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Register a new userThe interaction between H-dibaryons
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We investigate the interaction between H-dibaryons employing a quark cluster model with a one-gluon-exchange potential and an effective meson exchange potential (EMEP). A deeply-bound state of two H-dibaryons due to the medium range attraction of the EMEP is obtained. The bound H--H system has a size of about 0.8 $sim$ 0.9 fm because of the short-range repulsion generated by the color-magnetic interaction and the Pauli principle.
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Using the QCD sum rule approach, we show that the flavor-nonsinglet $H$ dibaryon states with J$^{pi} = 1^+$, J$^{pi} = 0^+$, I=1 (27plet) are nearly degenerate with the J$^{pi} = 0^+$, I=0 singlet $H_0$ dibaryon, which has been predicted to be stable against strong decay, but has not been observed. Our calculation, which does not require an instanton correction, suggests that the $H_0$ is slightly heavier than these flavor-nonsinglet $H$s over a wide range of the parameter space. If the singlet $H_0$ mass lies above the $Lambda Lambda$ threshold (2231~MeV), then the strong interaction breakup to $Lambda Lambda$ would produce a very broad resonance in the $Lambda Lambda$ invariant mass spectrum which would be very difficult to observe. On the other hand, if these flavor-nonsinglet J=0 and 1 $H$ dibaryons are also above the $Lambda Lambda$ threshold, but below the $Xi^0n$ breakup threshold (2254 MeV), then because the direct, strong interaction decay to the $Lambda Lambda$ channel is forbidden, these flavor-nonsinglet states might be more amenable to experimental observation. The present results allow a possible reconciliation between the reported observation of $Lambda Lambda$ hypernuclei, which argue against a stable $H_0$, and the possible existence of $H$ dibaryons in general.
Hexaquarks constitute a natural extension of complex quark systems like also tetra- and pentaquarks do. To this end the current status of $d^*(2380)$ in both experiment and theory is shortly reviewed. Recent high-precision measurements in the nucleon-nucleon channel and analyses thereof have established $d^*(2380)$ as an indisputable resonance in the long-sought dibaryon channel. Important features of this $I(J^P) = 0(3^+)$ state are its narrow width and its deep binding relative to the $Delta(1232)Delta(1232)$ threshold. Its decay branchings favor theoretical calculations predicting a compact hexaquark nature of this state. We review the current status of experimental and theoretical studies on $d^*(2380)$ as well as new physics aspects it may bring in the future. In addition, we review the situation at the $Delta(1232) N$ and $N^*(1440)N$ thresholds, where evidence for a number of resonances of presumably molecular nature have been found -- similar to the situation in charmed and beauty sectors. Finally we briefly discuss the situation of dibaryon searches in the flavored quark sectors.
The characteristic feature of the ground state configuration of the Skyrme model description of nuclei is the absence of recognizable individual nucleons. The ground state of the skyrmion with baryon number 2 is axially symmetric, and is well approximated by a simple rational map, which represents a direct generalization of Skyrmes hedgehog ansatz for the nucleon. If the Lagrangian density is canonically quantized this configuration may support excitations that lie close and possible below the threshold for pion decay, and therefore describe dibaryons. The quantum corrections stabilize these solutions, the mass density of which have the correct exponential fall off at large distances.
Properties of six-quark dibaryons in nuclear medium are considered by example of $A=6$ nuclei within the three-cluster $alpha+2N$ model. Dibaryon production in nuclei leads to the appearance of a three-body force between the dibaryon and nuclear core. This non-conventional scalar force is shown to provide an additional attractive contribution to the three-body binding energy. This three-body contribution improves noticeably agreement between theoretical results and experimental data for the majority of observables. The most serious difference between the traditional $NN$-force models and the dibaryon-induced model is found for the nucleon momentum distribution, the latter model providing a strong enrichment of the high-momentum components both for $^6$Li and $^6$He cases.
Dibaryon candidates with strangeness S=-2,-3,-4,-5,-6 are studied in terms of the extended quark delocalization and color screening model. The results show that there are only a few promising low lying dibaryon states: The H and di-Omega may be marginally strong interaction stable but model uncertainties are too large to allow any definitive statement. The SIJ=-3,1/2,2 N-Omega state is 62 MeV lower than the N-Omega threshold and 24 MeV lower than the Lambda-Xi-pi threshold. It might appear as a narrow dibaryon resonance and be detectable in the RHIC detector through the reconstruction of the vertex mass of the Lambda-Xi two body decay. The effects of explicit K and eta meson exchange have been studied and found to be negligible in this model. The mechanisms of effective intermediate range attraction, sigma meson exchange and kinetic energy reduction due to quark delocalization are discussed.
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