Abstract
The helicity-dependent single \(\pi ^{0}\) photoproduction cross section on the deuteron and the angular dependence of the double polarisation observable E for the quasi-free single \(\pi ^0\) production off the proton and the neutron have been measured, for the first time, from the threshold region up to the photon energy 1.4 GeV. The experiment was performed at the tagged photon facility of the MAMI accelerator and used a circularly polarised photon beam and longitudinally polarised deuteron target. The reaction products were detected using the large acceptance Crystal Ball/TAPS calorimeter, which covered 97% of the full solid angle. Comparing the cross section from the deuteron with the sum of free nucleon cross sections provides a quantitative estimate of the effects of the nuclear medium on pion production. In contrast, comparison of the E helicity asymmetry data from quasi-free protons off deuterium with data from a free proton target indicates that nuclear effects do not significantly affect this observable. As a consequence, it is deduced that the helicity asymmetry E on a free neutron can be reliably extracted from measurements on a deuteron in quasi-free kinematics.
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Data Availability
This manuscript has no associated data or the data will not be deposited. [Authors’ comment: The data are available from the corresponding author and will be deposited on the HEPData repository.]
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Acknowledgements
The authors wish to acknowledge the excellent support of the accelerator group of MAMI. This work has been supported by the U.K. STFC (ST/L00478X/1, ST/T002077/1, ST/L005824/1, 57071/1, 50727/1, ST/V001035/1) grants, the Deutsche Forschungsgemeinschaft (SFB443, SFB/TR16, and SFB1044), DFG-RFBR (Grant no. 09-02-91330), Schweizerischer Nationalfonds (Contracts No. 200020-175807, No. 200020-156983, No. 132799, No. 121781, No. 117601), the U.S. Department of Energy (Offices of Science and Nuclear Physics, Awards No. DE-SC0014323, DEFG02-99-ER41110, No. DE-FG02-88ER40415, No. DEFG02-01-ER41194) and National Science Foundation (Grants NSF OISE-1358175; PHY-1039130, PHY-1714833, No. IIA-1358175), INFN (Italy), and NSERC of Canada (Grant no. FRN-SAPPJ2015-00023).
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Communicated by K. Peters.
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Cividini, F., Dieterle, M., Abt, S. et al. Measurement of the helicity dependence for single \(\pi ^{0}\) photoproduction from the deuteron. Eur. Phys. J. A 58, 113 (2022). https://doi.org/10.1140/epja/s10050-022-00760-4
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DOI: https://doi.org/10.1140/epja/s10050-022-00760-4