COSINE-100 is a direct dark matter search experiment, with
the primary goal of testing the annual modulation signal observed by
DAMA/LIBRA, using the same target material, NaI(Tl). In previous
analyses, we achieved the same 1 keV energy threshold used in the
DAMA/LIBRA's analysis that reported an annual modulation signal with
11.6σ significance. In this article, we report an improved
analysis that lowered the threshold to 0.7 keV, thanks to the
application of Multi-Layer Perception network and a new likelihood
parameter with waveforms in the frequency domain. The lower
threshold would enable a better comparison of COSINE-100 with new
DAMA results with a 0.75 keV threshold and account for differences
in quenching factors. Furthermore the lower threshold can enhance
COSINE-100's sensitivity to sub-GeV dark matter searches.