Beam–target helicity asymmetry E in K+Σ− photoproduction on the neutron

We report a measurement of a beam-target double-polarisation observable (E) for the (gamma) over right arrow(n) over right arrow (p) -> K+Sigma(-) (p) reaction. The data were obtained impinging the circularly-polarised energy-tagged photon beam of Hall B at Jefferson Lab on a longitudinally-polarised frozen-spin hydrogen deuteride (HD) nuclear target. The E observable for an effective neutron target was determined for centre-of-mass energies 1.70 <= W <= 2.30 GeV, with reaction products detected over a wide angular acceptance by the CLAS spectrometer. These new double-polarisation data give unique constraints on the strange decays of excited neutron states. Inclusion of the new data within the Bonn-Gatchina theoretical model results in significant changes for the extracted photocouplings of a number of established nucleon resonances. Possible improvements in the PWA description of the experimental data with additional "missing" resonance states, including the N(2120)(3/2-) resonance, are also quantified. Crown Copyright (C) 2020 Published by Elsevier B.V.