Speaker
Description
We report new constraints on the spin-dependent (SD) WIMP-proton cross section using the COSINE-100 experiment at the Yangyang Underground Laboratory. This analysis achieves a pioneering detection threshold of 3 and 4 pulse clusters corresponding to the measured photoelectrons. This allows us to access the unstudied few-photoelectron regime, significantly below the previous 8-photoelectron threshold. Using four years of stable data, we find no statistically significant evidence of annual modulation. Furthermore, we establish the world's most stringent SD WIMP-proton constraints for NaI(Tl) in the $1.75–2.25$ GeV/$c^2$ mass range. By incorporating the Migdal effect, we further extend our sensitivity into the $15–58$ MeV/$c^2$regime, setting new world-leading limits. These results demonstrate the unique capability of NaI(Tl) targets to probe previously unexplored regions of the dark matter parameter space.
