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HK: Fachverband Physik der Hadronen und Kerne

HK 36: Hauptvorträge III

HK 36.4: Hauptvortrag

Donnerstag, 20. März 2014, 12:30–13:00, HZ 1+2

Encounters with Di-Baryons – from the ABC Effect to a Resonance in the Neutron-Proton System^*. — •Mikhail Bashkanov for the WASA-at-COSY collaboration — Physikalisches Institut der Universität Tübingen

Despite their long painful history dibaryon searches have recently received new interest, in particular by the recognition that there are more complex quark configurations than just the familiar qq and qqq systems. The "hidden color" aspect makes dibaryons a particularly interesting object in QCD.

Within our two-pion production program we recently started to investigate the intriguing ABC effect, which denotes a low-mass enhancement in the ππ-invariant mass spectrum produced in double-pionic fusion. We observe that this phenomenon is correlated with a resonance structure at √s = 2.37 GeV with Γ ≈ 70 MeV and I(J^P) = 0(3⁺). In order to reveal the nature of this structure we measured its possible decay channels dπ⁰π⁰, dπ⁺π⁻, ppπ⁰π⁻, np π⁰π⁰, NNπ and pn by pd collisions in the quasi-free reaction mode utilizing WASA at COSY.

The pn decay channel of the resonance, the experimentum crucis, was measured by use of polarized deuterons in inverse kinematics. First preliminary results for the np analyzing power exhibit a pronounced resonance effect in the ³G₃ partial wave.

The observed ρ channel π⁺π⁻ production is capable to explain the missing strength in pn induced e⁺e⁻ production providing thus a possible explanation of the DLS puzzle.

^*supported by BMBF and COSY-FFE (FZ Jülich)