Session 3WKB: Spectroscopy of Hyperons and Heavy Baryons at JLab and J-PARC II

Heavy exotic hadrons as hadronic molecules

Recent observations of peak-like structures near two-hadron thresholds imply that their structures are dominated by molecules of two hadrons. To have such states realized, suitable conditions are needed for the interaction between the constituent hadrons. Because many of them are open charm hadrons, quark dynamics associated with the presence of heavy quarks and chiral dynamics associated with light quarks are expected to work coherently. To implement these features, we have constructed a coupled channel model for the hidden-charm pentaquarks without and with strangeness whose quark contents are ccbar-qqq or ccbar-sqq (q = u, d quarks); Pc and Pcs [1, 2]. The model includes all possible open charm hadron channels which also couples to five-quark compact states. The model incorporates naturally one-pion exchange force at long distances and virtual excitations of the compact five quark states in two-hadrron scattering channels, both of which provides attractive interaction that is responsible for the generation of the molecular states near two-hadron thresholds. By tuning only one parameter in the model, it is possible to explain the existing data of Pc and Pcs including many of their masses and decay widths, and to further predict other molecular states. We emphasize that the long range dynamics associated with chiral symmetry and short range one of quark dynamics due to the internal structure of hadrons are important. The present analysis was done for hadrons containing charm quarks, but some relevance to those containing strange quarks will be also discussed.   

Search for Hidden-strangeness Pentaquark States near φp Threshold

Multiquark hadrons have attracted much attention since the discovery of tetraquark and pentaquark states containing a charm quark. Observing such many multiquark candidates poses a question on the dripline of further multiquark states. In the baryon sector, hidden-charm pentaquark states, Pc(4380) and Pc(4440) (likely J^P=3/2-), lie near the Λc*D and ΣcD*, respectively. These states have been observed only in the J/ψp channel. Similarly, their strangeness partners, Ps states, near the Λ*K and ΣK* mass thresholds could exist and decay mainly to φp. Unveiling the nature of Ps states is fascinating. We propose complementary measurements of Ps production reactions using photon and meson beams, which include γp->πφN at SPring-8 and π-p->φn reactions at J-PARC. This talk will discuss simulation results with the LEPS2 and P95 detectors.     

Spectroscopy of charmed baryons using hadron beam at J-PARC

Understanding hadron formation is one of the fundamental goals of hadron physics. It is essential way to investigate the effective degrees of freedom of hadrons with extended constituents such as the quark-quark correlation, namely the diquark correlation. In the case of light baryons, three pairs of diquarks are correlated with equal weight so that the diquark correlation cannot be extracted. When one quark in the baryon is replaced by a heavier quark called charm, the diquark correlation is expected to develop in the excited state of the charmed baryon. As a result, two excitation modes, called isotope shifts, appear in the level structure. The lambda- and rho-modes are the orbital excitation of the diquark and charm quark and the rotation of the diquark, respectively. These excited states are produced by the diquark correlation that could not be observed in lighter quark baryons. The study of the excitation spectra of charmed baryons allows us to investigate the lambda- and rho-excitation modes, which are strongly related to the internal structure of charmed baryons. The production and decay rates of charmed baryons [1] are expected to provide essential information for establishing the diquark correlation.

The charmed baryon spectroscopy experiment (E50) [2] is planned at the π20 beam line of the J-PARC Hadron Experimental Facility to reveal the structure of hadrons using the world's most intense meson beam. The π20 beam line, currently under construction, can deliver unseparated secondary beams with momentum up to 20 GeV/c at intensities above 10 MHz with a momentum resolution of 0.1%(sigma). High-momentum secondary beams with high-intensity and high-resolution can be used for the E50 experiment. In the experimental area, we will construct a large size magnetic spectrometer system which is designed to measure all charged particles produced by the pi- p → Yc*+ D*- reaction at 20 GeV/c and reconstructed the missing masses of the produced charmed baryons. From the measurement of the cross section, we can observe the charmed baryon states as missing masses with different yields depending on the lambda- and rho-excitation modes. Hadron beams are an essential tool for studying charmed baryon excited states, and J-PARC promotes important research in hadron physics.