CYGNUS
The WIMP search has spawned numerous innovations in particle detector technology. To give a sense of the rapid rate of progress, the experimental sensitivity to WIMPs over the last two decades has increased more quickly than computer speeds (as described by ‘Moore’s Law’) during the 80s to 00s. However, as the field pushes to even higher sensitivity, detectors also become sensitive to new types of background that would otherwise be too weak to observe.
The most important new background comes from neutrinos. Much like WIMPs, neutrinos only interact weakly and, importantly, cannot be shielded. So once detectors become sensitive to neutrinos (and this is expected to occur in the next generation of detectors), the search for WIMPs will be slowed – an effect known as the ‘neutrino floor’.
The neutrino floor can be overcome using a detector that can measure the direction of the recoiling nucleus that is generated when a WIMP scatters in the detector. Such a directional detector can reject neutrino backgrounds, which predominantly come from the sun. WIMPs, on the other hand, should predominantly come back along the direction of the solar system’s orbit of the galaxy, which happens to point towards the constellation Cygnus.
The concept of a directional detector is currently being explored by an international group of researchers under the name Cygnus, with the goal to build a number of large directional detector modules in underground laboratories around the world, including at SUPL. When combined, these modules will form a large distributed detector that capable of could search for WIMPs below the neutrino floor. An experimental directional detector prototype called Cygnus-1 is being developed at the ANU node, which will commence operation this year.
