A new search for dark matter will soon be underway after a second generation experiment was selected by US funding agencies.

Most physicists believe that dark matter particles make up most of the mass of the universe, but these particles have never been observed directly since they neither emit nor absorb light at any wavelength.

They are thought to have mass like normal particles and create a tiny gravitational pull, but they do not fit the Standard Model of Particle Physics and if found they would radically further our understanding of the laws of nature.

Nestled deep in an underground mine in the Black Hills in the American State of South Dakota, the new experiment, which is called the Lux-Zeplin (LZ) dark matter detection experiment, brings together over 120 scientists and engineers from 30 global institutions. Scientists from Imperial College London are leading the UK collaboration.

Alongside two other experiments, LZ was recently selected by the US Department of Energy's Office of High Energy Physics (DOE) and the National Science Foundation's Physics Division (NSF) to become a formal project later this year. The DOE and NSF believe the design and unprecedented sensitivity of the LZ experiment will give the most impressive results. LZ will be 30 times larger than its predecessor, the Large Underground Xenon (LUX), which is the current most sensitive dark matter detector, and will have over 100 times better reach to find the elusive dark matter particles.

Dr Henrique Araujo from Imperial’s Department of Physics who heads up the UK contribution said: “It’s really exciting to get the go ahead from the US government. Now we can begin to put theory into practice and construct an experiment that could finally settle the dark matter debate once and for all.

“Dark matter is incredibly difficult to see because the particles neither emit nor absorb light, but hopefully they still interact through the very tenuous weak nuclear force. The LZ experiment is vastly more sensitive than any other detector ever built so I’m hopeful that we will get conclusive results. And if we find dark matter particles and are able to measure their mass and other properties we can begin to answer much bigger questions about how our universe came to look the way it does today,” added Dr Araujo.

LZ will look for Weakly Interacting Massive Particles, or WIMPs, which are extremely numerous but their interactions with ordinary matter are very rare, so that they are challenging to detect.

The LZ design includes a chamber filled with seven tonnes of a rare element called xenon, which becomes liquid when it is cooled to -100 degrees Celsius. The scientists will use photon sensors to look for flashes of light that could indicate dark matter collisions with the xenon atoms.

The detector will be encased in an eight metre tall water tank and operated one mile underground so that the machine is shielded from harmful cosmic radiation and any disrupting background noise.

The UK based scientists are now looking for funding from the Science and Technology Facilities Council to begin building all the instrumentation and calibration apparatus needed for the detector. The construction phase should take three years and once working the scientists aim to collect data over a four to six year period.

The LZ experiment joins two previously separate experiments, which Imperial physicists were heavily involved in - the UK-based Zeplin programme, which was established over a decade ago in the Boulby mine in North Yorkshire, and the LUX experiment based at the Sanford Underground Laboratory at the Homestake mine, South Dakota, US.

LZ is a collaboration of 30 institutes in the US, UK, Portugal and Russia. Dr Araújo from Imperial leads the UK team on LZ, which counts also with colleagues from Edinburgh, UCL, Oxford, Sheffield and Liverpool universities as well as the Rutherford Appleton and Daresbury national laboratories.