XLZD Pre-Construction

Few problems in fundamental physics are as clearly motivated or as important as discovering the nature of the elusive dark matter that accounts for most of the mass of the universe. Direct detection experiments located deep underground are searching for the rare interactions of these well-motivated, relic particles in very sensitive detectors. Liquid xenon (LXe) technology has led these searches for over a decade. Recently, the top international collaborations in the field have come together in the XLZD consortium to build the definitive experiment: one able to discover or rule out electroweak-scale particle dark matter in the accessible parameter space remaining above the very challenging neutrino background. Exciting opportunities exist also in neutrino physics, including establishing the existence of neutrinoless double-beta decay; this is another paradigm-shifting discovery which may be accessible to such an experiment, which could explain the matter-antimatter asymmetry in the universe. This proposed 'rare event observatory' will deploy a LXe detector with up to 80 tonnes of 'active' mass in an ultra-low-background experiment to address these and other questions, at least two of which could entail Nobel-Prize worthy discoveries.

This Pre-Construction project prepares the UK contribution to the XLZD experiment and builds the case to bring this ambitious international experiment to the UK. STFC is developing a major new underground laboratory at the Boulby mine, and XLZD would be the centrepiece of the new state-of-the-art facility. A future construction project must be carefully prepared, and this development work is delivered through this Pre-Construction project.

The proposed UK contribution to XLZD includes major experimental hardware systems, especially those most naturally suited to the host nation; these will be designed and prepared in this phase. In addition, we will deliver with key industrial partners bold programmes for clean manufacture underground, for engineering and skills development, and for environmental sustainability. These programmes relate to challenges that must be addressed, but which we deliberately develop into opportunities: to provide return to UK industry and wider economic impact, to develop capabilities that support future STFC and UKRI projects, and to be a pathfinder in how Big Science moves towards Net Zero.