Abstract
New measurements of the helicity dependence of the total inclusive photoabsorption cross section and of the partial cross sections for several reaction channels on the proton and on the neutron were carried out at MAMI (Mainz) in the energy region 200 He targets.These new doubly-polarised pion-photoproduction data sets give new input to the partial wave analyses and allow to constrain the multipole solution of the different analyses; they also allow to study the double-polarisation observables G and E. Furthermore, the results obtained give information on the well-known Gerasimov-Drell-Hearn sum rule.
Highlights
EPJ Web of Conferences 164, 07034 (2017)EPJ Web of Conferences polarisation observables, for every fixed value of energy and angle (W, θ)
The target cell was placed inside the central detector system, devoted to the detection of the reaction products. It was composed by the Crystall Ball (CB) NaI spectrometer, a large solid angle, highly segmented photon and hadron spectrometer, and it was complemented by the Multi-Wire Proportional Chambers (MWPCs), used to discriminate between the charged and the neutral particles detected in CB
The preliminary results of the helicity dependence of the total inclusive cross section ∆σtot = on the proton and on the neutron are depicted in Fig. 5
Summary
Polarisation observables, for every fixed value of energy and angle (W, θ). In addition to the unpolarised cross section σ, there are 3 single polarisation observables and 12 double polarisation observables, grouped in beam-target, beam-recoil nucleon and target-recoil polarisation classes (Table 1). The measurement of 7 (8) properly chosen observables is necessary to yield a model-independent complete analysis [2, 3]. Recoil nucleon Target and recoil polarisation polarisation polarisation polarisation
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