  New Experiments With Spheres-Gas (NEWS-G) is a direct dark matter detection
experiment using Spherical Proportional Counters (SPCs) with light noble gases
to search for low-mass Weakly Interacting Massive Particles (WIMPs). We report
the results from the first physics run taken at the Laboratoire Souterrain de
Modane (LSM) with SEDINE, a 60 cm diameter prototype SPC operated with a
mixture of $\mathrm{Ne}+\mathrm{CH}_{4}$ (0.7 %) at 3.1 bars for a total
exposure of $9.7\;\mathrm{kg\cdot days}$. New constraints are set on the
spin-independent WIMP-nucleon scattering cross-section in the
sub-$\mathrm{GeV/c^2}$ mass region. We exclude cross-sections above $4.4 \times
\mathrm{10^{-37}\;cm^2}$ at 90 % confidence level (C.L.) for a 0.5
$\mathrm{GeV/c^2}$ WIMP. The competitive results obtained with SEDINE are
promising for the next phase of the NEWS-G experiment: a 140 cm diameter SPC to
be installed at SNOLAB by summer 2018.
