Mainz 2012 – scientific programme
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HK: Fachverband Physik der Hadronen und Kerne
HK 55: Hadronenstruktur und -spektroskopie
HK 55.1: Group Report
Friday, March 23, 2012, 11:00–11:30, RW 2
On the Observation of a Narrow Resonance Structure in pn-scattering and Two-Pion Production* — •Mikhail Bashkanov — Physikalisches Institut, Univ. Tübingen
Whereas for the isovector two-pion production in NN-collisions a smooth energy dependence is observed, which is well described by t-channel meson exchange, the purely isoscalar reaction pn → dπ0π0 exhibits a pronounced narrow resonance structure at m = 2.37 GeV = 2mΔ - 90 MeV, which is strictly correlated with the appearance of a large low-mass enhancement (ABC-Effect) in the π0π0-invariant mass spectrum. From the angular distributions we deduce I(JP) = 0(3+) for the resonance structure [1].
If this structure originates from a genuine pn resonance, then it has to be sensed also in other two-pion production channels with isoscalar contributions as well as in pn scattering. Indeed, the pn total cross section exhibits a structure at the energy of interest, which is well described by inclusion of the hypothetical resonance.
Experimental results are shown for the two-pion channels d π0π0, d π+π− and ppπ0π−. Scheduled measurements on quasifree p→n-scattering and the p→n → pnπ0π0 reaction are discussed.
The fact that the ABC effect is observed also for double-pionic fusion processes to heavier nuclei, suggests that this resonance structure is robust enough to survive even in nuclei.
* supported by BMBF and COSY-FFE
[1] P. Adlarson et al., Phys. Rev. Lett. 106, 242302 (2011)