LUX-ZEPLIN

Abstract:

The LUX-ZEPLIN (LZ) experiment is a direct-detection dark matter experiment, optimized to search for weakly interacting massive particles (WIMPs) through WIMP-nucleon interactions. The main challenge in dark matter detection is differentiating between WIMP signals and background events. In LZ, the ratio of ionization to scintillation signals (charge-to-light) is the primary method for rejecting electronic recoil (ER) background. Pulse shape discrimination (PSD) offers a method for additional ER backgrounds rejection in liquid xenon detectors. In this paper, the discrimination power of PSD with the LZ experiment is discussed. To precisely characterize the scintillation pulse shape, an analysis framework is developed to reconstruct the detection time of individual photons. Using LZ calibration data, the photon-timing tail fraction discriminator is optimized and achieves ER leakage as low as 15%$$15\%$$. For specific background processes such as 124$$^{124}$$Xe double electron capture, the leakage is reduced further to about 5%$$5\%$$. PSD is combined with charge-to-light to form two-factor discrimination (TFD). The optimized TFD performance is compared with the performance of the charge-to-light method, with the corresponding false positive rate reduced by up to a factor of two for large scintillation pulses. Finally, PSD and TFD are applied to data from LZ’s WS2024 run and their performance is summarized.

Abstract:

We report results from searches for new physics models through electron recoils using data collected by the LUX-ZEPLIN experiment during its first two science runs, with a total exposure of $4.2\mathrm{tonne}\text{−}\mathrm{years}$ . The observed data are consistent with a background-only hypothesis. Constraints are derived for electromagnetic interactions of solar neutrinos, solar axionlike particles (ALPs), mirror dark matter, and the absorption of bosonic dark matter candidates. The inverse Primakoff process for ${}^{57}\mathrm{Fe}$ deexcitation solar ALPs is considered for the first time. These results represent the most stringent constraints to date on keV-scale Primakoff and ${}^{57}\mathrm{Fe}$ solar ALPs, bosonic dark matter, mirror dark matter, and neutrino millicharge, while remaining competitive for the other signal models investigated.

Abstract:

DarkSide-20k is a Weakly Interacting Massive Particles (WIMPs) search experiment using liquid argon as a target, designed to perform a background-free search for dark matter with unprecedented sensitivity, and is currently under construction at INFN Laboratori Nazionali del Gran Sasso, Italy. The detector comprises a dual-phase Time Projection Chamber (TPC) complemented with external veto systems and is equipped with a total of 2720 Silicon PhotoMultiplier (SiPM)-based readout channels. This work presents the Data Acquisition (DAQ) system designed for DarkSide-20k. The system is capable of continuous, triggerless digitisation of the waveforms with high single-photoelectron detection efficiency and online processing, ensuring data reduction for long-term storage. The DarkSide-20k DAQ system employs commercial CAEN VX2745 digitisers with custom FPGA firmware implementation, identifying pulses in the digitised waveforms. Timing and synchronisation across all 48 digitisers are provided by custom Global and Crate Data Manager boards distributing a phase-aligned clock derived from a disciplined rubidium standard. Waveform segments are processed in real time by Front End Processor machines. Data are organised into collections containing whole detector information and distributed across a farm of Time Slice Processors for event reconstruction, classification, and further reduction before storage and offline analysis. A full “Quadrant” of the system, corresponding to one quarter of the final DAQ, has been assembled and validated at TRIUMF laboratory in Canada. The Quadrant has been stress-tested with simultaneous pulses and demonstrated sustained digitiser readout exceeding expected physics rates and stable long-term performance.

Abstract:

We present searches for light dark matter (DM) with masses $3–9\mathrm{GeV}/c^2$ in the presence of coherent elastic neutrino-nucleus scattering ( $\mathrm{CE}\nu \mathrm{NS}$ ) from ${}^8\mathrm{B}$ solar neutrinos with the LUX-ZEPLIN experiment. This analysis uses a 5.7 tonne-yr exposure with data collected between March 2023 and April 2025. In an energy range spanning 1–6 keV, we report no significant excess of events attributable to dark matter nuclear recoils, but we observe a significant signal from ${}^8\mathrm{B}$ $\mathrm{CE}\nu \mathrm{NS}$ interactions that is consistent with expectation. We set world-leading limits on spin-independent and spin-dependent-neutron DM-nucleon interactions for masses down to $5\mathrm{GeV}/c^2$ . In the no-dark-matter scenario, we observe a signal consistent with ${}^8\mathrm{B}$ $\mathrm{CE}\nu \mathrm{NS}$ events, corresponding to a $4.5\sigma$ statistical significance. This is the most significant evidence of ${}^8\mathrm{B}$ $\mathrm{CE}\nu \mathrm{NS}$ interactions and is enabled by robust background modeling and mitigation techniques. This demonstrates LZ’s ability to detect rare signals at keV-scale energies.