First measurement of the polarization observable E and helicity-dependent cross sections in single π0 photoproduction from quasi-free nucleons

M. Dieterle, L. Witthauer, F. Cividini, S. Abt, P. Achenbach, P. Adlarson, F. Afzal, Z. Ahmed, C. S. Akondi, J. R.M. Annand, H. J. Arends, M. Bashkanov, R. Beck, M. Biroth, N. S. Borisov, A. Braghieri, W. J. Briscoe, S. Costanza, C. Collicott, A. DenigE. J. Downie, P. Drexler, M. I. Ferretti-Bondy, S. Gardner, S. Garni, D. I. Glazier, D. Glowa, W. Gradl, M. Günther, G. M. Gurevich, D. Hamilton, D. Hornidge, G. M. Huber, A. Käser, V. L. Kashevarov, S. Kay, I. Keshelashvili, R. Kondratiev, M. Korolija, B. Krusche*, A. B. Lazarev, J. M. Linturi, V. Lisin, K. Livingston, S. Lutterer, I. J.D. MacGregor, J. Mancell, D. M. Manley, P. P. Martel, V. Metag, W. Meyer, R. Miskimen, E. Mornacchi, A. Mushkarenkov, A. B. Neganov, A. Neiser, M. Oberle, M. Ostrick, P. B. Otte, D. Paudyal, P. Pedroni, A. Polonski, S. N. Prakhov, A. Rajabi, G. Reicherz, G. Ron, T. Rostomyan, A. Sarty, C. Sfienti, M. H. Sikora, V. Sokhoyan, K. Spieker, O. Steffen, I. I. Strakovsky, Th Strub, I. Supek, A. Thiel, M. Thiel, A. Thomas, M. Unverzagt, Yu A. Usov, S. Wagner, N. K. Walford, D. P. Watts, D. Werthmüller, J. Wettig, M. Wolfes, L. Zana

*Corresponding author for this work

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The double-polarization observable E and the helicity-dependent cross sections σ1/2 and σ3/2 have been measured for the first time for single π0 photoproduction from protons and neutrons bound in the deuteron at the electron accelerator facility MAMI in Mainz, Germany. The experiment used a circularly polarized photon beam and a longitudinally polarized deuterated butanol target. The reaction products, recoil nucleons and decay photons from the π0 meson were detected with the Crystal Ball and TAPS electromagnetic calorimeters. Effects from nuclear Fermi motion were removed by a kinematic reconstruction of the π0N final state. A comparison to data measured with a free proton target showed that the absolute scale of the cross sections is significantly modified by nuclear final-state interaction (FSI) effects. However, there is no significant effect on the asymmetry E since the σ1/2 and σ3/2 components appear to be influenced in a similar way. Thus, the best approximation of the two helicity-dependent cross sections for the free neutron is obtained by combining the asymmetry E measured with quasi-free neutrons and the unpolarized cross section corrected for FSI effects under the assumption that the FSI effects are similar for neutrons and protons.

Original languageAmerican English
Pages (from-to)523-531
Number of pages9
JournalPhysics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
StatePublished - 10 Jul 2017

Bibliographical note

Funding Information:
We wish to acknowledge the outstanding support of the accelerator group and operators of MAMI. 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 , and DE-FG02-01-ER41194 and by the National Science Foundation , under Grant Nos. PHY-1039130 and IIA-1358175 .

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© 2017 The Authors


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