Detector response model based on multi-scatter neutron calibration in the LUX-ZEPLIN experiment

The LUX-ZEPLIN (LZ) experiment uses a dual-phase liquid xenon time projection chamber (TPC) to primarily detect low-energy nuclear recoils (NRs) from signals such as WIMP dark matter particle interactions and boron-8 solar neutrinos. Particle interactions in the LZ TPC generate scintillation and ionization signals, both of which can be measured by arrays of photomultiplier tubes. Accurate calibration of the microphysics of interactions in the TPC is critical for the construction of the detector response model to characterize these signals from low-energy NRs. In this work, we selected double-scatter NR events from 2.45 MeV neutrons generated by a deuterium-deuterium (DD) generator source. Using scattering angle measurements derived from the reconstructed double-scatter vertices, we estimate the nuclear recoil energy and calculate the corresponding ionization yield, a key component of the response model. This analysis provides crucial information to determine the LZ detector sensitivity to low-energy NR signals.