Energy resolution and linearity of XENON1T in the MeV energy range

Xenon dual-phase time projection chambers designed to search for weakly interacting massive particles have so far shown a relative energy resolution which degrades with energy above ∼ 200 keV due to the saturation effects. This has limited their sensitivity in the search for rare events like the neutrinoless double-beta decay of ¹³⁶Xe at its Q value, Q_ββ ≃ 2.46MeV. For the XENON1T dual-phase time projection chamber, we demonstrate that the relative energy resolution at 1 σ/μ is as low as (0.80 ± 0.02) % in its one-ton fiducial mass, and for single-site interactions at Q_ββ . We also present a new signal correction method to rectify the saturation effects of the signal readout system, resulting in more accurate position reconstruction and indirectly improv- ing the energy resolution. The very good result achieved in XENON1T opens up new windows for the xenon dual-phase dark matter detectors to simultaneously search for other rare events.