We have recently discovered a pressure-induced quantum phase transition (QPT) at 4.3 kbar in the gapped quantum magnet piperazinium hexachlorodicuprate (PHCC) by means of muon-spin rotation and inelastic neutron scattering (INS) measurements. The Heisenberg nature of the spins and the quasi 2-dimensional spin network of PHCC allows, for the first time, the study of SO(3) symmetry breaking in two spatial dimensions. This transition is of particular interest due to the presence of a longitudinal Higgs excitation. Previous INS experiments deep in the ordered phase have allowed us to identify the ordering wave vector. Here, we propose to study the universal scaling of the dynamic structure factor around the ordering vector at the QCP in order to test specific predictions of the so-called non-linear sigma model.