Dibaryons at COSY
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Dibaryons at COSY M. Bashkanov1 · H. Clement1 · T. Skorodko for the WASA-at-COSY Collaboration2
© Springer International Publishing Switzerland 2015
Abstract Experiments at the Juelich Cooler Synchrotron (COSY) have now found compelling evidence for a new state in the two-baryon system with mass 2380 MeV and width 70 MeV. The structure, containing six valence quarks, constitutes a so-called dibaryon, either a hexaquark or a hadronic molecule. The new particle denoted now d ∗ (2380) has quantum numbers I (J p ) = 0(3+ ). The present knowledge about the d ∗ dibaryon as well as other implications and possible future experiments are discussed. Di-baryonic systems with strangeness, like K − pp or hypothetical H-dibaryon are outside the scope of this paper. Keywords Dibaryon · Hexaquark · Hadronic molecule
1 Introduction Despite their long painful history [1, 2] dibaryon searches (where dibaryon means a baryon number B = 2 state independently on the internal structure [genuine six-quark state/baryonic-molecule]) have recently received new interest, in particular by the recognition that there are more complex quark configurations than just the familiar q q¯ and qqq systems. The “hidden color” aspect makes dibaryons a particularly interesting object in QCD [3] A resonance like structure recently observed in double-pionic fusion to deuteron [4–6], see Fig. 1, at M = 2.38 GeV with = 70 MeV and I (J p ) = 0(3+ ) meanwhile proved Proceedings of the International Conference on Exotic Atoms and Related Topics (EXA 2014), Vienna, Austria, 15–19 September 2014. M. Bashkanov
[email protected] 1
Physikalisches Institut, Eberhard–Karls–Universit¨at T¨ubingen, Auf der Morgenstelle 14, 72076 T¨ubingen, Germany
2
Department of Physics, Tomsk State University, 36 Lenina Avenue, 634050 Tomsk, Russia
M. Bashkanov et al.
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Fig. 1 Energy dependence of the total cross section for the double-pionic fusion reaction pn → dπ + π − (red triangles) and its isospin decomposition into isoscalar part – corresponding to 2σ (pn → dπ 0 π 0 ) (blue circles) – and isovector part – corresponding to 1/2 σ (pp → dπ + π 0 ) (black squares), see Ref. [6]
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Fig. 2 Energy dependence of two-pion production to the non-fusion channels pn → ppπ − π 0 (left), pn → pnπ 0 π 0 (middle) and pn → pnπ + π − (right). Black, solid lines denote calculations of conventional tchannel processes leading to Roper, and (1600) excitations in the modified Valencia model. Red, dashed lines show the d ∗ contributions and blue, dash-dotted lines their coherent sum. Filled blue circles give the WASA data, open symbols correspond to previous experimental results, see Refs. [8, 9]
to be a genuine dibaryon resonance - obviously the so-called inevitable dibaryon [7], which has been sought after since long.
2 Experimenta
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