Mainz 2012 – wissenschaftliches Programm
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HK: Fachverband Physik der Hadronen und Kerne
HK 55: Hadronenstruktur und -spektroskopie
HK 55.3: Vortrag
Freitag, 23. März 2012, 11:45–12:00, RW 2
In Search of the ABC Resonance Structure in the Reactions pn → ppπ0π− and pn → pn π0π0 * — •Tatiana Skorodko — Physikalisches Institut der Universität Tübingen
As we have shown recently [1] the basic double-pionic fusion reaction pn → d π0π0 exhibits a pronounced narrow resonance structure with m = 2.37 GeV, Γ = 70 MeV and I(JP) = 0(3+), which is correlated with a low-mass enhancement in the π0π0-invariant mass distribution, the so-called ABC effect. If the scenario of a s-channel resonance with a reaction process pn → d* → Δ+Δ0 → d π0π0 is correct, then the resonance should be observed also in pn scattering as well as in other two-pion production channels like pn π0π0 and also pp π0π−. These channels can be accessed in quasifree proton reactions on the deuteron. The latter channel is particularly well suited for a reliable data analysis, since the four-momenta of all ejectiles can be detected in WASA.
A corresponding WASA run at Tp = 1.2 GeV has been analyzed providing first results for the pn → pp π0π− reaction, which cover also the region of the putative ABC resonance.
The experimental results exhibit surprisingly large cross sections at low energies pointing to so far unknown processes. In the ABC region neither an ABC effect nor a resonance behavior is observed, which is understood by the fact that the π0π− pair must be in relative p-wave, whereas the pp pair prefers to be in the 1S0 state.
[1] P. Adlarson et al., Phys. Rev. Lett. 106 242302 (2011)
*supported by BMBF and COSY-FFE (FZ Jülich)