Two New Publications on Dark Matter Searches with Spherical Proportional Counters

14 April 2025

Photo: KN

Researchers from our group at the University of Hamburg have had major involvement in two new research articles published on April 11, 2025.

In the first article, published in Physical Review Letters, new results are presented from a 10-day physics run of a 135 cm diameter spherical proportional counter operated at the Laboratoire Souterrain de Modane. Using methane as target, the experiment contributes new constraints in the spin-dependent dark matter-proton interactions in the mass range between 0.18 and 1.28 times the mass of the proton. These results significantly improve our understanding of dark matter interactions in the sub-GeV regime.

In a companion articles, published in Physical Review D, detailed measurements of the mean ionization yield and its fluctuations in methane-filled spherical proportional counters are reported. Dedicated calibration studies, including UV laser measurements of gas gain and campaigns with ³⁷Ar and aluminum fluorescence sources, provide key input for modeling the detector energy response in future dark matter searches.

These publications are a milestone in the search for sub-GeV particle dark matter with spherical proportional counters, and set the scene for future searches, including with the DarkSPHERE detector.

More information on the spherical proportional counters and its application in dark matter searches can be found in the our recent review article: https://arxiv.org/pdf/2502.11870