A: The free electron laser (FEL), as a next-generation light source, is an attractive tool in scientific frontier research because of its advantages of full coherence, ultra-short pulse duration, and controllable polarization. Owing to the demand of real-time bunch diagnosis during FEL experiments, precise nondestructive measurements of the polarization and X-ray energy spectrum using one instrument are preferred. In this paper, such an instrument based on the electron time-of-flight technique is proposed. By considering the complexity and nonlinearity, a numerical model in the framework of Geant4 has been developed for optimization. Taking the Shanghai Soft X-ray FEL user facility as an example, its measurement performances' dependence on the critical parameters was studied systematically, and, finally, an optimal design was obtained, achieving resolutions of 0.5% for the polarization degree and 0.3 eV for the X-ray energy spectrum.
K: X-ray FEL, e-TOF, Polarization, Energy spectrum A X P : 1702.066521Corresponding author. 2Corresponding author.
In this work, we perform a study of nucleon resonance production in the γp → pηφ reaction within an effective Lagrangian approach. In our model, we consider the excitation of the N * (1535), N * (1650), N * (1710) and N * (1720) in the intermediate state and the background term. We find that this reaction is dominated by the excitation of the N * (1535) in the near threshold region. Especially, we study the possible role of the scalar meson exchange in this reaction. It is found that the f0(980) exchange may give a significant contribution and the parity asymmetry can be used to identify its role in this reaction.PACS numbers:
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.