複数の粒子が結合することで形成されるクラスターは、物質の様々な階層 に現れる普遍的な現象であり、原子核系においても重要な役割を果たします。
本講義では、原子核系でのクラスター現象を取り上げ、元素合成に重要な 役割を果たす「ホイル状態」やアルファ崩壊に関係した「核表面でのアルファ クラスター形成」、理研などで行われた実験で明らかとなった、「不安定核の クラスター化」などの現象を紹介します。同時に、クラスター現象を記述する 理論模型を基礎から解説します。
また、量子コンピューターを用いた原子核系の数値計算も併せて紹介しま す。基本的な原理やアルゴリズムの解説だけでなく、実際にシミュレーターや 実機を用いた計算演習を行います。

In this talk, I will talk on recent results from Belle and future experiments at J-PARC regarding threshold cusps. In the first part, I will report a cusp at the Lambda-eta threshold, and another cusp candidate in Lambda_c decays. In the second part, I will introduce near-future experiments at J-PARC, and discuss how scattering lengths can be derived from the shapes of threshold cusps. J-PARC E90 is a dedicated experiment for the purpose to study Sigma-N scattering length using the d K- -> Lambda p pi-reaction with a very good mass resolution. Such a study can be also done as a byproduct of J-PARC E72 for the Lambda eta scattering length using K-p -> X reactions. Furthermore, it may be possible to derive Kbar-N (I=1) scattering length using a cusp in the Lambda pi channel. I would like to discuss the possibility at J-PARC.

I revisit the short-range interactions between light baryons from the spin-flavor SU(6) symmetry viewpoints. The role of quark anti-symmetrization is discussed for two-baryon systems in terms of the SU(6)⊃SU(3)f×SU(2)s classification scheme. I would like to show a few examples, such as NΞ-ΛΛsystem, where the symmetry argument works.

Understanding the baryon-baryon interactions has been an interesting topic in hadron physics, as they provide important clues to the quark dynamics inside baryons. In particular, due to experimental and numerical developments, the interactions between two baryons belonging to the octet (N, Lambda, Sigma, and Xi) and decuplet (Delta, Sigma*, Xi*, and Omega) in the flavor SU(3) sector have recently received much attention. In this context, systematic studies of the baryon-baryon interactions in the whole flavor SU(3) sector are helpful to unravel the mechanism of the baryon-baryon interactions.
In this talk, I present our calculation of the baryon-baryon interactions in the non-relativistic constituent quark model, where two-baryon systems are described as six-quark states using the so-called resonating group method. This is an extension of the quark model studies of Oka-Yazaki to cover all possible combinations of two baryons in the flavor SU(3) sector. As a result of the survey, we find that the flavor anti-decuplet states with total spin J = 3, namely Delta Delta, Delta Sigma*,Delta Xi*-Sigma* Sigma*, and Delta Omega-Sigma* Xi*, have attractive interactions sufficient to generate dibaryon bound states as hadronic molecules. We also discuss our method for evaluating the local potentials from the general baryon-baryon interactions.

The compositeness is useful to quantitatively characterize the internal structure of states whether it is composite dominant (molecular dominant) or not. There have been many studies to analyze the internal structure of the exotic hadrons with the compositeness, in particular, for weakly bound states [1,2]. It is known that the near-threshold states are dominated by the molecular structure in the limit of the vanishing binding energy [3]. However, the decay and coupled-channel effects modify the compositeness as shown in Ref.[1], and therefore the composite nature of the near-threshold states with finite binding might be affected by these contributions. We study the compositeness of weakly bound states with the effective field theory from the viewpoint of the low-energy universality [4]. We introduce a model with the coupling of the single-channel scattering to the bare state, and study the compositeness of the bound state by varying the bare state energy. In contrast to the naive expectation from the universality, we demonstrate that a non-composite state can always be realized even with the small binding energy. At the same time, however, it is shown that a fine tuning is necessary to obtain the non-composite weakly bound state. In other words, the probability to find a model with the composite dominant state becomes larger with the decrease of the binding energy in accordance with the low-energy universality. For the application to the exotic hadrons, we then discuss the modification of the compositeness by the decay and coupled-channel effects. We quantitatively show that these contributions suppress the compositeness, because of the increase of the fraction of other components. Finally, as the examples of the near-threshold exotic hadrons, the structure of Tcc and X(3872) is studied by evaluating the compositeness. We find the importance of the coupled-channel and decay contributions for the structure of Tcc and X(3872), respectively. We also discuss an interpretation of the complex compositeness of unstable states [5].
[1] Y. Kamiya and T. Hyodo, PTEP 2017, 023D02 (2017).
[2] T. Kinugawa and T. Hyodo, Phys. Rev. C 106, 015205 (2022).
[3] T. Hyodo, Phys. Rev. C 90, 055208 (2014).
[4] T. Kinugawa and T. Hyodo, arXiv:2303.07038 [hep-ph].
[5] T. Kinugawa and T. Hyodo, in preparation.

There is presently no consensus on how the phi meson mass and width will change once it is put in a dense environment such as nuclear matter. While many theoretical works exist, connecting them with experimental measurements remains a non-trivial task, as the phi meson in nuclear matter is usually produced in relatively high-energy pA reactions, which are generally non-equilibrium processes. In this seminar, the status of recent theoretical research related to the behavior of the phi meson in nuclear matter is reviewed, including works based on QCD sum rules, hadronic effective theories and ongoing transport simulations of pA reactions in which the phi meson is produced in nuclei, focusing on observables that will be measured at the J-PARC E16 experiment, which will start operating soon. I will furthermore discuss the possibility of experimentally studying the in-medium behavior of other meson species, such as the omega and the f_1(1285).