mass-overlapping Σ(1385). Combining a large aperture forward magnetic spectrometer and a central BGO crystal calorimeter, the BGO-OD experiment is ideally suited to measure this decay with the K+ in the forward direction. Preliminary results are presented. *Supported by DFG (PN 388979758, 405882627)

Exotic meson decays and polarization asymmetry in hadron environment with chiral imbalance

The possibility of the formation of a local parity breaking in a quark-hadron medium is described as a result of a violation of chiral symmetry, i.e, the difference between the average numbers of right and left -handing quarks in the fireball after HIC.The phenomenology of LPB in the fireball induces the introduction of a topological charge and, accordingly, a topological (chiral) chemical potential. Using the effective meson Lagrangian motivated by QCD in the chiral medium the properties of light scalar and pseudoscalar mesons are analyzed. It is establish that exotic decays of scalar mesons arise as a result of mixing of π and a0 vacuum states in the presence of chiral imbalance. The pion electromagnetic formfactor obtains a parity-odd supplement which generates a photon polarization asymmetry in pion polarizability. We consider that the above-mentioned properties of LPB can be revealed in experiments on LHC, RHIC, CBM FAIR and NICA accelerators.

On some models of the exotic hadron states

There are several kinds of exotic hadron states. In this paper, we are concerned with the flavor exotic meson states: the tetraquarks and meson molecules. Two distinct models of tetraquarks are studied: diquark-antidiquark bound states and uncorrelated quarks. Although diquark is not a color singlet, there is a strong theoretical evidence that such states do exist within hadrons. Both tetraquark models as well as methods used to study such states are reviewed. The meson-meson molecules are also mentioned. It is remarked that hadron spectroscopy per se may not always be sufficient to discern between physically distinct models.