We theoretically analyze the intensity of the resonant inelastic X-ray scattering (RIXS) based on Ansatz that the electron is fractionalized into two components. By fitting the angle resolved photoemission spectroscopy (ARPES) data of a cuprate high-Tc superconductor Bi2Sr2CaCu2O8+δ and the subsequent machine learning results obtained before by Yamaji et al. (arXiv:1903.08060), we determine the parameters of the two-component fermion model that describes the electron fractionalization. The RIXS spectra are predicted based on this formulation. We find that the intensity is enhanced in the superconducting phase relative to the normal or pseudogap phase. Since the enhancement is unusual, we propose this can be used as a critical test whether the unconventional electron fractionalization captures the essence of the cuprate superconductivity. This type of combined analyses using multiple independent spectroscopy data, with the help of theoretical and machine learning insights, regarded as integrated spectroscopy opens a new route to study difficult open issues in strongly correlated electron systems.
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