Abstract
Data on the reaction γp → pπ0π0 were taken with the CBELSA/TAPS experiment at ELSA where linearly polarized photons impinged on a transversely polarized butanol target. Target asymmetries and double polarization observables were extracted and entered the BnGa-PWA. Systematic differences in the branching ratios of N* and Δ* resonances hint at the internal structure of these states
Highlights
The excited states in hadron spectroscopy are broad and overlapping
The neutral double pion channel is especially advantageous compared to the charged pion channel, since it suffers much less from non-resonant contributions: There is no diffractive ρ production, no Kroll-Ruderman term and t-channel processes are supressed, enhancing the sensitivity to resonance contributions
Possible detector asymmetries were expanded in a Fourier series and coefficients which interfere with the polarization observables were fitted
Summary
The excited states in hadron spectroscopy are broad and overlapping. A partial wave analysis (PWA) needs to be performed where polarization observables are essential to resolve ambiguities in the PWA solutions. Resonance contributions cannot be extracted from the (unpolarized) cross section alone. At higher center-of-mass energy the importance of multi-meson final states increases and cascading decays via intermediate resonances occur. The neutral double pion channel is especially advantageous compared to the charged pion channel, since it suffers much less from non-resonant contributions: There is no diffractive ρ production, no Kroll-Ruderman term (direct Δπ production) and t-channel processes are supressed, enhancing the sensitivity to resonance contributions
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