Quantum phase transitions (QPT) continue to attract the attention of experimentalists and theorists alike. Experiments on quantum magnets have been crucial to understand their underlying physics. Famous examples include the Bose-Einstein condensation of magnons (which spontaneously breaks O(2) or the isomorphic U(1) symmetry, dynamical critical exponent z = 2), the Ising chain in transverse fields (emergent E8 symmetry), and the pressure-induced QPT in TlCuCl3 (O(3), z = 1) which displays a longitudinal Higgs excitation. Here we propose to perform time-of-flight spectroscopy on what we believe is the first realization of a 3D O(2)-breaking z = 1 QPT in the material dichloro-tetrakis-thiourea-nickel (DTN), in which we have recently discovered a pressure-induced quantum critical point (QCP) at around 1 kbar.