&Bullet; physics 14, p71
The potential detection of dark matter by the DAMA / LIBRA experiment has not been confirmed for 20 years. A similar experiment now provides evidence against the result.
For about two decades, physicists have been fascinated by the results of the DAMA / LIBRA experiment in Italy, which point to the detection of dark matter particles. Now a team from the University of Zaragoza and the Canfranc Underground Laboratory in Spain is presenting an analysis of three years of data from the almost identical annual modulation with NaI scintillators (ANAIS)  . The new data provisionally refutes the claim that DAMA / LIBRA discovered dark matter, but does not yet completely rule out the possibility.
Although several searches have excluded dark matter particles in parts of their respective parameter spaces, no experiment prior to ANAIS had repeated the DAMA / LIBRA search accurately enough to confirm or disprove its finding. Both DAMA / LIBRA and ANAIS are based on thallium-doped sodium iodide scintillators, which generate photons when they interact with ionizing radiation. If some of these interactions involve dark matter particles, the experiments should see a seasonal variation in the number of photons detected. This periodic pattern should arise because the Earth’s annual rotation around the Sun changes the speed of our planet relative to the galaxy’s dark matter cloud.
The DAMA / LIBRA team reported such an annual modulation, which implies the detection of dark matter. However, the ANAIS experiment finds no evidence of this modulation in three years of data at a sensitivity of around 2.7 sigma, suggesting that the finding of the earlier experiment could be due to an unconsidered systematic artifact. By the end of 2022, the team said, ANAIS will have enough data to exceed the 3-sigma sensitivity threshold that is normally required to be considered evidence for or against a hypothesis.
–Erika K. Carlson
Erika K. Carlson is Corresponding Editor for physics based in New York City.
- J. Amare et al., “Annual modulation results from exposure to ANAIS-112 for three years” Phys. Rev. D.103102005 (2021).