Constraints on sub-GeV dark matter scattering on electrons with COSINE-100

We present results of the search for sub-GeV dark matter interaction with electrons in the NaI(Tl) crystals of the COSINE-100 experiment. The two benchmark scenarios of a heavy and a light vector boson as mediator of the interaction were studied. We found no excess events over the expected background in a dataset of 2.82 years, with a total exposure of 172.9 kg − year . The derived 90% confidence level upper limits exclude a dark matter (DM)-electron scattering cross section above 6.4 × 10 − 33 cm 2 for a DM mass of 0.25 GeV, assuming a light mediator; and above 3.4 × 10 − 37 cm 2 for a 0.4 GeV DM, assuming a heavy mediator, and represent the most stringent constraints for a NaI(Tl) target to date. We also briefly discuss a planned analysis using an annual modulation method below the current 0.7 keV threshold of COSINE-100, down to few photoelectrons yield.