University of Coimbra
Research has reached the best limits ever in the direct search for low-mass dark matter.
It is seen as a historic milestone in particle physics and something that opens a new window into the study of the Sun’s interior.
Scientists observed for the first time, interactions of solar neutrinos with atomic nuclei. And they achieved the best limits ever in the direct search for low-mass dark matter.
The was carried out by an international collaboration of scientists, LUX-ZEPLIN (LZ), which includes, for example, the founder Laboratory Instrumentation and Experimental Particle Physics (LIP) of the Faculty of Science and Technology of the University of Coimbra (FCTUC).
It was made Largest-ever analysis of data obtained by a dark matter detector: 417 days of effective operation, between March 2023 and April 2025.
The LZ established the most restrictive limits known for dark matter particles of the type WIMPs (weakly interacting massive particles), in particular for masses below 9 GeV/c².
No direct signals from these particles were observed, but the new results reinforce the LZ’s position as the most sensitive experiment in the world for WIMPs with masses above 5 GeV/c², describes the University of Coimbra in a statement sent to ZAP.
The sensitivity of the detector made it possible to observe, for the first time, interactions of solar neutrinos with atomic nuclei. This was achieved through the rare process known as nucleus-elastic coherent neutrino scattering (CEvNS).
In this process, observed for the first time only in 2017 using a high flux of neutrinos produced in nuclear reactors, a neutrino interacts with the entire atomic nucleus, transferring a tiny amount of energy.
This was the first time this process was observed in solar neutrinos with a significance of 4.5 sigma, above the threshold of 3 sigma traditionally used to consider an observation as “evidence”.
The PandaX-4T and XENONnT experiments reported evidence of this process last year, but with a confidence level below 3 sigma.
This is the first “evidence” of a CEvNS signal from extraterrestrial neutrinos.
This is not the first time that neutrinos from the Sun have been detected in this laboratory. In the 1960s and 1970s, Raymond Davis Jr. and John Bahcall measured, for the first time, the flux of solar neutrinos with a 380 m3 detector in this same cave, now known as “Davis Cave”. This result earned Ray Davis the 2002 Nobel Prize in Physics.
“The novelty is not just the detection of solar neutrinos, but the extremely subtle mechanism by which they were observed. We are talking about just a few photons and electrons per interaction, which demonstrates the extraordinary sensitivity of the LZ detector», describes researcher Paulo Brás.
