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Dibaryon probed with photons – a new aspect of the two nucleon system

Intermediate Energy Nuclear Physics group

The quantum chromodynamics (QCD) allows the existence of the baryon because it contains three quarks with “color-charges” of red, blue and green to construct a color singlet state. Another color singlet state with 6 quarks is called as a dibaryon and was predicted from the beginning of the quark hypothesis. Some phenomena which suggest its evidence have been reported as a result of long years of nucleon scattering experiments. Its quantum numbers of isospin 0 and spin 3 are consistent with the bound state of two Δ baryons. However, it is not considered as a simple ΔΔ bound state because its mass and width are significantly less than the sums of masses and widths of two Δ baryons. It suggests the mixing of more general two baryon systems, such as a bound state of two color octet states or a 6 quark system.
We have explored the photonuclear reaction at the Research Center for Electron Photon Sciences, Tohoku University, with the Neutral Kaon Spectrometer (NKS2) and photon beams produced with an electron storage ring (BST). We confirmed that the excitation of two Δ baryons in the measurement of two pions emitted from the photoabsorption of the deuteron. Currently, we plan to perform the experiment in the threshold region of the dibaryon. Investigation of the dibaryon with the photoabsorption of the deuteron will open a new horizon of the study of the dibaryon and the interaction between baryons.

Eng_Fig1
Fig. 1 Two baryon states considered to create a dibaryon:
(a) a bound state of two color-singlet Δ baryons, (b) a bound state of two color octet baryons to form a color singlet state, (c) a bound state of independent 6 quarks in a color singlet state.
 
Eng_Fig2
Fig. 2 Photograph of the BST and the NKS2.
A schematic diagram of the photon tagger is shown in the right panel.
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