Neutron polarisation transfer, Cxjavax.xml.bind.JAXBElement@3c69ec1, in π+ photoproduction off the proton, d(γ⊙,n→π+)nspec

We report a first measurement of the double-polarisation observable, Cxjavax.xml.bind.JAXBElement@1844512f, in π+ photoproduction off the proton. The Cxjavax.xml.bind.JAXBElement@1ad4629f double-polarisation observable represents the transfer of polarisation from a circularly polarised photon beam to the recoiling neutron. The MAMI circularly polarised photon beam impinged on a liquid deuterium target cell, with reaction products detected in the Crystal Ball calorimeter. Ancillary apparatus surrounding the target provided tracking, particle identification and determination of recoil nucleon polarisation. The Cxjavax.xml.bind.JAXBElement@4b377096 observable is determined for photon energies 800-1400 MeV, providing new constraints on models aiming to elucidate the spectrum and properties of nucleon resonances. This is the first determination of any polarisation observable from the beam-recoil group of observables for this reaction. Inclusion of the new data in the database of the SAID partial wave analysis shifted the solution to a new global minima which, not only gives better agreement with the current data, but also improves the description of a range of other single and double polarisation observables for charged pion photoproduction.