Fully coupled-channel study of K−pp resonance in a chiral SU(3)-based K¯N potential

Abstract

Nuclear system with antikaons, so-called kaonic nuclei, has been a longstanding issue in strange nuclear physics and hadron physics, because they might have exotic nature; In particular, they could be a doorway to the dense matter due to the strong attraction between antikaon and nucleon. Among kaonic nuclei, the three-body system composed of two protons and a single K − meson, K − pp, is the most essential. In this article 1 , we will report on the recent situation of K − pp studies in both theoretical and experimental sides. Afterwards, we will explain our latest study of the K − pp with a fully coupled-channel complex scaling method (Full ccCSM) using a chiral SU(3)-basedKN(-πY) potential. In Full ccCSM, the K − pp is completely treated as a resonant state of aKNN-πΣN-πΛN coupled-channel system. The energy dependence involved in the chiral potential is handled with a selfconsistent calculation in which two extreme ansatzes are examined: field picture and particle picture. With our chiral SU(3)-based potential constrained by the precise data of kaonic hydrogen atom (SIDDHARTA experiment), the K − pp resonance is obtained as a shallowly bound state measured from theKNN threshold with a narrow width, if the field picture is employed in the calculation: the binding energy is 14 − 28 MeV and half value of the mesonic decay width are 8 − 15 MeV. On the other hand, if the particle picture is employed, it is found that the binding energy could be as large as about 50 MeV, even though such a chiral potential is used. Based on these results of Full ccCSM calculation, we have discussed on the possibility for kaonic nuclei to form a dense matter and on the latest experimental result reported by J-PARC E15 collaboration.Thus, kaonic nuclei are expected to be an exotic system. In order to reveal the properties of kaonic nuclei, many researchers have focused on the K − pp, which is a three-body system composed of a single K − meson and two protons. Certainly, general kaonic nuclei might possess interesting properties. However, it is difficult to investigate such a strongly-interacting quantum many-body system. Therefore, before proceeding to general systems, the simple three-body system, K − pp, has been investigated eagerly from both theoretical and experimental sides. As mentioned in the previous paragraph, the Λ(1405) is a quasi-bound state of two-bodyKN system. In our viewpoint, the Λ(1405) is a building block of kaonic nuclei, and the K − pp is a prototype of kaonic nuclei, which means the most essential kaonic nucleus. The K − pp could be a bridge from the excited hyperon Λ(1405) to general systems of kaonic nuclei.The current situation of the K − pp study is as follows. There have been many experiments to search for the K − pp quasi-bound states. However, the results are different in each experiment. In an early experiment by FINUDA collaboration [8], a bump structure was reported in the observed Λp invariant-mass distribution at far below thē KNN threshold. In addition, DISTO [9] and J-PARC E27 [10] collaborations re...

\(\bar{K}\)-Nuclear Bound State at J-PARC

“…The obtained binding energy of ∼ 50 MeV is deeper than chiral SU(3) motivated calculations [13][14][15][16][17][18][19], while the almost consistent with the phenomenological based calculations [6][7][8][9][10][11][12][13]. The width of ∼ 100 MeV is rather wide compared to theoretical calculations which take into account only mesonic decay channels such as πΣN decay branches.…”

“…From extensive measurements of anti-kaonic hydrogen atom [1][2][3] and low-energyKN scattering [4], the strongly attractiveKN interaction has been revealed in I = 0 channel. The strong attraction inKN system leads to the possible existence of deeply-bound kaonic nuclear states, which has been widely discussed today [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. The investigation of those exotic states will provide unique information of theKN interaction below the threshold, which can not be accessed by the conventional methods.…”

“…and the decay width (Γ), strongly depend on theKN interaction models. With the energy-independent models (phenomenological models), the binding energy has been predicted to be ∼ 40 -90 MeV [6][7][8][9][10][11][12][13], whereas, it becomes ∼ 10 -30 MeV in energy-dependent cases (chiral unitary models) [13][14][15][16][17][18][19]. In the framework of the chiral model, a double pole structure of theKNN is also proposed in relation to Λ(1405) [21].…”

Fully Coupled-Channel Study of K−pp Resonance

“…In our study within Full ccCSM [7,8], the K − pp is treated as aKNN-πΣN-πΛN coupled-channel system with quantum numbers of spin-parity J π = 0 − , isospin T = 1/2 and its projection T z = 1/2 the same way as in earlier studies. Such a state is symbolically denoted as "K − pp" (K − pp with double quotations).…”

Results of \(\bar{K}NN\) Search via the (K−, n) Reaction at J-PARC

“…Theoretical works based on phenomenologicalKN potential reported the binding energies of 40 -95 MeV [6][7][8][9][10][11][12]. On the other hand, relatively small binding energies, in a range of 10 -50 MeV, were predicted from theoretical calculations using a chiral SU(3)-basedKN potential [11][12][13][14][15]. This difference of predicted binding energies is caused by lack of understanding ofKN interaction in the energy region below MK N , which can not be directly probed by scattering experiments or X-ray measurements.…”