Data on <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"><mml:msup><mml:mrow><mml:mi>I</mml:mi></mml:mrow><mml:mrow><mml:mi>s</mml:mi></mml:mrow></mml:msup></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si2.gif" overflow="scroll"><mml:msup><mml:mrow><mml:mi>I</mml:mi></mml:mrow><mml:mrow><mml:mi>c</mml:mi></mml:mrow></mml:msup></mml:math> in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.gif" overflow="scroll"><mml:mover accent="true"><mml:mrow><mml:mi>γ</mml:mi></mml:mrow><mml:mrow><mml:mo stretchy="false">→</mml:mo></mml:mrow></mml:mover><mml:mi>p</mml:mi><mml:mo stretchy="false">→</mml:mo><mml:mi>p</mml:mi><mml:msup><mml:mrow><mml:mi>π</mml:mi></mml:mrow><mml:mrow><mml:mn>0</mml:mn></mml:mrow></mml:msup><mml:msup><mml:mrow><mml:mi>π</mml:mi></mml:mrow><mml:mrow><mml:mn>0</mml:mn></mml:mrow></mml:msup></mml:math> reveal cascade decays of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si4.gif" overflow="scroll"><mml:mi>N</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:mn>1900</mml:mn><mml:mo stretchy="false">)</mml:mo></mml:math> via <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si5.gif" overflow="scroll"><mml:mi>N</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:mn>1520</mml:mn><mml:mo stretchy="false">)</mml:mo><mml:mi>π</mml:mi></mml:math>
Annotatsiya
Photoproduction of two neutral pions off the proton is studied using linearly polarized photons, and the polarization observables I s and I c are measured for the first time. These two observables are unique to multi-meson final states; they characterize correlations between the linear photon polarization and the direction of outgoing single particles in photoproduction of three-body final states. The I s and I c distributions suggest that, in the 1.8 to 2.0 GeV mass region, the N(1520)3/2 - intermediate state is reached with reaction dynamics consistent with a dominant J P = 3/2 + wave. These data are included in the Bonn-Gatchina (BnGa) partial wave analysis which is based on a large variety of data; the analysis confirms a significant contribution from the reaction chain p N(1900)3/2 + N(1520)3/2 - 0 p 0 0 .
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