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A bright future for dark-matter searches

23 September 2014

The US Department of Energy Office of High Energy Physics and the National Science Foundation Physics Division have announced their joint programme for second-generation dark-matter experiments, aiming at direct detection of the elusive dark-matter particles in Earth-based detectors. It will include ADMX-Gen2 – a microwave cavity searching for axions – and the LUX-Zeplin (LZ) and SuperCDMS-SNOLAB experiments targeted at weakly interacting massive particles (WIMPs). These selections were partially in response to recommendations of the P5 subpanel of the US High-Energy Physics Advisory Panel for a broad second-generation dark-matter direct-detection programme at a funding level significantly above that originally planned.

While ADMX-Gen2 consists mainly of an upgrade of the existing apparatus to reach a lower operation temperature of around 100 mK, and is rather inexpensive, the two WIMP projects are significantly larger. SuperCDMS will initially operate around 50 kg of ultra-pure germanium and silicon crystals at the SNOLAB laboratory in Ontario, for a search focused on WIMPs with low masses, below 10 GeV/c2. The detectors will be optimized for low-energy thresholds and for very good particle discrimination. The experiment will be designed such that up to 400 kg of crystals can be installed at a later stage. The massive LZ experiment will employ about 7 tonnes of liquid xenon as a dark-matter target in a dual-phase time-projection chamber (TPC), installed at the Sanford Underground Research Facility in South Dakota. It is targeted mainly towards WIMPs with masses above 10 GeV/ c2. The timescale for these experiments foresees that the detector construction will start in 2016, with commissioning in 2018. All three experiments need to run for several years to reach their design sensitivities.

Meanwhile, other projects are operational and taking data, and several new second-generation experiments, with target masses beyond the tonne scale, are fully funded and currently being installed. The Canadian–UK project DEAP-3600, installed at SNOLAB, should take its first data with a 3.6-tonne single-phase liquid-argon detector by the end of this year. Its sensitivity goal is a factor 10–25 beyond the current best limit, depending on the WIMP mass. XENON1T, a joint effort by US, European, Swiss and Israeli groups, aims to surpass this goal using 3 tonnes of liquid xenon, of which 2 tonnes will be inside a dual-phase TPC. Construction is progressing fast at the Gran Sasso National Laboratory, and first data are expected by 2015. These experiments and their upgrades, the newly funded US projects, and other efforts around the globe, should open up a bright future for direct-dark-matter searches in the years to come.

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