https://doi.org/10.1140/epja/s10050-025-01612-7
Regular Article - Experimental Physics
Polarization observables in double neutral pion photoproduction
1 Helmholtz-Institut für Strahlen- und Kernphysik, Universität Bonn, 53115, Bonn, Germany
2 Physikalisches Institut, Universität Bonn, 53115, Bonn, Germany
3 Physikalisches Institut, Universität Gießen, 35392, Gießen, Germany
4 Physikalisches Institut, Universität Basel, 4056, Basel, Switzerland
5 Institut für Experimentalphysik I, Ruhr-Universität Bochum, 44780, Bochum, Germany
6 Department of Physics, Florida State University, 32306, Tallahassee, USA
7 Universität Hamburg, Hamburg, Germany
8 Lunds universitet, Lund, Sweden
9 Universität Mainz, Mainz, Germany
10 Joint Institute for Nuclear Research, Dubna, Russia
a
seifen@hiskp.uni-bonn.de
b
thoma@hiskp.uni-bonn.de
Received:
16
April
2025
Accepted:
2
June
2025
Published online: 30 July 2025
Measurements of target asymmetries and double-polarization observables for the reaction
γp → pπ0 π0
are reported. The data were taken with the CBELSA/TAPS experiment at the ELSA facility (Bonn University) using the Bonn frozen-spin butanol (
OH) target, which provided transversely polarized protons. Linearly polarized photons were produced via bremsstrahlung off a diamond crystal. The data cover the photon energy range from Eγ = 650 MeV to Eγ = 2600 MeV and nearly the complete angular range. The results have been included in the BnGa partial wave analysis. Experimental results and the fit agree very well. Observed systematic differences in the branching ratios for decays of 
and 
resonances are attributed to the internal structure of these excited nucleon states. Resonances which can be assigned to SU(6)
O(3) two-oscillator configurations show larger branching ratios to intermediate states with non-zero intrinsic orbital angular momenta than resonances assigned to one-oscillator configurations.
© The Author(s) 2025
Open Access
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