NEON experiment shares results from first direct search for light dark matter

Detecting dark matter, the elusive type of matter predicted to account for most of the universe’s mass, has so far proved to be very challenging. While physicists have not yet been able to determine what exactly this matter consists of, various large-scale experiments worldwide have been trying to detect different theoretical dark matter particles.

One of these candidates is so-called light dark matter (LDM), particles with low masses below a few giga-electron volts (GeV/c²). Theories suggest that these particles could weakly interact with ordinary matter, yet the weakness of these interactions could make them difficult to detect.

The NEON (Neutrino Elastic Scattering Observation with Nal) collaboration, a group of researchers analyzing data collected by the NEON detector at the Hanbit nuclear reactor in South Korea, have published the results of their first direct search for LDM.

Their paper, published in Physical Review Letters, sets new constraints on the properties of this key dark matter candidate, which could inform future efforts aimed at detecting it.

“Our paper emerged from the NEON Collaboration’s innovative approach to searching for light dark matter using a unique experimental setup near a nuclear reactor,” Hyunsu Lee, co-author of the paper, told Phys.org.

“We were inspired by the idea that nuclear reactors, which emit an abundance of high-energy photons, could provide a natural environment for testing new dark matter theories.”

One of the main goals of the NEON experiment is to search for LDM by exploring its interactions with electrons. The first run of the experiment specifically searched for particles with a mass ranging between 1 keV/c² and 1 MeV/c².

“This was an uncharted region for direct dark matter searches and we aimed to push the boundaries of what can be achieved with reactor-based experiments,” explained Lee.

To search for LDM, the NEON collaboration relies on a highly sensitive detector located in proximity to the Hanbit nuclear reactor in South Korea. This detector could pick up tiny signals that could be associated with interactions between LDM particles and electrons.

The Hanbit nuclear reactor produces high-energy photons that could potentially convert into dark photons, hypothetical particles expected to interact weakly with ordinary matter. These dark photons, which theoretically mix with regular photons (i.e., light particles), could decay into LDM. Notably, detecting LDM interactions requires a highly sensitive detector capable of capturing these elusive signals.

“Our detector, shielded with advanced materials to reduce background noise, is designed to capture these rare interactions,” said Lee.

“In our recent paper, we analyzed 1.2 years of data collected by the detector and established new limits on how strongly light dark matter can interact with electrons. For dark matter particles with a mass around 100 keV/c², we improved the previous limits by a factor of 1,000, and for the first time, we set constraints on masses below this range.”

Compared to previous LDM searches, the NEON experiment probes new and uncharted mass ranges for these particles that were previously inaccessible. While the researchers did not pick up any signals that could be linked to interactions between LDM particles and electrons, they were able to refine existing constraints on the properties of these hypothetical particles, particularly for masses below 100 keV/c²

“Using a nuclear reactor as both a source of high-energy photons and a controlled environment for experiments, we demonstrated the potential of reactor-based dark matter searches,” said Lee.

“The implications of our work are significant, as our approach opens the door for future experiments to probe even lighter dark matter candidates and offers a complementary method to accelerator- and cosmology-based dark matter searches.”

The recent paper by the NEON collaboration could soon inform other searches for LDM worldwide, as well as theoretical studies focusing on these particles. The researchers are now planning to extend the scope of their research by collecting more data and further improving their detector’s sensitivity.

“Specifically, we aim to further lower the energy threshold of our analysis, allowing us to explore lighter dark matter particles with even weaker interaction strengths,” added Lee.

“Additionally, we are exploring ways to improve shielding and noise reduction to enhance the reliability of our results. Our long-term goal is to integrate our findings with other experimental and theoretical dark matter efforts to build a comprehensive understanding of this elusive component of the universe.”

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