  The Coherent Neutrino-Nucleus Interaction Experiment (CONNIE) aims to detect
the coherent scattering (CE$\nu$NS) of reactor antineutrinos off silicon nuclei
using thick fully-depleted high-resistivity silicon CCDs. Two Skipper-CCD
sensors with sub-electron readout noise capability were installed at the
experiment next to the Angra-2 reactor in 2021, making CONNIE the first
experiment to employ Skipper-CCDs for reactor neutrino detection. We report on
the performance of the Skipper-CCDs, the new data processing and data quality
selection techniques and the event selection for CE$\nu$NS interactions, which
enable CONNIE to reach a record low detection threshold of 15 eV. The data were
collected over 300 days in 2021-2022 and correspond to exposures of 14.9 g-days
with the reactor-on and 3.5 g-days with the reactor-off. The difference between
the reactor-on and off event rates shows no excess and yields upper limits at
95% confidence level for the neutrino interaction rates comparable with
previous CONNIE limits from standard CCDs and higher exposures. Searches for
new neutrino interactions beyond the Standard Model were performed, yielding an
improvement on the previous CONNIE limit on a simplified model with light
vector mediators. A first dark matter (DM) search by diurnal modulation was
performed by CONNIE and the results represent the best limits on the
DM-electron scattering cross-section, obtained by a surface-level experiment.
These promising results, obtained using a very small-mass sensor, illustrate
the potential of Skipper-CCDs to probe rare neutrino interactions and motivate
the plans to increase the detector mass in the near future.
