Measurement of the helicity asymmetry E for the reaction $$ \gamma p\rightarrow \pi ^0 p$$
M. Gottschall, F. Afzal, A. V. Anisovich, D. Bayadilov, R. Beck, M. Bichow, K.-Th. Brinkmann, V. Credé, M. Dieterle, F. Dietz, H. Dutz, H. Eberhardt, D. Elsner, R. Ewald, K. Fornet-Ponse, St. Friedrich, F. Frommberger, A. Gridnev, M. Grüner, E. Gutz, Ch. Hammann, J. Hannappel, J. Hartmann, W. Hillert, P. Hoffmeister, Ch. Honisch, T. C. Jude, S. Kammer, H. Kalinowsky, I. Keshelashvili, P. Klassen, F. Klein, E. Klempt, K. Koop, B. Krusche, M. Kube, Μ. Lang, I. Lopatin, P. Mahlberg, K. Makónyi, V. Metag, W. Meyer, J. Müller, J. Müllers, M. Nanova, V. A. Nikonov, R. Novotny, D. Piontek, G. Reicherz, T. Rostomyan, A. Sarantsev, Christian Schmidt, H. Schmieden, T. Seifen, V. Sokhoyan, K. Spieker, A. Thiel, U. Thoma, M. Urban, H. van Pee, D. Walther, Ch. Wendel, D. Werthmüller, U. Wiedner, A. Wilson, A. Winnebeck, L. Witthauer, Y. Wunderlich
Abstract
Abstract A measurement of the double-polarization observable E for the reaction $$\gamma p\rightarrow \pi ^0 p$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>γ</mml:mi> <mml:mi>p</mml:mi> <mml:mo>→</mml:mo> <mml:msup> <mml:mi>π</mml:mi> <mml:mn>0</mml:mn> </mml:msup> <mml:mi>p</mml:mi> </mml:mrow> </mml:math> is reported. The data were taken with the CBELSA/TAPS experiment at the ELSA facility in Bonn using the Bonn frozen-spin butanol (C $$_4$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mrow/> <mml:mn>4</mml:mn> </mml:msub> </mml:math> H $$_9$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mrow/> <mml:mn>9</mml:mn> </mml:msub> </mml:math> OH) target, which provided longitudinally-polarized protons. Circularly-polarized photons were produced via bremsstrahlung of longitudinally-polarized electrons. The data cover the photon energy range from $$E_\gamma =600$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>E</mml:mi> <mml:mi>γ</mml:mi> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>600</mml:mn> </mml:mrow> </mml:math> to 2310 MeV and nearly the complete angular range. The results are compared to and have been included in recent partial wave analyses.