Kenta Miyahara

Weak decays of heavy hadrons into dynamically generated resonances

In this paper, we present a review of recent works on weak decay of heavy mesons and baryons with two mesons, or a meson and a baryon, interacting strongly in the final state. The aim is to learn about the interaction of hadrons and how some particular resonances are produced in the reactions. It is shown that these reactions have peculiar features and act as filters for some quantum numbers which allow to identify easily some resonances and learn about their nature. The combination of basic elements of the weak interaction with the framework of the chiral unitary approach allow for an interpretation of results of many reactions and add a novel information to different aspects of the hadron interaction and the properties of dynamically generated resonances.

Antikaon–nucleon interaction and Λ(1405) in chiral SU(3) dynamics

Abstract The properties of the Λ ( 1405 ) resonance are key ingredients for determining the antikaon–nucleon interaction in strangeness nuclear physics, and the novel internal structure of the Λ ( 1405 ) is of great interest in hadron physics, as a prototype case of a baryon that does not fit into the simple three-quark picture. We show that a quantitative description of the antikaon–nucleon interaction with the Λ ( 1405 ) is achieved in the framework of chiral SU(3) dynamics, with the help of recent experimental progress. Further constraints on the K ¯ N subthreshold interaction are provided by analyzing πΣ spectra in various processes, such as the K − d → π Σ n reaction and the Λ c → π π Σ decay. The structure of the Λ ( 1405 ) is found to be dominated by an antikaon–nucleon molecular configuration, based on its wavefunction derived from a realistic K ¯ N potential and the compositeness criteria from a model-independent weak-binding relation.

Exotic hadrons from heavy ion collisions

High energy heavy ion collisions are excellent ways for producing heavy hadrons and composite particles, including the light (anti)nuclei. With upgraded detectors at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC), it has become possible to measure hadrons beyond their ground states. Therefore, heavy ion collisions provide a new method for studying exotic hadrons that are either molecular states made of various hadrons or compact system consisting of multiquarks. Because their structures are related to the fundamental properties of Quantum Chromodynamics (QCD), studying exotic hadrons is currently one of the most active areas of research in hadron physics. Experiments carried out at various accelerator facilities have indicated that some exotic hadrons may have already been produced. The present review is a summary of the current understanding of a selected set of exotic particle candidates that can be potentially measured in heavy ion collisions. It also includes discussions on the production of resonances, exotics and hadronic molecular states in these collisions based on the coalescence model and the statistical model. A more detailed discussion is given on the results from these models, leading to the conclusion that the yield of a hadron that is a compact multiquark state is typically an order of magnitude smaller than if it is an excited hadronic state with normal quark numbers or a loosely bound hadronic molecule. Attention is also given to some of the proposed heavy exotic hadrons that could be produced with sufficient abundance in heavy ion collisions because of the significant numbers of charm and bottom quarks that are produced at RHIC and even larger numbers at LHC, making it possible to study them in these experiments. Further included in the discussion are the general formalism for the coalescence model that involves resonance particles and its implication on the present estimated yield for resonance production. Finally, a review is given on recent studies to constrain the hadron–hadron interaction through correlation measurements in heavy ion collisions and their implications on the interpretation and the possible existence of exotic states in hadronic interactions.

Weak decay of

We study the Λc decay process to π+ and the meson-baryon final state for the analysis of Λ resonances. Considering the Cabibbo-Kobayashi-Maskawa matrix, color suppression, diquark correlation, and the kinematical condition, we show that the final meson-baryon state should be in a pure I=0 combination, when the meson-baryon invariant mass is small. Because the I=1 contamination usually makes it difficult to analyze Λ resonances directly from experiments, the Λc decay is an ideal process to study Λ resonances. Calculating the final-state interaction by chiral unitary approaches, we find that the πΣ invariant mass distributions have the same peak structure in the all charge combination of the πΣ states related to the higher pole of the two poles of the Λ(1405). Furthermore, we obtain a clear Λ(1670) peak structure in the K¯N and ηΛ spectra.

\Lambda_{c}^+

We develop the single-channel local potential for the KbarN system, which is applicable to quantitative studies of Kbar bound states in nuclei. Because the high precision measurement of the kaonic hydrogen by SIDDHARTA reduces the uncertainty of the KbarN amplitude below the KbarN threshold, the local potential should be calibrated in a wide energy region. We establish a new method to construct the local potential focusing on the behavior of the scattering amplitude in the complex energy plane. Applying this method, we construct the KbarN potential based on the chiral coupled-channel approach with the SIDDHARTA constraint. The wave function from the new potential indicates the KbarN molecular structure of Lambda(1405).

for the study of

The structure of light antikaon-nuclear quasibound states, which consist of an antikaon

\Lambda

(\overline{K}={K}^{\ensuremath{-}},{\overline{K}}^{0})

(1405) and

and a few nucleons

\Lambda

(N=p,n)

(1670)

, such as