  The COSINUS direct dark matter experiment situated at Laboratori Nazionali
del Gran Sasso in Italy is set to investigate the nature of the annually
modulating signal detected by the DAMA/LIBRA experiment. COSINUS has already
demonstrated that sodium iodide crystals can be operated at mK temperature as
cryogenic scintillating calorimeters using transition edge sensors, despite the
complication of handling a hygroscopic and low melting point material. With
results from a new COSINUS prototype, we show that particle discrimination on
an event-by-event basis in NaI is feasible using the dual-channel readout of
both phonons and scintillation light. The detector was mounted in the novel
remoTES design and operated in an above-ground facility for 9.06 g$\cdot$d of
exposure. With a 3.7 g NaI crystal, e$^-$/$\gamma$ events could be clearly
distinguished from nuclear recoils down to the nuclear recoil energy threshold
of 15 keV.
