/ nucl-ex arXiv:1705.07342

First measurement of the polarization observable $E$ and helicity-dependent cross sections in single $\pi^{0}$ photoproduction from quasi-free nucleons

Dieterle, M. (Basel U.) ; Witthauer, L. (Basel U.) ; Cividini, F. (Mainz U., Inst. Kernphys.) ; Abt, S. (Basel U.) ; Achenbach, P. (Mainz U., Inst. Kernphys.) ; Adlarson, P. (Mainz U., Inst. Kernphys.) ; Afzal, F. (Bonn U., HISKP) ; Ahmed, Z. (Regina U.) ; Akondi, C.S. (Kent State U.) ; Annand, J.R.M. (Glasgow U.) ; Arends, H.J. (Mainz U., Inst. Kernphys.) ; Bashkanov, M. (Edinburgh U.) ; Beck, R. (Bonn U., HISKP) ; Biroth, M. (Mainz U., Inst. Kernphys.) ; Borisov, N.S. (Dubna, JINR) ; Braghieri, A. (INFN, Pavia) ; Briscoe, W.J. (George Washington U.) ; Costanza, S. (INFN, Pavia) ; Collicott, C. (St. Mary's U., Halifax) ; Denig, A. (Mainz U., Inst. Kernphys.) ; Downie, E.J. (George Washington U.) ; Drexler, P. (Mainz U., Inst. Kernphys.) ; Ferretti-Bondy, M.I. (Mainz U., Inst. Kernphys.) ; Gardner, S. (Glasgow U.) ; Garni, S. (Basel U.) ; Glazier, D.I. (Edinburgh U.) ; Glowa, D. (Edinburgh U.) ; Gradl, W. (Mainz U., Inst. Kernphys.) ; Günther, M. (Basel U.) ; Gurevich, G.M. (Moscow, INR) ; Hamilton, D. (Glasgow U.) ; Hornidge, D. (Mt. Allison U.) ; Huber, G.M. (Regina U.) ; Käser, A. (Basel U.) ; Kashevarov, V.L. (Mainz U., Inst. Kernphys.) ; Kay, S. (Edinburgh U.) ; Keshelashvili, I. (Basel U.) ; Kondratiev, R. (Moscow, INR) ; Korolija, M. (Boskovic Inst., Zagreb) ; Krusche, B. (Basel U.) ; Lazarev, A.B. (Dubna, JINR) ; Linturi, J.M. (Mainz U., Inst. Kernphys.) ; Lisin, V. (Moscow, INR) ; Livingston, K. (Glasgow U.) ; Lutterer, S. (Basel U.) ; MacGregor, I.J.D. (Glasgow U.) ; Mancell, J. (Glasgow U.) ; Manley, D.M. (Kent State U.) ; Martel, P.P. (Mt. Allison U.) ; Metag, V. (U. Giessen, II. Phys. Inst.) ; Meyer, W. (Ruhr U., Bochum) ; Miskimen, R. (Massachusetts U., Amherst) ; Mornacchi, E. (Mainz U., Inst. Kernphys.) ; Mushkarenkov, A. (Massachusetts U., Amherst) ; Neganov, A.B. (Dubna, JINR) ; Neiser, A. (Mainz U., Inst. Kernphys.) ; Oberle, M. (Basel U.) ; Ostrick, M. (Mainz U., Inst. Kernphys.) ; Otte, P.B. (Mainz U., Inst. Kernphys.) ; Paudyal, D. (Regina U.) ; Pedroni, P. (INFN, Pavia) ; Polonski, A. (Moscow, INR) ; Prakhov, S.N. (UCLA, Los Angeles (main)) ; Rajabi, A. (Massachusetts U., Amherst) ; Reicherz, G. (Ruhr U., Bochum) ; Ron, G. (Hebrew U.) ; Rostomyan, T. (Basel U.) ; Sarty, A. (St. Mary's U., Halifax) ; Sfienti, C. (Mainz U., Inst. Kernphys.) ; Sikora, M.H. (Edinburgh U.) ; Sokhoyan, V. (George Washington U.) ; Spieker, K. (Bonn U., HISKP) ; Steffen, O. (Mainz U., Inst. Kernphys.) ; Strakovsky, I.I. (George Washington U.) ; Strub, Th. (Basel U.) ; Supek, I. (Boskovic Inst., Zagreb) ; Thiel, A. (Bonn U., HISKP) ; Thiel, M. (Mainz U., Inst. Kernphys.) ; Thomas, A. (Mainz U., Inst. Kernphys.) ; Unverzagt, M. (Mainz U., Inst. Kernphys.) ; Usov, Yu.A. (Dubna, JINR) ; Wagner, S. (Mainz U., Inst. Kernphys.) ; Walford, N.K. (Basel U.) ; Watts, D.P. (Edinburgh U.) ; Werthmüller, D. (Glasgow U.) ; Wettig, J. (Mainz U., Inst. Kernphys.) ; Wolfes, M. (Mainz U., Inst. Kernphys.) ; Zana, L. (Edinburgh U.)

Abstract: The double-polarization observable $E$ and the helicity-dependent cross sections $\sigma_{1/2}$ and $\sigma_{3/2}$ have been measured for the first time for single $\pi^{0}$ 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 $\pi^0$ meson were detected with the Crystal Ball and TAPS electromagnetic calorimeters. Effects from nuclear Fermi motion were removed by a kinematic reconstruction of the $\pi^{0}N$ 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 $\sigma_{1/2}$ and $\sigma_{3/2}$ 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.

Web-Page: http://inspirehep.net/record/1600836/files/fig_02.png; http://inspirehep.net/record/1600836/files/fig_05.png; http://inspirehep.net/record/1600836/files/fig_04.png; http://inspirehep.net/record/1600836/files/fig_03.png; http://inspirehep.net/record/1600836/files/fig_08b.png; http://inspirehep.net/record/1600836/files/fig_08a.png; http://inspirehep.net/record/1600836/files/fig_01.png; http://inspirehep.net/record/1600836/files/fig_07.png; http://inspirehep.net/record/1600836/files/fig_06.png; http://inspirehep.net/record/1600836/files/arXiv:1705.07342.pdf

Note: *Brief entry*; *Temporary entry*; accepted for publication in Phys. Lett. B

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