The expansion of the XENON experiment at Gran Sasso in Italy is bearing fruit. The larger detector works better than its predecessors.
So reports the XENON collaboration today in presentations at Gran Sasso and the Moriond winter conference in Italy of the first results following the detector volume expansion. In the first hundred days of measurements, a new, sharper upper limit has been set for any dark-matter particles. The results have been published on Arxiv.
Big Rock
Nikhef is one of the partners in the XENON project, which is being conducted deep underground in Italy, shielded from cosmic rays by the granite of the Gran Sasso (Great Rock) above it. At the LNGS laboratory, the Dutch made a major contribution to innovation in recent years, and to the project’s physical measurement program.
XENON hunts so-called WIMPs, weakly interacting massive particles. These are still unknown particles that the dark matter in the universe could theoretically consist of. Dark matter is invisible, but would explain about four-fifths of all gravity in the universe. There are no existing particles that could explain it.
Background radiation
In XENON, this is done by observing a barrel of ultracold and ultrapure liquid xenon. In theory, passing WIMPs from the universe should emit a flash of light in the barrel and then another characteristic electric pulse.
In recent years, the previous detector with about 1 ton of xenon (1T) at Gran Sasso was replaced by a volume with 8.6 tons of xenon, of which 5.9 tons are active (nT). Much effort has gone into reducing background radiation, especially from radioactive traces in the liquefied gas.
In the nT detector, there is five times less background signal than before, due to better material choices and better cleaning of the xenon used. This makes it possible to see even rarer events.
Sharper limit
One hundred days of measurements were analyzed for the publication in Phys.Rev.Lets. XENONnT sees no evidence of passing new particles. This does allow us to derive a new limit for what properties dark matter particles may still have. This limit is tighter than what XENON1T found.
That result fits into a series of increasingly tight limits that XENON and other dark matter detectors have set. Program leader Patrick Decowski of the Dark Matter group at Nikhef, who presented the results Wednesday at Moriond, calls the new measurements very encouraging.
Decowski: “It’s a nice first result with only 100 days of measurement time. We have now lowered the backgrounds even further and plan for ten times more data. XENONnT thus holds wonderful cards to continue the search for dark matter.”