PPD has been involved in and played a central role in dark matter searches in the UK since its inception almost two decades ago. One of the co-founders of the UK dark matter searches was Peter Smith from PPD who pioneered liquid xenon technology and initiated the ZEPLIN programme at Boulby Underground Laboratory.
The ZEPLIN-I experiment was one of the first dark matter experiments in the world using a xenon singe-phase detector. The follow-on, ZEPLIN-II was the first world's dark matter experiment using xenon double-phase technology, while ZEPLIN-III led by Imperial College concluded the programme. It operated at a high electric field achieving the best discrimination of any xenon detector. Its second science run, lasting almost a year, was the world's longest continuously run of any dark matter experiment with a double-phase xenon detector, proving the maturity of the technology to be used in future investigations and achieving competitive limits in WIMP searches. The PPD DOM group participated in the ZEPLIN-III experiment exploitation and its decommissioning. Primary responsibilities were: project management, liaison between the Boulby Underground Laboratory and the experiment, detector calibration, radiation protection supervision, management of the data centrally stored at RAL and relevant equipment repatriation to RAL.
After many years of working on liquid xenon for dark matter searches and helping two-phase xenon to become a world-leading technology, the PPD DOM group is now part of the LUX-ZEPLIN (LZ) collaboration.
The LUX-ZEPLIN double-phase detector uses ten tonnes of cryogenic liquid xenon to search for dark matter with unprecedented sensitivity and is located a mile underground at the Sanford Underground Research Facility (SURF) in South Dakota.
PPD, one of the founding LZ members, has participated in the LUXZEPLIN project throughout the R&D (2012-2015), construction, commissioning and exploitation (2022 onwards) phases. It has led the delivery of the ultra-pure titanium cryostat and calibration source deployment (CSD) system, has carried out material screening at the Boulby Underground Laboratory and has project-managed a broader UK effort from several leading universities. The first scientific results reporting on the detector’s excellent performance and the world’s best dark matter limit were announced on the 7th of July 2022.
In the commissioning and exploitation phases, PPD played an important role in assisting the detector calibration activities using the CSD system allowing to deployment of calibration sources, both neutron sources and gamma sources, along a dedicated 6-m long calibration tube. The CSD systems have been successfully used in the calibration campaign preceding LZ Science Run 1 and the group has provided continuous support to the on-site CSD calibration efforts. As the collaboration is preparing for Run 2, the CSD systems will be intensively used, playing a critical role throughout the lifetime of LZ.