https://doi.org/10.1140/epja/s10050-022-00760-4
Regular Article - Experimental Physics
Measurement of the helicity dependence for single 
photoproduction from the deuteron
1
Institut für Kernphysik, University of Mainz, 55099, Mainz, Germany
2
Departement Physik, Universität Basel, 4056, Basel, Switzerland
3
Helmholtz-Institut für Strahlen- und Kernphysik, Universität Bonn, 53115, Bonn, Germany
4
University of Regina, S4S 0A2, Regina, SK, Canada
5
SUPA School of Physics and Astronomy, University of Glasgow, G12 8QQ, Glasgow, UK
6
Department of Physics, University of York, Heslington, Y010 5DD, York, UK
7
Joint Institute for Nuclear Research, 141980, Dubna, Russia
8
INFN Sezione di Pavia, 27100, Pavia, Italy
9
Dipartimento di Fisica, Università di Pavia, Pavia, Italy
10
The George Washington University, 20052-0001, Washington, DC, USA
11
Tomsk Polytechnic University, 634034, Tomsk, Russia
12
Institute for Nuclear Research, 125047, Moscow, Russia
13
Mount Allison University, E4L 1E6, Sackville, NB, Canada
14
Rudjer Boskovic Institute, 10000, Zagreb, Croatia
15
Kent State University, 44242-0001, Kent, OH, USA
16
University of Massachusetts, 01003, Amherst, MA, USA
17
Paul Scherrer Institute (PSI), 5232, Villigen, Switzerland
Received:
1
March
2022
Accepted:
2
June
2022
Published online:
30
June
2022
The helicity-dependent single photoproduction cross section on the deuteron and the angular dependence of the double polarisation observable E for the quasi-free single 
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.
© The Author(s), under exclusive licence to Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature 2022
