LZ: Searching for Dark Matter
The latest estimates show that the total energy balance of the Universe has contributions from ordinary matter (4.9%), Dark Matter (26.8%) and Dark Energy (68.3%). The two latest contributions require new physics models to explain their nature. Measurements are consistent with Dark Matter particles interacting weakly and having density of about 0.3 GeV/cm3 near the Earth. LUX-ZEPLIN (LZ) experiment searches for Dark Matter using a Time Projection Chamber (TPC) containing 7 tonnes of liquefied xenon as a target material. LZ is expected to achieve the best sensitivity for Dark Matter particles with masses from 10GeV to 10TeV. The detector is based in the former Homestake gold mine (South Dakota, USA) at the depth of about 1 mile. Though the rocks protect the detector from cosmic radiation, it has a dedicated active veto system protecting from very rare remaining cosmic muons as well as from external and internal radiation. Outer detector surrounding the TPC is a part of this veto system. The outer detector consists of approximately 17 tonnes of gadolinium-loaded liquid scintillator confined to 10 acrylic tanks surrounding the cryostat and 228,000 litres of water as the outermost layer. It is monitored by 120 inward-facing 8-inch photomultiplier tubes. An optical calibration system has been designed and built by our group to calibrate and monitor these photomultiplier tubes and light transmission in the outer detector. This will allow the veto system to reach its required efficiency and thus ensure that LUX-ZEPLIN meets its target sensitivity.
The Liverpool Dark Matter group joined the LZ project in 2014. In addition to the optical calibration system the group developed data analysis and data quality monitoring frameworks, software for outer detector calibration and visualisation. Group members actively participated in installation of the LZ detector at SURF. The group leads estimates of external laboratory background contributions to the main physics analyses. The group also contributed to LUX physics analyses, in particular, to Effective Field Theory and Inelastic Dark Matter interpretations of LUX results.
Simultaneously, the Liverpool LZ group is involved into the Xenon Futures R&D project which aims to develop a future liquid xenon Global Rare Event Observatory. The expected target mass of 50-100 tonnes of liquid xenon will allow to improve the sensitivity by an order of magnitude. The Liverpool group is responsible for development of interconnects for photosensors in the future detector.
Personnel
| Name | Picture | Role | LZ years | Where next? |
|---|---|---|---|---|
| Sergey Bundin |  |
PI | 2014-present | |
| Joachim Rose |  |
Co-I | 2014-2016 | SNO+ Liverpool Faculty |
| Carl Gwilliam |  |
Post-doc | 2017-2020 | ATLAS Liverpool Faculty |
| Will Turner | Post-doc | 2018-2022 | The Future Forest Company | |
| Billy Boxer | PhD student | 2016-2020 | UC Davis Post-doc | |
| Alice Hamer (Baxter) |  |
PhD student | 2017-2022 | RHUL/Edinburgh Post-doc |
| Ewan Fraser | PhD student | 2018-present | ||
| Harvey Birch |  |
MSc student | 2018-2020 | University Michigan PhD |
| Sam Woodford |  |
PhD student | 2020-present | |
| Sam Powell |  |
Engineer | 2015-2019 | University of Liverpool PhD |
| Ash Greenall |  |
Engineer | 2016-present | |
| Balint Bogdan | Engineer | 2021-present |