The first step on our way to an experimental test of the GDH sum rule was an unpolarized pilot experiment in the PHOENICS area of ELSA in the year 1996 [Hel97],[Sau98].
The objective of this first experiment was a test of the newly built Bonn GDH detector components and the confirmation of the methods of data taking and analysis. Therefore, an inclusive measurement of total photohadronic cross section was carried out, employing a tagged photon beam and 12C, CH2 and CD2 solid state targets. The thicknesses of the used targets were comparable to those of the polarized BICEPS target. The setup of the pilot experiment is shown below.
By measuring the yields on 12C, CH2 and CD2 targets, the total cross sections on 1H, 2H (or D) and on the neutron can be extracted via the difference methode. Some preliminary results are shown below. Their comparison to other results from DAPHNE experiments and the Particle Data Group (PDG) Particle Data Group (PDG)
shows reasonable agreement. Note in partucilar, that the literature data were obtained with liquid targets, which were much more suitable for unpolarized measurements.
