Nikhef researcher Tina Pollmann has received funding from NWO for a test setup that could prove crucial in the global hunt for dark matter.
UvA lecturer Pollmann is affiliated with the XENONnT experiment in Gran Sasso, Italy. This experiment uses a large underground vessel filled with cold liquid xenon to search for ultraviolet light traces from incoming dark matter particles.
Dark matter is one of the great mysteries of physics. Approximately 85 per cent of all mass in the universe is invisible, but it does shape galaxies, for example, through gravity. If this matter consists of particles, these should occasionally be detectable in a detector.
XENONnT is one of the detectors that has been trying to capture dark matter particles for many years, so far without success. Although the sensitivity of the detector has been continuously increased, there are still many false light signals that are brighter than what is expected from dark matter.
In all noble-gas dark matter detectors such false signals are caused by radioactive radiation from the environment, which causes a flash of light in the detector a few times per second.
After these very shortflashes of UV light, light continues to be detected for a hundred times longer than expected. This effect blinds the detector up to a quarter of the time, but the source of this additional light has been unclear.
Pollmann and her colleagues want to test a new hypothesis for the origin of these delayed light flashes. The group is focusing on organic solder fluid or flux, which is used as standard in the cabling of the light sensors in the detectors. Traces of this fluid are photoluminescent under uv light and dissolve easily in noble gas liquids such as xenon, as is now known.
Calculations show that even very slight luminescence could explain all the background light in the detector. According to Pollmann, reducing the amount of delayed light is necessary to make dark matter detectors significantly more sensitive. ‘We need to turn off the light to see dark matter,’ she says.
A test setup is under construction in one of Nikhef’s laboratories in Amsterdam to better study the role of solder and test possible alternatives. Pollmann wants to further expand this instrument in the coming year into a test installation for XENONnT, where materials from other dark matter experiments can also be tested and inspected.
The fact that these are sometimes scientific competitors is not a problem, according to Pollmann. ‘Ultimately, it’s about the discovery of dark matter, not the discoverers.’
Pollmann is receiving an ENW-XS grant of nearly 50,000 euros from NWO for the expansion. This week, NWO announced the award of 72 such grants for potentially groundbreaking but risky research.
