Two direct-detection experiments see no evidence of a signal reported by their predecessor.
The doctoral thesis of Sophia Hollick, Ph.D. ‘25, a recent graduate of Yale’s Wright Lab in professor Reina Maruyama’s group, has significantly contributed to answering a decades-long question in her field about whether or not a signal observed in an experiment that has taken data since 1997 was indicative of a direct detection of dark matter.
The results of her analysis, which have excluded the dark matter explanation with greater confidence, were published in Physics Review Letters in the article “Combined Annual Modulation Dark Matter Search with COSINE-100 and ANAIS-112.
Testing DAMA
In 1997, the DAMA/NaI experiment at the Gran Sasso National Laboratory in Italy observed a signal whose annual variability was suggestive of dark matter. Despite the follow-up DAMA/LIBRA experiment producing similar results, claims of direct dark matter detection drew skepticism from the physics community. To test the claims independently, sister experiments ANAIS-112 and COSINE-100 were constructed using the same basic design as DAMA/NaI and DAMA/LIBRA. COSINE-100, located at the Yangyang Underground Laboratory in South Korea, began taking data in 2016. ANAIS-112, located at the Canfranc Underground Laboratory (LSC) in Spain, began taking data in 2017. Maruyama is the Principal Investigator (PI) and scientific co-spokesperson of COSINE-100.
All of these experiments were designed to search for the signature of a dark matter candidate scattering off the sodium iodide detector. Such a signature should contain a distinct annual modulation because the detector’s speed relative to the Milky Way’s dark matter varies as Earth orbits the Sun. Observations of such modulation by DAMA/NaI and DAMA/LIBRA are inconsistent with other direct-detection experiments and with model predictions. But the reproducibility of these observations had not been tested robustly using identical techniques.
ANAIS-112 and COSINE-100 enabled such a test by using the same sodium iodide detector material as the DAMA experiments, while including some extra analysis techniques designed to reduce background noise and increase event-detection rates.
The data sets from both ANAIS-112 and COSINE-100, each working independently, were found to contain no such variability, tentatively ruling out dark matter as the cause of the earlier observations. Hollick’s 2025 thesis combined the data from both ANAIS-112 and COSINE-100, and statistical analysis of the combined dataset showed no significant evidence of annual modulation in the relevant energy regions. This result effectively rules out dark matter as the origin for the DAMA/LIBRA signal.
Hollick explained, “These results end a longstanding debate (almost 30 years) about the source of the DAMA/LIBRA annual modulation signal. They show that, due to the irreproducibility of the signal in COSINE-100 and ANAIS-112, the modulation cannot be attributed to dark matter.”
Looking to the future
Although the study doesn’t provide an explanation for what the source of the modulation in the DAMA experiment is, the researchers say it allows the dark matter community to conduct future searches unencumbered by an unresolved detection claim.
Maruyama said, “Although we do not yet know the origin of DAMA’s signal, the dark matter community can now focus on finding a signal from dark matter rather than to chase after a ghost. The COSINE and ANAIS collaborations will now focus on using the sodium iodide dark matter detectors as they were originally intended—detectors that can be grown in large quantities and access low-mass dark matter, as well as several different interactions using the different nuclei with different masses and nuclear spin.”
Maruyama continued, “It’s been a long road to test DAMA’s claim for a detection of dark matter, and I am happy to put DAMA behind us.”
Hollick is now a postdoctoral researcher at the University of Zaragoza in Spain. Hollick said, “This project was what inspired my move to Spain, where I have been living for three years now. Since the release of our results, I have given talks across Spain and Europe, meeting many talented physicists along the way.”
Hollick continued, “Leading a combined dark matter search between two well established experiments that come from opposite sides of the world has fostered a unique international exchange alongside a deep knowledge of nuclear particle physics and dark matter.”
This article includes content adapted from an article in Physics Magazine by Rachel Berkowitz, originally published on September 17, 2025.
This story is a duplicate of the Wright Lab news story of March 31, 2026, by Victoria Misenti. See below for a link to the original story plus other related links.