Background modelling for ${}^{124}$Xe double electron capture search with XENON1T

XENON1T located at Laboratori Nazionali del Gran Sasso is the most sensitive WIMP dark matter detector to date. It uses a dual phase time projection chamber with a sensitive liquid xenon volume of $\sim$ 2 tons for detection. The low background and large target mass also make it suitable for investigating other rare phenomena such as double beta decays and alternative dark matter candidates. Analyses in these physics channels require a detailed understanding of the electronic recoil background spectrum at higher energies than for the standard WIMP search. This talk will outline relevant background components, neutron activation studies, as well as the background modelling up to the 100 keV range. In addition, the application in a search for ${}^{124}$Xe two-neutrino double electron capture with XENON1T will be presented.