@article{0295d2f533424aabb11860e03c71502d,
title = "First measurement of helicity-dependent cross sections in π0η photoproduction from quasi-free nucleons",
abstract = "The helicity-dependent cross sections for the photoproduction of π0η pairs have been measured for the first time. The experiment was performed at the tagged photon facility of the Mainz MAMI accelerator with the combined Crystal Ball – TAPS calorimeter. The experiment used a polarized deuterated butanol target and a circularly polarized photon beam. This arrangement allowed the σ1/2 (photon and target spin antiparallel) and σ3/2 (parallel spins) components to be measured for quasi-free production of π0η pairs off protons and neutrons. The main finding is that the two helicity components contribute identically, within uncertainties, for both participant protons and neutrons. The absolute couplings for protons and neutrons are also identical. This means that nucleon resonances contributing to this reaction in the investigated energy range have almost equal electromagnetic helicity couplings, A1/2 n,p and A3/2 n,p. Identical couplings for protons and neutrons are typical for Δ resonances and identical A1/2 and A3/2 components are only possible for J≥3/2 states, which constrains possible contributions of nucleon resonances.",
author = "{(A2 Collaboration at MAMI)} and A. K{\"a}ser and M. Dieterle and L. Witthauer and S. Abt and P. Achenbach and P. Adlarson and F. Afzal and Z. Ahmed and J. Ahrens and Annand, {J. R.M.} and Arends, {H. J.} and M. Bashkanov and R. Beck and M. Biroth and Borisov, {N. S.} and A. Braghieri and Briscoe, {W. J.} and F. Cividini and C. Collicott and S. Costanza and A. Denig and Downie, {E. J.} and P. Drexler and A. Fix and S. Garni and Glazier, {D. I.} and I. Gorodnov and W. Gradl and M. G{\"u}nther and Gurevich, {G. M.} and L. Heijkenskj{\"o}ld and D. Hornidge and Huber, {G. M.} and Kashevarov, {V. L.} and S. Kay and I. Keshelashvili and R. Kondratiev and M. Korolija and B. Krusche and Lazarev, {A. B.} and V. Lisin and K. Livingston and S. Lutterer and MacGregor, {I. J.D.} and Manley, {D. M.} and Martel, {P. P.} and V. Metag and W. Meyer and R. Miskimen and E. Mornacchi",
note = "Funding Information: We wish to acknowledge the outstanding support of the accelerator group and operators of MAMI. We thank L. Tiator for very useful discussions. This work was supported by Schweizerischer Nationalfonds ( 200020-156983 , 132799 , 121781 , 117601 ), Deutsche Forschungsgemeinschaft ( SFB 443 , SFB 1044 , SFB/TR16 ), the INFN -Italy, the European Community-Research Infrastructure Activity under FP7 programme (Hadron Physics, grant agreement No. 227431 ), the UK Science and Technology Facilities Council ( ST/J000175/1 , ST/G008604/1 , ST/G008582/1 , ST/J00006X/1 , and ST/L00478X/1 ), the Natural Sciences and Engineering Research Council ( NSERC , FRN: SAPPJ-2015-00023 ), Canada. This material is based upon work also supported by the U.S. Department of Energy , Office of Science, Office of Nuclear Physics Research Division, under Award Numbers DE-FG02-99-ER41110 , DE-FG02-88ER40415 , DE-FG02-01-ER41194 , and DE-SC0014323 and by the National Science Foundation , under Grant Nos. PHY-1039130 and IIA-1358175 .",
year = "2018",
month = nov,
day = "10",
doi = "10.1016/j.physletb.2018.10.006",
language = "English",
volume = "786",
pages = "305--312",
journal = "Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics",
issn = "0370-2693",
publisher = "Elsevier",
}