%0 Journal Article
%T Measurement of the beam-helicity asymmetry $I^{\odot}$ in the photoproduction of $¦Ð^0¦Ð^{\pm}$-pairs off protons and off neutrons
%A M. Oberle
%A J. Ahrens
%A J. R. M. Annand
%A H. J. Arends
%A K. Bantawa
%A P. A. Bartolome
%A R. Beck
%A V. Bekrenev
%A H. Berghaeuser
%A A. Braghieri
%A D. Branford
%A W. J. Briscoe
%A J. Brudvik
%A S. Cherepnya
%A B. Demissie
%A M. Dieterle
%A E. J. Downie
%A P. Drexler
%A L. V. Fil'kov
%A A. Fix
%A D. I. Glazier
%A E. Heid
%A D. Hornidge
%A D. Howdle
%A G. M. Huber
%A O. Jahn
%A I. Jaegle
%A T. C. Jude
%A A. Kaeser
%A V. L. Kashevarov
%A I. Keshelashvili
%A R. Kondratiev
%A M. Korolija
%A S. P. Kruglov
%A B. Krusche
%A A. Kulbardis
%A V. Lisin
%A K. Livingston
%A I. J. D. MacGregor
%A Y. Maghrbi
%A J. Mancell
%A D. M. Manley
%A Z. Marinides
%A M. Martinez
%A J. C. McGeorge
%A E. McNicoll
%A D. Mekterovic
%A V. Metag
%A S. Micanovic
%A D. G. Middleton
%A A. Mushkarenkov
%A B. M. K. Nefkens
%A A. Nikolaev
%A R. Novotny
%A M. Ostrick
%A B. Oussena
%A P. Pedroni
%A F. Pheron
%A A. Polonski
%A S. N. Prakhov
%A J. Robinson
%A G. Rosner
%A T. Rostomyan
%A S. Schumann
%A M. H. Sikora
%A D. I. Sober
%A A. Starostin
%A I. Supek
%A M. Thiel
%A A. Thomas
%A M. Unverzagt
%A D. P. Watts
%A D. Werthmueller
%A L. Witthauer
%A F. Zehr
%J Physics
%D 2014
%I arXiv
%R 10.1140/epja/i2014-14054-5
%X Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz for the photoproduction of mixed-charge pion pairs in the reactions $\boldsymbol{\gamma}p\rightarrow n\pi^0\pi^+$ off free protons and $\boldsymbol{\gamma}d\rightarrow (p)p\pi^0\pi^-$ and $\boldsymbol{\gamma}d\rightarrow (n)n\pi^0\pi^+$ off quasi-free nucleons bound in the deuteron for incident photon energies up to 1.4 GeV. Circularly polarized photons were produced from bremsstrahlung of longitudinally polarized electrons and tagged with the Glasgow-Mainz magnetic spectrometer. The charged pions, recoil protons, recoil neutrons, and decay photons from $\pi^0$ mesons were detected in the 4$\pi$ electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. Using a complete kinematic reconstruction of the final state, excellent agreement was found between the results for free and quasi-free protons, suggesting that the quasi-free neutron results are also a close approximation of the free-neutron asymmetries. A comparison of the results to the predictions of the Two-Pion-MAID reaction model shows that the reaction mechanisms are still not well understood, in particular at low incident photon energies in the second nucleon-resonance region.
%U http://arxiv.org/abs/1403.1989v1